Repository: websockets/ws (js)

Issue:
Clear the send queue when the other peer closes the connection
#### Description

permessage-deflate is enabled and one of the peer has queued data waiting for it to be compressed, framed and sent over the connection. Meanwhile, the other peer closes the connection. What should we do?

Currently the data processing keeps going as nothing happened and the [callback](https://github.com/websockets/ws/blob/48b0496879899f35602856d80460926a4a6c299d/doc/ws.md#websocketsenddata-options-callback) of each enqueued send operation, if any, is invoked with an error when trying to write to the closed socket (after the `'close'` event). This a waste of computational power. There is no reason to compress, frame, and try to send the data if we know beforehand that the socket is closed.

One way to work around the issue is to remove the enqueued send operations after invoking their callback with an error and before emitting the `'close'` event.
The issue happens when a message is already being compressed so the [queue](https://github.com/websockets/ws/blob/48b0496879899f35602856d80460926a4a6c299d/lib/Sender.js#L37) should be cleared when compression [completes](https://github.com/websockets/ws/blob/48b0496879899f35602856d80460926a4a6c299d/lib/Sender.js#L333).

Thoughts?

#### Reproducible in:

version: >=0.6.0
Node.js version(s): all
OS version(s): all

#### Steps to reproduce:

```js
const crypto = require('crypto');
const WebSocket = require('ws');

const wss = new WebSocket.Server({
  perMessageDeflate: { threshold: 0 },
  port: 3000
}, () => {
  const ws = new WebSocket('ws://localhost:3000');

  ws.on('open', () => {
    setTimeout(() => ws.terminate(), 10);
  });
});

wss.on('connection', (ws) => {
  ws.on('close', () => console.log('close'));

  const data = crypto.randomBytes(1024);

  for (let i = 0; i < 1024; i++) {
    ws.send(data, (err) => {
      if (err) console.log(err);
    });
  }
});
```

Pull request:
Ignore callbacks when clearing the send queue
Do not invoke callbacks when clearing the send queue due to premature
socket closure.

Refs: https://github.com/websockets/ws/pull/1464#issuecomment-435578571
Fixes #1226

Patch:
diff --git a/lib/sender.js b/lib/sender.js
index 500bd98c..12ee25a3 100644
--- a/lib/sender.js
+++ b/lib/sender.js
@@ -27,20 +27,6 @@ class Sender {
     this._bufferedBytes = 0;
     this._deflating = false;
     this._queue = [];
-
-    if (this._extensions[PerMessageDeflate.extensionName]) {
-      this._socket.once('close', () => {
-        const err = new Error('WebSocket is not open: readyState 2 (CLOSING)');
-
-        while (this._queue.length) {
-          const params = this._queue.shift();
-          const cb = params[params.length - 1];
-
-          this._bufferedBytes -= params[1].length;
-          if (typeof cb === 'function') cb(err);
-        }
-      });
-    }
   }
 
   /**
@@ -346,9 +332,19 @@ class Sender {
 
     this._deflating = true;
     perMessageDeflate.compress(data, options.fin, (_, buf) => {
+      this._deflating = false;
+
+      if (!this._socket.readable && !this._socket.writable) {
+        //
+        // The socket is closed. Clear the queue and bail out.
+        //
+        this._bufferedBytes = 0;
+        this._queue.length = 0;
+        return;
+      }
+
       options.readOnly = false;
       this.sendFrame(Sender.frame(buf, options), cb);
-      this._deflating = false;
       this.dequeue();
     });
   }
diff --git a/lib/websocket.js b/lib/websocket.js
index 79cb219f..5b8497d6 100644
--- a/lib/websocket.js
+++ b/lib/websocket.js
@@ -123,11 +123,6 @@ class WebSocket extends EventEmitter {
       maxPayload
     );
 
-    //
-    // `Sender` must be instantiated before adding the `socketOnClose` listener.
-    // This allows the sender queue, when used, to be emptied before
-    // `socketOnClose` is called.
-    //
     this._sender = new Sender(socket, this._extensions);
     this._receiver = receiver;
     this._socket = socket;


Test patch:
diff --git a/test/sender.test.js b/test/sender.test.js
index e7c7dd10..04407527 100644
--- a/test/sender.test.js
+++ b/test/sender.test.js
@@ -6,13 +6,14 @@ const PerMessageDeflate = require('../lib/permessage-deflate');
 const Sender = require('../lib/sender');
 
 class MockSocket {
-  constructor ({ write, once } = {}) {
+  constructor ({ write } = {}) {
+    this.readable = true;
+    this.writable = true;
+
     if (write) this.write = write;
-    if (once) this.once = once;
   }
 
   write () {}
-  once () {}
 }
 
 describe('Sender', function () {
@@ -69,41 +70,43 @@ describe('Sender', function () {
     });
 
     it('does not compress enqueued messages after socket closes', function (done) {
-      const numMessages = 100;
-      let numErrors = 0;
-
       const mockSocket = new MockSocket({
-        write: (data) => {
-          // Test that `PerMessageDeflate#compress()` and `Socket#write()` is
-          // called only once (for the first message that is not queued).
-          assert.strictEqual(numErrors, numMessages);
-          done();
-        },
-        once: (ev, cb) => {
-          if (ev === 'close') process.nextTick(cb);
-        }
+        write: () => done(new Error('Unexpected call to socket.write()'))
       });
 
       const perMessageDeflate = new PerMessageDeflate({ threshold: 0 });
       perMessageDeflate.accept([{}]);
 
+      const compress = perMessageDeflate.compress;
       const sender = new Sender(mockSocket, {
         'permessage-deflate': perMessageDeflate
       });
 
-      const options = { compress: true, fin: true };
-      sender.send('hi', options);
+      perMessageDeflate.compress = (data, fin, callback) => {
+        compress.call(perMessageDeflate, data, fin, (_, buf) => {
+          assert.strictEqual(sender._bufferedBytes, 198);
+          assert.strictEqual(sender._queue.length, 99);
+          assert.strictEqual(mockSocket.readable, false);
+          assert.strictEqual(mockSocket.writable, false);
 
-      for (let i = 0; i < numMessages; i++) {
-        sender.send('hi', options, (err) => {
-          assert.ok(err instanceof Error);
-          assert.strictEqual(
-            err.message,
-            'WebSocket is not open: readyState 2 (CLOSING)'
-          );
-          numErrors++;
+          process.nextTick(() => {
+            assert.strictEqual(sender._bufferedBytes, 0);
+            assert.strictEqual(sender._queue.length, 0);
+            done();
+          });
+
+          callback(_, buf);
         });
-      }
+      };
+
+      const options = { compress: true, fin: true };
+
+      for (let i = 0; i < 100; i++) sender.send('hi', options);
+
+      process.nextTick(() => {
+        mockSocket.readable = false;
+        mockSocket.writable = false;
+      });
     });
 
     it('does not compress data for small payloads', function (done) {
diff --git a/test/websocket.test.js b/test/websocket.test.js
index dc945865..c849ade6 100644
--- a/test/websocket.test.js
+++ b/test/websocket.test.js
@@ -2041,40 +2041,6 @@ describe('WebSocket', function () {
       });
     });
 
-    it('reports the state as `CLOSING` in callbacks of discarded queued messages', function (done) {
-      const wss = new WebSocket.Server({
-        perMessageDeflate: { threshold: 0 },
-        port: 0
-      }, () => {
-        const ws = new WebSocket(`ws://localhost:${wss.address().port}`);
-      });
-
-      wss.on('connection', (ws) => {
-        const map = () => crypto.randomBytes(16);
-        let count = 100;
-
-        Array.from({ length: count }).map(map).forEach((data, i) => {
-          ws.send(data, (err) => {
-            assert.ok(err instanceof Error);
-
-            if (i > 0) {
-              // The first message is not queued and compression completes after
-              // the `'close'` event is emitted on the `net.Socket`.
-              assert.strictEqual(ws.readyState, WebSocket.CLOSING);
-              assert.strictEqual(
-                err.message,
-                'WebSocket is not open: readyState 2 (CLOSING)'
-              );
-            }
-
-            if (--count === 0) done();
-          });
-        });
-
-        wss.close();
-      });
-    });
-
     describe('#send', function () {
       it('ignores the `compress` option if the extension is disabled', function (done) {
         const wss = new WebSocket.Server({ port: 0 }, () => {
@@ -2106,13 +2072,16 @@ describe('WebSocket', function () {
           });
 
           ws.on('open', () => {
-            ws.send('hi', (err) => {
-              assert.ok(err instanceof Error);
-              wss.close(done);
-            });
+            ws.send('hi', () => done(new Error('Unexpected callback invocation')));
             ws.terminate();
           });
         });
+
+        wss.on('connection', (ws) => {
+          ws.on('close', () => {
+            wss.close(done);
+          });
+        });
       });
 
       it('can be used while data is being decompressed', function (done) {