fix: do not drain the queue while the socket is offline

In the previous implementation added in [1], the socket would try to
send the packet even if it was disconnected, which would needlessly
exhaust the number of retries.

[1]: 655dce9

lib/socket.ts

@@ -543,15 +543,17 @@ export class Socket<
 
   /**
    * Send the first packet of the queue, and wait for an acknowledgement from the server.
+   * @param force - whether to resend a packet that has not been acknowledged yet
+   *
    * @private
    */
-  private _drainQueue() {
+  private _drainQueue(force = false) {
     debug("draining queue");
-    if (this._queue.length === 0) {
+    if (!this.connected || this._queue.length === 0) {
       return;
     }
     const packet = this._queue[0];
-    if (packet.pending) {
+    if (packet.pending && !force) {
       debug(
         "packet [%d] has already been sent and is waiting for an ack",
         packet.id
@@ -776,6 +778,7 @@ export class Socket<
     this.connected = true;
     this.emitBuffered();
     this.emitReserved("connect");
+    this._drainQueue(true);
   }
 
   /**

test/retry.ts

@@ -89,4 +89,25 @@ describe("retry", () => {
       });
     });
   });
+
+  it("should not drain the queue while the socket is disconnected", () => {
+    return wrap((done) => {
+      const socket = io(BASE_URL, {
+        forceNew: true,
+        autoConnect: false,
+        retries: 3,
+        ackTimeout: 10,
+      });
+
+      socket.emit("echo", 1, (err) => {
+        expect(err).to.be(null);
+
+        success(done, socket);
+      });
+
+      setTimeout(() => {
+        socket.connect();
+      }, 100);
+    });
+  });
 });