Internal improvement to avoid unhandled rejection for future Promise API

src/HappyEyeBallsConnectionBuilder.php

@@ -84,8 +84,8 @@ public function connect()
 
             $that->resolverPromises[Message::TYPE_AAAA] = $that->resolve(Message::TYPE_AAAA, $reject)->then($lookupResolve(Message::TYPE_AAAA));
             $that->resolverPromises[Message::TYPE_A] = $that->resolve(Message::TYPE_A, $reject)->then(function (array $ips) use ($that, &$timer) {
-                // happy path: IPv6 has resolved already, continue with IPv4 addresses
-                if ($that->resolved[Message::TYPE_AAAA] === true) {
+                // happy path: IPv6 has resolved already (or could not resolve), continue with IPv4 addresses
+                if ($that->resolved[Message::TYPE_AAAA] === true || !$ips) {
                     return $ips;
                 }
 
@@ -117,8 +117,9 @@ public function connect()
      * @internal
      * @param int      $type   DNS query type
      * @param callable $reject
-     * @return \React\Promise\PromiseInterface<string[],\Exception> Returns a promise
-     *     that resolves list of IP addresses on success or rejects with an \Exception on error.
+     * @return \React\Promise\PromiseInterface<string[]> Returns a promise that
+     *     always resolves with a list of IP addresses on success or an empty
+     *     list on error.
      */
     public function resolve($type, $reject)
     {
@@ -145,7 +146,8 @@ public function resolve($type, $reject)
                 $reject(new \RuntimeException($that->error()));
             }
 
-            throw $e;
+            // Exception already handled above, so don't throw an unhandled rejection here
+            return array();
         });
     }
 

tests/HappyEyeBallsConnectionBuilderTest.php

@@ -677,6 +677,27 @@ public function testCancelConnectWillRejectPromiseAndCancelPendingIpv6Connection
         $this->assertEquals('Connection to tcp://reactphp.org:80 cancelled', $exception->getMessage());
     }
 
+    public function testResolveWillReturnResolvedPromiseWithEmptyListWhenDnsResolverFails()
+    {
+        $loop = $this->getMockBuilder('React\EventLoop\LoopInterface')->getMock();
+
+        $connector = $this->getMockBuilder('React\Socket\ConnectorInterface')->getMock();
+
+        $resolver = $this->getMockBuilder('React\Dns\Resolver\ResolverInterface')->getMock();
+        $resolver->expects($this->once())->method('resolveAll')->with('reactphp.org', Message::TYPE_A)->willReturn(\React\Promise\reject(new \RuntimeException()));
+
+        $uri = 'tcp://reactphp.org:80';
+        $host = 'reactphp.org';
+        $parts = parse_url($uri);
+
+        $builder = new HappyEyeBallsConnectionBuilder($loop, $connector, $resolver, $uri, $host, $parts);
+
+        $promise = $builder->resolve(Message::TYPE_A, $this->expectCallableNever());
+
+        $this->assertInstanceof('React\Promise\PromiseInterface', $promise);
+        $promise->then($this->expectCallableOnceWith(array()), $this->expectCallableNever());
+    }
+
     public function testAttemptConnectionWillConnectViaConnectorToGivenIpWithPortAndHostnameFromUriParts()
     {
         $loop = $this->getMockBuilder('React\EventLoop\LoopInterface')->getMock();