proxy: add a multiplexing server frontend

On a Hyper-V system we can only register one listening endpoint (with
a GUID), so we need to accept connections, read a header and then
start the proxy.

If the binary has argv[0] == "proxy-vsockd" then run this new frontend.

Signed-off-by: David Scott <dave.scott@docker.com>

alpine/packages/proxy/libproxy/tcp_proxy.go

@@ -35,10 +35,10 @@ func NewTCPProxy(listener net.Listener, backendAddr *net.TCPAddr) (*TCPProxy, er
 	}, nil
 }
 
-func (proxy *TCPProxy) clientLoop(client Conn, quit chan bool) {
-	backend, err := net.DialTCP("tcp", nil, proxy.backendAddr)
+func HandleTCPConnection(client Conn, backendAddr *net.TCPAddr, quit chan bool) {
+	backend, err := net.DialTCP("tcp", nil, backendAddr)
 	if err != nil {
-		logrus.Printf("Can't forward traffic to backend tcp/%v: %s\n", proxy.backendAddr, err)
+		logrus.Printf("Can't forward traffic to backend tcp/%v: %s\n", backendAddr, err)
 		client.Close()
 		return
 	}
@@ -89,7 +89,7 @@ func (proxy *TCPProxy) Run() {
 			logrus.Printf("Stopping proxy on tcp/%v for tcp/%v (%s)", proxy.frontendAddr, proxy.backendAddr, err)
 			return
 		}
-		go proxy.clientLoop(client.(Conn), quit)
+		go HandleTCPConnection(client.(Conn), proxy.backendAddr, quit)
 	}
 }
 

alpine/packages/proxy/libproxy/udp_encapsulation.go

@@ -75,6 +75,19 @@ func (u *udpEncapsulator) Close() error {
 	return nil
 }
 
+func NewUDPConn(conn net.Conn) udpListener {
+	var m sync.Mutex
+	var r sync.Mutex
+	var w sync.Mutex
+	return &udpEncapsulator{
+		conn:     &conn,
+		listener: nil,
+		m:        &m,
+		r:        &r,
+		w:        &w,
+	}
+}
+
 func NewUDPListener(listener net.Listener) udpListener {
 	var m sync.Mutex
 	var r sync.Mutex