Method _maybeUpgrade

packages/engine.io/lib/socket.ts:293–380

(transport: Transport)

   * @private
   */
  /* private */ _maybeUpgrade(transport: Transport) {
    debug(
      'might upgrade socket transport from "%s" to "%s"',
      this.transport.name,
      transport.name,
    );

    this.upgrading = true;

    // set transport upgrade timer
    const upgradeTimeoutTimer = setTimeout(() => {
      debug("client did not complete upgrade - closing transport");
      cleanup();
      if ("open" === transport.readyState) {
        transport.close();
      }
    }, this.server.opts.upgradeTimeout);

    let checkIntervalTimer;

    const onPacket = (packet) => {
      if ("ping" === packet.type && "probe" === packet.data) {
        debug("got probe ping packet, sending pong");
        transport.send([{ type: "pong", data: "probe" }]);
        this.emit("upgrading", transport);
        clearInterval(checkIntervalTimer);
        checkIntervalTimer = setInterval(check, 100);
      } else if ("upgrade" === packet.type && this.readyState !== "closed") {
        debug("got upgrade packet - upgrading");
        cleanup();
        this.transport.discard();
        this.upgraded = true;
        this.clearTransport();
        this.setTransport(transport);
        this.emit("upgrade", transport);
        this.flush();
        if (this.readyState === "closing") {
          transport.close(() => {
            this.onClose("forced close");
          });
        }
      } else {
        cleanup();
        transport.close();
      }
    };

    // we force a polling cycle to ensure a fast upgrade
    const check = () => {
      if ("polling" === this.transport.name && this.transport.writable) {
        debug("writing a noop packet to polling for fast upgrade");
        this.transport.send([{ type: "noop" }]);
      }
    };

    const cleanup = () => {
      this.upgrading = false;