Improve Unix domain socket (UDS) server error messages

README.md

@@ -706,6 +706,14 @@ $first = new UnixServer('/tmp/same.sock', $loop);
 $second = new UnixServer('/tmp/same.sock', $loop);
 ```
 
+> Note that these error conditions may vary depending on your system and/or
+  configuration.
+  In particular, Zend PHP does only report "Unknown error" when the UDS path
+  already exists and can not be bound. You may want to check `is_file()` on the
+  given UDS path to report a more user-friendly error message in this case.
+  See the exception message and code for more details about the actual error
+  condition.
+
 Whenever a client connects, it will emit a `connection` event with a connection
 instance implementing [`ConnectionInterface`](#connectioninterface):
 

src/UnixServer.php

@@ -61,7 +61,18 @@ public function __construct($path, LoopInterface $loop, array $context = array()
             stream_context_create(array('socket' => $context))
         );
         if (false === $this->master) {
-            throw new RuntimeException('Failed to listen on unix domain socket "' . $path . '": ' . $errstr, $errno);
+            // PHP does not seem to report errno/errstr for Unix domain sockets (UDS) right now.
+            // This only applies to UDS server sockets, see also https://3v4l.org/NAhpr.
+            // Parse PHP warning message containing unknown error, HHVM reports proper info at least.
+            if ($errno === 0 && $errstr === '') {
+                $error = error_get_last();
+                if (preg_match('/\(([^\)]+)\)|\[(\d+)\]: (.*)/', $error['message'], $match)) {
+                    $errstr = isset($match[3]) ? $match['3'] : $match[1];
+                    $errno = isset($match[2]) ? (int)$match[2] : 0;
+                }
+            }
+
+            throw new RuntimeException('Failed to listen on Unix domain socket "' . $path . '": ' . $errstr, $errno);
         }
         stream_set_blocking($this->master, 0);
 

tests/ServerTest.php

@@ -50,6 +50,10 @@ public function testConstructorCreatesExpectedTcpServer()
 
     public function testConstructorCreatesExpectedUnixServer()
     {
+        if (!in_array('unix', stream_get_transports())) {
+            $this->markTestSkipped('Unix domain sockets (UDS) not supported on your platform (Windows?)');
+        }
+
         $loop = Factory::create();
 
         $server = new Server($this->getRandomSocketUri(), $loop);
@@ -64,6 +68,28 @@ public function testConstructorCreatesExpectedUnixServer()
         $server->close();
     }
 
+    public function testConstructorThrowsForExistingUnixPath()
+    {
+        if (!in_array('unix', stream_get_transports())) {
+            $this->markTestSkipped('Unix domain sockets (UDS) not supported on your platform (Windows?)');
+        }
+
+        $loop = Factory::create();
+
+        try {
+            $server = new Server('unix://' . __FILE__, $loop);
+            $this->fail();
+        } catch (\RuntimeException $e) {
+            if ($e->getCode() === 0) {
+                // Zend PHP does not currently report a sane error
+                $this->assertStringEndsWith('Unknown error', $e->getMessage());
+            } else {
+                $this->assertEquals(SOCKET_EADDRINUSE, $e->getCode());
+                $this->assertStringEndsWith('Address already in use', $e->getMessage());
+            }
+        }
+    }
+
     public function testEmitsConnectionForNewConnection()
     {
         $loop = Factory::create();

tests/UnixServerTest.php

@@ -19,6 +19,10 @@ class UnixServerTest extends TestCase
      */
     public function setUp()
     {
+        if (!in_array('unix', stream_get_transports())) {
+            $this->markTestSkipped('Unix domain sockets (UDS) not supported on your platform (Windows?)');
+        }
+
         $this->loop = Factory::create();
         $this->uds = $this->getRandomSocketUri();
         $this->server = new UnixServer($this->uds, $this->loop);