[1.x] Ensure connection close handler is cleaned up for each request

This changeset resolves a small memory leak that causes roughly 1KB per connection tops. Which isn't a big issue but will make memory fluctuate more. The changeset doesn't introduce any performance degradation.

Resolves: reactphp#514
Builds on top of: reactphp#405, reactphp#467, and many others

src/Io/StreamingServer.php

@@ -157,10 +157,12 @@ public function handleRequest(ConnectionInterface $conn, ServerRequestInterface
         }
 
         // cancel pending promise once connection closes
+        $connectionOnCloseResponseCanceler = null;
         if ($response instanceof PromiseInterface && \method_exists($response, 'cancel')) {
-            $conn->on('close', function () use ($response) {
+            $connectionOnCloseResponseCanceler = function () use ($response) {
                 $response->cancel();
-            });
+            };
+            $conn->on('close', $connectionOnCloseResponseCanceler);
         }
 
         // happy path: response returned, handle and return immediately
@@ -201,7 +203,11 @@ function ($error) use ($that, $conn, $request) {
                 $that->emit('error', array($exception));
                 return $that->writeError($conn, Response::STATUS_INTERNAL_SERVER_ERROR, $request);
             }
-        );
+        )->always(static function () use ($connectionOnCloseResponseCanceler, $conn) {
+            if ($connectionOnCloseResponseCanceler !== null) {
+                $conn->removeListener('close', $connectionOnCloseResponseCanceler);
+            }
+        });
     }
 
     /** @internal */

tests/Io/StreamingServerTest.php

@@ -3245,6 +3245,44 @@ public function testNewConnectionWillInvokeParserTwiceAfterInvokingRequestHandle
         $this->assertCount(1, $this->connection->listeners('close'));
     }
 
+    public function testCompletingARequestWillRemoveConnectionOnCloseListener()
+    {
+        $connection = $this->getMockBuilder('React\Socket\Connection')
+            ->disableOriginalConstructor()
+            ->setMethods(
+                array(
+                    'write',
+                    'end',
+                    'close',
+                    'pause',
+                    'resume',
+                    'isReadable',
+                    'isWritable',
+                    'getRemoteAddress',
+                    'getLocalAddress',
+                    'pipe',
+                    'removeListener'
+                )
+            )
+            ->getMock();
+
+        $connection->method('isWritable')->willReturn(true);
+        $connection->method('isReadable')->willReturn(true);
+        $request = new ServerRequest('GET', 'http://localhost/');
+
+        $server = new StreamingServer(Loop::get(), function () {
+            return \React\Promise\resolve(new Response());
+        });
+
+        $server->listen($this->socket);
+        $this->socket->emit('connection', array($connection));
+
+        $connection->expects($this->once())->method('removeListener');
+
+        // pretend parser just finished parsing
+        $server->handleRequest($connection, $request);
+    }
+
     private function createGetRequest()
     {
         $data = "GET / HTTP/1.1\r\n";