Add automatic ping on websockets

Signed-off-by: Luca Niccoli <l.niccoli@awtech.it>

source/vibe/http/websockets.d

@@ -193,6 +193,9 @@ final class WebSocket {
 		Task m_reader;
 		TaskMutex m_readMutex, m_writeMutex;
 		TaskCondition m_readCondition;
+		Timer m_pingTimer;
+		uint m_lastPingIndex;
+		bool m_pongReceived;
 	}
 
 	this(ConnectionStream conn, in HTTPServerRequest request)
@@ -204,6 +207,8 @@ final class WebSocket {
 		m_writeMutex = new TaskMutex;
 		m_readMutex = new TaskMutex;
 		m_readCondition = new TaskCondition(m_readMutex);
+		m_pingTimer = setTimer(dur!"seconds"(60), &sendPing, true);
+		m_pongReceived = true;
 	}
 
 	/**
@@ -310,7 +315,7 @@ final class WebSocket {
 				frame.writeFrame(m_conn);
 			}
 		}
-
+		if (m_pingTimer) m_pingTimer.stop();
 		if (Task.getThis() != m_reader) m_reader.join();
 	}
 
@@ -368,6 +373,12 @@ final class WebSocket {
 			while (!m_conn.empty) {
 				assert(!m_nextMessage);
 				scope msg = new IncomingWebSocketMessage(m_conn);
+				if (msg.frameOpcode == FrameOpcode.pong) {
+					enforce(msg.peek().length == uint.sizeof, "Pong payload has wrong length");
+					enforce(m_lastPingIndex == littleEndianToNative!uint(msg.peek()[0..uint.sizeof]), "Pong payload has wrong value");
+					m_pongReceived = true;
+					continue;
+				}
 				if(msg.frameOpcode == FrameOpcode.close) {
 					logDebug("Got closing frame (%s)", m_sentCloseFrame);
 					if(!m_sentCloseFrame) close();
@@ -387,8 +398,24 @@ final class WebSocket {
 		}
 		m_conn.close();
 	}
-}
 
+	private void sendPing() {
+		if (!m_pongReceived) {
+			logDebug("Pong not received");
+			m_conn.close();
+			if (m_pingTimer) m_pingTimer.stop();
+			return;
+		}
+		m_pongReceived = false;
+		Frame ping;
+		ping.opcode = FrameOpcode.ping;
+		ping.fin = true;
+		ping.payload = nativeToLittleEndian(++m_lastPingIndex);
+
+		ping.writeFrame(m_conn);
+		logDebug("Ping sent");
+	}
+}
 
 /**
 	Represents a single outgoing _WebSocket message as an OutputStream.
@@ -500,6 +527,7 @@ final class IncomingWebSocketMessage : InputStream {
 				case FrameOpcode.text:
 				case FrameOpcode.binary:
 				case FrameOpcode.close:
+				case FrameOpcode.pong:
 					m_currentFrame = frame;
 					break;
 				case FrameOpcode.ping: