Method handleUpgrade

packages/engine.io/lib/server.ts:831–877

* Handles an Engine.IO HTTP Upgrade.

(
    req: IncomingMessage,
    socket: Duplex,
    upgradeHead: Buffer,
  )

   * Handles an Engine.IO HTTP Upgrade.
   */
  public handleUpgrade(
    req: IncomingMessage,
    socket: Duplex,
    upgradeHead: Buffer,
  ) {
    const engineRequest = req as EngineRequest;

    this.prepare(engineRequest);

    const res = new WebSocketResponse(engineRequest, socket);
    const callback: ErrorCallback = (errorCode, errorContext) => {
      if (errorCode !== undefined) {
        this.emit("connection_error", {
          req: engineRequest,
          code: errorCode,
          message: Server.errorMessages[errorCode],
          context: errorContext,
        });
        abortUpgrade(socket, errorCode, errorContext);
        return;
      }

      const head = Buffer.from(upgradeHead);
      upgradeHead = null;

      // some middlewares (like express-session) wait for the writeHead() call to flush their headers
      // see https://github.com/expressjs/session/blob/1010fadc2f071ddf2add94235d72224cf65159c6/index.js#L220-L244
      res.writeHead();

      // delegate to ws
      this.ws.handleUpgrade(engineRequest, socket, head, (websocket) => {
        this.onWebSocket(engineRequest, socket, websocket);
      });
    };

    this._applyMiddlewares(
      engineRequest,
      res as unknown as ServerResponse,
      (err) => {
        if (err) {
          callback(Server.errors.BAD_REQUEST, { name: "MIDDLEWARE_FAILURE" });
        } else {
          this.verify(engineRequest, true, callback);
        }
      },
    );
  }

  /**
   * Called upon a ws.io connection.