Use the bufrw

Instead of the using the conn returned by the hijack, using the returned
buffrw as the reader, because there can be unprocessed data sent by the
client.

Author: Chao Xu

pkg/agent/agentserver/tunnel.go

@@ -49,7 +49,7 @@ func (t *Tunnel) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 	w.WriteHeader(http.StatusOK)
 
-	conn, _, err := hijacker.Hijack()
+	conn, bufrw, err := hijacker.Hijack()
 	if err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
@@ -103,7 +103,7 @@ func (t *Tunnel) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	pkt := make([]byte, 1<<12)
 
 	for {
-		n, err := conn.Read(pkt[:])
+		n, err := bufrw.Read(pkt[:])
 		if err == io.EOF {
 			klog.Warningf("EOF from %v", r.Host)
 			break