Add new connection error notifier and error field to union

The user provided connection notifier was called on startup only in case
of an successfully established connection or if an error happened while
connecting. This patch adds a new (internal) client connection error
notifier that is called from the ISelectClient `error` method, in that
case the client Connection class. That happens when the ISelectClient is
unregistered from epoll due to a exception thrown in the RequestOnConn
fiber.

The exception is passed to the user by utilizing a new error field in
the ConnNotificationUnion (defined in the ConnectionSet).

Author: matthias-wende-sociomantic

src/swarm/neo/client/Connection.d

@@ -166,9 +166,18 @@ public final class Connection: ConnectionBase
 
     ***************************************************************************/
 
-    public alias void delegate ( Connection connection, Exception e = null ) StartupNotifier;
+    public alias void delegate ( Connection connection, Exception e = null ) Notifier;
 
-    private StartupNotifier startup_notifier = null;
+    private Notifier startup_notifier = null;
+
+    /***************************************************************************
+
+        Callback for notification when the an error happened
+        (`e` then reflects the error).
+
+    ***************************************************************************/
+
+    private Notifier connection_error_notifier = null;
 
     /***************************************************************************
 
@@ -225,14 +234,16 @@ public final class Connection: ConnectionBase
     ***************************************************************************/
 
     public this ( Const!(Credentials) credentials, IRequestSet request_set,
-                  EpollSelectDispatcher epoll )
+                  EpollSelectDispatcher epoll,
+                  Notifier connection_error_notifier )
     {
         this.client_socket = new ClientSocket;
 
         super(this.client_socket.socket, epoll);
 
         this.conn_init = new ClientConnect(credentials);
         this.request_set = request_set;
+        this.connection_error_notifier = connection_error_notifier;
     }
 
     /***************************************************************************
@@ -258,7 +269,7 @@ public final class Connection: ConnectionBase
 
     ***************************************************************************/
 
-    public Status start ( AddrPort node_address, StartupNotifier startup_notifier )
+    public Status start ( AddrPort node_address, Notifier startup_notifier )
     {
         debug ( SwarmConn )
         {
@@ -287,6 +298,19 @@ public final class Connection: ConnectionBase
         return this.status_;
     }
 
+    /***************************************************************************
+
+        Shuts the connection down if epoll reports an error event for the
+        socket.
+
+    ***************************************************************************/
+
+    override protected void error_ ( Exception exception, Event event )
+    {
+        super.error_(exception, event);
+        connection_error_notifier(this, exception);
+    }
+
     /***************************************************************************
 
         Shuts the engine down:

src/swarm/neo/client/ConnectionSet.d

@@ -118,6 +118,9 @@ public final class ConnectionSet : RequestOnConn.IConnectionGetter
         /// An error (indicated by the `e` field) occurred while connecting. The
         /// connection attempt will automatically be retried.
         NodeExceptionInfo error_while_connecting;
+
+        /// An error (indicated by the `e` field) occurred
+        NodeExceptionInfo error;
     }
 
     /***************************************************************************
@@ -287,7 +290,8 @@ public final class ConnectionSet : RequestOnConn.IConnectionGetter
         bool added;
         auto connection = this.connections.put(node_address, added,
             this.connection_pool.get(new Connection(
-                this.credentials, this.request_set_, this.epoll
+                this.credentials, this.request_set_, this.epoll,
+                &this.notifyConnectionError
             ))
         );
 
@@ -572,6 +576,28 @@ public final class ConnectionSet : RequestOnConn.IConnectionGetter
 
         this.conn_notifier(info);
     }
+
+    /***************************************************************************
+
+        Connection error notification callback method. Calls the user notifier.
+
+        Params:
+            connection = the connection giving the startup notification
+            e          = information about an error connecting; the
+                          connection will retry connecting in this case
+
+    ***************************************************************************/
+
+    private void notifyConnectionError ( Connection connection,
+        Exception e )
+    {
+        ConnNotification info;
+
+        info.error_while_connecting =
+            NodeExceptionInfo(connection.remote_address, e);
+
+        this.conn_notifier(info);
+    }
 }
 
 /*******************************************************************************