Forward upgrade error from backend

forward/fwd.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"reflect"
 	"strconv"
 	"strings"
 	"time"
@@ -261,8 +262,32 @@ func (f *websocketForwarder) serveHTTP(w http.ResponseWriter, req *http.Request,
 	}
 	targetConn, resp, err := dialer.Dial(outReq.URL.String(), outReq.Header)
 	if err != nil {
-		ctx.log.Errorf("Error dialing `%v`: %v", outReq.Host, err)
-		ctx.errHandler.ServeHTTP(w, req, err)
+		if resp == nil {
+			ctx.errHandler.ServeHTTP(w, req, err)
+		} else {
+			ctx.log.Errorf("Error dialing `%s`: %v with resp: %d %s", outReq.Host, err, resp.StatusCode, resp.Status)
+			hijacker, ok := w.(http.Hijacker)
+			if !ok {
+				ctx.log.Errorf("%s can not be hijack", reflect.TypeOf(w))
+				ctx.errHandler.ServeHTTP(w, req, err)
+				return
+			}
+
+			conn, _, err := hijacker.Hijack()
+			if err != nil {
+				ctx.log.Errorf("Failed to hijack responseWriter")
+				ctx.errHandler.ServeHTTP(w, req, err)
+				return
+			}
+			defer conn.Close()
+
+			err = resp.Write(conn)
+			if err != nil {
+				ctx.log.Errorf("Failed to forward response")
+				ctx.errHandler.ServeHTTP(w, req, err)
+				return
+			}
+		}
 		return
 	}
 

forward/fwd_websocket_test.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"crypto/tls"
 	"fmt"
+	"io"
 	"net"
 	"net/http"
 	"net/http/httptest"
@@ -290,7 +291,7 @@ func (s *FwdSuite) TestWebsocketUpgradeFailed(c *C) {
 	br := bufio.NewReader(conn)
 	resp, err := http.ReadResponse(br, req)
 
-	c.Assert(resp.StatusCode, Equals, 500)
+	c.Assert(resp.StatusCode, Equals, 400)
 
 	req, err = http.NewRequest(http.MethodGet, "ws://127.0.0.1/ws2", nil)
 	req.Header.Add("upgrade", "websocket")
@@ -299,7 +300,7 @@ func (s *FwdSuite) TestWebsocketUpgradeFailed(c *C) {
 
 	br = bufio.NewReader(conn)
 	resp, err = http.ReadResponse(br, req)
-	c.Assert(resp.StatusCode, Equals, 200)
+	c.Assert(err, Equals, io.ErrUnexpectedEOF)
 }
 
 func (s *FwdSuite) TestForwardsWebsocketTraffic(c *C) {