@microsoft/signalr/src/LongPollingTransport.ts

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

import { AbortController } from "./AbortController";
import { HttpError, TimeoutError } from "./Errors";
import { HttpClient, HttpRequest } from "./HttpClient";
import { ILogger, LogLevel } from "./ILogger";
import { ITransport, TransferFormat } from "./ITransport";
import { Arg, getDataDetail, sendMessage } from "./Utils";

// Not exported from 'index', this type is internal.
/** @private */
export class LongPollingTransport implements ITransport {
    private readonly httpClient: HttpClient;
    private readonly accessTokenFactory: (() => string | Promise<string>) | undefined;
    private readonly logger: ILogger;
    private readonly logMessageContent: boolean;
    private readonly pollAbort: AbortController;

    private url?: string;
    private running: boolean;
    private receiving?: Promise<void>;
    private closeError?: Error;

    public onreceive: ((data: string | ArrayBuffer) => void) | null;
    public onclose: ((error?: Error) => void) | null;

    // This is an internal type, not exported from 'index' so this is really just internal.
    public get pollAborted() {
        return this.pollAbort.aborted;
    }

    constructor(httpClient: HttpClient, accessTokenFactory: (() => string | Promise<string>) | undefined, logger: ILogger, logMessageContent: boolean) {
        this.httpClient = httpClient;
        this.accessTokenFactory = accessTokenFactory;
        this.logger = logger;
        this.pollAbort = new AbortController();
        this.logMessageContent = logMessageContent;

        this.running = false;

        this.onreceive = null;
        this.onclose = null;
    }

    public async connect(url: string, transferFormat: TransferFormat): Promise<void> {
        Arg.isRequired(url, "url");
        Arg.isRequired(transferFormat, "transferFormat");
        Arg.isIn(transferFormat, TransferFormat, "transferFormat");

        this.url = url;

        this.logger.log(LogLevel.Trace, "(LongPolling transport) Connecting.");

        // Allow binary format on Node and Browsers that support binary content (indicated by the presence of responseType property)
        if (transferFormat === TransferFormat.Binary &&
            (typeof XMLHttpRequest !== "undefined" && typeof new XMLHttpRequest().responseType !== "string")) {
            throw new Error("Binary protocols over XmlHttpRequest not implementing advanced features are not supported.");
        }

        const pollOptions: HttpRequest = {
            abortSignal: this.pollAbort.signal,
            headers: {},
            timeout: 100000,
        };

        if (transferFormat === TransferFormat.Binary) {
            pollOptions.responseType = "arraybuffer";
        }

        const token = await this.getAccessToken();
        this.updateHeaderToken(pollOptions, token);

        // Make initial long polling request
        // Server uses first long polling request to finish initializing connection and it returns without data
        const pollUrl = `${url}&_=${Date.now()}`;
        this.logger.log(LogLevel.Trace, `(LongPolling transport) polling: ${pollUrl}.`);
        const response = await this.httpClient.get(pollUrl, pollOptions);
        if (response.statusCode !== 200) {
            this.logger.log(LogLevel.Error, `(LongPolling transport) Unexpected response code: ${response.statusCode}.`);

            // Mark running as false so that the poll immediately ends and runs the close logic
            this.closeError = new HttpError(response.statusText || "", response.statusCode);
            this.running = false;
        } else {
            this.running = true;
        }

        this.receiving = this.poll(this.url, pollOptions);
    }

    private async getAccessToken(): Promise<string | null> {
        if (this.accessTokenFactory) {
            return await this.accessTokenFactory();
        }

        return null;
    }

    private updateHeaderToken(request: HttpRequest, token: string | null) {
        if (!request.headers) {
            request.headers = {};
        }
        if (token) {
            // tslint:disable-next-line:no-string-literal
            request.headers["Authorization"] = `Bearer ${token}`;
            return;
        }
        // tslint:disable-next-line:no-string-literal
        if (request.headers["Authorization"]) {
            // tslint:disable-next-line:no-string-literal
            delete request.headers["Authorization"];
        }
    }

    private async poll(url: string, pollOptions: HttpRequest): Promise<void> {
        try {
            while (this.running) {
                // We have to get the access token on each poll, in case it changes
                const token = await this.getAccessToken();
                this.updateHeaderToken(pollOptions, token);

                try {
                    const pollUrl = `${url}&_=${Date.now()}`;
                    this.logger.log(LogLevel.Trace, `(LongPolling transport) polling: ${pollUrl}.`);
                    const response = await this.httpClient.get(pollUrl, pollOptions);

                    if (response.statusCode === 204) {
                        this.logger.log(LogLevel.Information, "(LongPolling transport) Poll terminated by server.");

                        this.running = false;
                    } else if (response.statusCode !== 200) {
                        this.logger.log(LogLevel.Error, `(LongPolling transport) Unexpected response code: ${response.statusCode}.`);

                        // Unexpected status code
                        this.closeError = new HttpError(response.statusText || "", response.statusCode);
                        this.running = false;
                    } else {
                        // Process the response
                        if (response.content) {
                            this.logger.log(LogLevel.Trace, `(LongPolling transport) data received. ${getDataDetail(response.content, this.logMessageContent)}.`);
                            if (this.onreceive) {
                                this.onreceive(response.content);
                            }
                        } else {
                            // This is another way timeout manifest.
                            this.logger.log(LogLevel.Trace, "(LongPolling transport) Poll timed out, reissuing.");
                        }
                    }
                } catch (e) {
                    if (!this.running) {
                        // Log but disregard errors that occur after stopping
                        this.logger.log(LogLevel.Trace, `(LongPolling transport) Poll errored after shutdown: ${e.message}`);
                    } else {
                        if (e instanceof TimeoutError) {
                            // Ignore timeouts and reissue the poll.
                            this.logger.log(LogLevel.Trace, "(LongPolling transport) Poll timed out, reissuing.");
                        } else {
                            // Close the connection with the error as the result.
                            this.closeError = e;
                            this.running = false;
                        }
                    }
                }
            }
        } finally {
            this.logger.log(LogLevel.Trace, "(LongPolling transport) Polling complete.");

            // We will reach here with pollAborted==false when the server returned a response causing the transport to stop.
            // If pollAborted==true then client initiated the stop and the stop method will raise the close event after DELETE is sent.
            if (!this.pollAborted) {
                this.raiseOnClose();
            }
        }
    }

    public async send(data: any): Promise<void> {
        if (!this.running) {
            return Promise.reject(new Error("Cannot send until the transport is connected"));
        }
        return sendMessage(this.logger, "LongPolling", this.httpClient, this.url!, this.accessTokenFactory, data, this.logMessageContent);
    }

    public async stop(): Promise<void> {
        this.logger.log(LogLevel.Trace, "(LongPolling transport) Stopping polling.");

        // Tell receiving loop to stop, abort any current request, and then wait for it to finish
        this.running = false;
        this.pollAbort.abort();

        try {
            await this.receiving;

            // Send DELETE to clean up long polling on the server
            this.logger.log(LogLevel.Trace, `(LongPolling transport) sending DELETE request to ${this.url}.`);

            const deleteOptions: HttpRequest = {
                headers: {},
            };
            const token = await this.getAccessToken();
            this.updateHeaderToken(deleteOptions, token);
            await this.httpClient.delete(this.url!, deleteOptions);

            this.logger.log(LogLevel.Trace, "(LongPolling transport) DELETE request sent.");
        } finally {
            this.logger.log(LogLevel.Trace, "(LongPolling transport) Stop finished.");

            // Raise close event here instead of in polling
            // It needs to happen after the DELETE request is sent
            this.raiseOnClose();
        }
    }

    private raiseOnClose() {
        if (this.onclose) {
            let logMessage = "(LongPolling transport) Firing onclose event.";
            if (this.closeError) {
                logMessage += " Error: " + this.closeError;
            }
            this.logger.log(LogLevel.Trace, logMessage);
            this.onclose(this.closeError);
        }
    }
}