http-connect: error to be written on connection

Incorrect error mesage from server to client because of hijack and error
message being written to http.Error or w.Write, instead the error
message should be written to the connection

fixes: #630

Signed-off-by: Imran Pochi <imranpochi@microsoft.com>

Author: ipochi

pkg/server/tunnel.go

@@ -53,13 +53,21 @@ func (t *Tunnel) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "hijacking not supported", http.StatusInternalServerError)
 		return
 	}
-	w.WriteHeader(http.StatusOK)
 
 	conn, bufrw, err := hijacker.Hijack()
 	if err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}
+
+	// Send the HTTP 200 OK status after a successful hijack
+	_, err = conn.Write([]byte("HTTP/1.1 200 Connection Established\r\n\r\n"))
+	if err != nil {
+		klog.ErrorS(err, "failed to send 200 connection established")
+		conn.Close()
+		return
+	}
+
 	var closeOnce sync.Once
 	defer closeOnce.Do(func() { conn.Close() })
 
@@ -78,7 +86,9 @@ func (t *Tunnel) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	klog.V(4).Infof("Set pending(rand=%d) to %v", random, w)
 	backend, err := t.Server.getBackend(r.Host)
 	if err != nil {
-		http.Error(w, fmt.Sprintf("currently no tunnels available: %v", err), http.StatusInternalServerError)
+		klog.ErrorS(err, "no tunnels available")
+		conn.Write([]byte(fmt.Sprintf("HTTP/1.1 500 Internal Server Error\r\nContent-Type: text/plain\r\n\r\ncurrently no tunnels available: %v", err)))
+		conn.Close()
 		return
 	}
 	closed := make(chan struct{})