test: add more tests for the retry mechanism

lib/socket.ts

@@ -75,7 +75,6 @@ type QueuedPacket = {
   flags: Flags;
   pending: boolean;
   tryCount: number;
-  ack?: (err?: Error, ...args: unknown[]) => void;
 };
 
 /**
@@ -382,19 +381,7 @@ export class Socket<
     args.unshift(ev);
 
     if (this._opts.retries && !this.flags.fromQueue && !this.flags.volatile) {
-      let ack;
-      if (typeof args[args.length - 1] === "function") {
-        ack = args.pop();
-      }
-      this._queue.push({
-        id: this.ids++,
-        tryCount: 0,
-        pending: false,
-        args,
-        ack,
-        flags: Object.assign({ fromQueue: true }, this.flags),
-      });
-      this._drainQueue();
+      this._addToQueue(args);
       return this;
     }
 
@@ -503,29 +490,25 @@ export class Socket<
   }
 
   /**
-   * Send the first packet of the queue, and wait for an acknowledgement from the server.
+   * Add the packet to the queue.
+   * @param args
    * @private
    */
-  private _drainQueue() {
-    debug("draining queue");
-    if (this._queue.length === 0) {
-      return;
+  private _addToQueue(args: unknown[]) {
+    let ack;
+    if (typeof args[args.length - 1] === "function") {
+      ack = args.pop();
     }
-    const packet = this._queue[0];
-    if (packet.pending) {
-      debug(
-        "packet [%d] has already been sent and is waiting for an ack",
-        packet.id
-      );
-      return;
-    }
-    packet.pending = true;
-    packet.tryCount++;
-    debug("sending packet [%d] (try n°%d)", packet.id, packet.tryCount);
-    const currentId = this.ids;
-    this.ids = packet.id; // the same id is reused for consecutive retries, in order to allow deduplication on the server side
-    this.flags = packet.flags;
-    packet.args.push((err, ...responseArgs) => {
+
+    const packet = {
+      id: this.ids++,
+      tryCount: 0,
+      pending: false,
+      args,
+      flags: Object.assign({ fromQueue: true }, this.flags),
+    };
+
+    args.push((err, ...responseArgs) => {
       if (packet !== this._queue[0]) {
         // the packet has already been acknowledged
         return;
@@ -539,21 +522,49 @@ export class Socket<
             packet.tryCount
           );
           this._queue.shift();
-          if (packet.ack) {
-            packet.ack(err);
+          if (ack) {
+            ack(err);
           }
         }
       } else {
         debug("packet [%d] was successfully sent", packet.id);
         this._queue.shift();
-        if (packet.ack) {
-          packet.ack(null, ...responseArgs);
+        if (ack) {
+          ack(null, ...responseArgs);
         }
       }
       packet.pending = false;
       return this._drainQueue();
     });
 
+    this._queue.push(packet);
+    this._drainQueue();
+  }
+
+  /**
+   * Send the first packet of the queue, and wait for an acknowledgement from the server.
+   * @private
+   */
+  private _drainQueue() {
+    debug("draining queue");
+    if (this._queue.length === 0) {
+      return;
+    }
+    const packet = this._queue[0];
+    if (packet.pending) {
+      debug(
+        "packet [%d] has already been sent and is waiting for an ack",
+        packet.id
+      );
+      return;
+    }
+    packet.pending = true;
+    packet.tryCount++;
+    debug("sending packet [%d] (try n°%d)", packet.id, packet.tryCount);
+    const currentId = this.ids;
+    this.ids = packet.id; // the same id is reused for consecutive retries, in order to allow deduplication on the server side
+    this.flags = packet.flags;
+
     this.emit.apply(this, packet.args);
     this.ids = currentId; // restore offset
   }

test/retry.ts

@@ -11,6 +11,19 @@ describe("retry", () => {
         ackTimeout: 50,
       });
 
+      let i = 0;
+      const expected = [
+        "0",
+        '20["echo",1]',
+        '21["echo",2]',
+        '22["echo",3]',
+        "1",
+      ];
+
+      socket.io.engine.on("packetCreate", ({ data }) => {
+        expect(data).to.eql(expected[i++]);
+      });
+
       socket.emit("echo", 1, () => {
         // @ts-ignore
         expect(socket._queue.length).to.eql(2);
@@ -51,6 +64,20 @@ describe("retry", () => {
 
       let count = 0;
 
+      let i = 0;
+      const expected = [
+        "0",
+        '20["ack"]',
+        '20["ack"]',
+        '20["ack"]',
+        '20["ack"]',
+        "1",
+      ];
+
+      socket.io.engine.on("packetCreate", ({ data }) => {
+        expect(data).to.eql(expected[i++]);
+      });
+
       socket.emit("ack", () => {
         expect(count).to.eql(4);