Start better error reporting for sockets

runtime/bin/socket.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 interface ServerSocket default _ServerSocket {
   /**
    * Constructs a new server socket, binds it to a given address and port,
    * and listens on it.
    */
   ServerSocket(String bindAddress, int port, int backlog);
 
   /**
    * The connection handler gets called when there is a new incoming
    * connection on the socket.
    */
   void set onConnection(void callback(Socket connection));
 
   /**
    * The error handler gets called when a socket error occurs.
    */
-  void set onError(void callback());
+  void set onError(void callback(Exception e));
 
   /**
    * Returns the port used by this socket.
    */
   int get port();
 
   /**
    * Closes the socket.
    */
   void close();
 }
 
 
 interface Socket extends Hashable default _Socket {
   /**
-   * Constructs a new socket and connects it to the given host on the given
-   * port.
+   * Constructs a new socket and initiate connecting it to the given
+   * host on the given port. The returned socket is not yet connected
+   * but ready for registration of callbacks.
    */
   Socket(String host, int port);
 
   /**
    * Returns the number of received and non-read bytes in the socket that
    * can be read.
    */
   int available();
 
   /**
@@ skipping 32 matching lines @@
   /**
    * The close handler gets called when a the last byte have been read
    * from a socket. At this point the socket might still be open for
    * writing for sending more data.
    */
   void set onClosed(void callback());
 
   /**
    * The error handler gets called when a socket error occurs.
    */
-  void set onError(void callback());
+  void set onError(void callback(Exception e));
 
   /**
    * Returns input stream to the socket.
    */
   InputStream get inputStream();
 
   /**
    * Returns output stream of the socket.
    */
   OutputStream get outputStream();
@@ skipping 13 matching lines @@
   void close([bool halfClose]);
 
   /**
    * Socket is hashable.
    */
   int hashCode();
 }
 
 
 class SocketIOException implements Exception {
-  const SocketIOException([String this.message = ""]);
-  String toString() => "SocketIOException: $message";
+  const SocketIOException([String this.message = "",
+                           OSError this.osError = null]);
+  String toString() {
+    StringBuffer sb = new StringBuffer();
+    sb.add("SocketIOException");
+    if (!message.isEmpty()) {
+      sb.add(": $message");
+      if (osError != null) {
+        sb.add(" ($osError)");
+      }
+    } else if (osError != null) {
+      sb.add(": osError");
+    }
+    return sb.toString();
+  }
   final String message;
+  final OSError osError;
 }