Support promise cancellation (cancellation of underlying DNS lookup)

composer.json

@@ -18,7 +18,7 @@
         "evenement/evenement": "~1.0|~2.0",
         "react/event-loop": ">=0.2, <0.5",
         "react/dns": ">=0.2, <0.5",
-        "react/promise": "~2.0|~1.1"
+        "react/promise": "~2.1|~1.2"
     },
     "require-dev": {
         "clue/block-react": "~1.0"

src/Factory.php

@@ -7,6 +7,7 @@
 use React\Promise;
 use React\Datagram\Socket;
 use \Exception;
+use React\Promise\CancellablePromiseInterface;
 
 class Factory
 {
@@ -108,6 +109,23 @@ protected function resolveHost($host)
             return Promise\reject(new Exception('No resolver given in order to get IP address for given hostname'));
         }
 
-        return $this->resolver->resolve($host);
+        $promise = $this->resolver->resolve($host);
+
+        // wrap DNS lookup in order to control cancellation behavior
+        return new Promise\Promise(
+            function ($resolve, $reject) use ($promise) {
+                // forward promise resolution
+                $promise->then($resolve, $reject);
+            },
+            function ($_, $reject) use ($promise) {
+                // reject with custom message once cancelled
+                $reject(new \RuntimeException('Cancelled creating socket during DNS lookup'));
+
+                // (try to) cancel pending DNS lookup, otherwise ignoring its results
+                if ($promise instanceof CancellablePromiseInterface) {
+                    $promise->cancel();
+                }
+            }
+        );
     }
 }

tests/FactoryTest.php

@@ -119,4 +119,28 @@ public function testCreateServerWithInvalidHostnameWillReject()
     {
         Block\await($this->factory->createServer('/////'), $this->loop);
     }
+
+    public function testCancelCreateClientWithCancellableHostnameResolver()
+    {
+        $promise = new Promise\Promise(function () { }, $this->expectCallableOnce());
+        $this->resolver->expects($this->once())->method('resolve')->with('example.com')->willReturn($promise);
+
+        $promise = $this->factory->createClient('example.com:0');
+        $promise->cancel();
+
+        $this->setExpectedException('RuntimeException');
+        Block\await($promise, $this->loop);
+    }
+
+    public function testCancelCreateClientWithUncancellableHostnameResolver()
+    {
+        $promise = $this->getMock('React\Promise\PromiseInterface');
+        $this->resolver->expects($this->once())->method('resolve')->with('example.com')->willReturn($promise);
+
+        $promise = $this->factory->createClient('example.com:0');
+        $promise->cancel();
+
+        $this->setExpectedException('RuntimeException');
+        Block\await($promise, $this->loop);
+    }
 }