add bind for relay

pkg/handler/relay/forward.go

@@ -8,11 +8,18 @@ import (
 
 	"github.com/go-gost/gost/pkg/chain"
 	"github.com/go-gost/gost/pkg/handler"
+	"github.com/go-gost/relay"
 )
 
 func (h *relayHandler) handleForward(ctx context.Context, conn net.Conn, network string) {
+	resp := relay.Response{
+		Version: relay.Version1,
+		Status:  relay.StatusOK,
+	}
 	target := h.group.Next()
 	if target == nil {
+		resp.Status = relay.StatusServiceUnavailable
+		resp.WriteTo(conn)
 		h.logger.Error("no target available")
 		return
 	}
@@ -30,15 +37,51 @@ func (h *relayHandler) handleForward(ctx context.Context, conn net.Conn, network
 
 	cc, err := r.Dial(ctx, network, target.Addr())
 	if err != nil {
-		h.logger.Error(err)
 		// TODO: the router itself may be failed due to the failed node in the router,
 		// the dead marker may be a wrong operation.
 		target.Marker().Mark()
+
+		resp.Status = relay.StatusHostUnreachable
+		resp.WriteTo(conn)
+		h.logger.Error(err)
+
 		return
 	}
 	defer cc.Close()
 	target.Marker().Reset()
 
+	if h.md.noDelay {
+		if _, err := resp.WriteTo(conn); err != nil {
+			h.logger.Error(err)
+			return
+		}
+	}
+
+	switch network {
+	case "udp", "udp4", "udp6":
+		rc := &udpConn{
+			Conn: conn,
+		}
+		if !h.md.noDelay {
+			// cache the header
+			if _, err := resp.WriteTo(&rc.wbuf); err != nil {
+				return
+			}
+		}
+		conn = rc
+	default:
+		rc := &tcpConn{
+			Conn: conn,
+		}
+		if !h.md.noDelay {
+			// cache the header
+			if _, err := resp.WriteTo(&rc.wbuf); err != nil {
+				return
+			}
+		}
+		conn = rc
+	}
+
 	t := time.Now()
 	h.logger.Infof("%s <-> %s", conn.RemoteAddr(), target.Addr())
 	handler.Transport(conn, cc)