fix(sio-client): discard a volatile packet when the namespace is not connected

packages/socket.io-client/lib/socket.ts

@@ -447,9 +447,12 @@ export class Socket<
     const isTransportWritable = this.io.engine?.transport?.writable;
     const isConnected = this.connected && !this.io.engine?._hasPingExpired();
 
-    const discardPacket = this.flags.volatile && !isTransportWritable;
+    const discardPacket =
+      this.flags.volatile && !(isTransportWritable && isConnected);
     if (discardPacket) {
-      debug("discard packet as the transport is not currently writable");
+      debug(
+        "discard packet as the socket is not connected or the transport is not currently writable",
+      );
     } else if (isConnected) {
       this.notifyOutgoingListeners(packet);
       this.packet(packet);

packages/socket.io-client/test/socket.ts

@@ -421,6 +421,35 @@ describe("socket", () => {
       });
     });
 
+    it("should discard a volatile packet when the namespace is not connected yet", () => {
+      return wrap((done) => {
+        const socket = io(BASE_URL, {
+          forceNew: true,
+          transports: ["websocket"],
+        });
+
+        socket.on("connect", () => {
+          // the server delays the acknowledgement of the CONNECT packet of this namespace
+          const delayedSocket = socket.io.socket("/delayed");
+
+          // wait until the transport is writable again after the CONNECT packet
+          setTimeout(() => {
+            expect(socket.io.engine.transport.writable).to.be(true);
+            expect(delayedSocket.connected).to.be(false);
+
+            delayedSocket.volatile.emit("getId", () => {
+              done(new Error("should not happen"));
+            });
+
+            delayedSocket.emit("getId", () => {
+              delayedSocket.disconnect();
+              success(done, socket);
+            });
+          }, 20);
+        });
+      });
+    });
+
     it("should send a volatile packet when the socket is connected and the pipe is ready", () => {
       return wrap((done) => {
         const socket = io(BASE_URL, { forceNew: true });

packages/socket.io-client/test/support/server.ts

@@ -17,6 +17,18 @@ export function createServer() {
     });
   });
 
+  server
+    .of("/delayed")
+    .use((socket, next) => {
+      // delay the acknowledgement of the CONNECT packet
+      setTimeout(next, 100);
+    })
+    .on("connection", (socket) => {
+      socket.on("getId", (cb) => {
+        cb(socket.id);
+      });
+    });
+
   server.of("/timeout_socket").on("connection", () => {
     // register namespace
   });