libbnetapi: Add socket messenger class.

- Introduces new network API class BSocketMessenger, allowing one to send
  and receive BMessages across a network socket in a BMessenger-like
  fashion. Still very much WIP, hence currently not exposed via public headers.
  Based partly on previous work by Axel.

headers/private/net/SocketMessenger.h

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2011-2016, Haiku, Inc. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef SOCKET_MESSENGER_H
+#define SOCKET_MESSENGER_H
+
+#include <Socket.h>
+
+class BMessage;
+class BMessenger;
+
+
+class BSocketMessenger {
+public:
+								BSocketMessenger();
+								BSocketMessenger(
+									const BNetworkAddress& address,
+									bigtime_t timeout = B_INFINITE_TIMEOUT);
+								// adopt an existing already connected socket.
+								BSocketMessenger(const BSocket& socket);
+	virtual						~BSocketMessenger();
+
+			void				Unset();
+			status_t			SetTo(const BNetworkAddress& address,
+									bigtime_t timeout = B_INFINITE_TIMEOUT);
+			status_t			SetTo(const BSocketMessenger& target,
+									bigtime_t timeout = B_INFINITE_TIMEOUT);
+
+			status_t			InitCheck() const { return fInitStatus; }
+
+			const BNetworkAddress& Address() const { return fSocket.Peer(); }
+
+	virtual	status_t			SendMessage(const BMessage& message);
+	virtual	status_t			SendMessage(const BMessage& message,
+									BMessage& _reply,
+									bigtime_t timeout = B_INFINITE_TIMEOUT);
+	virtual	status_t			SendMessage(const BMessage& message,
+									BMessenger& replyTarget,
+									bigtime_t timeout = B_INFINITE_TIMEOUT);
+
+								// wait for unsolicited message on socket
+	virtual	status_t			ReceiveMessage(BMessage& _message,
+									bigtime_t timeout = B_INFINITE_TIMEOUT);
+
+private:
+			status_t			_SendMessage(const BMessage& message);
+			status_t			_ReadMessage(BMessage& _message,
+									bigtime_t timeout);
+
+private:
+			BSocket				fSocket;
+			status_t			fInitStatus;
+};
+
+#endif	// SOCKET_MESSENGER_H