Method onWebSocket

packages/engine.io/lib/server.ts:886–947

* Called upon a ws.io connection. * @param req * @param socket * @param websocket * @private

(
    req: EngineRequest,
    socket: Duplex,
    websocket: WsWebSocket,
  )

   * @private
   */
  private onWebSocket(
    req: EngineRequest,
    socket: Duplex,
    websocket: WsWebSocket,
  ) {
    websocket.on("error", onUpgradeError);

    if (
      transports[req._query.transport] !== undefined &&
      !transports[req._query.transport].prototype.handlesUpgrades
    ) {
      debug("transport doesnt handle upgraded requests");
      websocket.close();
      return;
    }

    // get client id
    const id = req._query.sid;

    // keep a reference to the ws.Socket
    req.websocket = websocket;

    if (id) {
      const client = this.clients[id];
      if (!client) {
        debug("upgrade attempt for closed client");
        websocket.close();
      } else if (client.upgrading) {
        debug("transport has already been trying to upgrade");
        websocket.close();
      } else if (client.upgraded) {
        debug("transport had already been upgraded");
        websocket.close();
      } else {
        debug("upgrading existing transport");

        // transport error handling takes over
        websocket.removeListener("error", onUpgradeError);

        const transport = this.createTransport(
          req._query.transport as TransportName,
          req,
        );
        // @ts-expect-error this option is only for WebSocket impl
        transport.perMessageDeflate = this.opts.perMessageDeflate;
        client._maybeUpgrade(transport);
      }
    } else {
      const closeConnection = (errorCode, errorContext) =>
        abortUpgrade(socket, errorCode, errorContext);
      this.handshake(
        req._query.transport as TransportName,
        req,
        closeConnection,
      );
    }

    function onUpgradeError() {