Improve error reporting when custom error handler is used

src/Factory.php

@@ -128,15 +128,23 @@ public function createReceiver($address)
             throw new RuntimeException('Unable to enable SO_REUSEADDR');
         }
 
+        set_error_handler(function () {
+            // ignore PHP warning, error is reported via socket_last_error() below
+        });
+
         // join multicast group and bind to port
         $ret = socket_set_option(
             $socket,
             IPPROTO_IP,
             MCAST_JOIN_GROUP,
             array('group' => $parts['host'], 'interface' => 0)
         );
+
+        restore_error_handler();
+
         if ($ret === false) {
-            throw new RuntimeException('Unable to join multicast group');
+            $errno = socket_last_error($socket);
+            throw new RuntimeException('Unable to join multicast group: ' . socket_strerror($errno), $errno);
         }
 
         return new DatagramSocket($this->loop, $stream);

tests/FunctionalTest.php

@@ -58,6 +58,31 @@ public function testMultipleReceivers()
         $this->loop->run();
     }
 
+    public function testCreateReceiverThrowsForNonMulticastAddressWithoutCallingCustomErrorHandler()
+    {
+        if (!defined('MCAST_JOIN_GROUP') || !function_exists('socket_import_stream')) {
+            $this->markTestSkipped('No multicast support');
+        }
+
+        $error = null;
+        set_error_handler(function ($_, $errstr) use (&$error) {
+            $error = $errstr;
+        });
+
+        $this->setExpectedException('RuntimeException', 'Unable to join multicast group: ' . socket_strerror(SOCKET_EINVAL), SOCKET_EINVAL);
+
+        try {
+            $this->factory->createReceiver('127.0.0.1:2244');
+
+            restore_error_handler();
+        } catch (\Exception $e) {
+            restore_error_handler();
+            $this->assertNull($error);
+
+            throw $e;
+        }
+    }
+
     public function testConstructWithoutLoopAssignsLoopAutomatically()
     {
         $factory = new Factory();