Support websocket upgrades in private HTTP proxy

Preserve optional ResponseWriter interfaces through statusCapture so httputil.ReverseProxy can hijack upgraded websocket connections. Add a regression test covering websocket traffic through the HTTP handler path.

netstack2/http_handler.go

@@ -6,8 +6,10 @@
 package netstack2
 
 import (
+	"bufio"
 	"context"
 	"crypto/tls"
+	"errors"
 	"fmt"
 	"net"
 	"net/http"
@@ -29,7 +31,7 @@ import (
 type HTTPTarget struct {
 	DestAddr string `json:"destAddr"` // IP address or hostname of the downstream service
 	DestPort uint16 `json:"destPort"` // TCP port of the downstream service
-	Scheme string   `json:"scheme"` // When true the outbound leg uses HTTPS
+	Scheme   string `json:"scheme"`   // When true the outbound leg uses HTTPS
 }
 
 // ---------------------------------------------------------------------------
@@ -322,6 +324,24 @@ func (sc *statusCapture) WriteHeader(code int) {
 	sc.ResponseWriter.WriteHeader(code)
 }
 
+func (sc *statusCapture) Unwrap() http.ResponseWriter {
+	return sc.ResponseWriter
+}
+
+func (sc *statusCapture) Flush() {
+	if flusher, ok := sc.ResponseWriter.(http.Flusher); ok {
+		flusher.Flush()
+	}
+}
+
+func (sc *statusCapture) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	hijacker, ok := sc.ResponseWriter.(http.Hijacker)
+	if !ok {
+		return nil, nil, errors.New("underlying response writer does not support hijacking")
+	}
+	return hijacker.Hijack()
+}
+
 // handleRequest is the http.Handler entry point. It retrieves the SubnetRule
 // attached to the connection by ConnContext, selects the first configured
 // downstream target, and forwards the request via the cached ReverseProxy.

netstack2/http_handler_test.go

@@ -0,0 +1,97 @@
+package netstack2
+
+import (
+	"context"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+
+	"github.com/gorilla/websocket"
+)
+
+func TestHTTPHandlerProxiesWebSocketUpgrade(t *testing.T) {
+	upgrader := websocket.Upgrader{}
+	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		conn, err := upgrader.Upgrade(w, r, nil)
+		if err != nil {
+			t.Errorf("upgrade failed: %v", err)
+			return
+		}
+		defer conn.Close()
+
+		messageType, payload, err := conn.ReadMessage()
+		if err != nil {
+			t.Errorf("read failed: %v", err)
+			return
+		}
+		if err := conn.WriteMessage(messageType, append([]byte("echo:"), payload...)); err != nil {
+			t.Errorf("write failed: %v", err)
+		}
+	}))
+	defer backend.Close()
+
+	backendURL, err := url.Parse(backend.URL)
+	if err != nil {
+		t.Fatalf("parse backend URL: %v", err)
+	}
+	backendHost, backendPort, err := net.SplitHostPort(backendURL.Host)
+	if err != nil {
+		t.Fatalf("split backend host: %v", err)
+	}
+	port, err := net.LookupPort("tcp", backendPort)
+	if err != nil {
+		t.Fatalf("parse backend port: %v", err)
+	}
+
+	handler := NewHTTPHandler(nil, nil)
+	rule := &SubnetRule{
+		Protocol: "http",
+		HTTPTargets: []HTTPTarget{
+			{
+				DestAddr: backendHost,
+				DestPort: uint16(port),
+				Scheme:   backendURL.Scheme,
+			},
+		},
+	}
+
+	frontend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		ctx := context.WithValue(r.Context(), connCtxKey{}, rule)
+		handler.handleRequest(w, r.WithContext(ctx))
+	}))
+	defer frontend.Close()
+
+	frontendURL, err := url.Parse(frontend.URL)
+	if err != nil {
+		t.Fatalf("parse frontend URL: %v", err)
+	}
+	wsURL := url.URL{
+		Scheme:   "ws",
+		Host:     frontendURL.Host,
+		Path:     "/socket",
+		RawQuery: "token=test",
+	}
+
+	conn, _, err := websocket.DefaultDialer.Dial(wsURL.String(), nil)
+	if err != nil {
+		t.Fatalf("dial websocket through proxy: %v", err)
+	}
+	defer conn.Close()
+
+	if err := conn.WriteMessage(websocket.TextMessage, []byte("hello")); err != nil {
+		t.Fatalf("write websocket message: %v", err)
+	}
+
+	messageType, payload, err := conn.ReadMessage()
+	if err != nil {
+		t.Fatalf("read websocket message: %v", err)
+	}
+	if messageType != websocket.TextMessage {
+		t.Fatalf("message type = %d, want %d", messageType, websocket.TextMessage)
+	}
+	if got, want := string(payload), "echo:hello"; got != want {
+		t.Fatalf("payload = %q, want %q", got, want)
+	}
+}