fix: properly report timeout error when connecting

In some specific cases (Node.js client with WebSocket only), the reason
attached to the "connect_error" event was "websocket error" instead of
"timeout".

Related: socketio/socket.io#4062

lib/manager.ts

@@ -328,35 +328,32 @@ export class Manager<
       fn && fn();
     });
 
-    // emit `error`
-    const errorSub = on(socket, "error", (err) => {
+    const onError = (err) => {
       debug("error");
-      self.cleanup();
-      self._readyState = "closed";
+      this.cleanup();
+      this._readyState = "closed";
       this.emitReserved("error", err);
       if (fn) {
         fn(err);
       } else {
         // Only do this if there is no fn to handle the error
-        self.maybeReconnectOnOpen();
+        this.maybeReconnectOnOpen();
       }
-    });
+    };
+
+    // emit `error`
+    const errorSub = on(socket, "error", onError);
 
     if (false !== this._timeout) {
       const timeout = this._timeout;
       debug("connect attempt will timeout after %d", timeout);
 
-      if (timeout === 0) {
-        openSubDestroy(); // prevents a race condition with the 'open' event
-      }
-
       // set timer
       const timer = this.setTimeoutFn(() => {
         debug("connect attempt timed out after %d", timeout);
         openSubDestroy();
+        onError(new Error("timeout"));
         socket.close();
-        // @ts-ignore
-        socket.emit("error", new Error("timeout"));
       }, timeout);
 
       if (this.opts.autoUnref) {

test/socket.ts

@@ -70,6 +70,38 @@ describe("socket", () => {
     });
   });
 
+  it("fire a connect_error event on open timeout (polling)", () => {
+    return wrap((done) => {
+      const socket = io(BASE_URL, {
+        forceNew: true,
+        transports: ["polling"],
+        timeout: 0,
+      });
+
+      socket.on("connect_error", (err) => {
+        expect(err.message).to.eql("timeout");
+        socket.disconnect();
+        done();
+      });
+    });
+  });
+
+  it("fire a connect_error event on open timeout (websocket)", () => {
+    return wrap((done) => {
+      const socket = io(BASE_URL, {
+        forceNew: true,
+        transports: ["websocket"],
+        timeout: 0,
+      });
+
+      socket.on("connect_error", (err) => {
+        expect(err.message).to.eql("timeout");
+        socket.disconnect();
+        done();
+      });
+    });
+  });
+
   it("doesn't fire a connect_error event when the connection is already established", () => {
     return wrap((done) => {
       const socket = io(BASE_URL, { forceNew: true });

test/support/server.ts

@@ -5,6 +5,10 @@ export function createServer() {
   const server = new Server(3210, {
     pingInterval: 2000,
     connectionStateRecovery: {},
+    allowRequest: (req, callback) => {
+      // add a fixed delay to test the connection timeout on the client side
+      setTimeout(() => callback(null, true), 10);
+    },
   });
 
   server.of("/foo").on("connection", (socket) => {