/* eslint-disable complexity */
/**
 * @module node-opcua-server
 */
import { randomBytes } from "crypto";
import { EventEmitter } from "events";
import { callbackify, types } from "util";

import async from "async";
import chalk from "chalk";

import { extractFullyQualifiedDomainName, getFullyQualifiedDomainName } from "node-opcua-hostname";

import { assert } from "node-opcua-assert";
import { isNullOrUndefined } from "node-opcua-utils";

import {
    AddressSpace,
    PseudoVariantBoolean,
    PseudoVariantByteString,
    PseudoVariantDateTime,
    PseudoVariantDuration,
    PseudoVariantExtensionObject,
    PseudoVariantExtensionObjectArray,
    PseudoVariantLocalizedText,
    PseudoVariantNodeId,
    PseudoVariantString,
    RaiseEventData,
    SessionContext,
    UAObject,
    UAVariable,
    ISessionContext,
    UAView,
    EventTypeLike,
    UAObjectType,
    PseudoVariantStringPredefined,
    innerBrowse,
    innerBrowseNext,
    UAEventType
} from "node-opcua-address-space";
import { getDefaultCertificateManager, OPCUACertificateManager } from "node-opcua-certificate-manager";
import { ServerState } from "node-opcua-common";
import { Certificate, exploreCertificate, Nonce } from "node-opcua-crypto/web";
import {
    AttributeIds,
    filterDiagnosticOperationLevel,
    filterDiagnosticServiceLevel,
    NodeClass,
    RESPONSE_DIAGNOSTICS_MASK_ALL
} from "node-opcua-data-model";
import { DataValue } from "node-opcua-data-value";
import { dump, make_debugLog, make_errorLog, make_warningLog } from "node-opcua-debug";
import { NodeId } from "node-opcua-nodeid";
import { ObjectRegistry } from "node-opcua-object-registry";
import {
    AsymmetricAlgorithmSecurityHeader,
    coerceSecurityPolicy,
    computeSignature,
    fromURI,
    getCryptoFactory,
    Message,
    MessageSecurityMode,
    nonceAlreadyBeenUsed,
    Request,
    Response,
    SecurityPolicy,
    ServerSecureChannelLayer,
    SignatureData,
    verifySignature
} from "node-opcua-secure-channel";
import { BrowseNextRequest, BrowseNextResponse, BrowseRequest, BrowseResponse } from "node-opcua-service-browse";
import { CallRequest, CallResponse } from "node-opcua-service-call";
import { ApplicationType, UserTokenType } from "node-opcua-service-endpoints";
import { HistoryReadRequest, HistoryReadResponse, HistoryReadResult, HistoryUpdateResponse } from "node-opcua-service-history";
import {
    AddNodesResponse,
    AddReferencesResponse,
    DeleteNodesResponse,
    DeleteReferencesResponse
} from "node-opcua-service-node-management";
import { QueryFirstResponse, QueryNextResponse } from "node-opcua-service-query";
import { ReadRequest, ReadResponse, ReadValueId, TimestampsToReturn } from "node-opcua-service-read";
import {
    RegisterNodesRequest,
    RegisterNodesResponse,
    UnregisterNodesRequest,
    UnregisterNodesResponse
} from "node-opcua-service-register-node";
import {
    ActivateSessionRequest,
    ActivateSessionResponse,
    AnonymousIdentityToken,
    CloseSessionRequest,
    CloseSessionResponse,
    CreateSessionRequest,
    CreateSessionResponse,
    UserNameIdentityToken,
    X509IdentityToken
} from "node-opcua-service-session";
import {
    CreateMonitoredItemsRequest,
    CreateMonitoredItemsResponse,
    CreateSubscriptionRequest,
    CreateSubscriptionResponse,
    DeleteMonitoredItemsRequest,
    DeleteMonitoredItemsResponse,
    DeleteSubscriptionsRequest,
    DeleteSubscriptionsResponse,
    ModifyMonitoredItemsRequest,
    ModifyMonitoredItemsResponse,
    ModifySubscriptionRequest,
    ModifySubscriptionResponse,
    MonitoredItemModifyResult,
    PublishRequest,
    PublishResponse,
    RepublishRequest,
    RepublishResponse,
    SetMonitoringModeRequest,
    SetMonitoringModeResponse,
    SetPublishingModeRequest,
    SetPublishingModeResponse,
    SetTriggeringRequest,
    SetTriggeringResponse,
    TransferSubscriptionsRequest,
    TransferSubscriptionsResponse
} from "node-opcua-service-subscription";
import {
    TranslateBrowsePathsToNodeIdsRequest,
    TranslateBrowsePathsToNodeIdsResponse
} from "node-opcua-service-translate-browse-path";
import { WriteRequest, WriteResponse } from "node-opcua-service-write";
import { CallbackT, ErrorCallback, StatusCode, StatusCodes } from "node-opcua-status-code";
import {
    ApplicationDescriptionOptions,
    BrowseResult,
    BuildInfo,
    CallMethodResultOptions,
    CancelResponse,
    EndpointDescription,
    MonitoredItemModifyRequest,
    MonitoringMode,
    UserIdentityToken,
    UserTokenPolicy,
    BuildInfoOptions,
    MonitoredItemCreateResult,
    IssuedIdentityToken,
    BrowseResultOptions,
    ServiceFault,
    ServerDiagnosticsSummaryDataType,
    BrowseDescriptionOptions
} from "node-opcua-types";
import { DataType } from "node-opcua-variant";
import { VariantArrayType } from "node-opcua-variant";
import { matchUri } from "node-opcua-utils";

import { UAString } from "node-opcua-basic-types";
import { ObjectIds, ObjectTypeIds } from "node-opcua-constants";
import { OPCUABaseServer, OPCUABaseServerOptions } from "./base_server";
import { Factory } from "./factory";
import { IRegisterServerManager } from "./i_register_server_manager";
import { MonitoredItem } from "./monitored_item";
import { RegisterServerManager } from "./register_server_manager";
import { RegisterServerManagerHidden } from "./register_server_manager_hidden";
import { RegisterServerManagerMDNSONLY } from "./register_server_manager_mdns_only";
import { ServerCapabilitiesOptions } from "./server_capabilities";
import { EndpointDescriptionEx, IServerTransportSettings, OPCUAServerEndPoint } from "./server_end_point";
import { ClosingReason, CreateSessionOption, ServerEngine } from "./server_engine";
import { ServerSession } from "./server_session";
import { CreateMonitoredItemHook, DeleteMonitoredItemHook, Subscription } from "./server_subscription";
import { ISocketData } from "./i_socket_data";
import { IChannelData } from "./i_channel_data";
import { UAUserManagerBase, makeUserManager, UserManagerOptions } from "./user_manager";
import { bindRoleSet } from "./user_manager_ua";
import { SamplingFunc } from "./sampling_func";

function isSubscriptionIdInvalid(subscriptionId: number): boolean {
    return subscriptionId < 0 || subscriptionId >= 0xffffffff;
}

// tslint:disable-next-line:no-var-requires
import { withCallback } from "thenify-ex";
// tslint:disable-next-line:no-var-requires
const package_info = require("../package.json");
const debugLog = make_debugLog(__filename);
const errorLog = make_errorLog(__filename);
const warningLog = make_warningLog(__filename);

const default_maxConnectionsPerEndpoint = 10;

function g_sendError(channel: ServerSecureChannelLayer, message: Message, ResponseClass: any, statusCode: StatusCode): void {
    const response = new ServiceFault({
        responseHeader: { serviceResult: statusCode }
    });
    return channel.send_response("MSG", response, message);
}

const default_build_info: BuildInfoOptions = {
    manufacturerName: "NodeOPCUA : MIT Licence ( see http://node-opcua.github.io/)",
    productName: "NodeOPCUA-Server",
    productUri: null, // << should be same as default_server_info.productUri?
    softwareVersion: package_info.version,
    buildNumber: "0",
    buildDate: new Date(2020, 1, 1)
    // xx buildDate: fs.statSync(package_json_file).mtime
};

const minSessionTimeout = 100; // 100 milliseconds
const defaultSessionTimeout = 1000 * 30; // 30 seconds
const maxSessionTimeout = 1000 * 60 * 50; // 50 minutes
let unnamed_session_count = 0;

type ResponseClassType =
    | typeof BrowseResponse
    | typeof BrowseNextResponse
    | typeof CallResponse
    | typeof CreateMonitoredItemsResponse
    | typeof CreateSubscriptionResponse
    | typeof DeleteSubscriptionsResponse
    | typeof HistoryReadResponse
    | typeof ModifyMonitoredItemsResponse
    | typeof ModifySubscriptionResponse
    | typeof ReadResponse
    | typeof RegisterNodesResponse
    | typeof RepublishResponse
    | typeof SetPublishingModeResponse
    | typeof SetTriggeringResponse
    | typeof TransferSubscriptionsResponse
    | typeof TranslateBrowsePathsToNodeIdsResponse
    | typeof UnregisterNodesResponse
    | typeof WriteResponse;

function _adjust_session_timeout(sessionTimeout: number) {
    let revisedSessionTimeout = sessionTimeout || defaultSessionTimeout;
    revisedSessionTimeout = Math.min(revisedSessionTimeout, maxSessionTimeout);
    revisedSessionTimeout = Math.max(revisedSessionTimeout, minSessionTimeout);
    return revisedSessionTimeout;
}

function channel_has_session(channel: ServerSecureChannelLayer, session: ServerSession): boolean {
    if (session.channel === channel) {
        assert(Object.prototype.hasOwnProperty.call(channel.sessionTokens, session.authenticationToken.toString()));
        return true;
    }
    return false;
}

function moveSessionToChannel(session: ServerSession, channel: ServerSecureChannelLayer) {
    debugLog("moveSessionToChannel sessionId", session.nodeId, " channelId=", channel.channelId);
    if (session.publishEngine) {
        session.publishEngine.cancelPendingPublishRequestBeforeChannelChange();
    }

    session._detach_channel();
    session._attach_channel(channel);

    assert(session.channel!.channelId === channel.channelId);
}

async function _attempt_to_close_some_old_unactivated_session(server: OPCUAServer) {
    const session = server.engine!.getOldestInactiveSession();
    if (session) {
        await server.engine!.closeSession(session.authenticationToken, false, "Forcing");
    }
}

function getRequiredEndpointInfo(endpoint: EndpointDescription) {
    assert(endpoint instanceof EndpointDescription);
    // https://reference.opcfoundation.org/v104/Core/docs/Part4/5.6.2/
    // https://reference.opcfoundation.org/v105/Core/docs/Part4/5.6.2/
    const e = new EndpointDescription({
        endpointUrl: endpoint.endpointUrl,
        securityLevel: endpoint.securityLevel,
        securityMode: endpoint.securityMode,
        securityPolicyUri: endpoint.securityPolicyUri,
        server: {
            applicationUri: endpoint.server.applicationUri,
            applicationType: endpoint.server.applicationType,
            applicationName: endpoint.server.applicationName,
            productUri: endpoint.server.productUri
        },
        transportProfileUri: endpoint.transportProfileUri,
        userIdentityTokens: endpoint.userIdentityTokens
    });
    // reduce even further by explicitly setting unwanted members to null
    e.server.applicationName = null as any;
    // xx e.server.applicationType = null as any;
    e.server.gatewayServerUri = null;
    e.server.discoveryProfileUri = null;
    e.server.discoveryUrls = null;
    e.serverCertificate = null as any;
    return e;
}

// serverUri  String This value is only specified if the EndpointDescription has a gatewayServerUri.
//            This value is the applicationUri from the EndpointDescription which is the applicationUri for the
//            underlying Server. The type EndpointDescription is defined in 7.10.

function _serverEndpointsForCreateSessionResponse(server: OPCUAServer, endpointUrl: string | null, serverUri: string | null) {
    serverUri = null; // unused then

    // https://reference.opcfoundation.org/v104/Core/docs/Part4/5.6.2/
    // https://reference.opcfoundation.org/v105/Core/docs/Part4/5.6.2/
    return server
        ._get_endpoints(endpointUrl)
        .filter((e) => !(e as any).restricted) // remove restricted endpoints
        .filter((e) => matchUri(e.endpointUrl, endpointUrl))
        .map(getRequiredEndpointInfo);
}

function adjustSecurityPolicy(channel: ServerSecureChannelLayer, userTokenPolicy_securityPolicyUri: UAString): SecurityPolicy {
    // check that userIdentityToken
    let securityPolicy = fromURI(userTokenPolicy_securityPolicyUri);

    // if the security policy is not specified we use the session security policy
    if (securityPolicy === SecurityPolicy.Invalid) {
        securityPolicy = fromURI(channel.securityPolicy);
        assert(securityPolicy !== SecurityPolicy.Invalid);
    }
    return securityPolicy;
}

function findUserTokenByPolicy(
    endpoint_description: EndpointDescription,
    userTokenType: UserTokenType,
    policyId: SecurityPolicy | string | null
): UserTokenPolicy | null {
    assert(endpoint_description instanceof EndpointDescription);
    const r = endpoint_description.userIdentityTokens!.filter(
        (userIdentity: UserTokenPolicy) =>
            userIdentity.tokenType === userTokenType && (!policyId || userIdentity.policyId === policyId)
    );
    return r.length === 0 ? null : r[0];
}

function findUserTokenPolicy(endpoint_description: EndpointDescription, userTokenType: UserTokenType): UserTokenPolicy | null {
    assert(endpoint_description instanceof EndpointDescription);
    const r = endpoint_description.userIdentityTokens!.filter((userIdentity: UserTokenPolicy) => {
        assert(userIdentity.tokenType !== undefined);
        return userIdentity.tokenType === userTokenType;
    });
    return r.length === 0 ? null : r[0];
}

function createAnonymousIdentityToken(endpoint_desc: EndpointDescription) {
    assert(endpoint_desc instanceof EndpointDescription);
    const userTokenPolicy = findUserTokenPolicy(endpoint_desc, UserTokenType.Anonymous);
    if (!userTokenPolicy) {
        throw new Error("Cannot find ANONYMOUS user token policy in end point description");
    }
    return new AnonymousIdentityToken({ policyId: userTokenPolicy.policyId });
}

function sameIdentityToken(token1: UserIdentityToken, token2: UserIdentityToken): boolean {
    if (token1 instanceof UserNameIdentityToken) {
        if (!(token2 instanceof UserNameIdentityToken)) {
            return false;
        }
        if (token1.userName !== token2.userName) {
            return false;
        }
        if (token1.password.toString("hex") !== token2.password.toString("hex")) {
            // note pasword hash may be different from two request and cannot be verified at this stage
            // we assume that we have a valid password
            // NOT CALLING return false;
        }
        return true;
    } else if (token1 instanceof AnonymousIdentityToken) {
        if (!(token2 instanceof AnonymousIdentityToken)) {
            return false;
        }
        if (token1.policyId !== token2.policyId) {
            return false;
        }
        return true;
    }
    assert(false, " Not implemented yet");
    return false;
}
function getTokenType(userIdentityToken: UserIdentityToken): UserTokenType {
    if (userIdentityToken instanceof AnonymousIdentityToken) {
        return UserTokenType.Anonymous;
    } else if (userIdentityToken instanceof UserNameIdentityToken) {
        return UserTokenType.UserName;
    } else if (userIdentityToken instanceof IssuedIdentityToken) {
        return UserTokenType.IssuedToken;
    } else if (userIdentityToken instanceof X509IdentityToken) {
        return UserTokenType.Certificate;
    }
    return UserTokenType.Invalid;
}
function thumbprint(certificate?: Certificate): string {
    return certificate ? certificate.toString("base64") : "";
}

/*=== private
 *
 * perform the read operation on a given node for a monitored item.
 * this method DOES NOT apply to Variable Values attribute
 *
 * @param self
 * @param oldValue
 * @param node
 * @param itemToMonitor
 * @private
 */
function monitoredItem_read_and_record_value(
    self: MonitoredItem,
    context: ISessionContext,
    oldValue: DataValue,
    node: UAVariable,
    itemToMonitor: any,
    callback: (err: Error | null, dataValue?: DataValue) => void
) {
    assert(self instanceof MonitoredItem);
    assert(oldValue instanceof DataValue);
    assert(itemToMonitor.attributeId === AttributeIds.Value);

    const dataValue = node.readAttribute(context, itemToMonitor.attributeId, itemToMonitor.indexRange, itemToMonitor.dataEncoding);

    callback(null, dataValue);
}

/*== private
 * this method applies to Variable Values attribute
 * @private
 */
function monitoredItem_read_and_record_value_async(
    self: MonitoredItem,
    context: ISessionContext,
    oldValue: DataValue,
    node: UAVariable,
    itemToMonitor: any,
    callback: (err: Error | null, dataValue?: DataValue) => void
) {
    assert(context instanceof SessionContext);
    assert(itemToMonitor.attributeId === AttributeIds.Value);
    assert(self instanceof MonitoredItem);
    assert(oldValue instanceof DataValue);
    // do it asynchronously ( this is only valid for value attributes )
    assert(itemToMonitor.attributeId === AttributeIds.Value);

    node.readValueAsync(context, (err: Error | null, dataValue?: DataValue) => {
        callback(err, dataValue);
    });
}

function build_scanning_node_function(addressSpace: AddressSpace, itemToMonitor: any): SamplingFunc {
    assert(itemToMonitor instanceof ReadValueId);

    const node = addressSpace.findNode(itemToMonitor.nodeId) as UAVariable;

    /* istanbul ignore next */
    if (!node) {
        errorLog(" INVALID NODE ID  , ", itemToMonitor.nodeId.toString());
        dump(itemToMonitor);
        return (
            _sessionContext: ISessionContext,
            _oldData: DataValue,
            callback: (err: Error | null, dataValue?: DataValue) => void
        ) => {
            callback(
                null,
                new DataValue({
                    statusCode: StatusCodes.BadNodeIdUnknown,
                    value: { dataType: DataType.Null, value: 0 }
                })
            );
        };
    }

    ///// !!monitoredItem.setNode(node);

    if (itemToMonitor.attributeId === AttributeIds.Value) {
        const monitoredItem_read_and_record_value_func =
            itemToMonitor.attributeId === AttributeIds.Value && typeof node.readValueAsync === "function"
                ? monitoredItem_read_and_record_value_async
                : monitoredItem_read_and_record_value;

        return function func(
            this: MonitoredItem,
            sessionContext: ISessionContext,
            oldDataValue: DataValue,
            callback: (err: Error | null, dataValue?: DataValue) => void
        ) {
            assert(this instanceof MonitoredItem);
            assert(oldDataValue instanceof DataValue);
            assert(typeof callback === "function");
            monitoredItem_read_and_record_value_func(this, sessionContext, oldDataValue, node, itemToMonitor, callback);
        };
    } else {
        // Attributes, other than the  Value  Attribute, are only monitored for a change in value.
        // The filter is not used for these  Attributes. Any change in value for these  Attributes
        // causes a  Notification  to be  generated.

        // only record value when it has changed
        return function func(
            this: MonitoredItem,
            sessionContext: ISessionContext,
            oldDataValue: DataValue,
            callback: (err: Error | null, dataValue?: DataValue) => void
        ) {
            assert(this instanceof MonitoredItem);
            assert(oldDataValue instanceof DataValue);
            assert(typeof callback === "function");
            const newDataValue = node.readAttribute(sessionContext, itemToMonitor.attributeId);
            callback(null, newDataValue);
        };
    }
}

function prepareMonitoredItem(context: ISessionContext, addressSpace: AddressSpace, monitoredItem: MonitoredItem) {
    const itemToMonitor = monitoredItem.itemToMonitor;
    const readNodeFunc = build_scanning_node_function(addressSpace, itemToMonitor);
    monitoredItem.samplingFunc = readNodeFunc;
}

function isMonitoringModeValid(monitoringMode: MonitoringMode): boolean {
    assert(MonitoringMode.Invalid !== undefined);
    return monitoringMode !== MonitoringMode.Invalid && monitoringMode <= MonitoringMode.Reporting;
}

function _installRegisterServerManager(self: OPCUAServer) {
    assert(self instanceof OPCUAServer);
    assert(!self.registerServerManager);

    /* istanbul ignore next */
    if (!self.registerServerMethod) {
        throw new Error("Internal Error");
    }

    switch (self.registerServerMethod) {
        case RegisterServerMethod.HIDDEN:
            self.registerServerManager = new RegisterServerManagerHidden({
                server: self
            });
            break;
        case RegisterServerMethod.MDNS:
            self.registerServerManager = new RegisterServerManagerMDNSONLY({
                server: self
            });
            break;
        case RegisterServerMethod.LDS:
            self.registerServerManager = new RegisterServerManager({
                discoveryServerEndpointUrl: self.discoveryServerEndpointUrl,
                server: self
            });
            break;
        /* istanbul ignore next */
        default:
            throw new Error("Invalid switch");
    }

    self.registerServerManager.on("serverRegistrationPending", () => {
        /**
         * emitted when the server is trying to registered the LDS
         * but when the connection to the lds has failed
         * serverRegistrationPending is sent when the backoff signal of the
         * connection process is raised
         * @event serverRegistrationPending
         */
        debugLog("serverRegistrationPending");
        self.emit("serverRegistrationPending");
    });
    self.registerServerManager.on("serverRegistered", () => {
        /**
         * emitted when the server is successfully registered to the LDS
         * @event serverRegistered
         */
        debugLog("serverRegistered");
        self.emit("serverRegistered");
    });
    self.registerServerManager.on("serverRegistrationRenewed", () => {
        /**
         * emitted when the server has successfully renewed its registration to the LDS
         * @event serverRegistrationRenewed
         */
        debugLog("serverRegistrationRenewed");
        self.emit("serverRegistrationRenewed");
    });

    self.registerServerManager.on("serverUnregistered", () => {
        debugLog("serverUnregistered");
        /**
         * emitted when the server is successfully unregistered to the LDS
         * ( for instance during shutdown)
         * @event serverUnregistered
         */
        self.emit("serverUnregistered");
    });
}

function validate_applicationUri(channel: ServerSecureChannelLayer, request: CreateSessionRequest): boolean {
    const applicationUri = request.clientDescription.applicationUri!;
    const clientCertificate = request.clientCertificate;
    // if session is insecure there is no need to check certificate information
    if (channel.securityMode === MessageSecurityMode.None) {
        return true; // assume correct
    }
    if (!clientCertificate || clientCertificate.length === 0) {
        return true; // can't check
    }
    const e = exploreCertificate(clientCertificate);
    const uniformResourceIdentifier = e.tbsCertificate.extensions!.subjectAltName?.uniformResourceIdentifier ?? null;
    const applicationUriFromCert =
        uniformResourceIdentifier && uniformResourceIdentifier.length > 0 ? uniformResourceIdentifier[0] : null;

    /* istanbul ignore next */
    if (applicationUriFromCert !== applicationUri) {
        errorLog("BadCertificateUriInvalid!");
        errorLog("applicationUri           = ", applicationUri);
        errorLog("applicationUriFromCert   = ", applicationUriFromCert);
    }

    return applicationUriFromCert === applicationUri;
}

function validate_security_endpoint(
    server: OPCUAServer,
    request: CreateSessionRequest,
    channel: ServerSecureChannelLayer
): {
    errCode: StatusCode;
    endpoint?: EndpointDescription;
} {
    debugLog("validate_security_endpoint = ", request.endpointUrl);
    let endpoints = server._get_endpoints(request.endpointUrl);
    // endpointUrl String The network address that the Client used to access the Session Endpoint.
    //             The HostName portion of the URL should be one of the HostNames for the application that are
    //             specified in the Server’s ApplicationInstanceCertificate (see 7.2). The Server shall raise an
    //             AuditUrlMismatchEventType event if the URL does not match the Server’s HostNames.
    //             AuditUrlMismatchEventType event type is defined in Part 5.
    //             The Server uses this information for diagnostics and to determine the set of
    //             EndpointDescriptions to return in the response.
    // ToDo: check endpointUrl validity and emit an AuditUrlMismatchEventType event if not

    // sometime endpoints have a extra leading "/" that can be ignored
    // don't be too harsh.
    if (endpoints.length === 0 && request.endpointUrl?.endsWith("/")) {
        endpoints = server._get_endpoints(request.endpointUrl.slice(0, -1));
    }

    if (endpoints.length === 0) {
        // we have a UrlMismatch here
        const ua_server = server.engine.addressSpace!.rootFolder.objects.server;
        if (!request.endpointUrl?.match(/localhost/i) || OPCUAServer.requestExactEndpointUrl) {
            warningLog("Cannot find suitable endpoints in available endpoints. endpointUri =", request.endpointUrl);
        }
        ua_server.raiseEvent("AuditUrlMismatchEventType", {
            endpointUrl: { dataType: DataType.String, value: request.endpointUrl }
        });
        if (OPCUAServer.requestExactEndpointUrl) {
            return { errCode: StatusCodes.BadServiceUnsupported };
        } else {
            endpoints = server._get_endpoints(null);
        }
    }
    // ignore restricted endpoints
    endpoints = endpoints.filter((e: EndpointDescription) => !(e as EndpointDescriptionEx).restricted);

    const endpoints_matching_security_mode = endpoints.filter((e: EndpointDescription) => {
        return e.securityMode === channel.securityMode;
    });

    if (endpoints_matching_security_mode.length === 0) {
        return { errCode: StatusCodes.BadSecurityModeRejected };
    }
    const endpoints_matching_security_policy = endpoints_matching_security_mode.filter((e: EndpointDescription) => {
        return e.securityPolicyUri === channel!.securityPolicy;
    });

    if (endpoints_matching_security_policy.length === 0) {
        return { errCode: StatusCodes.BadSecurityPolicyRejected };
    }
    if (endpoints_matching_security_policy.length !== 1) {
        debugLog("endpoints_matching_security_policy= ", endpoints_matching_security_policy.length);
    }
    return { errCode: StatusCodes.Good, endpoint: endpoints_matching_security_policy[0] };
}

export function filterDiagnosticInfo(returnDiagnostics: number, response: CallResponse): void {
    if (RESPONSE_DIAGNOSTICS_MASK_ALL & returnDiagnostics) {
        response.responseHeader.serviceDiagnostics = filterDiagnosticServiceLevel(
            returnDiagnostics,
            response.responseHeader.serviceDiagnostics
        );

        if (response.diagnosticInfos && response.diagnosticInfos.length > 0) {
            response.diagnosticInfos = response.diagnosticInfos.map((d) => filterDiagnosticOperationLevel(returnDiagnostics, d));
        } else {
            response.diagnosticInfos = [];
        }

        if (response.results) {
            for (const entry of response.results) {
                if (entry.inputArgumentDiagnosticInfos && entry.inputArgumentDiagnosticInfos.length > 0) {
                    entry.inputArgumentDiagnosticInfos = entry.inputArgumentDiagnosticInfos.map((d) =>
                        filterDiagnosticOperationLevel(returnDiagnostics, d)
                    );
                } else {
                    entry.inputArgumentDiagnosticInfos = [];
                }
            }
        }
    }
}

export enum RegisterServerMethod {
    HIDDEN = 1, // the server doesn't expose itself to the external world
    MDNS = 2, // the server publish itself to the mDNS Multicast network directly
    LDS = 3 // the server registers itself to the LDS or LDS-ME (Local Discovery Server)
}

export interface OPCUAServerEndpointOptions {
    /**
     * the primary hostname of the endpoint.
     * @default getFullyQualifiedDomainName()
     */
    hostname?: string;
    /**
     * Host IP address or hostname where the TCP server listens for connections.
     * If omitted, defaults to listening on all network interfaces:
     * - Unspecified IPv6 address (::) if IPv6 is available,
     * - Unspecified IPv4 address (0.0.0.0) otherwise.
     * Use this to bind the server to a specific interface or IP.
     */
    host?: string;
    /**
     * the TCP port to listen to.
     * @default 26543
     */
    port?: number;
    /**
     * the possible security policies that the server will expose
     * @default  [SecurityPolicy.None, SecurityPolicy.Basic128Rsa15, SecurityPolicy.Basic256Sha256, SecurityPolicy.Aes128_Sha256_RsaOaep, SecurityPolicy.Aes256_Sha256_RsaPss  ]
     */
    securityPolicies?: SecurityPolicy[];
    /**
     * the possible security mode that the server will expose
     * @default [MessageSecurityMode.None, MessageSecurityMode.Sign, MessageSecurityMode.SignAndEncrypt]
     */
    securityModes?: MessageSecurityMode[];
    /**
     * tells if the server default endpoints should allow anonymous connection.
     * @default true
     */
    allowAnonymous?: boolean;

    /** alternate hostname  or IP to use */
    alternateHostname?: string | string[];

    /**
     *  true, if discovery service on secure channel shall be disabled
     */
    disableDiscovery?: boolean;
}

export interface OPCUAServerOptions extends OPCUABaseServerOptions, OPCUAServerEndpointOptions {
    /**
     * @deprecated
     */
    alternateEndpoints?: OPCUAServerEndpointOptions[];
    endpoints?: OPCUAServerEndpointOptions[];

    /**
     * the server certificate full path filename
     *
     * the certificate should be in PEM format
     */
    certificateFile?: string;
    /**
     * the server private key full path filename
     *
     * This file should contains the private key that has been used to generate
     * the server certificate file.
     *
     * the private key should be in PEM format
     *
     */
    privateKeyFile?: string;

    /**
     * the default secure token life time in ms.
     */
    defaultSecureTokenLifetime?: number;
    /**
     * the HEL/ACK transaction timeout in ms.
     *
     * Use a large value ( i.e 15000 ms) for slow connections or embedded devices.
     * @default 10000
     */
    timeout?: number;

    /**
     * the maximum number of simultaneous sessions allowed.
     * @default 10
     * @deprecated use serverCapabilities: { maxSessions: } instead

     */
    maxAllowedSessionNumber?: number;

    /**
     * the maximum number authorized simultaneous connections per endpoint
     * @default 10
     */
    maxConnectionsPerEndpoint?: number;

    /**
     * the nodeset.xml file(s) to load
     *
     * node-opcua comes with pre-installed node-set files that can be used
     *
     * example:
     *
     * ```javascript
     * import { nodesets } from "node-opcua-nodesets";
     * const server = new OPCUAServer({
     *     nodeset_filename: [
     *         nodesets.standard,
     *         nodesets.di,
     *         nodesets.adi,
     *         nodesets.machinery,
     *     ],
     * });
     * ```
     */
    nodeset_filename?: string[] | string;

    /**
     * the server Info
     *
     * this object contains the value that will populate the
     * Root/ObjectS/Server/ServerInfo OPCUA object in the address space.
     */
    serverInfo?: ApplicationDescriptionOptions;
    /*{
          applicationUri?: string;
          productUri?: string;
          applicationName?: LocalizedTextLike | string;
          gatewayServerUri?: string | null;
          discoveryProfileUri?: string | null;
          discoveryUrls?: string[];
      };
  */
    buildInfo?: {
        productName?: string;
        productUri?: string | null; // << should be same as default_server_info.productUri?
        manufacturerName?: string;
        softwareVersion?: string;
        buildNumber?: string;
        buildDate?: Date;
    };

    /**
     *  an object that implements user authentication methods
     */
    userManager?: UserManagerOptions;

    /** resource Path is a string added at the end of the url such as "/UA/Server" */
    resourcePath?: string;

    /**
     *
     */
    serverCapabilities?: ServerCapabilitiesOptions;
    /**
     * if server shall raise AuditingEvent
     * @default true
     */
    isAuditing?: boolean;

    /**
     * strategy used by the server to declare itself to a discovery server
     *
     * - HIDDEN: the server doesn't expose itself to the external world
     * - MDNS: the server publish itself to the mDNS Multicast network directly
     * - LDS: the server registers itself to the LDS or LDS-ME (Local Discovery Server)
     *
     *  @default    .HIDDEN - by default the server
     *            will not register itself to the local discovery server
     *
     */
    registerServerMethod?: RegisterServerMethod;
    /**
     *
     * @default "opc.tcp://localhost:4840"]
     */
    discoveryServerEndpointUrl?: string;
    /**
     *
     *  supported server capabilities for the Multicast (mDNS)
     *  @default ["NA"]
     *  the possible values are any of node-opcua-discovery.serverCapabilities)
     *
     */
    capabilitiesForMDNS?: string[];

    /**
     * user Certificate Manager
     * this certificate manager holds the X509 certificates used
     * by client that uses X509 certificate token to impersonate a user
     */
    userCertificateManager?: OPCUACertificateManager;
    /**
     * Server Certificate Manager
     *
     * this certificate manager will be used by the server to access
     * and store certificates from the connecting clients
     */
    serverCertificateManager?: OPCUACertificateManager;

    /**
     *
     */
    onCreateMonitoredItem?: CreateMonitoredItemHook;
    onDeleteMonitoredItem?: DeleteMonitoredItemHook;

    /**
     * skipOwnNamespace to true, if you don't want the server to create
     * a dedicated namespace for its own (namespace=1).
     * Use this flag if you intend to load the server own namespace
     * from an external source.
     * @default false
     */
    skipOwnNamespace?: boolean;
    transportSettings?: IServerTransportSettings;
}

// eslint-disable-next-line @typescript-eslint/no-unsafe-declaration-merging
export interface OPCUAServer {
    /**
     *
     */
    engine: ServerEngine;
    /**
     *
     */
    registerServerMethod: RegisterServerMethod;
    /**
     *
     */
    discoveryServerEndpointUrl: string;
    /**
     *
     */
    registerServerManager?: IRegisterServerManager;
    /**
     *
     */
    capabilitiesForMDNS: string[];
    /**
     *
     */
    userCertificateManager: OPCUACertificateManager;
}

const g_requestExactEndpointUrl = !!process.env.NODEOPCUA_SERVER_REQUEST_EXACT_ENDPOINT_URL;
/**
 *
 */
export class OPCUAServer extends OPCUABaseServer {
    static defaultShutdownTimeout = 100; // 250 ms
    /**
     * if requestExactEndpointUrl is set to true the server will only accept createSession that have a endpointUrl that strictly matches
     * one of the provided endpoint.
     * This mean that if the server expose a endpoint with url such as opc.tcp://MYHOSTNAME:1234, client will not be able to reach the server
     * with the ip address of the server.
     * requestExactEndpointUrl = true => emulates the Prosys Server behavior
     * requestExactEndpointUrl = false => emulates the Unified Automation behavior.
     */
    static requestExactEndpointUrl: boolean = g_requestExactEndpointUrl;
    /**
     * total number of bytes written  by the server since startup
     */
    public get bytesWritten(): number {
        return this.endpoints.reduce((accumulated: number, endpoint: OPCUAServerEndPoint) => {
            return accumulated + endpoint.bytesWritten;
        }, 0);
    }

    /**
     * total number of bytes read  by the server since startup
     */
    public get bytesRead(): number {
        return this.endpoints.reduce((accumulated: number, endpoint: OPCUAServerEndPoint) => {
            return accumulated + endpoint.bytesRead;
        }, 0);
    }

    /**
     * Number of transactions processed by the server since startup
     */
    public get transactionsCount(): number {
        return this.endpoints.reduce((accumulated: number, endpoint: OPCUAServerEndPoint) => {
            return accumulated + endpoint.transactionsCount;
        }, 0);
    }

    /**
     * The server build info
     */
    public get buildInfo(): BuildInfo {
        return this.engine.buildInfo;
    }

    /**
     * the number of connected channel on all existing end points
     */
    public get currentChannelCount(): number {
        // TODO : move to base
        return this.endpoints.reduce((currentValue: number, endPoint: OPCUAServerEndPoint) => {
            return currentValue + endPoint.currentChannelCount;
        }, 0);
    }

    /**
     * The number of active subscriptions from all sessions
     */
    public get currentSubscriptionCount(): number {
        return this.engine ? this.engine.currentSubscriptionCount : 0;
    }

    /**
     * the number of session activation requests that have been rejected
     */
    public get rejectedSessionCount(): number {
        return this.engine ? this.engine.rejectedSessionCount : 0;
    }

    /**
     * the number of request that have been rejected
     */
    public get rejectedRequestsCount(): number {
        return this.engine ? this.engine.rejectedRequestsCount : 0;
    }

    /**
     * the number of sessions that have been aborted
     */
    public get sessionAbortCount(): number {
        return this.engine ? this.engine.sessionAbortCount : 0;
    }

    /**
     * the publishing interval count
     */
    public get publishingIntervalCount(): number {
        return this.engine ? this.engine.publishingIntervalCount : 0;
    }

    /**
     * the number of sessions currently active
     */
    public get currentSessionCount(): number {
        return this.engine ? this.engine.currentSessionCount : 0;
    }

    /**
     * true if the server has been initialized
     *
     */
    public get initialized(): boolean {
        return this.engine && this.engine.addressSpace !== null;
    }

    /**
     * is the server auditing ?
     */
    public get isAuditing(): boolean {
        return this.engine ? this.engine.isAuditing : false;
    }

    public static registry = new ObjectRegistry();
    public static fallbackSessionName = "Client didn't provide a meaningful sessionName ...";
    /**
     * the maximum number of subscription that can be created per server
     * @deprecated
     */
    public static deprecated_MAX_SUBSCRIPTION = 50;

    /**
     * the maximum number of concurrent sessions allowed on the server
     */
    public get maxAllowedSessionNumber(): number {
        return this.engine.serverCapabilities.maxSessions;
    }

    /**
     * the maximum number for concurrent connection per end point
     */
    public maxConnectionsPerEndpoint: number;

    /**
     * false if anonymous connection are not allowed
     */
    public allowAnonymous = false;

    /**
     * the user manager
     */
    public userManager: UAUserManagerBase;

    public readonly options: OPCUAServerOptions;

    private objectFactory?: Factory;

    private _delayInit?: () => Promise<void>;

    constructor(options?: OPCUAServerOptions) {
        super(options);

        this.allowAnonymous = false;
        options = options || {};

        this.options = options;

        if (options.maxAllowedSessionNumber !== undefined) {
            warningLog(
                "[NODE-OPCUA-W21] maxAllowedSessionNumber property is now deprecated , please use serverCapabilities.maxSessions instead"
            );
            options.serverCapabilities = options.serverCapabilities || {};
            options.serverCapabilities.maxSessions = options.maxAllowedSessionNumber;
        }
        // adjust securityPolicies if any
        if (options.securityPolicies) {
            options.securityPolicies = options.securityPolicies.map(coerceSecurityPolicy);
        }

        /**
         * @property maxConnectionsPerEndpoint
         */
        this.maxConnectionsPerEndpoint = options.maxConnectionsPerEndpoint || default_maxConnectionsPerEndpoint;

        // build Info
        const buildInfo: BuildInfoOptions = {
            ...default_build_info,
            ...options.buildInfo
        };

        // repair product name
        buildInfo.productUri = buildInfo.productUri || this.serverInfo.productUri;
        this.serverInfo.productUri = this.serverInfo.productUri || buildInfo.productUri;

        this.userManager = makeUserManager(options.userManager);

        options.allowAnonymous = options.allowAnonymous === undefined ? true : !!options.allowAnonymous;
        /**
         * @property allowAnonymous
         */
        this.allowAnonymous = options.allowAnonymous;

        this.discoveryServerEndpointUrl = options.discoveryServerEndpointUrl || "opc.tcp://%FQDN%:4840";
        assert(typeof this.discoveryServerEndpointUrl === "string");

        this.serverInfo.applicationType =
            options.serverInfo?.applicationType === undefined ? ApplicationType.Server : options.serverInfo.applicationType;

        this.capabilitiesForMDNS = options.capabilitiesForMDNS || ["NA"];
        this.registerServerMethod = options.registerServerMethod || RegisterServerMethod.HIDDEN;
        _installRegisterServerManager(this);

        if (!options.userCertificateManager) {
            this.userCertificateManager = getDefaultCertificateManager("UserPKI");
        } else {
            this.userCertificateManager = options.userCertificateManager;
        }

        // note: we need to delay initialization of endpoint as certain resources
        // such as %FQDN% might not be ready yet at this stage
        this._delayInit = async () => {
            /* istanbul ignore next */
            if (!options) {
                throw new Error("Internal Error");
            }
            // to check => this.serverInfo.applicationName = this.serverInfo.productName || buildInfo.productName;

            // note: applicationUri is handled in a special way
            this.engine = new ServerEngine({
                applicationUri: () => this.serverInfo.applicationUri!,
                buildInfo,
                isAuditing: options.isAuditing,
                serverCapabilities: options.serverCapabilities,

                serverConfiguration: {
                    serverCapabilities: () => {
                        return this.capabilitiesForMDNS || ["NA"];
                    },
                    supportedPrivateKeyFormat: ["PEM"],
                    applicationType: () => this.serverInfo.applicationType,
                    applicationUri: () => this.serverInfo.applicationUri || "",
                    productUri: () => this.serverInfo.productUri || "",
                    // hasSecureElement: () => false,
                    multicastDnsEnabled: () => this.registerServerMethod === RegisterServerMethod.MDNS
                }
            });

            this.objectFactory = new Factory(this.engine);

            const endpointDefinitions: OPCUAServerEndpointOptions[] = [
                ...(options.endpoints || []),
                ...(options.alternateEndpoints || [])
            ];

            const hostname = getFullyQualifiedDomainName();
            endpointDefinitions.forEach((endpointDefinition) => {
                endpointDefinition.port = endpointDefinition.port === undefined ? 26543 : endpointDefinition.port;
                endpointDefinition.hostname = endpointDefinition.hostname || hostname;
            });

            if (!options.endpoints) {
                endpointDefinitions.push({
                    port: options.port === undefined ? 26543 : options.port,
                    hostname: options.hostname || hostname,
                    host: options.host,
                    allowAnonymous: options.allowAnonymous,
                    alternateHostname: options.alternateHostname,
                    disableDiscovery: options.disableDiscovery,
                    securityModes: options.securityModes,
                    securityPolicies: options.securityPolicies
                });
            }
            // todo  should self.serverInfo.productUri  match self.engine.buildInfo.productUri ?
            for (const endpointOptions of endpointDefinitions) {
                const endPoint = this.createEndpointDescriptions(options!, endpointOptions);
                this.endpoints.push(endPoint);
                endPoint.on("message", (message: Message, channel: ServerSecureChannelLayer) => {
                    this.on_request(message, channel);
                });

                // endPoint.on("error", (err: Error) => {
                //     errorLog("OPCUAServer endpoint error", err);
                //     // set serverState to ServerState.Failed;
                //     this.engine.setServerState(ServerState.Failed);
                //     this.shutdown(() => {
                //         /* empty */
                //     });
                // });
            }
        };
    }

    /**
     * Initialize the server by installing default node set.
     *
     * and instruct the server to listen to its endpoints.
     *
     * ```javascript
     * const server = new OPCUAServer();
     * await server.initialize();
     *
     * // default server namespace is now initialized
     * // it is a good time to create life instance objects
     * const namespace = server.engine.addressSpace.getOwnNamespace();
     * namespace.addObject({
     *     browseName: "SomeObject",
     *     organizedBy: server.engine.addressSpace.rootFolder.objects
     * });
     *
     * // the addressSpace is now complete
     * // let's now start listening to clients
     * await server.start();
     * ```
     */
    public initialize(): Promise<void>;
    public initialize(done: () => void): void;
    public initialize(...args: [any?, ...any[]]): any {
        const done = args[0] as (err?: Error) => void;
        assert(!this.initialized, "server is already initialized"); // already initialized ?

        this._preInitTask.push(async () => {
            /* istanbul ignore else */
            if (this._delayInit) {
                await this._delayInit();
                this._delayInit = undefined;
            }
        });

        this.performPreInitialization()
            .then(() => {
                OPCUAServer.registry.register(this);
                this.engine.initialize(this.options, () => {
                    bindRoleSet(this.userManager, this.engine.addressSpace!);
                    setImmediate(() => {
                        this.emit("post_initialize");
                        done();
                    });
                });
            })
            .catch((err) => {
                done(err);
            });
    }

    /**
     * Initiate the server by starting all its endpoints
     */
    public start(): Promise<void>;
    public start(done: () => void): void;
    public start(...args: [any?, ...any[]]): any {
        const done = args[0] as () => void;
        const tasks: any[] = [];

        tasks.push(callbackify(extractFullyQualifiedDomainName));

        if (!this.initialized) {
            tasks.push((callback: ErrorCallback) => {
                this.initialize(callback);
            });
        }
        tasks.push((callback: ErrorCallback) => {
            super.start((err?: Error | null) => {
                if (err) {
                    this.shutdown((/*err2*/ err2?: Error) => {
                        callback(err);
                    });
                } else {
                    // we start the registration process asynchronously
                    // as we want to make server immediately available
                    this.registerServerManager!.start(() => {
                        /* empty */
                    });

                    setImmediate(callback);
                }
            });
        });

        async.series(tasks, done);
    }

    /**
     * shutdown all server endpoints
     * @param  timeout the timeout (in ms) before the server is actually shutdown
     *
     * @example
     *
     * ```javascript
     *    // shutdown immediately
     *    server.shutdown(function(err) {
     *    });
     * ```
     * ```ts
     *   // in typescript with promises
     *   server.shutdown(10000).then(()=>{
     *      console.log("Server has shutdown");
     *   });
     * ```
     * ```javascript
     *    // shutdown within 10 seconds
     *    server.engine.shutdownReason = coerceLocalizedText("Shutdown for maintenance");
     *    server.shutdown(10000,function(err) {
     *    });
     *   ```
     */
    public shutdown(timeout?: number): Promise<void>;
    public shutdown(callback: (err?: Error) => void): void;
    public shutdown(timeout: number, callback: (err?: Error) => void): void;
    public shutdown(...args: [any?, ...any[]]): any {
        const timeout = args.length === 1 ? OPCUAServer.defaultShutdownTimeout : (args[0] as number);
        const callback = (args.length === 1 ? args[0] : args[1]) as (err?: Error) => void;
        assert(typeof callback === "function");
        debugLog("OPCUAServer#shutdown (timeout = ", timeout, ")");

        /* istanbul ignore next */
        if (!this.engine) {
            return callback();
        }
        assert(this.engine);
        if (!this.engine.isStarted()) {
            // server may have been shot down already  , or may have fail to start !!
            const err = new Error("OPCUAServer#shutdown failure ! server doesn't seems to be started yet");
            return callback(err);
        }

        this.userCertificateManager.dispose();

        this.engine.setServerState(ServerState.Shutdown);

        const shutdownTime = new Date(Date.now() + timeout);
        this.engine.setShutdownTime(shutdownTime);

        debugLog("OPCUAServer is now un-registering itself from  the discovery server " + this.buildInfo);
        this.registerServerManager!.stop((err?: Error | null) => {
            debugLog("OPCUAServer unregistered from discovery server", err);
            setTimeout(async () => {
                await this.engine.shutdown();

                debugLog("OPCUAServer#shutdown: started");
                OPCUABaseServer.prototype.shutdown.call(this, (err1?: Error) => {
                    debugLog("OPCUAServer#shutdown: completed");

                    this.dispose();
                    callback(err1);
                });
            }, timeout);
        });
    }

    public dispose(): void {
        for (const endpoint of this.endpoints) {
            endpoint.dispose();
        }
        this.endpoints = [];

        this.removeAllListeners();

        if (this.registerServerManager) {
            this.registerServerManager.dispose();
            this.registerServerManager = undefined;
        }
        OPCUAServer.registry.unregister(this);

        /* istanbul ignore next */
        if (this.engine) {
            this.engine.dispose();
        }
    }

    public raiseEvent(eventType: "AuditSessionEventType", options: RaiseEventAuditSessionEventData): void;
    public raiseEvent(eventType: "AuditCreateSessionEventType", options: RaiseEventAuditCreateSessionEventData): void;
    public raiseEvent(eventType: "AuditActivateSessionEventType", options: RaiseEventAuditActivateSessionEventData): void;
    public raiseEvent(eventType: "AuditCreateSessionEventType", options: RaiseEventData): void;
    public raiseEvent(eventType: "AuditConditionCommentEventType", options: RaiseEventAuditConditionCommentEventData): void;
    public raiseEvent(eventType: "AuditUrlMismatchEventType", options: RaiseEventAuditUrlMismatchEventTypeData): void;
    public raiseEvent(eventType: "TransitionEventType", options: RaiseEventTransitionEventData): void;
    public raiseEvent(eventType: "AuditCertificateInvalidEventType", options: RaiseAuditCertificateInvalidEventData): void;
    public raiseEvent(eventType: "AuditCertificateExpiredEventType", options: RaiseAuditCertificateExpiredEventData): void;
    public raiseEvent(eventType: "AuditCertificateUntrustedEventType", options: RaiseAuditCertificateUntrustedEventData): void;
    public raiseEvent(eventType: "AuditCertificateRevokedEventType", options: RaiseAuditCertificateRevokedEventData): void;
    public raiseEvent(eventType: "AuditCertificateMismatchEventType", options: RaiseAuditCertificateMismatchEventData): void;

    public raiseEvent(eventType: EventTypeLike | UAObjectType, options: RaiseEventData): void {
        /* istanbul ignore next */
        if (!this.engine.addressSpace) {
            errorLog("addressSpace missing");
            return;
        }

        const server = this.engine.addressSpace.findNode("Server") as UAObject;

        /* istanbul ignore next */
        if (!server) {
            // xx throw new Error("OPCUAServer#raiseEvent : cannot find Server object");
            return;
        }

        let eventTypeNode: EventTypeLike | UAObjectType | null = eventType;
        if (typeof eventType === "string") {
            eventTypeNode = this.engine.addressSpace.findEventType(eventType);
            if (eventTypeNode) {
                return server.raiseEvent(eventTypeNode, options);
            } else {
                console.warn(" cannot find event type ", eventType);
            }
        } else {
            return server.raiseEvent(eventTypeNode, options);
        }
    }

    /**
     * create and register a new session
     * @private
     */
    protected createSession(options: CreateSessionOption): ServerSession {
        /* istanbul ignore next */
        if (!this.engine) {
            throw new Error("Internal Error");
        }
        return this.engine.createSession(options);
    }

    /**
     * retrieve a session by authentication token
     * @private
     */
    public getSession(authenticationToken: NodeId, activeOnly?: boolean): ServerSession | null {
        return this.engine ? this.engine.getSession(authenticationToken, activeOnly) : null;
    }

    /**
     *
     * @param channel
     * @param clientCertificate
     * @param clientNonce
     * @private
     */
    protected computeServerSignature(
        channel: ServerSecureChannelLayer,
        clientCertificate: Certificate,
        clientNonce: Nonce
    ): SignatureData | undefined {
        return computeSignature(clientCertificate, clientNonce, this.getPrivateKey(), channel.securityPolicy);
    }

    /**
     *
     * @param session
     * @param channel
     * @param clientSignature
     */
    protected verifyClientSignature(
        session: ServerSession,
        channel: ServerSecureChannelLayer,
        clientSignature: SignatureData
    ): boolean {
        const clientCertificate = channel.clientCertificate!;
        const securityPolicy = channel.securityPolicy;
        const serverCertificate = this.getCertificate();
        const result = verifySignature(serverCertificate, session.nonce!, clientSignature, clientCertificate, securityPolicy);
        return result;
    }

    protected isValidUserNameIdentityToken(
        channel: ServerSecureChannelLayer,
        session: ServerSession,
        userTokenPolicy: UserTokenPolicy,
        userIdentityToken: UserNameIdentityToken,
        userTokenSignature: SignatureData,
        callback: (err: Error | null, statusCode?: StatusCode) => void
    ): void {
        assert(userIdentityToken instanceof UserNameIdentityToken);

        const securityPolicy = adjustSecurityPolicy(channel, userTokenPolicy.securityPolicyUri);
        if (securityPolicy === SecurityPolicy.None) {
            return callback(null, StatusCodes.Good);
        }
        const cryptoFactory = getCryptoFactory(securityPolicy);

        /* istanbul ignore next */
        if (!cryptoFactory) {
            return callback(null, StatusCodes.BadSecurityPolicyRejected);
        }

        /* istanbul ignore next */
        if (userIdentityToken.encryptionAlgorithm !== cryptoFactory.asymmetricEncryptionAlgorithm) {
            errorLog("invalid encryptionAlgorithm");
            errorLog("userTokenPolicy", userTokenPolicy.toString());
            errorLog("userTokenPolicy", userIdentityToken.toString());
            return callback(null, StatusCodes.BadIdentityTokenInvalid);
        }
        const userName = userIdentityToken.userName;
        const password = userIdentityToken.password;
        if (!userName || !password) {
            return callback(null, StatusCodes.BadIdentityTokenInvalid);
        }
        return callback(null, StatusCodes.Good);
    }

    protected isValidX509IdentityToken(
        channel: ServerSecureChannelLayer,
        session: ServerSession,
        userTokenPolicy: UserTokenPolicy,
        userIdentityToken: X509IdentityToken,
        userTokenSignature: SignatureData,
        callback: (err: Error | null, statusCode?: StatusCode) => void
    ): void {
        assert(userIdentityToken instanceof X509IdentityToken);
        assert(typeof callback === "function");

        const securityPolicy = adjustSecurityPolicy(channel, userTokenPolicy.securityPolicyUri);

        const cryptoFactory = getCryptoFactory(securityPolicy);
        /* istanbul ignore next */
        if (!cryptoFactory) {
            return callback(null, StatusCodes.BadSecurityPolicyRejected);
        }

        if (!userTokenSignature || !userTokenSignature.signature) {
            this.raiseEvent("AuditCreateSessionEventType", {});

            return callback(null, StatusCodes.BadUserSignatureInvalid);
        }

        if (userIdentityToken.policyId !== userTokenPolicy.policyId) {
            errorLog("invalid encryptionAlgorithm");
            errorLog("userTokenPolicy", userTokenPolicy.toString());
            errorLog("userTokenPolicy", userIdentityToken.toString());
            return callback(null, StatusCodes.BadSecurityPolicyRejected);
        }
        const certificate = userIdentityToken.certificateData; /* as Certificate*/
        const nonce = session.nonce!;
        const serverCertificate = this.getCertificate();

        assert(serverCertificate instanceof Buffer);
        assert(certificate instanceof Buffer, "expecting certificate to be a Buffer");
        assert(nonce instanceof Buffer, "expecting nonce to be a Buffer");
        assert(userTokenSignature.signature instanceof Buffer, "expecting userTokenSignature to be a Buffer");

        // verify proof of possession by checking certificate signature & server nonce correctness
        if (!verifySignature(serverCertificate, nonce, userTokenSignature, certificate, securityPolicy)) {
            return callback(null, StatusCodes.BadUserSignatureInvalid);
        }

        // verify if certificate is Valid
        this.userCertificateManager!.checkCertificate(certificate, (err, certificateStatus) => {
            /* istanbul ignore next */
            if (err) {
                return callback(err);
            }
            if (this.isAuditing) {
                switch (certificateStatus) {
                    case StatusCodes.Good:
                        break;
                    case StatusCodes.BadCertificateUntrusted:
                        this.raiseEvent("AuditCertificateUntrustedEventType", {
                            certificate: { dataType: DataType.ByteString, value: certificate },
                            sourceName: { dataType: DataType.String, value: "Security/Certificate" }
                        });
                        break;
                    case StatusCodes.BadCertificateTimeInvalid:
                    case StatusCodes.BadCertificateIssuerTimeInvalid:
                        this.raiseEvent("AuditCertificateExpiredEventType", {
                            certificate: { dataType: DataType.ByteString, value: certificate },
                            sourceName: { dataType: DataType.String, value: "Security/Certificate" }
                        });
                        break;
                    case StatusCodes.BadCertificateRevoked:
                    case StatusCodes.BadCertificateRevocationUnknown:
                    case StatusCodes.BadCertificateIssuerRevocationUnknown:
                        this.raiseEvent("AuditCertificateRevokedEventType", {
                            certificate: { dataType: DataType.ByteString, value: certificate },
                            sourceName: { dataType: DataType.String, value: "Security/Certificate" }
                        });
                        break;
                    case StatusCodes.BadCertificateIssuerUseNotAllowed:
                    case StatusCodes.BadCertificateUseNotAllowed:
                    case StatusCodes.BadSecurityChecksFailed:
                        this.raiseEvent("AuditCertificateMismatchEventType", {
                            certificate: { dataType: DataType.ByteString, value: certificate },
                            sourceName: { dataType: DataType.String, value: "Security/Certificate" }
                        });
                        break;
                }
            }
            if (
                certificateStatus &&
                (StatusCodes.BadCertificateUntrusted.equals(certificateStatus) ||
                    StatusCodes.BadCertificateTimeInvalid.equals(certificateStatus) ||
                    StatusCodes.BadCertificateIssuerTimeInvalid.equals(certificateStatus) ||
                    StatusCodes.BadCertificateIssuerUseNotAllowed.equals(certificateStatus) ||
                    StatusCodes.BadCertificateIssuerRevocationUnknown.equals(certificateStatus) ||
                    StatusCodes.BadCertificateRevocationUnknown.equals(certificateStatus) ||
                    StatusCodes.BadCertificateRevoked.equals(certificateStatus) ||
                    StatusCodes.BadCertificateUseNotAllowed.equals(certificateStatus) ||
                    StatusCodes.BadSecurityChecksFailed.equals(certificateStatus) ||
                    !StatusCodes.Good.equals(certificateStatus))
            ) {
                debugLog("isValidX509IdentityToken => certificateStatus = ", certificateStatus?.toString());

                return callback(null, StatusCodes.BadIdentityTokenRejected);
            }
            if (StatusCodes.Good !== certificateStatus) {
                assert(certificateStatus instanceof StatusCode);
                return callback(null, certificateStatus);
                // return callback(null, StatusCodes.BadIdentityTokenInvalid);
            }

            // verify if certificate is truster or rejected
            // todo: StatusCodes.BadCertificateUntrusted

            // store untrusted certificate to rejected folder
            // todo:
            return callback(null, StatusCodes.Good);
        });
    }

    /**
     * @internal
     */
    protected userNameIdentityTokenAuthenticateUser(
        channel: ServerSecureChannelLayer,
        session: ServerSession,
        userTokenPolicy: UserTokenPolicy,
        userIdentityToken: UserNameIdentityToken,
        callback: (err: Error | null, isAuthorized?: boolean) => void
    ): void {
        assert(userIdentityToken instanceof UserNameIdentityToken);
        // assert(this.isValidUserNameIdentityToken(channel, session, userTokenPolicy, userIdentityToken));

        const securityPolicy = adjustSecurityPolicy(channel, userTokenPolicy.securityPolicyUri);

        const userName = userIdentityToken.userName!;
        let password: any = userIdentityToken.password;

        // decrypt password if necessary
        if (securityPolicy === SecurityPolicy.None) {
            // not good, password was sent in clear text ...
            password = password.toString();
        } else {
            const serverPrivateKey = this.getPrivateKey();

            const serverNonce = session.nonce!;
            assert(serverNonce instanceof Buffer);

            const cryptoFactory = getCryptoFactory(securityPolicy);
            /* istanbul ignore next */
            if (!cryptoFactory) {
                return callback(new Error(" Unsupported security Policy"));
            }

            const buff = cryptoFactory.asymmetricDecrypt(password, serverPrivateKey);

            // server certificate may be invalid and asymmetricDecrypt may fail
            if (!buff || buff.length < 4) {
                async.setImmediate(() => callback(null, false));
                return;
            }

            const length = buff.readUInt32LE(0) - serverNonce.length;
            password = buff.subarray(4, 4 + length).toString("utf-8");
        }

        this.userManager
            .isValidUser(session, userName, password)
            .then((isValid) => callback(null, isValid))
            .catch((err) => callback(err));
    }

    /**
     * @internal
     */
    protected isValidUserIdentityToken(
        channel: ServerSecureChannelLayer,
        session: ServerSession,
        userIdentityToken: UserIdentityToken,
        userTokenSignature: SignatureData,
        endpointDescription: EndpointDescription,
        callback: (err: Error | null, statusCode?: StatusCode) => void
    ): void {
        assert(typeof callback === "function");
        /* istanbul ignore next */
        if (!userIdentityToken) {
            throw new Error("Invalid token");
        }

        const userTokenType = getTokenType(userIdentityToken);

        const userTokenPolicy = findUserTokenByPolicy(endpointDescription, userTokenType, userIdentityToken.policyId!);
        if (!userTokenPolicy) {
            // cannot find token with this policyId
            return callback(null, StatusCodes.BadIdentityTokenInvalid);
        }
        //
        if (userIdentityToken instanceof UserNameIdentityToken) {
            return this.isValidUserNameIdentityToken(
                channel,
                session,
                userTokenPolicy,
                userIdentityToken,
                userTokenSignature,
                callback
            );
        }
        if (userIdentityToken instanceof X509IdentityToken) {
            return this.isValidX509IdentityToken(
                channel,
                session,
                userTokenPolicy,
                userIdentityToken,
                userTokenSignature,
                callback
            );
        }

        return callback(null, StatusCodes.Good);
    }

    /**
     *
     * @internal
     * @param channel
     * @param session
     * @param userIdentityToken
     * @param callback
     * @returns {*}
     */
    protected isUserAuthorized(
        channel: ServerSecureChannelLayer,
        session: ServerSession,
        userIdentityToken: UserIdentityToken,
        callback: (err: Error | null, isAuthorized?: boolean) => void
    ): void {
        assert(userIdentityToken);
        assert(typeof callback === "function");

        const userTokenType = getTokenType(userIdentityToken);
        const userTokenPolicy = findUserTokenByPolicy(session.getEndpointDescription(), userTokenType, userIdentityToken.policyId!);
        /** istanbul ignore next */
        if (!userTokenPolicy) {
            return callback(null, false);
        }
        // find if a userToken exists
        if (userIdentityToken instanceof UserNameIdentityToken) {
            return this.userNameIdentityTokenAuthenticateUser(channel, session, userTokenPolicy, userIdentityToken, callback);
        }
        async.setImmediate(callback.bind(null, null, true));
    }

    protected makeServerNonce(): Nonce {
        return randomBytes(32);
    }

    // session services
    // eslint-disable-next-line max-statements
    protected async _on_CreateSessionRequest(message: Message, channel: ServerSecureChannelLayer): Promise<void> {
        const request = message.request as CreateSessionRequest;
        assert(request instanceof CreateSessionRequest);

        function rejectConnection(server: OPCUAServer, statusCode: StatusCode): void {
            server.engine.incrementSecurityRejectedSessionCount();

            const response1 = new ServiceFault({
                responseHeader: { serviceResult: statusCode }
            });
            channel.send_response("MSG", response1, message);
            // and close !
        }

        // From OPCUA V1.03 Part 4 5.6.2 CreateSession
        // A Server application should limit the number of Sessions. To protect against misbehaving Clients and denial
        // of service attacks, the Server shall close the oldest Session that is not activated before reaching the
        // maximum number of supported Sessions
        if (this.currentSessionCount >= this.engine.serverCapabilities.maxSessions) {
            await _attempt_to_close_some_old_unactivated_session(this);
        }

        // check if session count hasn't reach the maximum allowed sessions
        if (this.currentSessionCount >= this.engine.serverCapabilities.maxSessions) {
            return rejectConnection(this, StatusCodes.BadTooManySessions);
        }

        // Release 1.03 OPC Unified Architecture, Part 4 page 24 - CreateSession Parameters
        // client should prove a sessionName
        // Session name is a Human readable string that identifies the Session. The Server makes this name and the
        // sessionId visible in its AddressSpace for diagnostic purposes. The Client should provide a name that is
        // unique for the instance of the Client.
        // If this parameter is not specified the Server shall assign a value.

        if (isNullOrUndefined(request.sessionName)) {
            // see also #198
            // let's the server assign a sessionName for this lazy client.

            debugLog(
                "assigning OPCUAServer.fallbackSessionName because client's sessionName is null ",
                OPCUAServer.fallbackSessionName
            );

            request.sessionName = OPCUAServer.fallbackSessionName;
        }

        // Duration Requested maximum number of milliseconds that a Session should remain open without activity.
        // If the Client fails to issue a Service request within this interval, then the Server shall automatically
        // terminate the Client Session.
        const revisedSessionTimeout = _adjust_session_timeout(request.requestedSessionTimeout);

        // Release 1.02 page 27 OPC Unified Architecture, Part 4: CreateSession.clientNonce
        // A random number that should never be used in any other request. This number shall have a minimum length of 32
        // bytes. Profiles may increase the required length. The Server shall use this value to prove possession of
        // its application instance Certificate in the response.
        if (!request.clientNonce || request.clientNonce.length < 32) {
            if (channel.securityMode !== MessageSecurityMode.None) {
                errorLog(
                    chalk.red("SERVER with secure connection: Missing or invalid client Nonce "),
                    request.clientNonce && request.clientNonce.toString("hex")
                );

                return rejectConnection(this, StatusCodes.BadNonceInvalid);
            }
        }
        if (nonceAlreadyBeenUsed(request.clientNonce)) {
            errorLog(
                chalk.red("SERVER with secure connection: None has already been used"),
                request.clientNonce && request.clientNonce.toString("hex")
            );

            return rejectConnection(this, StatusCodes.BadNonceInvalid);
        }
        // check application spoofing
        // check if applicationUri in createSessionRequest matches applicationUri in client Certificate
        if (!validate_applicationUri(channel, request)) {
            return rejectConnection(this, StatusCodes.BadCertificateUriInvalid);
        }

        const { errCode, endpoint } = validate_security_endpoint(this, request, channel);
        if (errCode !== StatusCodes.Good) {
            return rejectConnection(this, errCode);
        }

        // see Release 1.02  27  OPC Unified Architecture, Part 4
        const session = this.createSession({
            clientDescription: request.clientDescription,
            sessionTimeout: revisedSessionTimeout,
            server: this
        });
        session.endpoint = endpoint;

        assert(session);
        assert(session.sessionTimeout === revisedSessionTimeout);

        session.clientDescription = request.clientDescription;
        session.sessionName = request.sessionName || `<unknown session name ${unnamed_session_count++}>`;

        // Depending upon on the  SecurityPolicy  and the  SecurityMode  of the  SecureChannel,  the exchange of
        // ApplicationInstanceCertificates   and  Nonces  may be optional and the signatures may be empty. See
        // Part  7  for the definition of  SecurityPolicies  and the handling of these parameters

        // serverNonce:
        // A random number that should never be used in any other request.
        // This number shall have a minimum length of 32 bytes.
        // The Client shall use this value to prove possession of its application instance
        // Certificate in the ActivateSession request.
        // This value may also be used to prove possession of the userIdentityToken it
        // specified in the ActivateSession request.
        //
        // ( this serverNonce will only be used up to the _on_ActivateSessionRequest
        //   where a new nonce will be created)
        session.nonce = this.makeServerNonce();
        session.channelId = channel.channelId;

        session._attach_channel(channel);

        const serverCertificateChain = this.getCertificateChain();

        const hasEncryption = true;
        // If the securityPolicyUri is None and none of the UserTokenPolicies requires encryption
        if (session.channel!.securityMode === MessageSecurityMode.None) {
            // ToDo: Check that none of our insecure endpoint has a a UserTokenPolicy that require encryption
            // and set hasEncryption = false under this condition
        }

        const response = new CreateSessionResponse({
            // A identifier which uniquely identifies the session.
            sessionId: session.nodeId,

            // A unique identifier assigned by the Server to the Session.
            // The token used to authenticate the client in subsequent requests.
            authenticationToken: session.authenticationToken,

            revisedSessionTimeout,

            serverNonce: session.nonce,

            // serverCertificate: type ApplicationServerCertificate
            // The application instance Certificate issued to the Server.
            // A Server shall prove possession by using the private key to sign the Nonce provided
            // by the Client in the request. The Client shall verify that this Certificate is the same as
            // the one it used to create the SecureChannel.
            // The ApplicationInstanceCertificate type is defined in OpCUA 1.03 part 4 - $7.2 page 108
            // If the securityPolicyUri is None and none of the UserTokenPolicies requires
            // encryption, the Server shall not send an ApplicationInstanceCertificate and the Client
            // shall ignore the ApplicationInstanceCertificate.
            serverCertificate: hasEncryption ? serverCertificateChain : undefined,

            // The endpoints provided by the server.
            // The Server shall return a set of EndpointDescriptions available for the serverUri
            // specified in the request.[...]
            // The Client shall verify this list with the list from a Discovery Endpoint if it used a Discovery
            // Endpoint to fetch the EndpointDescriptions.
            // It is recommended that Servers only include the endpointUrl, securityMode,
            // securityPolicyUri, userIdentityTokens, transportProfileUri and securityLevel with all
            // other parameters set to null. Only the recommended parameters shall be verified by
            // the client.
            serverEndpoints: _serverEndpointsForCreateSessionResponse(this, session.endpoint!.endpointUrl, request.serverUri),

            // This parameter is deprecated and the array shall be empty.
            serverSoftwareCertificates: null,

            // This is a signature generated with the private key associated with the
            // serverCertificate. This parameter is calculated by appending the clientNonce to the
            // clientCertificate and signing the resulting sequence of bytes.
            // The SignatureAlgorithm shall be the AsymmetricSignatureAlgorithm specified in the
            // SecurityPolicy for the Endpoint.
            // The SignatureData type is defined in 7.30.
            serverSignature: this.computeServerSignature(channel, request.clientCertificate, request.clientNonce),

            // The maximum message size accepted by the server
            // The Client Communication Stack should return a Bad_RequestTooLarge error to the
            // application if a request message exceeds this limit.
            // The value zero indicates that this parameter is not used.
            maxRequestMessageSize: 0x4000000
        });

        this.emit("create_session", session);

        session.on("session_closed", (session1: ServerSession, deleteSubscriptions: boolean, reason: string) => {
            assert(typeof reason === "string");
            if (this.isAuditing) {
                assert(reason === "Timeout" || reason === "Terminated" || reason === "CloseSession" || reason === "Forcing");
                const sourceName = "Session/" + reason;

                this.raiseEvent("AuditSessionEventType", {
                    /* part 5 -  6.4.3 AuditEventType */
                    actionTimeStamp: { dataType: "DateTime", value: new Date() },
                    status: { dataType: "Boolean", value: true },

                    serverId: { dataType: "String", value: "" },

                    // ClientAuditEntryId contains the human-readable AuditEntryId defined in Part 3.
                    clientAuditEntryId: { dataType: "String", value: "" },

                    // The ClientUserId identifies the user of the client requesting an action. The ClientUserId can be
                    // obtained from the UserIdentityToken passed in the ActivateSession call.
                    clientUserId: { dataType: "String", value: "" },

                    sourceName: { dataType: "String", value: sourceName },

                    /* part 5 - 6.4.7 AuditSessionEventType */
                    sessionId: { dataType: "NodeId", value: session1.nodeId }
                });
            }

            this.emit("session_closed", session1, deleteSubscriptions);
        });

        if (this.isAuditing) {
            // ------------------------------------------------------------------------------------------------------
            this.raiseEvent("AuditCreateSessionEventType", {
                /* part 5 -  6.4.3 AuditEventType */
                actionTimeStamp: { dataType: "DateTime", value: new Date() },
                status: { dataType: "Boolean", value: true },

                serverId: { dataType: "String", value: "" },

                // ClientAuditEntryId contains the human-readable AuditEntryId defined in Part 3.
                clientAuditEntryId: { dataType: "String", value: "" },

                // The ClientUserId identifies the user of the client requesting an action. The ClientUserId can be
                // obtained from the UserIdentityToken passed in the ActivateSession call.
                clientUserId: { dataType: "String", value: "" },

                sourceName: { dataType: "String", value: "Session/CreateSession" },

                /* part 5 - 6.4.7 AuditSessionEventType */
                sessionId: { dataType: "NodeId", value: session.nodeId },

                /* part 5 - 6.4.8 AuditCreateSessionEventType */
                // SecureChannelId shall uniquely identify the SecureChannel. The application shall use the same
                // identifier in all AuditEvents related to the Session Service Set (AuditCreateSessionEventType,
                // AuditActivateSessionEventType and their subtypes) and the SecureChannel Service Set
                // (AuditChannelEventType and its subtypes
                secureChannelId: { dataType: "String", value: session.channel!.channelId!.toString() },

                // Duration
                revisedSessionTimeout: { dataType: "Duration", value: session.sessionTimeout },

                // clientCertificate
                clientCertificate: { dataType: "ByteString", value: session.channel!.clientCertificate },

                // clientCertificateThumbprint
                clientCertificateThumbprint: {
                    dataType: "String",
                    value: thumbprint(session.channel!.clientCertificate!)
                }
            });
        }
        // -----------------------------------------------------------------------------------------------------------

        assert(response.authenticationToken);
        channel.send_response("MSG", response, message);
    }

    // TODO : implement this:
    //
    // When the ActivateSession Service is called for the first time then the Server shall reject the request
    // if the SecureChannel is not same as the one associated with the CreateSession request.
    // Subsequent calls to ActivateSession may be associated with different SecureChannels. If this is the
    // case then the Server shall verify that the Certificate the Client used to create the new
    // SecureChannel is the same as the Certificate used to create the original SecureChannel. In addition,
    // the Server shall verify that the Client supplied a UserIdentityToken that is identical to the token
    // currently associated with the Session. Once the Server accepts the new SecureChannel it shall
    // reject requests sent via the old SecureChannel.
    /**
     *
     * @private
     *
     *
     */
    protected _on_ActivateSessionRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as ActivateSessionRequest;
        assert(request instanceof ActivateSessionRequest);

        // get session from authenticationToken
        const authenticationToken = request.requestHeader.authenticationToken;

        const session = this.getSession(authenticationToken);

        function rejectConnection(server: OPCUAServer, statusCode: StatusCode): void {
            if (statusCode.equals(StatusCodes.BadSessionIdInvalid)) {
                server.engine.incrementRejectedSessionCount();
            } else {
                server.engine.incrementRejectedSessionCount();
                server.engine.incrementSecurityRejectedSessionCount();
            }

            const response1 = new ActivateSessionResponse({ responseHeader: { serviceResult: statusCode } });

            channel.send_response("MSG", response1, message);
        }

        let response;

        /* istanbul ignore next */
        if (!session) {
            // this may happen when the server has been restarted and a client tries to reconnect, thinking
            // that the previous session may still be active
            debugLog(chalk.yellow.bold(" Bad Session in  _on_ActivateSessionRequest"), authenticationToken.toString());

            return rejectConnection(this, StatusCodes.BadSessionIdInvalid);
        }

        // tslint:disable-next-line: no-unused-expression
        session.keepAlive ? session.keepAlive() : void 0;

        // OpcUA 1.02 part 3 $5.6.3.1 ActiveSession Set page 29
        // When the ActivateSession  Service  is called f or the first time then the Server shall reject the request
        // if the  SecureChannel  is not same as the one associated with the  CreateSession  request.
        if (session.status === "new") {
            // xx if (channel.session_nonce !== session.nonce) {
            if (!channel_has_session(channel, session)) {
                // it looks like session activation is being using a channel that is not the
                // one that have been used to create the session
                errorLog(" channel.sessionTokens === " + Object.keys(channel.sessionTokens).join(" "));
                return rejectConnection(this, StatusCodes.BadSessionNotActivated);
            }
        }

        // OpcUA 1.02 part 3 $5.6.3.1 ActiveSession Set page 29
        // ... Subsequent calls to  ActivateSession  may be associated with different  SecureChannels.  If this is the
        // case then  the  Server  shall verify that the  Certificate  the  Client  used to create the new
        // SecureChannel  is the same as the  Certificate  used to create the original  SecureChannel.

        if (session.status === "active") {
            if (session.channel!.channelId !== channel.channelId) {
                warningLog(
                    " Session ",
                    session.sessionName,
                    " is being transferred from channel",
                    chalk.cyan(session.channel!.channelId!.toString()),
                    " to channel ",
                    chalk.cyan(channel.channelId!.toString())
                );

                // session is being reassigned to a new Channel,
                // we shall verify that the certificate used to create the Session is the same as the current
                // channel certificate.
                const old_channel_cert_thumbprint = thumbprint(session.channel!.clientCertificate!);
                const new_channel_cert_thumbprint = thumbprint(channel.clientCertificate!);

                if (old_channel_cert_thumbprint !== new_channel_cert_thumbprint) {
                    return rejectConnection(this, StatusCodes.BadNoValidCertificates); // not sure about this code !
                }

                // ... In addition the Server shall verify that the  Client  supplied a  UserIdentityToken  that is
                // identical to the token currently associated with the  Session reassign session to new channel.
                if (!sameIdentityToken(session.userIdentityToken!, request.userIdentityToken as UserIdentityToken)) {
                    return rejectConnection(this, StatusCodes.BadIdentityChangeNotSupported); // not sure about this code !
                }
            }
        } else if (session.status === "screwed") {
            // session has been used before being activated => this should be detected and session should be dismissed.
            return rejectConnection(this, StatusCodes.BadSessionClosed);
        } else if (session.status === "closed") {
            warningLog(chalk.yellow.bold(" Bad Session Closed in  _on_ActivateSessionRequest"), authenticationToken.toString());
            return rejectConnection(this, StatusCodes.BadSessionClosed);
        }

        // verify clientSignature provided by the client
        if (!this.verifyClientSignature(session, channel, request.clientSignature)) {
            return rejectConnection(this, StatusCodes.BadApplicationSignatureInvalid);
        }

        // userIdentityToken may be missing , assume anonymous access then
        request.userIdentityToken = request.userIdentityToken || createAnonymousIdentityToken(session.endpoint!);

        // check request.userIdentityToken is correct ( expected type and correctly formed)
        this.isValidUserIdentityToken(
            channel,
            session,
            request.userIdentityToken as UserIdentityToken,
            request.userTokenSignature,
            session.endpoint!,
            (err: Error | null, statusCode?: StatusCode) => {
                if (!statusCode || statusCode.isNotGood()) {
                    /* istanbul ignore next */
                    if (!(statusCode && statusCode instanceof StatusCode)) {
                        return rejectConnection(this, StatusCodes.BadCertificateInvalid);
                    }
                    return rejectConnection(this, statusCode);
                }

                // check if user access is granted
                this.isUserAuthorized(
                    channel,
                    session,
                    request.userIdentityToken as UserIdentityToken,
                    (err1: Error | null, authorized?: boolean) => {
                        /* istanbul ignore next */
                        if (err1) {
                            return rejectConnection(this, StatusCodes.BadInternalError);
                        }

                        if (!authorized) {
                            return rejectConnection(this, StatusCodes.BadUserAccessDenied);
                        } else {
                            if (session.status === "active") {
                                moveSessionToChannel(session, channel);
                            }
                            session.userIdentityToken = request.userIdentityToken as UserIdentityToken;

                            // extract : OPC UA part 4 - 5.6.3
                            // Once used, a serverNonce cannot be used again. For that reason, the Server returns a new
                            // serverNonce each time the ActivateSession Service is called.
                            session.nonce = this.makeServerNonce();

                            session.status = "active";

                            response = new ActivateSessionResponse({ serverNonce: session.nonce });
                            channel.send_response("MSG", response, message);

                            // send OPCUA Event Notification
                            // see part 5 : 6.4.3 AuditEventType
                            //              6.4.7 AuditSessionEventType
                            //              6.4.10 AuditActivateSessionEventType
                            assert(session.nodeId); // sessionId
                            // xx assert(session.channel.clientCertificate instanceof Buffer);
                            assert(session.sessionTimeout > 0);

                            raiseAuditActivateSessionEventType.call(this, session);

                            this.emit("session_activated", session, userIdentityTokenPasswordRemoved(session.userIdentityToken));

                            session.resendMonitoredItemInitialValues();
                        }
                    }
                );
            }
        );
    }

    protected prepare(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request;

        // --- check that session is correct
        const authenticationToken = request.requestHeader.authenticationToken;
        const session = this.getSession(authenticationToken, /*activeOnly*/ true);
        if (!session) {
            message.session_statusCode = StatusCodes.BadSessionIdInvalid;
            return;
        }
        message.session = session;

        // --- check that provided session matches session attached to channel
        if (channel.channelId !== session.channelId) {
            if (!(request instanceof ActivateSessionRequest)) {
                errorLog(
                    chalk.red.bgWhite(
                        "ERROR: channel.channelId !== session.channelId  on processing request " + request.constructor.name
                    ),
                    channel.channelId,
                    session.channelId
                );
            }
            message.session_statusCode = StatusCodes.BadSecureChannelIdInvalid;
        } else if (channel_has_session(channel, session)) {
            message.session_statusCode = StatusCodes.Good;
        } else {
            // session ma y have been moved to a different channel
            message.session_statusCode = StatusCodes.BadSecureChannelIdInvalid;
        }
    }

    /**
     * ensure that action is performed on a valid session object,
     * @param ResponseClass the constructor of the response Class
     * @param message
     * @param channel
     * @param actionToPerform
     * @param actionToPerform.session {ServerSession}
     * @param actionToPerform.sendResponse
     * @param actionToPerform.sendResponse.response
     * @param actionToPerform.sendError
     * @param actionToPerform.sendError.statusCode
     * @param actionToPerform.sendError.diagnostics
     *
     * @private
     */
    protected async _apply_on_SessionObject(
        ResponseClass: ResponseClassType,
        message: Message,
        channel: ServerSecureChannelLayer,
        actionToPerform: (
            session: ServerSession,
            sendResponse: (response: Response) => void,
            sendError: (statusCode: StatusCode) => void
        ) => void | Promise<void>
    ): Promise<void> {
        assert(typeof actionToPerform === "function");

        function sendResponse(response1: Response) {
            try {
                assert(response1 instanceof ResponseClass || response1 instanceof ServiceFault);
                if (message.session) {
                    const counterName = ResponseClass.schema.name.replace("Response", "");
                    message.session.incrementRequestTotalCounter(counterName);
                }
                return channel.send_response("MSG", response1, message);
            } catch (err) {
                warningLog(err);
                // istanbul ignore next
                if (types.isNativeError(err)) {
                    // istanbul ignore next
                    errorLog(
                        "Internal error in issuing response\nplease contact support@sterfive.com",
                        message.request.toString(),
                        "\n",
                        response1.toString()
                    );
                }
                // istanbul ignore next
                throw err;
            }
        }

        function sendError(statusCode: StatusCode) {
            if (message.session) {
                message.session.incrementRequestErrorCounter(ResponseClass.schema.name.replace("Response", ""));
            }
            return g_sendError(channel, message, ResponseClass, statusCode);
        }

        let response: any;
        /* istanbul ignore next */
        if (!message.session || message.session_statusCode !== StatusCodes.Good) {
            const errMessage = "=>" + message.session_statusCode?.toString();
            response = new ServiceFault({ responseHeader: { serviceResult: message.session_statusCode } });
            debugLog(chalk.red.bold(errMessage), chalk.yellow(message.session_statusCode!.toString()), response.constructor.name);
            return sendResponse(response);
        }

        assert(message.session_statusCode.isGood());

        // OPC UA Specification 1.02 part 4 page 26
        // When a  Session  is terminated, all outstanding requests on the  Session  are aborted and
        // Bad_SessionClosed  StatusCodes  are returned to the  Client. In addition,   the  Server  deletes the entry
        // for the  Client  from its  SessionDiagnostics Array  Variable  and notifies any other  Clients  who were
        // subscribed to this entry.
        if (message.session.status === "closed") {
            // note : use StatusCodes.BadSessionClosed , for pending message for this session
            return sendError(StatusCodes.BadSessionIdInvalid);
        }

        if (message.session.status === "new") {
            // mark session as being screwed ! so it cannot be activated anymore
            message.session.status = "screwed";

            return sendError(StatusCodes.BadSessionNotActivated);
        }

        if (message.session.status !== "active") {
            // mark session as being screwed ! so it cannot be activated anymore
            message.session.status = "screwed";

            // note : use StatusCodes.BadSessionClosed , for pending message for this session
            return sendError(StatusCodes.BadSessionIdInvalid);
        }

        // lets also reset the session watchdog so it doesn't
        // (Sessions are terminated by the Server automatically if the Client fails to issue a Service
        // request on the Session within the timeout period negotiated by the Server in the
        // CreateSession Service response. )
        if (message.session.keepAlive) {
            assert(typeof message.session.keepAlive === "function");
            message.session.keepAlive();
        }
        message.session.incrementTotalRequestCount();
        await actionToPerform(message.session as ServerSession, sendResponse, sendError);
    }

    protected async _apply_on_Subscription(
        ResponseClass: ResponseClassType,
        message: Message,
        channel: ServerSecureChannelLayer,
        actionToPerform: (
            session: ServerSession,
            subscription: Subscription,
            sendResponse: (response: Response) => void,
            sendError: (statusCode: StatusCode) => void
        ) => Promise<void>
    ): Promise<void> {
        assert(typeof actionToPerform === "function");
        const request = message.request as unknown as { subscriptionId: number };
        assert(Object.prototype.hasOwnProperty.call(request, "subscriptionId"));

        this._apply_on_SessionObject(
            ResponseClass,
            message,
            channel,
            async (
                session: ServerSession,
                sendResponse: (response: Response) => void,
                sendError: (statusCode: StatusCode) => void
            ) => {
                const subscription = session.getSubscription(request.subscriptionId);
                if (!subscription) {
                    return sendError(StatusCodes.BadSubscriptionIdInvalid);
                }
                subscription.resetLifeTimeAndKeepAliveCounters();
                await actionToPerform(session, subscription, sendResponse, sendError);
            }
        );
    }

    protected _apply_on_SubscriptionIds<T>(
        ResponseClass: typeof SetPublishingModeResponse | typeof TransferSubscriptionsResponse | typeof DeleteSubscriptionsResponse,
        message: Message,
        channel: ServerSecureChannelLayer,
        actionToPerform: (session: ServerSession, subscriptionId: number) => Promise<T>
    ): void {
        assert(typeof actionToPerform === "function");
        const request = message.request as unknown as { subscriptionIds: number[] };
        assert(Object.prototype.hasOwnProperty.call(request, "subscriptionIds"));

        this._apply_on_SessionObject(
            ResponseClass,
            message,
            channel,
            async (
                session: ServerSession,
                sendResponse: (response: Response) => void,
                sendError: (statusCode: StatusCode) => void
            ) => {
                const subscriptionIds = request.subscriptionIds;

                if (!request.subscriptionIds || request.subscriptionIds.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }

                // check minimal
                if (
                    request.subscriptionIds.length >
                    Math.min(
                        this.engine.serverCapabilities.maxSubscriptionsPerSession,
                        this.engine.serverCapabilities.maxSubscriptions
                    )
                ) {
                    return sendError(StatusCodes.BadTooManyOperations);
                }

                const promises: Promise<T>[] = subscriptionIds.map((subscriptionId: number) =>
                    actionToPerform(session, subscriptionId)
                );
                const results: T[] = await Promise.all(promises);

                const serviceResult: StatusCode = StatusCodes.Good;
                const response = new ResponseClass({
                    responseHeader: {
                        serviceResult
                    },
                    results: results as any
                });
                sendResponse(response);
            }
        );
    }

    protected _apply_on_Subscriptions(
        ResponseClass: typeof SetPublishingModeResponse | typeof TransferSubscriptionsResponse | typeof DeleteSubscriptionsResponse,
        message: Message,
        channel: ServerSecureChannelLayer,
        actionToPerform: (session: ServerSession, subscription: Subscription) => Promise<StatusCode>
    ): void {
        this._apply_on_SubscriptionIds<StatusCode>(
            ResponseClass,
            message,
            channel,
            async (session: ServerSession, subscriptionId: number) => {
                /* istanbul ignore next */
                if (isSubscriptionIdInvalid(subscriptionId)) {
                    return StatusCodes.BadSubscriptionIdInvalid;
                }
                const subscription = session.getSubscription(subscriptionId);
                if (!subscription) {
                    return StatusCodes.BadSubscriptionIdInvalid;
                }
                return actionToPerform(session, subscription);
            }
        );
    }

    private async _closeSession(authenticationToken: NodeId, deleteSubscriptions: boolean, reason: ClosingReason): Promise<void> {
        if (deleteSubscriptions && this.options.onDeleteMonitoredItem) {
            const session = this.getSession(authenticationToken);
            if (session) {
                const subscriptions = session.publishEngine.subscriptions;
                for (const subscription of subscriptions) {
                    await subscription.applyOnMonitoredItem(this.options.onDeleteMonitoredItem.bind(null, subscription) as any);
                }
            }
        }
        await this.engine.closeSession(authenticationToken, deleteSubscriptions, reason);
    }
    /**
     * @param message
     * @param channel
     * @private
     */
    protected _on_CloseSessionRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as CloseSessionRequest;
        assert(request instanceof CloseSessionRequest);

        let response;

        message.session_statusCode = StatusCodes.Good;

        function sendError(statusCode: StatusCode) {
            return g_sendError(channel, message, CloseSessionResponse, statusCode);
        }

        function sendResponse(response1: CloseSessionResponse) {
            channel.send_response("MSG", response1, message);
        }

        // do not use _apply_on_SessionObject
        // this._apply_on_SessionObject(CloseSessionResponse, message, channel, function (session) {
        // });

        const session = message.session;
        if (!session) {
            return sendError(StatusCodes.BadSessionIdInvalid);
        }

        // session has been created but not activated !
        const wasNotActivated = session.status === "new";

        (async () => {
            try {
                await this._closeSession(request.requestHeader.authenticationToken, request.deleteSubscriptions, "CloseSession");

                // if (false && wasNotActivated) {
                //  return sendError(StatusCodes.BadSessionNotActivated);
                // }

                response = new CloseSessionResponse({});
                sendResponse(response);
            } catch (err) {
                sendError(StatusCodes.BadInternalError);
            }
        })();
    }

    // browse services
    /**
     * @param message
     * @param channel
     * @private
     */
    protected _on_BrowseRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as BrowseRequest;
        assert(request instanceof BrowseRequest);
        const diagnostic: any = {};

        this._apply_on_SessionObject(
            BrowseResponse,
            message,
            channel,
            (session: ServerSession, sendResponse: (response: Response) => void, sendError: (statusCode: StatusCode) => void) => {
                let response: BrowseResponse;
                // test view
                if (request.view && !request.view.viewId.isEmpty()) {
                    let theView: UAView | null = this.engine!.addressSpace!.findNode(request.view.viewId) as UAView;
                    if (theView && theView.nodeClass !== NodeClass.View) {
                        // Error: theView is not a View
                        diagnostic.localizedText = { text: "Expecting a view here" };
                        theView = null;
                    }
                    if (!theView) {
                        return sendError(StatusCodes.BadViewIdUnknown);
                    }
                }

                if (!request.nodesToBrowse || request.nodesToBrowse.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }

                if (this.engine.serverCapabilities.operationLimits.maxNodesPerBrowse > 0) {
                    if (request.nodesToBrowse.length > this.engine.serverCapabilities.operationLimits.maxNodesPerBrowse) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }

                // limit results to requestedMaxReferencesPerNode further so it never exceed a too big number
                const requestedMaxReferencesPerNode = Math.min(9876, request.requestedMaxReferencesPerNode);
                assert(request.nodesToBrowse[0].schema.name === "BrowseDescription");

                const context = session.sessionContext;
                const browseAll = (nodesToBrowse: BrowseDescriptionOptions[], callack: CallbackT<BrowseResult[]>) => {
                    const f = callbackify(this.engine.browseWithAutomaticExpansion).bind(this.engine);
                    (f as any)(request.nodesToBrowse, context, callack);
                };
                // handle continuation point and requestedMaxReferencesPerNode
                const maxBrowseContinuationPoints = this.engine.serverCapabilities.maxBrowseContinuationPoints;

                innerBrowse(
                    {
                        browseAll,
                        context,
                        continuationPointManager: session.continuationPointManager,
                        requestedMaxReferencesPerNode,
                        maxBrowseContinuationPoints
                    },
                    request.nodesToBrowse,
                    (err, results) => {
                        if (!results) {
                            return sendError(StatusCodes.BadInternalError);
                        }
                        assert(results[0].schema.name === "BrowseResult");
                        response = new BrowseResponse({
                            diagnosticInfos: undefined,
                            results
                        });
                        sendResponse(response);
                    }
                );
            }
        );
    }

    /**
     */
    protected _on_BrowseNextRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as BrowseNextRequest;
        assert(request instanceof BrowseNextRequest);
        this._apply_on_SessionObject(
            BrowseNextResponse,
            message,
            channel,
            (session: ServerSession, sendResponse: (response: Response) => void, sendError: (statusCode: StatusCode) => void) => {
                if (!request.continuationPoints || request.continuationPoints.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }
                innerBrowseNext(
                    {
                        continuationPointManager: session.continuationPointManager
                    },
                    request.continuationPoints,
                    request.releaseContinuationPoints,
                    (err, results) => {
                        if (err) {
                            return sendError(StatusCodes.BadInternalError);
                        }
                        const response = new BrowseNextResponse({
                            diagnosticInfos: undefined,
                            results
                        });
                        sendResponse(response);
                    }
                );
            }
        );
    }

    // read services
    protected _on_ReadRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as ReadRequest;
        assert(request instanceof ReadRequest);

        this._apply_on_SessionObject(
            ReadResponse,
            message,
            channel,
            (session: ServerSession, sendResponse: (response: Response) => void, sendError: (statusCode: StatusCode) => void) => {
                const context = session.sessionContext;

                const timestampsToReturn = request.timestampsToReturn;

                if (timestampsToReturn === TimestampsToReturn.Invalid) {
                    return sendError(StatusCodes.BadTimestampsToReturnInvalid);
                }

                if (request.maxAge < 0) {
                    return sendError(StatusCodes.BadMaxAgeInvalid);
                }

                request.nodesToRead = request.nodesToRead || [];

                if (!request.nodesToRead || request.nodesToRead.length <= 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }

                assert(request.nodesToRead[0].schema.name === "ReadValueId");

                // limit size of nodesToRead array to maxNodesPerRead
                if (this.engine.serverCapabilities.operationLimits.maxNodesPerRead > 0) {
                    if (request.nodesToRead.length > this.engine.serverCapabilities.operationLimits.maxNodesPerRead) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }

                // proceed with registered nodes alias resolution
                for (const nodeToRead of request.nodesToRead) {
                    nodeToRead.nodeId = session.resolveRegisteredNode(nodeToRead.nodeId);
                }

                // ask for a refresh of asynchronous variables
                this.engine.refreshValues(request.nodesToRead, request.maxAge, (err?: Error | null) => {
                    this.engine.read(context, request).then((results) => {
                        assert(results[0].schema.name === "DataValue");
                        assert(results.length === request.nodesToRead!.length);

                        const response = new ReadResponse({
                            diagnosticInfos: undefined,
                            results: undefined
                        });
                        // set it here for performance
                        response.results = results;
                        assert(response.diagnosticInfos!.length === 0);
                        sendResponse(response);
                    });
                });
            }
        );
    }

    // read services
    protected _on_HistoryReadRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as HistoryReadRequest;

        assert(request instanceof HistoryReadRequest);

        this._apply_on_SessionObject(
            HistoryReadResponse,
            message,
            channel,
            (session: ServerSession, sendResponse: (response: Response) => void, sendError: (statsCode: StatusCode) => void) => {
                let response;

                const timestampsToReturn = request.timestampsToReturn;

                if (timestampsToReturn === TimestampsToReturn.Invalid) {
                    return sendError(StatusCodes.BadTimestampsToReturnInvalid);
                }

                request.nodesToRead = request.nodesToRead || [];

                if (!request.nodesToRead || request.nodesToRead.length <= 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }

                assert(request.nodesToRead[0].schema.name === "HistoryReadValueId");

                // limit size of nodesToRead array to maxNodesPerRead
                if (this.engine.serverCapabilities.operationLimits.maxNodesPerRead > 0) {
                    if (request.nodesToRead.length > this.engine.serverCapabilities.operationLimits.maxNodesPerRead) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }
                // todo : handle
                if (this.engine.serverCapabilities.operationLimits.maxNodesPerHistoryReadData > 0) {
                    if (request.nodesToRead.length > this.engine.serverCapabilities.operationLimits.maxNodesPerHistoryReadData) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }
                if (this.engine.serverCapabilities.operationLimits.maxNodesPerHistoryReadEvents > 0) {
                    if (request.nodesToRead.length > this.engine.serverCapabilities.operationLimits.maxNodesPerHistoryReadEvents) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }

                const context = session.sessionContext;

                // ask for a refresh of asynchronous variables
                this.engine.refreshValues(request.nodesToRead, 0, (err?: Error | null) => {
                    assert(!err, " error not handled here , fix me"); // TODO

                    this.engine
                        .historyRead(context, request)
                        .then((results: HistoryReadResult[]) => {
                            assert(results[0].schema.name === "HistoryReadResult");
                            assert(results.length === request.nodesToRead!.length);

                            response = new HistoryReadResponse({
                                diagnosticInfos: undefined,
                                results
                            });

                            assert(response.diagnosticInfos!.length === 0);
                            sendResponse(response);
                        })
                        .catch((err) => {
                            return sendError(StatusCodes.BadHistoryOperationInvalid);
                        });
                });
            }
        );
    }

    /*
   // write services
   // OPCUA Specification 1.02 Part 3 : 5.10.4 Write
   // This Service is used to write values to one or more Attributes of one or more Nodes. For constructed
   // Attribute values whose elements are indexed, such as an array, this Service allows Clients to write
   // the entire set of indexed values as a composite, to write individual elements or to write ranges of
   // elements of the composite.
   // The values are written to the data source, such as a device, and the Service does not return until it writes
   // the values or determines that the value cannot be written. In certain cases, the Server will successfully
   // to an intermediate system or Server, and will not know if the data source was updated properly. In these cases,
   // the Server should report a success code that indicates that the write was not verified.
   // In the cases where the Server is able to verify that it has successfully written to the data source,
   // it reports an unconditional success.
   */
    protected _on_WriteRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as WriteRequest;
        assert(request instanceof WriteRequest);
        assert(!request.nodesToWrite || Array.isArray(request.nodesToWrite));

        this._apply_on_SessionObject(
            WriteResponse,
            message,
            channel,
            (session: ServerSession, sendResponse: (response: Response) => void, sendError: (statusCode: StatusCode) => void) => {
                let response;

                if (!request.nodesToWrite || request.nodesToWrite.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }

                if (this.engine.serverCapabilities.operationLimits.maxNodesPerWrite > 0) {
                    if (request.nodesToWrite.length > this.engine.serverCapabilities.operationLimits.maxNodesPerWrite) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }

                // proceed with registered nodes alias resolution
                for (const nodeToWrite of request.nodesToWrite) {
                    nodeToWrite.nodeId = session.resolveRegisteredNode(nodeToWrite.nodeId);
                }

                const context = session.sessionContext;

                assert(request.nodesToWrite[0].schema.name === "WriteValue");

                this.engine
                    .write(context, request.nodesToWrite)
                    .then((results: StatusCode[]) => {
                        assert(results!.length === request.nodesToWrite!.length);
                        response = new WriteResponse({
                            diagnosticInfos: undefined,
                            results
                        });
                        sendResponse(response);
                    })
                    .catch((err) => {
                        errorLog(err);
                        sendError(StatusCodes.BadInternalError);
                    });
            }
        );
    }

    // subscription services
    protected _on_CreateSubscriptionRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const engine = this.engine;
        const addressSpace = engine.addressSpace!;

        const request = message.request as CreateSubscriptionRequest;
        assert(request instanceof CreateSubscriptionRequest);

        this._apply_on_SessionObject(
            CreateSubscriptionResponse,
            message,
            channel,
            (session: ServerSession, sendResponse: (response: Response) => void, sendError: (statusCode: StatusCode) => void) => {
                const context = session.sessionContext;

                if (session.currentSubscriptionCount >= this.engine.serverCapabilities.maxSubscriptionsPerSession) {
                    return sendError(StatusCodes.BadTooManySubscriptions);
                }

                if (this.currentSubscriptionCount >= this.engine.serverCapabilities.maxSubscriptions) {
                    return sendError(StatusCodes.BadTooManySubscriptions);
                }

                const subscription = session.createSubscription(request);

                subscription.on("monitoredItem", (monitoredItem: MonitoredItem) => {
                    prepareMonitoredItem(context, addressSpace, monitoredItem);
                });

                const response = new CreateSubscriptionResponse({
                    revisedLifetimeCount: subscription.lifeTimeCount,
                    revisedMaxKeepAliveCount: subscription.maxKeepAliveCount,
                    revisedPublishingInterval: subscription.publishingInterval,
                    subscriptionId: subscription.id
                });
                sendResponse(response);
            }
        );
    }

    protected _on_DeleteSubscriptionsRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as DeleteSubscriptionsRequest;
        assert(request instanceof DeleteSubscriptionsRequest);
        this._apply_on_SubscriptionIds(
            DeleteSubscriptionsResponse,
            message,
            channel,
            async (session: ServerSession, subscriptionId: number) => {
                let subscription = this.engine.findOrphanSubscription(subscriptionId);
                // istanbul ignore next
                if (subscription) {
                    warningLog("Deleting an orphan subscription", subscriptionId);

                    await this._beforeDeleteSubscription(subscription);
                    return this.engine.deleteOrphanSubscription(subscription);
                }

                subscription = session.getSubscription(subscriptionId);
                if (subscription) {
                    await this._beforeDeleteSubscription(subscription);
                }

                return session.deleteSubscription(subscriptionId);
            }
        );
    }

    protected _on_TransferSubscriptionsRequest(message: Message, channel: ServerSecureChannelLayer): void {
        //
        // sendInitialValue Boolean
        //    A Boolean parameter with the following values:
        //    TRUE      the first Publish response(s) after the TransferSubscriptions call shall
        //              contain the current values of all Monitored Items in the Subscription where
        //              the Monitoring Mode is set to Reporting.
        //    FALSE     the first Publish response after the TransferSubscriptions call shall contain only the value
        //              changes since the last Publish response was sent.
        //    This parameter only applies to MonitoredItems used for monitoring Attribute changes.
        //

        const engine = this.engine;

        const request = message.request as TransferSubscriptionsRequest;
        assert(request instanceof TransferSubscriptionsRequest);
        this._apply_on_SubscriptionIds(
            TransferSubscriptionsResponse,
            message,
            channel,
            async (session: ServerSession, subscriptionId: number) =>
                await engine.transferSubscription(session, subscriptionId, request.sendInitialValues)
        );
    }

    protected _on_CreateMonitoredItemsRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const engine = this.engine;
        const addressSpace = engine.addressSpace!;

        const request = message.request as CreateMonitoredItemsRequest;
        assert(request instanceof CreateMonitoredItemsRequest);

        this._apply_on_Subscription(
            CreateMonitoredItemsResponse,
            message,
            channel,
            async (
                session: ServerSession,
                subscription: Subscription,
                sendResponse: (response: Response) => void,
                sendError: (statusCode: StatusCode) => void
            ): Promise<void> => {
                const timestampsToReturn = request.timestampsToReturn;
                if (timestampsToReturn === TimestampsToReturn.Invalid) {
                    return sendError(StatusCodes.BadTimestampsToReturnInvalid);
                }

                if (!request.itemsToCreate || request.itemsToCreate.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }
                if (this.engine.serverCapabilities.operationLimits.maxMonitoredItemsPerCall > 0) {
                    if (request.itemsToCreate.length > this.engine.serverCapabilities.operationLimits.maxMonitoredItemsPerCall) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }

                const options = this.options as OPCUAServerOptions;
                let results: MonitoredItemCreateResult[] = [];
                if (options.onCreateMonitoredItem) {
                    const resultsPromise = request.itemsToCreate.map(async (monitoredItemCreateRequest) => {
                        const { monitoredItem, createResult } = subscription.preCreateMonitoredItem(
                            addressSpace,
                            timestampsToReturn,
                            monitoredItemCreateRequest
                        );
                        if (monitoredItem) {
                            await options.onCreateMonitoredItem!(subscription, monitoredItem);
                            subscription.postCreateMonitoredItem(monitoredItem, monitoredItemCreateRequest, createResult);
                        }
                        return createResult;
                    });
                    results = await Promise.all(resultsPromise);
                } else {
                    results = request.itemsToCreate.map((monitoredItemCreateRequest) => {
                        const { monitoredItem, createResult } = subscription.preCreateMonitoredItem(
                            addressSpace,
                            timestampsToReturn,
                            monitoredItemCreateRequest
                        );
                        if (monitoredItem) {
                            subscription.postCreateMonitoredItem(monitoredItem, monitoredItemCreateRequest, createResult);
                        }
                        return createResult;
                    });
                }
                const response = new CreateMonitoredItemsResponse({
                    responseHeader: { serviceResult: StatusCodes.Good },
                    results
                    // ,diagnosticInfos: []
                });
                sendResponse(response);
            }
        );
    }

    protected _on_ModifySubscriptionRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as ModifySubscriptionRequest;
        assert(request instanceof ModifySubscriptionRequest);

        this._apply_on_Subscription(
            ModifySubscriptionResponse,
            message,
            channel,
            async (
                session: ServerSession,
                subscription: Subscription,
                sendResponse: (response: ModifySubscriptionResponse) => void,
                sendError: (statusCode: StatusCode) => void
            ) => {
                subscription.modify(request);

                const response = new ModifySubscriptionResponse({
                    revisedLifetimeCount: subscription.lifeTimeCount,
                    revisedMaxKeepAliveCount: subscription.maxKeepAliveCount,
                    revisedPublishingInterval: subscription.publishingInterval
                });

                sendResponse(response);
            }
        );
    }

    protected _on_ModifyMonitoredItemsRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as ModifyMonitoredItemsRequest;

        assert(request instanceof ModifyMonitoredItemsRequest);
        this._apply_on_Subscription(
            ModifyMonitoredItemsResponse,
            message,
            channel,
            async (
                session: ServerSession,
                subscription: Subscription,
                sendResponse: (response: ModifyMonitoredItemsResponse) => void,
                sendError: (statusCode: StatusCode) => void
            ) => {
                const timestampsToReturn = request.timestampsToReturn;
                if (timestampsToReturn === TimestampsToReturn.Invalid) {
                    return sendError(StatusCodes.BadTimestampsToReturnInvalid);
                }

                if (!request.itemsToModify || request.itemsToModify.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }

                /* istanbul ignore next */
                if (this.engine.serverCapabilities.operationLimits.maxMonitoredItemsPerCall > 0) {
                    if (request.itemsToModify.length > this.engine.serverCapabilities.operationLimits.maxMonitoredItemsPerCall) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }

                const itemsToModify = request.itemsToModify; // MonitoredItemModifyRequest

                function modifyMonitoredItem(item: MonitoredItemModifyRequest) {
                    const monitoredItemId = item.monitoredItemId;
                    const monitoredItem = subscription.getMonitoredItem(monitoredItemId);
                    if (!monitoredItem) {
                        return new MonitoredItemModifyResult({ statusCode: StatusCodes.BadMonitoredItemIdInvalid });
                    }

                    // adjust samplingInterval if === -1
                    if (item.requestedParameters.samplingInterval === -1) {
                        item.requestedParameters.samplingInterval = subscription.publishingInterval;
                    }
                    return monitoredItem.modify(timestampsToReturn, item.requestedParameters);
                }

                const results = itemsToModify.map(modifyMonitoredItem);

                const response = new ModifyMonitoredItemsResponse({
                    results
                });
                sendResponse(response);
            }
        );
    }

    protected _on_PublishRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as PublishRequest;
        assert(request instanceof PublishRequest);

        this._apply_on_SessionObject(
            PublishResponse,
            message,
            channel,
            (session: ServerSession, sendResponse: (response: Response) => void, sendError: (statusCode: StatusCode) => void) => {
                assert(session);
                assert(session.publishEngine); // server.publishEngine doesn't exists, OPCUAServer has probably shut down already
                session.publishEngine._on_PublishRequest(request, (_request1, response) => {
                    sendResponse(response);
                });
            }
        );
    }

    protected _on_SetPublishingModeRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as SetPublishingModeRequest;
        assert(request instanceof SetPublishingModeRequest);
        const publishingEnabled = request.publishingEnabled;
        this._apply_on_Subscriptions(
            SetPublishingModeResponse,
            message,
            channel,
            async (session: ServerSession, subscription: Subscription) => {
                return subscription.setPublishingMode(publishingEnabled);
            }
        );
    }

    protected _on_DeleteMonitoredItemsRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as DeleteMonitoredItemsRequest;
        assert(request instanceof DeleteMonitoredItemsRequest);

        this._apply_on_Subscription(
            DeleteMonitoredItemsResponse,
            message,
            channel,
            async (
                session: ServerSession,
                subscription: Subscription,
                sendResponse: (response: Response) => void,
                sendError: (statusCode: StatusCode) => void
            ) => {
                /* istanbul ignore next */
                if (!request.monitoredItemIds || request.monitoredItemIds.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }

                /* istanbul ignore next */
                if (this.engine.serverCapabilities.operationLimits.maxMonitoredItemsPerCall > 0) {
                    if (request.monitoredItemIds.length > this.engine.serverCapabilities.operationLimits.maxMonitoredItemsPerCall) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }

                const resultsPromises = request.monitoredItemIds.map(async (monitoredItemId: number) => {
                    if (this.options.onDeleteMonitoredItem) {
                        const monitoredItem = subscription.getMonitoredItem(monitoredItemId);
                        if (monitoredItem) {
                            await this.options.onDeleteMonitoredItem(subscription, monitoredItem);
                        }
                    }
                    return subscription.removeMonitoredItem(monitoredItemId);
                });

                try {
                    const results = await Promise.all(resultsPromises);

                    const response = new DeleteMonitoredItemsResponse({
                        diagnosticInfos: undefined,
                        results
                    });

                    sendResponse(response);
                } catch (err) {
                    warningLog(err);
                    return sendError(StatusCodes.BadInternalError);
                }
            }
        );
    }
    protected _on_SetTriggeringRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as SetTriggeringRequest;
        assert(request instanceof SetTriggeringRequest);

        this._apply_on_Subscription(
            SetTriggeringResponse,
            message,
            channel,
            async (
                session: ServerSession,
                subscription: Subscription,
                sendResponse: (response: Response) => void,
                sendError: (statusCode: StatusCode) => void
            ) => {
                /* */
                const { triggeringItemId, linksToAdd, linksToRemove } = request;

                /**
                 * The MaxMonitoredItemsPerCall Property indicates
                 * [...]
                 *  • the maximum size of the sum of the linksToAdd and linksToRemove arrays when a
                 *    Client calls the SetTriggering Service.
                 *
                 */
                const maxElements = (linksToAdd ? linksToAdd.length : 0) + (linksToRemove ? linksToRemove.length : 0);
                if (this.engine.serverCapabilities.operationLimits.maxMonitoredItemsPerCall > 0) {
                    if (maxElements > this.engine.serverCapabilities.operationLimits.maxMonitoredItemsPerCall) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }

                const { addResults, removeResults, statusCode } = subscription.setTriggering(
                    triggeringItemId,
                    linksToAdd,
                    linksToRemove
                );
                if (statusCode.isNotGood()) {
                    const response = new ServiceFault({ responseHeader: { serviceResult: statusCode } });
                    sendResponse(response);
                } else {
                    const response = new SetTriggeringResponse({
                        responseHeader: { serviceResult: statusCode },

                        addResults,
                        removeResults,
                        addDiagnosticInfos: null,
                        removeDiagnosticInfos: null
                    });
                    sendResponse(response);
                }
            }
        );
    }

    protected async _beforeDeleteSubscription(subscription: Subscription): Promise<void> {
        if (!this.options.onDeleteMonitoredItem) {
            return;
        }
        await subscription.applyOnMonitoredItem(this.options.onDeleteMonitoredItem.bind(null, subscription) as any);
    }
    protected _on_RepublishRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as RepublishRequest;
        assert(request instanceof RepublishRequest);

        this._apply_on_Subscription(
            RepublishResponse,
            message,
            channel,
            async (
                session: ServerSession,
                subscription: Subscription,
                sendResponse: (response: Response) => void,
                sendError: (statusCode: StatusCode) => void
            ) => {
                // update diagnostic counter
                subscription.subscriptionDiagnostics.republishRequestCount += 1;
                subscription.subscriptionDiagnostics.republishMessageRequestCount += 1;

                const retransmitSequenceNumber = request.retransmitSequenceNumber;
                const notificationMessage = subscription.getMessageForSequenceNumber(retransmitSequenceNumber);

                if (!notificationMessage) {
                    return sendError(StatusCodes.BadMessageNotAvailable);
                }
                const response = new RepublishResponse({
                    notificationMessage,
                    responseHeader: {
                        serviceResult: StatusCodes.Good
                    }
                });
                // update diagnostic counter
                subscription.subscriptionDiagnostics.republishMessageCount += 1;

                sendResponse(response);
            }
        );
    }

    // Bad_NothingToDo
    // Bad_TooManyOperations
    // Bad_SubscriptionIdInvalid
    // Bad_MonitoringModeInvalid
    protected _on_SetMonitoringModeRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as SetMonitoringModeRequest;
        assert(request instanceof SetMonitoringModeRequest);

        this._apply_on_Subscription(
            SetMonitoringModeResponse,
            message,
            channel,
            async (
                session: ServerSession,
                subscription: Subscription,
                sendResponse: (response: Response) => void,
                sendError: (statusCode: StatusCode) => void
            ) => {
                /* istanbul ignore next */
                if (!request.monitoredItemIds || request.monitoredItemIds.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }

                /* istanbul ignore next */
                if (this.engine.serverCapabilities.operationLimits.maxMonitoredItemsPerCall > 0) {
                    if (request.monitoredItemIds.length > this.engine.serverCapabilities.operationLimits.maxMonitoredItemsPerCall) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }
                const monitoringMode = request.monitoringMode;

                if (!isMonitoringModeValid(monitoringMode)) {
                    return sendError(StatusCodes.BadMonitoringModeInvalid);
                }

                const results = request.monitoredItemIds.map((monitoredItemId) => {
                    const monitoredItem = subscription.getMonitoredItem(monitoredItemId);
                    if (!monitoredItem) {
                        return StatusCodes.BadMonitoredItemIdInvalid;
                    }
                    monitoredItem.setMonitoringMode(monitoringMode);
                    return StatusCodes.Good;
                });

                const response = new SetMonitoringModeResponse({
                    results
                });
                sendResponse(response);
            }
        );
    }

    // _on_TranslateBrowsePathsToNodeIds service
    protected _on_TranslateBrowsePathsToNodeIdsRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as TranslateBrowsePathsToNodeIdsRequest;
        assert(request instanceof TranslateBrowsePathsToNodeIdsRequest);

        this._apply_on_SessionObject(
            TranslateBrowsePathsToNodeIdsResponse,
            message,
            channel,
            async (
                session: ServerSession,
                sendResponse: (response: Response) => void,
                sendError: (statusCode: StatusCode) => void
            ) => {
                if (!request.browsePaths || request.browsePaths.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }
                if (this.engine.serverCapabilities.operationLimits.maxNodesPerTranslateBrowsePathsToNodeIds > 0) {
                    if (
                        request.browsePaths.length >
                        this.engine.serverCapabilities.operationLimits.maxNodesPerTranslateBrowsePathsToNodeIds
                    ) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }

                this.engine
                    .translateBrowsePaths(request.browsePaths)
                    .then((browsePathsResults) => {
                        const response = new TranslateBrowsePathsToNodeIdsResponse({
                            diagnosticInfos: null,
                            results: browsePathsResults
                        });
                        sendResponse(response);
                    })
                    .catch((err) => {
                        sendError(StatusCodes.BadInternalError);
                    });
            }
        );
    }

    // Call Service Result Codes
    // Symbolic Id Description
    // Bad_NothingToDo       See Table 165 for the description of this result code.
    // Bad_TooManyOperations See Table 165 for the description of this result code.
    //
    protected _on_CallRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as CallRequest;
        assert(request instanceof CallRequest);

        this._apply_on_SessionObject(
            CallResponse,
            message,
            channel,
            (session: ServerSession, sendResponse: (response: Response) => void, sendError: (statusCode: StatusCode) => void) => {
                let response;

                if (!request.methodsToCall || request.methodsToCall.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }

                // the MaxNodesPerMethodCall Property indicates the maximum size of the methodsToCall array when
                // a Client calls the Call Service.
                let maxNodesPerMethodCall = this.engine.serverCapabilities.operationLimits.maxNodesPerMethodCall;
                maxNodesPerMethodCall = maxNodesPerMethodCall <= 0 ? 1000 : maxNodesPerMethodCall;
                if (request.methodsToCall.length > maxNodesPerMethodCall) {
                    return sendError(StatusCodes.BadTooManyOperations);
                }

                const context = session.sessionContext;
                this.engine
                    .call(context, request.methodsToCall)
                    .then((results) => {
                        const response = new CallResponse({ results });
                        filterDiagnosticInfo(request.requestHeader.returnDiagnostics, response);
                        sendResponse(response);
                    })
                    .catch((err) => {
                        sendError(StatusCodes.BadInternalError);
                    });
            }
        );
    }

    protected _on_RegisterNodesRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as RegisterNodesRequest;
        assert(request instanceof RegisterNodesRequest);

        this._apply_on_SessionObject(
            RegisterNodesResponse,
            message,
            channel,
            (session: ServerSession, sendResponse: (response: Response) => void, sendError: (statusCode: StatusCode) => void) => {
                if (!request.nodesToRegister || request.nodesToRegister.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }
                if (this.engine.serverCapabilities.operationLimits.maxNodesPerRegisterNodes > 0) {
                    if (request.nodesToRegister.length > this.engine.serverCapabilities.operationLimits.maxNodesPerRegisterNodes) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }
                // A list of NodeIds which the Client shall use for subsequent access operations. The
                // size and order of this list matches the size and order of the nodesToRegister
                // request parameter.
                // The Server may return the NodeId from the request or a new (an alias) NodeId. It
                // is recommended that the Server return a numeric NodeIds for aliasing.
                // In case no optimization is supported for a Node, the Server shall return the
                // NodeId from the request.
                const registeredNodeIds = request.nodesToRegister.map((nodeId) => session.registerNode(nodeId));

                const response = new RegisterNodesResponse({
                    registeredNodeIds
                });
                sendResponse(response);
            }
        );
    }

    protected _on_UnregisterNodesRequest(message: Message, channel: ServerSecureChannelLayer): void {
        const request = message.request as UnregisterNodesRequest;
        assert(request instanceof UnregisterNodesRequest);

        this._apply_on_SessionObject(
            UnregisterNodesResponse,
            message,
            channel,
            (session: ServerSession, sendResponse: (response: Response) => void, sendError: (statusCode: StatusCode) => void) => {
                request.nodesToUnregister = request.nodesToUnregister || [];

                if (!request.nodesToUnregister || request.nodesToUnregister.length === 0) {
                    return sendError(StatusCodes.BadNothingToDo);
                }

                if (this.engine.serverCapabilities.operationLimits.maxNodesPerRegisterNodes > 0) {
                    if (
                        request.nodesToUnregister.length > this.engine.serverCapabilities.operationLimits.maxNodesPerRegisterNodes
                    ) {
                        return sendError(StatusCodes.BadTooManyOperations);
                    }
                }

                request.nodesToUnregister.map((nodeId: NodeId) => session.unRegisterNode(nodeId));

                const response = new UnregisterNodesResponse({});
                sendResponse(response);
            }
        );
    }

    /* istanbul ignore next */
    protected _on_Cancel(message: Message, channel: ServerSecureChannelLayer): void {
        return g_sendError(channel, message, CancelResponse, StatusCodes.BadServiceUnsupported);
    }

    // NodeManagement Service Set Overview
    // This Service Set defines Services to add and delete AddressSpace Nodes and References between them. All added
    // Nodes continue to exist in the AddressSpace even if the Client that created them disconnects from the Server.
    //
    /* istanbul ignore next */
    protected _on_AddNodes(message: Message, channel: ServerSecureChannelLayer): void {
        return g_sendError(channel, message, AddNodesResponse, StatusCodes.BadServiceUnsupported);
    }

    /* istanbul ignore next */
    protected _on_AddReferences(message: Message, channel: ServerSecureChannelLayer): void {
        return g_sendError(channel, message, AddReferencesResponse, StatusCodes.BadServiceUnsupported);
    }

    /* istanbul ignore next */
    protected _on_DeleteNodes(message: Message, channel: ServerSecureChannelLayer): void {
        return g_sendError(channel, message, DeleteNodesResponse, StatusCodes.BadServiceUnsupported);
    }

    /* istanbul ignore next */
    protected _on_DeleteReferences(message: Message, channel: ServerSecureChannelLayer): void {
        return g_sendError(channel, message, DeleteReferencesResponse, StatusCodes.BadServiceUnsupported);
    }

    // Query Service
    /* istanbul ignore next */
    protected _on_QueryFirst(message: Message, channel: ServerSecureChannelLayer): void {
        return g_sendError(channel, message, QueryFirstResponse, StatusCodes.BadServiceUnsupported);
    }

    /* istanbul ignore next */
    protected _on_QueryNext(message: Message, channel: ServerSecureChannelLayer): void {
        return g_sendError(channel, message, QueryNextResponse, StatusCodes.BadServiceUnsupported);
    }

    /* istanbul ignore next */
    protected _on_HistoryUpdate(message: Message, channel: ServerSecureChannelLayer): void {
        return g_sendError(channel, message, HistoryUpdateResponse, StatusCodes.BadServiceUnsupported);
    }

    private createEndpoint(
        port1: number,
        serverOptions: {
            defaultSecureTokenLifetime?: number;
            timeout?: number;
            host?: string;
            transportSettings?: IServerTransportSettings;
        }
    ): OPCUAServerEndPoint {
        // add the tcp/ip endpoint with no security
        const endPoint = new OPCUAServerEndPoint({
            port: port1,
            host: serverOptions.host,
            certificateManager: this.serverCertificateManager,

            certificateChain: this.getCertificateChain(),
            privateKey: this.getPrivateKey(),

            defaultSecureTokenLifetime: serverOptions.defaultSecureTokenLifetime || 600000,
            timeout: serverOptions.timeout || 3 * 60 * 1000,

            maxConnections: this.maxConnectionsPerEndpoint,
            objectFactory: this.objectFactory,
            serverInfo: this.serverInfo,
            transportSettings: serverOptions.transportSettings
        });
        return endPoint;
    }

    private createEndpointDescriptions(
        serverOption: OPCUAServerOptions,
        endpointOptions: OPCUAServerEndpointOptions
    ): OPCUAServerEndPoint {
        /* istanbul ignore next */
        if (!endpointOptions) {
            throw new Error("internal error");
        }
        const hostname = getFullyQualifiedDomainName();
        endpointOptions.hostname = endpointOptions.hostname || hostname;
        endpointOptions.port = endpointOptions.port === undefined ? 26543 : endpointOptions.port;

        /* istanbul ignore next */
        if (
            !Object.prototype.hasOwnProperty.call(endpointOptions, "port") ||
            !isFinite(endpointOptions.port!) ||
            typeof endpointOptions.port !== "number"
        ) {
            throw new Error(
                "expecting a valid port (number) when specified. alternatively you can specify port:0 and node-opcua will choose the first available port"
            );
        }

        const port = Number(endpointOptions.port || 0);

        const endPoint = this.createEndpoint(port, serverOption);

        endpointOptions.alternateHostname = endpointOptions.alternateHostname || [];
        const alternateHostname =
            endpointOptions.alternateHostname instanceof Array
                ? endpointOptions.alternateHostname
                : [endpointOptions.alternateHostname];
        const allowAnonymous = endpointOptions.allowAnonymous === undefined ? true : !!endpointOptions.allowAnonymous;

        endPoint.addStandardEndpointDescriptions({
            allowAnonymous,
            securityModes: endpointOptions.securityModes,
            securityPolicies: endpointOptions.securityPolicies,

            hostname: endpointOptions.hostname,

            alternateHostname,

            disableDiscovery: !!endpointOptions.disableDiscovery,
            // xx                hostname,
            resourcePath: serverOption.resourcePath || ""

            // TODO  userTokenTypes: endpointOptions.userTokenTypes || undefined,

            // TODO allowUnsecurePassword: endpointOptions.allowUnsecurePassword || false
        });
        return endPoint;
    }

    public async initializeCM(): Promise<void> {
        await super.initializeCM();
        await this.userCertificateManager.initialize();
    }
}

const userIdentityTokenPasswordRemoved = (userIdentityToken?: UserIdentityToken): UserIdentityToken => {
    if (!userIdentityToken) return new AnonymousIdentityToken();
    const a: UserIdentityToken  = userIdentityToken.clone();
    // For Username/Password tokens the password shall not be included.
    if (a instanceof UserNameIdentityToken) {
        // remove password
        a.password = Buffer.from("*************","ascii");
    }
    // if (a instanceof X509IdentityToken) {
    //     a.certificateData = Buffer.alloc(0);
    // }
    return a;
};

function raiseAuditActivateSessionEventType(this: OPCUAServer, session: ServerSession) {
    if (this.isAuditing) {
        this.raiseEvent("AuditActivateSessionEventType", {
            /* part 5 -  6.4.3 AuditEventType */
            actionTimeStamp: { dataType: "DateTime", value: new Date() },
            status: { dataType: "Boolean", value: true },

            serverId: { dataType: "String", value: "" },

            // ClientAuditEntryId contains the human-readable AuditEntryId defined in Part 3.
            clientAuditEntryId: { dataType: "String", value: "" },

            // The ClientUserId identifies the user of the client requesting an action.
            // The ClientUserId can be obtained from the UserIdentityToken passed in the
            // ActivateSession call.
            clientUserId: { dataType: "String", value: "cc" },

            sourceName: { dataType: "String", value: "Session/ActivateSession" },

            /* part 5 - 6.4.7 AuditSessionEventType */
            sessionId: { dataType: "NodeId", value: session.nodeId },

            /* part 5 - 6.4.10 AuditActivateSessionEventType */
            clientSoftwareCertificates: {
                arrayType: VariantArrayType.Array,
                dataType: "ExtensionObject" /* SignedSoftwareCertificate */,
                value: []
            },
            // UserIdentityToken reflects the userIdentityToken parameter of the ActivateSession
            // Service call.
            // For Username/Password tokens the password should NOT be included.
            userIdentityToken: {
                dataType: "ExtensionObject" /*  UserIdentityToken */,
                value: userIdentityTokenPasswordRemoved(session.userIdentityToken)
            },

            // SecureChannelId shall uniquely identify the SecureChannel. The application shall
            // use the same identifier in all AuditEvents related to the Session Service Set
            // (AuditCreateSessionEventType, AuditActivateSessionEventType and their subtypes) and
            // the SecureChannel Service Set (AuditChannelEventType and its subtypes).
            secureChannelId: { dataType: "String", value: session.channel!.channelId!.toString() }
        });
    }
}

export interface RaiseEventAuditEventData extends RaiseEventData {
    actionTimeStamp: PseudoVariantDateTime;
    status: PseudoVariantBoolean;
    serverId: PseudoVariantString;
    /**
     * ClientAuditEntryId contains the human-readable AuditEntryId defined in Part 3.
     */
    clientAuditEntryId: PseudoVariantString;
    /**
     * The ClientUserId identifies the user of the client requesting an action. The ClientUserId can be
     * obtained from the UserIdentityToken passed in the ActivateSession call.
     */
    clientUserId: PseudoVariantString;
    sourceName: PseudoVariantString;
}

export interface RaiseEventAuditUpdateMethodEventData extends RaiseEventAuditEventData {
    methodId: PseudoVariantNodeId;
    inputArguments: any;
}

export interface RaiseEventAuditConditionCommentEventData extends RaiseEventAuditUpdateMethodEventData {
    eventId: PseudoVariantByteString;
    comment: PseudoVariantLocalizedText;
}

export interface RaiseEventAuditSessionEventData extends RaiseEventAuditEventData {
    /**
     *  part 5 - 6.4.7 AuditSessionEventType
     */
    sessionId: PseudoVariantNodeId;
}

export interface RaiseEventAuditCreateSessionEventData extends RaiseEventAuditSessionEventData {
    /**
     *  part 5 - 6.4.8 AuditCreateSessionEventType
     *  SecureChannelId shall uniquely identify the SecureChannel.
     *  The application shall use the same identifier in
     *  all AuditEvents related to the Session Service Set (AuditCreateSessionEventType, AuditActivateSessionEventType
     *  and their subtypes) and the SecureChannel Service Set (AuditChannelEventType and its subtype
     */
    secureChannelId: PseudoVariantString;
    revisedSessionTimeout: PseudoVariantDuration;
    clientCertificate: PseudoVariantByteString;
    clientCertificateThumbprint: PseudoVariantString;
}

export interface RaiseEventAuditActivateSessionEventData extends RaiseEventAuditSessionEventData {
    /**
     * part 5 - 6.4.10 AuditActivateSessionEventType
     */
    clientSoftwareCertificates: PseudoVariantExtensionObjectArray;
    /**
     * UserIdentityToken reflects the userIdentityToken parameter of the ActivateSession Service call.
     * For Username/Password tokens the password should NOT be included.
     */
    userIdentityToken: PseudoVariantExtensionObject;
    /**
     * SecureChannelId shall uniquely identify the SecureChannel. The application shall use the same identifier
     * in all AuditEvents related to the Session Service Set (AuditCreateSessionEventType,
     * AuditActivateSessionEventType and their subtypes) and the SecureChannel Service Set
     * (AuditChannelEventType and its subtypes).
     */
    secureChannelId: PseudoVariantString;
}

// tslint:disable:no-empty-interface
export interface RaiseEventTransitionEventData extends RaiseEventData {}

export interface RaiseEventAuditUrlMismatchEventTypeData extends RaiseEventData {
    endpointUrl: PseudoVariantString;
}

/**
 * The SourceName for Events of this type shall be “Security/Certificate”.
 */
export interface RaiseAuditCertificateEventData extends RaiseEventData {
    certificate: PseudoVariantByteString;
    sourceName: PseudoVariantStringPredefined<"Security/Certificate">;
}

/**
 * This EventType inherits all Properties of the AuditCertificateEventType.
 * Either the InvalidHostname or InvalidUri shall be provided.
 */
export interface RaiseAuditCertificateDataMismatchEventData extends RaiseAuditCertificateEventData {
    /**
     * InvalidHostname is the string that represents the host name passed in as part of the URL
     * that is found to be invalid. If the host name was not invalid it can be null.
     */
    invalidHostname: PseudoVariantString;
    /*
     * InvalidUri is the URI that was passed in and found to not match what is contained in
     * the certificate. If the URI was not invalid it can be null.
     */
    invalidUri: PseudoVariantString;
}
export interface RaiseAuditCertificateUntrustedEventData extends RaiseAuditCertificateEventData {}
/**
 * This EventType inherits all Properties of the AuditCertificateEventType.
 *
 * The SourceName for Events of this type shall be “Security/Certificate”.
 *
 * The Message Variable shall include a description of why the certificate was expired
 * (i.e. time before start or time after end).
 *
 * There are no additional Properties defined for this EventType.
 *
 */
export interface RaiseAuditCertificateExpiredEventData extends RaiseAuditCertificateEventData {}
/**
 * This EventType inherits all Properties of the AuditCertificateEventType.
 *
 * The SourceName for Events of this type shall be “Security/Certificate”.
 *
 * The Message shall include a description of why the certificate is invalid.
 *
 * There are no additional Properties defined for this EventType.
 */
export interface RaiseAuditCertificateInvalidEventData extends RaiseAuditCertificateEventData {}
/**
 * This EventType inherits all Properties of the AuditCertificateEventType.
 *
 * The SourceName for Events of this type shall be “Security/Certificate”.
 *
 * The Message Variable shall include a description of why the certificate is not trusted.
 * If a trust chain is involved then the certificate that failed in the trust chain should be described.
 * There are no additional Properties defined for this EventType.
 */
export interface RaiseAuditCertificateUntrustedEventData extends RaiseAuditCertificateEventData {}
/**
 * This EventType inherits all Properties of the AuditCertificateEventType.
 *
 * The SourceName for Events of this type shall be “Security/Certificate”.
 *
 * The Message Variable shall include a description of why the certificate is revoked
 * (was the revocation list unavailable or was the certificate on the list).
 *
 *  There are no additional Properties defined for this EventType.
 */
export interface RaiseAuditCertificateRevokedEventData extends RaiseAuditCertificateEventData {
    sourceName: PseudoVariantStringPredefined<"Security/Certificate">;
}
/**
 * This EventType inherits all Properties of the AuditCertificateEventType.
 *
 * The SourceName for Events of this type shall be “Security/Certificate”.
 *
 * The Message Variable shall include a description of misuse of the certificate.
 *
 * There are no additional Properties defined for this EventType
 */
export interface RaiseAuditCertificateMismatchEventData extends RaiseAuditCertificateEventData {}
export interface OPCUAServer {
    /**
     * @internal
     * @param eventType
     * @param options
     */
    raiseEvent(eventType: "AuditSessionEventType", options: RaiseEventAuditSessionEventData): void;

    raiseEvent(eventType: "AuditCreateSessionEventType", options: RaiseEventAuditCreateSessionEventData): void;

    raiseEvent(eventType: "AuditActivateSessionEventType", options: RaiseEventAuditActivateSessionEventData): void;

    raiseEvent(eventType: "AuditCreateSessionEventType", options: RaiseEventData): void;

    raiseEvent(eventType: "AuditConditionCommentEventType", options: RaiseEventAuditConditionCommentEventData): void;

    raiseEvent(eventType: "AuditUrlMismatchEventType", options: RaiseEventAuditUrlMismatchEventTypeData): void;

    raiseEvent(eventType: "TransitionEventType", options: RaiseEventTransitionEventData): void;

    raiseEvent(eventType: "AuditCertificateInvalidEventType", options: RaiseAuditCertificateInvalidEventData): void;
    raiseEvent(eventType: "AuditCertificateExpiredEventType", options: RaiseAuditCertificateExpiredEventData): void;
    raiseEvent(eventType: "AuditCertificateUntrustedEventType", options: RaiseAuditCertificateUntrustedEventData): void;
    raiseEvent(eventType: "AuditCertificateRevokedEventType", options: RaiseAuditCertificateRevokedEventData): void;
    raiseEvent(eventType: "AuditCertificateMismatchEventType", options: RaiseAuditCertificateMismatchEventData): void;
    raiseEvent(eventType: UAEventType, options: RaiseEventData): void;
}

// eslint-disable-next-line @typescript-eslint/no-unsafe-declaration-merging
export interface OPCUAServer extends EventEmitter {
    on(event: "create_session", eventHandler: (session: ServerSession) => void): this;

    on(event: "session_activated", eventHandler: (session: ServerSession) => void): this;

    on(event: "session_closed", eventHandler: (session: ServerSession, reason: string) => void): this;

    on(event: "post_initialize", eventHandler: () => void): this;

    /**
     * emitted when the server is trying to registered the LDS
     * but when the connection to the lds has failed
     * serverRegistrationPending is sent when the backoff signal of the
     * connection process is raised
     * @event serverRegistrationPending
     */
    on(event: "serverRegistrationPending", eventHandler: () => void): this;

    /**
     * event raised when server  has been successfully registered on the local discovery server
     * @event serverRegistered
     */
    on(event: "serverRegistered", eventHandler: () => void): this;

    /**
     * event raised when server registration has been successfully renewed on the local discovery server
     * @event serverRegistered
     */
    on(event: "serverRegistrationRenewed", eventHandler: () => void): this;

    /**
     * event raised when server  has been successfully unregistered from the local discovery server
     * @event serverUnregistered
     */
    on(event: "serverUnregistered", eventHandler: () => void): this;

    /**
     * event raised after the server has raised an OPCUA event toward a client
     */
    on(event: "event", eventHandler: (eventData: any) => void): this;

    /**
     * event raised when the server received a request from one of its connected client.
     * useful for trace purpose.
     */
    on(event: "request", eventHandler: (request: Request, channel: ServerSecureChannelLayer) => void): this;

    /**
     * event raised when the server send an response to a request to one of its connected client.
     * useful for trace purpose.
     */
    on(event: "response", eventHandler: (request: Response, channel: ServerSecureChannelLayer) => void): this;

    /**
     * event raised when a new secure channel is opened
     */
    on(event: "newChannel", eventHandler: (channel: ServerSecureChannelLayer, endpoint: OPCUAServerEndPoint) => void): this;

    /**
     * event raised when a new secure channel is closed
     */
    on(event: "closeChannel", eventHandler: (channel: ServerSecureChannelLayer, endpoint: OPCUAServerEndPoint) => void): this;

    /**
     * event raised when the server refused a tcp connection from a client. ( for instance because too any connections)
     */
    on(event: "connectionRefused", eventHandler: (socketData: ISocketData, endpoint: OPCUAServerEndPoint) => void): this;

    /**
     * event raised when a OpenSecureChannel has failed, it could be a invalid certificate or malformed message
     */
    on(
        event: "openSecureChannelFailure",
        eventHandler: (socketData: ISocketData, channelData: IChannelData, endpoint: OPCUAServerEndPoint) => void
    ): this;

    on(event: string, eventHandler: (...args: [any?, ...any[]]) => void): this;
}

const opts = { multiArgs: false };
OPCUAServer.prototype.start = withCallback(OPCUAServer.prototype.start, opts);
OPCUAServer.prototype.initialize = withCallback(OPCUAServer.prototype.initialize, opts);
OPCUAServer.prototype.shutdown = withCallback(OPCUAServer.prototype.shutdown, opts);