declare module "grpc" {
  import { Message, Service } from "protobufjs";
  import { Duplex, Readable, Writable } from "stream";
  import { SecureContext } from "tls";

  /**
   * Load a ProtoBuf.js object as a gRPC object.
   * @param value The ProtoBuf.js reflection object to load
   * @param options Options to apply to the loaded file
   * @return The resulting gRPC object.
   */
  export function loadObject(value: object, options?: LoadObjectOptions): GrpcObject;

  /**
   * Options for loading proto object as gRPC object
   * @param {(number|string)=} [options.protobufjsVersion='detect'] 5 and 6
   *     respectively indicate that an object from the corresponding version of
   *     Protobuf.js is provided in the value argument. If the option is 'detect',
   *     gRPC will guess what the version is based on the structure of the value.
   */
  export interface LoadObjectOptions {
    /**
     * Deserialize bytes values as base64 strings instead of Buffers.
     * Defaults to `false`.
     */
    binaryAsBase64?: boolean;

    /**
     * Deserialize long values as strings instead of objects.
     * Defaults to `true`.
     */
    longsAsStrings?: boolean;

    /**
     * Deserialize enum values as strings instead of numbers. Only works with
     * Protobuf.js 6 values.
     * Defaults to `true`.
     */
    enumsAsStrings?: boolean;

    /**
     * use the beta method argument order for client methods, with optional
     * arguments after the callback. This option is only a temporary stopgap
     * measure to smooth an API breakage. It is deprecated, and new code
     * should not use it.
     * Defaults to `false`
     */
    deprecatedArgumentOrder?: boolean;

    /**
     * 5 and 6 respectively indicate that an object from the corresponding
     * version of Protobuf.js is provided in the value argument. If the option
     * is 'detect', gRPC wll guess what the version is based on the structure
     * of the value.
     */
    protobufjsVersion?: 5 | 6 | "detect";
  }

  /**
   * Map from `.proto` file.
   * - Namespaces become maps from the names of their direct members to those member objects
   * - Service definitions become client constructors for clients for that service. They also
   *   have a service member that can be used for constructing servers.
   * - Message definitions become Message constructors like those that ProtoBuf.js would create
   * - Enum definitions become Enum objects like those that ProtoBuf.js would create
   * - Anything else becomes the relevant reflection object that ProtoBuf.js would create
   */
  export interface GrpcObject {
    [name: string]: GrpcObject | typeof Client | Message<any>;
  }

  /**
   * Load a gRPC object from a .proto file.
   * @param filename The file to load
   * @param format The file format to expect. Defaults to 'proto'
   * @param options Options to apply to the loaded file
   * @return The resulting gRPC object
   */
  export function load(filename: Filename, format?: "proto" | "json", options?: LoadOptions): GrpcObject;

  /**
   * A filename
   */
  export type Filename = string | { root: string, file: string };

  /**
   * Options for loading proto file as gRPC object
   */
  export interface LoadOptions {
    /**
     * Load this file with field names in camel case instead of their original case.
     * Defaults to `false`.
     */
    convertFieldsToCamelCase?: boolean;

    /**
     * Deserialize bytes values as base64 strings instead of Buffers.
     * Defaults to `false`.
     */
    binaryAsBase64?: boolean;

    /**
     * Deserialize long values as strings instead of objects.
     * Defaults to `true`.
     */
    longsAsStrings?: boolean;

    /**
     * Use the beta method argument order for client methods, with optional
     * arguments after the callback. This option is only a temporary stopgap
     * measure to smooth an API breakage. It is deprecated, and new code
     * should not use it.
     * Defaults to `false`
     */
    deprecatedArgumentOrder?: boolean;
  }

  /**
   * Sets the logger function for the gRPC module. For debugging purposes, the C
   * core will log synchronously directly to stdout unless this function is
   * called. Note: the output format here is intended to be informational, and
   * is not guaranteed to stay the same in the future.
   * Logs will be directed to logger.error.
   * @param logger A Console-like object.
   */
  export function setLogger(logger: Console): void;

  /**
   * Sets the logger verbosity for gRPC module logging. The options are members
   * of the grpc.logVerbosity map.
   * @param verbosity The minimum severity to log
   */
  export function setLogVerbosity(verbosity: logVerbosity): void;

  /**
   * Server object that stores request handlers and delegates incoming requests to those handlers
   */
  export class Server {
    /**
     * Constructs a server object that stores request handlers and delegates
     * incoming requests to those handlers
     * @param options Options that should be passed to the internal server
     *     implementation
     * ```
     * var server = new grpc.Server();
     * server.addProtoService(protobuf_service_descriptor, service_implementation);
     * server.bind('address:port', server_credential);
     * server.start();
     * ```
     */
    constructor(options?: object);

    /**
     * Start the server and begin handling requests
     */
    start(): void;

    /**
     * Registers a handler to handle the named method. Fails if there already is
     * a handler for the given method. Returns true on success
     * @param name The name of the method that the provided function should
     *     handle/respond to.
     * @param handler Function that takes a stream of
     *     request values and returns a stream of response values
     * @param serialize Serialization function for responses
     * @param deserialize Deserialization function for requests
     * @param type The streaming type of method that this handles
     * @return True if the handler was set. False if a handler was already
     *     set for that name.
     */
    register(name: string, handler: handleCall, serialize: serialize, deserialize: deserialize, type: string): boolean;

    /**
     * Gracefully shuts down the server. The server will stop receiving new calls,
     * and any pending calls will complete. The callback will be called when all
     * pending calls have completed and the server is fully shut down. This method
     * is idempotent with itself and forceShutdown.
     * @param {function()} callback The shutdown complete callback
     */
    tryShutdown(callback: () => void): void;

    /**
     * Forcibly shuts down the server. The server will stop receiving new calls
     * and cancel all pending calls. When it returns, the server has shut down.
     * This method is idempotent with itself and tryShutdown, and it will trigger
     * any outstanding tryShutdown callbacks.
     */
    forceShutdown(): void;

    /**
     * Add a service to the server, with a corresponding implementation.
     * @param service The service descriptor
     * @param implementation Map of method names to method implementation
     * for the provided service.
     */
    addService(service: Service, implementation: { [name: string]: handleCall }): void;

    /**
     * Add a proto service to the server, with a corresponding implementation
     * @deprecated Use `Server#addService` instead
     * @param service The proto service descriptor
     * @param implementation Map of method names to method implementation
     * for the provided service.
     */
    addProtoService(service: Service | ServiceDefinition, implementation: { [name: string]: handleCall }): void;

    /**
     * Binds the server to the given port, with SSL disabled if creds is an
     * insecure credentials object
     * @param port The port that the server should bind on, in the format
     * "address:port"
     * @param creds Server credential object to be used for SSL. Pass an
     * insecure credentials object for an insecure port.
     * @return The bound port number or 0 if the opreation failed.
     */
    bind(port: string, creds: ServerCredentials): number;
  }

  /**
   * An object that completely defines a service.
   * @typedef {Object.<string, grpc~MethodDefinition>} grpc~ServiceDefinition
   */
  export interface ServiceDefinition {
    [s: string]: MethodDefinition;
  }

  /**
   * An object that completely defines a service method signature.
   */
  export interface MethodDefinition {
    /**
     * The method's URL path
     */
    path: string;
    /**
     * Indicates whether the method accepts a stream of requests
     */
    requestStream: boolean;
    /**
     *  Indicates whether the method returns a stream of responses
     */
   responseStream: boolean;
   /**
    * Serialization function for request values
    */
    requestSerialize: serialize;
    /**
     * Serialization function for response values
     */
    responseSerialize: serialize;
    /**
     * Deserialization function for request data
     */
    requestDeserialize: deserialize;
    /**
     * Deserialization function for repsonse data
     */
    responseDeserialize: deserialize;
  }

  type handleCall = handleUnaryCall | handleClientStreamingCall | handleServerStreamingCall | handleBidiStreamingCall;

  /**
   * User-provided method to handle unary requests on a server
   */
  type handleUnaryCall = (call: ServerUnaryCall, callback: sendUnaryData) => void;

  /**
   * An EventEmitter. Used for unary calls.
   */
  export class ServerUnaryCall {
    /**
     * Indicates if the call has been cancelled
     */
    cancelled: boolean;

    /**
     * The request metadata from the client
     */
    metadata: Metadata;

    /**
     * The request message from the client
     */
    request: any;

    private constructor();

    /**
     * Get the endpoint this call/stream is connected to.
     * @return The URI of the endpoint
     */
    getPeer(): string;

    /**
     * Send the initial metadata for a writable stream.
     * @param responseMetadata Metadata to send
     */
    sendMetadata(responseMetadata: Metadata): void;
  }

  /**
   * User provided method to handle client streaming methods on the server.
   */
  type handleClientStreamingCall = (call: ServerReadableStream, callback: sendUnaryData) => void;

  /**
   * A stream that the server can read from. Used for calls that are streaming
   * from the client side.
   */
  export class ServerReadableStream extends Readable {
    /**
     * Indicates if the call has been cancelled
     */
    cancelled: boolean;

    /**
     * The request metadata from the client
     */
    metadata: Metadata;

    private constructor();

    /**
     * Get the endpoint this call/stream is connected to.
     * @return The URI of the endpoint
     */
    getPeer(): string;

    /**
     * Send the initial metadata for a writable stream.
     * @param responseMetadata Metadata to send
     */
    sendMetadata(responseMetadata: Metadata): void;
  }

  /**
   * User provided method to handle server streaming methods on the server.
   */
  type handleServerStreamingCall = (call: ServerWriteableStream) => void;

  /**
   * A stream that the server can write to. Used for calls that are streaming
   * from the server side.
   */
  export class ServerWriteableStream extends Writable {
    /**
     * Indicates if the call has been cancelled
     */
    cancelled: boolean;

    /**
     * The request metadata from the client
     */
    metadata: Metadata;

    /**
     * The request message from the client
     */
    request: any;

    private constructor();

    /**
     * Get the endpoint this call/stream is connected to.
     * @return The URI of the endpoint
     */
    getPeer(): string;

    /**
     * Send the initial metadata for a writable stream.
     * @param responseMetadata Metadata to send
     */
    sendMetadata(responseMetadata: Metadata): void;
  }

  /**
   * User provided method to handle bidirectional streaming calls on the server.
   */
  type handleBidiStreamingCall = (call: ServerDuplexStream) => void;

  /**
   * A stream that the server can read from or write to. Used for calls
   * with duplex streaming.
   */
  export class ServerDuplexStream extends Duplex {
    private constructor();

    /**
     * Get the endpoint this call/stream is connected to.
     * @return The URI of the endpoint
     */
    getPeer(): string;

    /**
     * Send the initial metadata for a writable stream.
     * @param responseMetadata Metadata to send
     */
    sendMetadata(responseMetadata: Metadata): void;
  }

  /**
   * A deserialization function
   * @param data The byte sequence to deserialize
   * @return The data deserialized as a value
   */
  type deserialize = (data: Buffer) => any;

  /**
   * A serialization function
   * @param value The value to serialize
   * @return The value serialized as a byte sequence
   */
  type serialize = (value: any) => Buffer;

  /**
   * Callback function passed to server handlers that handle methods with
   * unary responses.
   */
  type sendUnaryData = (error: ServiceError | null, value: any, trailer?: Metadata, flags?: number) => void;

  /**
   * A class for storing metadata. Keys are normalized to lowercase ASCII.
   */
  export class Metadata {
    /**
     * Sets the given value for the given key by replacing any other values
     * associated with that key. Normalizes the key.
     * @param key The key to whose value should be set.
     * @param value The value to set. Must be a buffer if and only
     *   if the normalized key ends with '-bin'.
     */
    set(key: string, value: MetadataValue): void;

    /**
     * Adds the given value for the given key by appending to a list of previous
     * values associated with that key. Normalizes the key.
     * @param key The key for which a new value should be appended.
     * @param value The value to add. Must be a buffer if and only
     *   if the normalized key ends with '-bin'.
     */
    add(key: string, value: MetadataValue): void;

    /**
     * Removes the given key and any associated values. Normalizes the key.
     * @param key The key whose values should be removed.
     */
    remove(key: string): void;

    /**
     * Gets a list of all values associated with the key. Normalizes the key.
     * @param key The key whose value should be retrieved.
     * @return A list of values associated with the given key.
     */
    get(key: string): MetadataValue[];

    /**
     * Gets a plain object mapping each key to the first value associated with it.
     * This reflects the most common way that people will want to see metadata.
     * @return A key/value mapping of the metadata.
     */
    getMap(): { [key: string]: MetadataValue };

    /**
     * Clones the metadata object.
     * @return The newly cloned object.
     */
    clone(): Metadata;
  }

  export type MetadataValue = string | Buffer;

  /**
   * Represents the status of a completed request. If `code` is
   * `grpc.status.OK`, then the request has completed successfully.
   * Otherwise, the request has failed, `details` will contain a description of
   * the error. Either way, `metadata` contains the trailing response metadata
   * sent by the server when it finishes processing the call.
   */
  export interface StatusObject {
    /**
     * The error code, a key of `grpc.status`
     */
    code: status;
    /**
     * Human-readable description of the status
     */
    details: string;
    /**
     * Trailing metadata sent with the status, if applicable
     */
    metadata: Metadata;
  }

  /**
   * Describes how a request has failed. The member `message` will be the same as
   * `details` in `StatusObject`, and `code` and `metadata` are the
   * same as in that object.
   */
  export interface ServiceError extends Error {
    /**
     * The error code, a key of {@link grpc.status} that is not `grpc.status.OK`
     */
    code?: status;
    /**
     * Trailing metadata sent with the status, if applicable
     */
    metadata?: Metadata;
  }

  /**
   * ServerCredentials factories
   */
  export class ServerCredentials {
    /**
     * Create insecure server credentials
     * @return The ServerCredentials
     */
    static createInsecure(): ServerCredentials;
    /**
     * Create SSL server credentials
     * @param rootCerts Root CA certificates for validating client certificates
     * @param keyCertPairs A list of private key and certificate chain pairs to
     * be used for authenticating the server
     * @param checkClientCertificate Indicates that the server should request
     * and verify the client's certificates.
     * Defaults to `false`.
     * @return The ServerCredentials
     */
    static createInsecure(rootCerts: Buffer | null, keyCertPairs: KeyCertPair[], checkClientCertificate?: boolean): ServerCredentials;
  }

  /**
   * A private key and certificate pair
   */
  export interface KeyCertPair {
    /**
     * The server's private key
     */
    privateKey: Buffer;

    /**
     * The server's certificate chain
     */
    certChain: Buffer;
  }

  /**
   * Enum of status codes that gRPC can return
   */
  export enum status {
    /**
     * Not an error; returned on success
     */
    OK = 0,
    /**
     * The operation was cancelled (typically by the caller).
     */
    CANCELLED = 1,
    /**
     * Unknown error.  An example of where this error may be returned is
     * if a status value received from another address space belongs to
     * an error-space that is not known in this address space.  Also
     * errors raised by APIs that do not return enough error information
     * may be converted to this error.
     */
    UNKNOWN = 2,
    /**
     * Client specified an invalid argument.  Note that this differs
     * from FAILED_PRECONDITION.  INVALID_ARGUMENT indicates arguments
     * that are problematic regardless of the state of the system
     * (e.g., a malformed file name).
     */
    INVALID_ARGUMENT = 3,
    /**
     * Deadline expired before operation could complete.  For operations
     * that change the state of the system, this error may be returned
     * even if the operation has completed successfully.  For example, a
     * successful response from a server could have been delayed long
     * enough for the deadline to expire.
     */
    DEADLINE_EXCEEDED = 4,
    /**
     * Some requested entity (e.g., file or directory) was not found.
     */
    NOT_FOUND = 5,
    /**
     * Some entity that we attempted to create (e.g., file or directory)
     * already exists.
     */
    ALREADY_EXISTS = 6,
    /**
     * The caller does not have permission to execute the specified
     * operation.  PERMISSION_DENIED must not be used for rejections
     * caused by exhausting some resource (use RESOURCE_EXHAUSTED
     * instead for those errors).  PERMISSION_DENIED must not be
     * used if the caller can not be identified (use UNAUTHENTICATED
     * instead for those errors).
     */
    PERMISSION_DENIED = 7,
    /**
     * Some resource has been exhausted, perhaps a per-user quota, or
     * perhaps the entire file system is out of space.
     */
    RESOURCE_EXHAUSTED = 8,
    /**
     * Operation was rejected because the system is not in a state
     * required for the operation's execution.  For example, directory
     * to be deleted may be non-empty, an rmdir operation is applied to
     * a non-directory, etc.
     *
     * A litmus test that may help a service implementor in deciding
     * between FAILED_PRECONDITION, ABORTED, and UNAVAILABLE:
     *
     *  - Use UNAVAILABLE if the client can retry just the failing call.
     *  - Use ABORTED if the client should retry at a higher-level
     *    (e.g., restarting a read-modify-write sequence).
     *  - Use FAILED_PRECONDITION if the client should not retry until
     *    the system state has been explicitly fixed.  E.g., if an "rmdir"
     *    fails because the directory is non-empty, FAILED_PRECONDITION
     *    should be returned since the client should not retry unless
     *    they have first fixed up the directory by deleting files from it.
     *  - Use FAILED_PRECONDITION if the client performs conditional
     *    REST Get/Update/Delete on a resource and the resource on the
     *    server does not match the condition. E.g., conflicting
     *    read-modify-write on the same resource.
     */
    FAILED_PRECONDITION = 9,
    /**
     * The operation was aborted, typically due to a concurrency issue
     * like sequencer check failures, transaction aborts, etc.
     *
     * See litmus test above for deciding between FAILED_PRECONDITION,
     * ABORTED, and UNAVAILABLE.
     */
    ABORTED = 10,
    /**
     * Operation was attempted past the valid range.  E.g., seeking or
     * reading past end of file.
     *
     * Unlike INVALID_ARGUMENT, this error indicates a problem that may
     * be fixed if the system state changes. For example, a 32-bit file
     * system will generate INVALID_ARGUMENT if asked to read at an
     * offset that is not in the range [0,2^32-1], but it will generate
     * OUT_OF_RANGE if asked to read from an offset past the current
     * file size.
     *
     * There is a fair bit of overlap between FAILED_PRECONDITION and
     * OUT_OF_RANGE.  We recommend using OUT_OF_RANGE (the more specific
     * error) when it applies so that callers who are iterating through
     * a space can easily look for an OUT_OF_RANGE error to detect when
     * they are done.
     */
    OUT_OF_RANGE = 11,
    /**
     * Operation is not implemented or not supported/enabled in this service.
     */
    UNIMPLEMENTED = 12,
    /**
     * Internal errors.  Means some invariants expected by underlying
     * system has been broken.  If you see one of these errors,
     * something is very broken.
     */
    INTERNAL = 13,
    /**
     * The service is currently unavailable.  This is a most likely a
     * transient condition and may be corrected by retrying with
     * a backoff.
     *
     * See litmus test above for deciding between FAILED_PRECONDITION,
     * ABORTED, and UNAVAILABLE.
     */
    UNAVAILABLE = 14,
    /**
     * Unrecoverable data loss or corruption.
     */
    DATA_LOSS = 15,
    /**
     * The request does not have valid authentication credentials for the
     * operation.
     */
    UNAUTHENTICATED = 16,
  }

  /**
   * Propagation flags: these can be bitwise or-ed to form the propagation option
   * for calls.
   *
   * Users are encouraged to write propagation masks as deltas from the default.
   * i.e. write `grpc.propagate.DEFAULTS & ~grpc.propagate.DEADLINE` to disable
   * deadline propagation.
   */
  export enum propagate {
    DEADLINE,
    CENSUS_STATS_CONTEXT,
    CENSUS_TRACING_CONTEXT,
    CANCELLATION,
    DEFAULTS,
  }

  /**
   * Call error constants. Call errors almost always indicate bugs in the gRPC
   * library, and these error codes are mainly useful for finding those bugs.
   */
  export enum callError  {
    OK,
    ERROR,
    NOT_ON_SERVER,
    NOT_ON_CLIENT,
    ALREADY_INVOKED,
    NOT_INVOKED,
    ALREADY_FINISHED,
    TOO_MANY_OPERATIONS,
    INVALID_FLAGS,
    INVALID_METADATA,
    INVALID_MESSAGE,
    NOT_SERVER_COMPLETION_QUEUE,
    BATCH_TOO_BIG,
    PAYLOAD_TYPE_MISMATCH,
  }

  /**
   * Write flags: these can be bitwise or-ed to form write options that modify
   * how data is written.
   */
  export enum writeFlags {
    /**
     * Hint that the write may be buffered and need not go out on the wire
     * immediately. GRPC is free to buffer the message until the next non-buffered
     * write, or until writes_done, but it need not buffer completely or at all.
     */
    BUFFER_HINT = 1,
    /**
     * Force compression to be disabled for a particular write
     */
    NO_COMPRESS,
  }

  /**
   * Log verbosity constants. Maps setting names to code numbers.
   */
  export enum logVerbosity {
    DEBUG,
    INFO,
    ERROR,
  }

  /**
   * Credentials module
   *
   * This module contains factory methods for two different credential types:
   * CallCredentials and ChannelCredentials. ChannelCredentials are things like
   * SSL credentials that can be used to secure a connection, and are used to
   * construct a Client object. CallCredentials genrally modify metadata, so they
   * can be attached to an individual method call.
   *
   * CallCredentials can be composed with other CallCredentials to create
   * CallCredentials. ChannelCredentials can be composed with CallCredentials
   * to create ChannelCredentials. No combined credential can have more than
   * one ChannelCredentials.
   *
   * For example, to create a client secured with SSL that uses Google
   * default application credentials to authenticate:
   *
   * ```
   * var channel_creds = credentials.createSsl(root_certs);
   * (new GoogleAuth()).getApplicationDefault(function(err, credential) {
   *   var call_creds = credentials.createFromGoogleCredential(credential);
   *   var combined_creds = credentials.combineChannelCredentials(
   *       channel_creds, call_creds);
   *   var client = new Client(address, combined_creds);
   * });
   * ```
   */
  export const credentials: {
    /**
     * Create an SSL Credentials object. If using a client-side certificate, both
     * the second and third arguments must be passed.
     * @param rootCerts The root certificate data
     * @param privateKey The client certificate private key, if applicable
     * @param certChain The client certificate cert chain, if applicable
     * @return The SSL Credentials object
     */
    createSsl(rootCerts?: Buffer, privateKey?: Buffer, certChain?: Buffer): ChannelCredentials;

    /**
     * Create a gRPC credentials object from a metadata generation function. This
     * function gets the service URL and a callback as parameters. The error
     * passed to the callback can optionally have a 'code' value attached to it,
     * which corresponds to a status code that this library uses.
     * @param metadataGenerator The function that generates metadata
     * @return The credentials object
     */
    createFromMetadataGenerator(metadataGenerator: metadataGenerator): CallCredentials;

    /**
     * Create a gRPC credential from a Google credential object.
     * @param googleCredential The Google credential object to use
     * @return The resulting credentials object
     */
    createFromGoogleCredential(googleCredential: GoogleOAuth2Client): CallCredentials;

    /**
     * Combine a ChannelCredentials with any number of CallCredentials into a single
     * ChannelCredentials object.
     * @param channelCredential The ChannelCredentials to start with
     * @param credentials The CallCredentials to compose
     * @return A credentials object that combines all of the input credentials
     */
    combineChannelCredentials(channelCredential: ChannelCredentials, ...credentials: CallCredentials[]): ChannelCredentials;

    /**
     * Combine any number of CallCredentials into a single CallCredentials object
     * @param credentials The CallCredentials to compose
     * @return A credentials object that combines all of the input credentials
     */
    combineCallCredentials(...credentials: CallCredentials[]): CallCredentials;

    /**
     * Create an insecure credentials object. This is used to create a channel that
     * does not use SSL. This cannot be composed with anything.
     * @return The insecure credentials object
     */
    createInsecure(): ChannelCredentials;
  };

  /**
   * Metadata generator function.
   */
  export type metadataGenerator = (params: { service_url: string }, callback: (error: Error | null, metadata?: Metadata) => void) => void;

  /**
   * This cannot be constructed directly. Instead, instances of this class should
   * be created using the factory functions in `grpc.credentials`
   */
  export interface ChannelCredentials {
    /**
     * Returns a copy of this object with the included set of per-call credentials
     * expanded to include callCredentials.
     * @param callCredentials A CallCredentials object to associate with this
     * instance.
     */
    compose(callCredentials: CallCredentials): ChannelCredentials;

    /**
     * Gets the set of per-call credentials associated with this instance.
     */
    getCallCredentials(): CallCredentials;

    /**
     * Gets a SecureContext object generated from input parameters if this
     * instance was created with createSsl, or null if this instance was created
     * with createInsecure.
     */
    getSecureContext(): SecureContext | null;
  }

  /**
   * This cannot be constructed directly. Instead, instances of this class should
   * be created using the factory functions in `grpc.credentials`
   */
  export interface CallCredentials {
    /**
     * Asynchronously generates a new Metadata object.
     * @param options Options used in generating the Metadata object.
     */
    generateMetadata(options: object): Promise<Metadata>;

    /**
     * Creates a new CallCredentials object from properties of both this and
     * another CallCredentials object. This object's metadata generator will be
     * called first.
     * @param callCredentials The other CallCredentials object.
     */
    compose(callCredentials: CallCredentials): CallCredentials;
  }

  /**
   * This is the required interface from the OAuth2Client object
   * from https://github.com/google/google-auth-library-nodejs lib.
   * The definition is copied from `ts/lib/auth/oauth2client.ts`
   */
  export interface GoogleOAuth2Client {
    getRequestMetadata(optUri: string, metadataCallback: (err: Error, headers: any) => void): void;
  }

  /**
   * Creates a constructor for a client with the given methods, as specified in
   * the methods argument. The resulting class will have an instance method for
   * each method in the service, which is a partial application of one of the
   * `grpc.Client` request methods, depending on `requestSerialize`
   * and `responseSerialize`, with the `method`, `serialize`, and `deserialize`
   * arguments predefined.
   * @param methods An object mapping method names to method attributes
   * @param serviceName The fully qualified name of the service
   * @param classOptions An options object.
   * @return New client constructor, which is a subclass of `grpc.Client`, and
   * has the same arguments as that constructor.
   */
  export function makeGenericClientConstructor(
    methods: ServiceDefinition,
    serviceName: string,
    classOptions: GenericClientOptions,
  ): typeof Client;

  /**
   * Options for generic client constructor.
   */
  export interface GenericClientOptions {
    /**
     * Indicates that the old argument order should be used for methods, with
     * optional arguments at the end instead of the callback at the end. This
     * option is only a temporary stopgap measure to smooth an API breakage.
     * It is deprecated, and new code should not use it.
     */
    deprecatedArgumentOrder?: boolean;
  }

  /**
   * Create a client with the given methods
   */
  export class Client {
    /**
     * A generic gRPC client. Primarily useful as a base class for generated clients
     * @param address Server address to connect to
     * @param credentials Credentials to use to connect to the server
     * @param options Options to apply to channel creation
     */
    constructor(address: string, credentials: ChannelCredentials, options?: object)

    /**
     * Make a unary request to the given method, using the given serialize
     * and deserialize functions, with the given argument.
     * @param method The name of the method to request
     * @param serialize The serialization function for inputs
     * @param deserialize The deserialization function for outputs
     * @param argument The argument to the call. Should be serializable with
     *     serialize
     * @param metadata Metadata to add to the call
     * @param options Options map
     * @param callback The callback to for when the response is received
     * @return An event emitter for stream related events
     */
    makeUnaryRequest(
      method: string,
      serialize: serialize,
      deserialize: deserialize,
      argument: any | null,
      metadata: Metadata | null,
      options: CallOptions | null,
      callback: requestCallback,
    ): ClientUnaryCall;

    /**
     * Make a client stream request to the given method, using the given serialize
     * and deserialize functions, with the given argument.
     * @param method The name of the method to request
     * @param serialize The serialization function for inputs
     * @param deserialize The deserialization function for outputs
     * @param metadata Array of metadata key/value pairs to add to the call
     * @param options Options map
     * @param callback The callback to for when the response is received
     * @return An event emitter for stream related events
     */
    makeClientStreamRequest(
      method: string,
      serialize: serialize,
      deserialize: deserialize,
      metadata: Metadata | null,
      options: CallOptions | null,
      callback: requestCallback,
    ): ClientWritableStream;

    /**
     * Make a server stream request to the given method, with the given serialize
     * and deserialize function, using the given argument
     * @param method The name of the method to request
     * @param serialize The serialization function for inputs
     * @param deserialize The deserialization function for outputs
     * @param argument The argument to the call. Should be serializable with
     *     serialize
     * @param metadata Array of metadata key/value pairs to add to the call
     * @param options Options map
     * @return An event emitter for stream related events
     */
    makeServerStreamRequest(
      method: string,
      serialize: serialize,
      deserialize: deserialize,
      argument: any,
      metadata?: Metadata | null,
      options?: CallOptions | null,
    ): ClientReadableStream;

    /**
     * Make a bidirectional stream request with this method on the given channel.
     * @param method The name of the method to request
     * @param serialize The serialization function for inputs
     * @param deserialize The deserialization
     *     function for outputs
     * @param metadata Array of metadata key/value
     *     pairs to add to the call
     * @param options Options map
     * @return An event emitter for stream related events
     */
    makeBidiStreamRequest(
      method: string,
      serialize: serialize,
      deserialize: deserialize,
      metadata?: Metadata | null,
      options?: CallOptions | null,
    ): ClientDuplexStream;

    /**
     * Close this client.
     */
    close(): void;

    /**
     * Return the underlying channel object for the specified client
     * @return The channel
     */
    getChannel(): Channel;

    /**
     * Wait for the client to be ready. The callback will be called when the
     * client has successfully connected to the server, and it will be called
     * with an error if the attempt to connect to the server has unrecoverablly
     * failed or if the deadline expires. This function will make the channel
     * start connecting if it has not already done so.
     * @param deadline When to stop waiting for a connection.
     * @param callback The callback to call when done attempting to connect.
     */
    waitForReady(deadline: Deadline, callback: (error: Error | null) => void): void;
  }

  /**
   * A gRPC channel.
   */
  export type Channel = any;

  /**
   * Options that can be set on a call.
   */
  export interface CallOptions {
    /**
     * The deadline for the entire call to complete.
     */
    deadline?: Deadline;
    /**
     * Server hostname to set on the call. Only meaningful if different from
     * the server address used to construct the client.
     */
    host?: string;
    /**
     * Parent call. Used in servers when making a call as part of the process
     * of handling a call. Used to propagate some information automatically,
     * as specified by propagate_flags.
     */
    parent?: Call;
    /**
     * Indicates which properties of a parent call should propagate to this
     * call. Bitwise combination of flags in `grpc.propagate`.
     */
    propagate_flags: number;
    /**
     * The credentials that should be used to make this particular call.
     */
    credentials: CallCredentials;
  }

  /**
   * The deadline of an operation. If it is a date, the deadline is reached at
   * the date and time specified. If it is a finite number, it is treated as
   * a number of milliseconds since the Unix Epoch. If it is Infinity, the
   * deadline will never be reached. If it is -Infinity, the deadline has already
   * passed.
   */
  export type Deadline = number | Date;

  /**
   * Any client call type
   */
  type Call = ClientUnaryCall | ClientReadableStream | ClientWritableStream | ClientDuplexStream;

  /**
   * An EventEmitter. Used for unary calls.
   */
  export class ClientUnaryCall {
    private constructor();

    /**
     * Cancel the ongoing call. Results in the call ending with a CANCELLED status,
     * unless it has already ended with some other status.
     */
    cancel(): void;

    /**
     * Get the endpoint this call/stream is connected to.
     * @return The URI of the endpoint
     */
    getPeer(): string;
  }

  /**
   * A stream that the client can read from. Used for calls that are streaming
   * from the server side.
   */
  export class ClientReadableStream extends Readable {
    private constructor();

    /**
     * Cancel the ongoing call. Results in the call ending with a CANCELLED status,
     * unless it has already ended with some other status.
     */
    cancel(): void;

    /**
     * Get the endpoint this call/stream is connected to.
     * @return The URI of the endpoint
     */
    getPeer(): string;
  }

  /**
   * A stream that the client can write to. Used for calls that are streaming from
   * the client side.
   */
  export class ClientWritableStream extends Writable {
    private constructor();

    /**
     * Write a message to the request stream. If serializing the argument fails,
     * the call will be cancelled and the stream will end with an error.
     * @param message The message to write. Must be a valid argument to the
     *     serialize function of the corresponding method
     * @param flags Flags to modify how the message is written
     * @param callback Callback for when this chunk of data is flushed
     * @return As defined for [Writable]{@link external:Writable}
     */
    write(message: any, flags?: any&writeFlags, callback?: Function): boolean;

    /**
     * Cancel the ongoing call. Results in the call ending with a CANCELLED status,
     * unless it has already ended with some other status.
     */
    cancel(): void;

    /**
     * Get the endpoint this call/stream is connected to.
     * @return The URI of the endpoint
     */
    getPeer(): string;
  }

  /**
   * A stream that the client can read from or write to. Used for calls with
   * duplex streaming.
   */
  export class ClientDuplexStream extends Duplex {
    private constructor();

    /**
     * Write a message to the request stream. If serializing the argument fails,
     * the call will be cancelled and the stream will end with an error.
     * @param message The message to write. Must be a valid argument to the
     *     serialize function of the corresponding method
     * @param flags Flags to modify how the message is written
     * @param callback Callback for when this chunk of data is flushed
     * @return As defined for [Writable]{@link external:Writable}
     */
    write(message: any, flags?: any&writeFlags, callback?: Function): boolean;

    /**
     * Cancel the ongoing call. Results in the call ending with a CANCELLED status,
     * unless it has already ended with some other status.
     */
    cancel(): void;

    /**
     * Get the endpoint this call/stream is connected to.
     * @return The URI of the endpoint
     */
    getPeer(): string;
  }

  /**
   * Client request callback
   * @param error The error, if the call failed
   * @param value The response value, if the call succeeded
   */
  export type requestCallback = (error: ServiceError | null, value: any) => void;

  /**
   * Return the underlying channel object for the specified client
   * @see grpc.Client#getChannel
   * @param client The client
   * @return The channel
   */
  export function getClientChannel(client: Client): Channel;

  /**
   * Wait for the client to be ready. The callback will be called when the
   * client has successfully connected to the server, and it will be called
   * with an error if the attempt to connect to the server has unrecoverablly
   * failed or if the deadline expires. This function will make the channel
   * start connecting if it has not already done so.
   * @see grpc.Client#waitForReady
   * @param client The client to wait on
   * @param deadline When to stop waiting for a connection. Pass Infinity to
   * wait forever.
   * @param callback The callback to call when done attempting to connect.
   */
  export function waitForClientReady(client: Client, deadline: Deadline, callback: (error: Error | null) => void): void;

  /**
   * Close client.
   * @param clientObj The client to close
   */
  export function closeClient(clientObj: Client): void;
}