fix: use safe type assertions and godoc for CloseNotify and Hijack

Author: odlev

response_writer.go

@@ -17,7 +17,10 @@ const (
 	defaultStatus = http.StatusOK
 )
 
-var errHijackAlreadyWritten = errors.New("gin: response body already written")
+var (
+	errHijackAlreadyWritten = errors.New("gin: response body already written")
+	errHijackNotSupported   = errors.New("gin: underlying ResponseWriter does not implement http.Hijacker")
+)
 
 // ResponseWriter ...
 type ResponseWriter interface {
@@ -117,12 +120,25 @@ func (w *responseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
 	if w.size < 0 {
 		w.size = 0
 	}
-	return w.ResponseWriter.(http.Hijacker).Hijack()
+	if hijacker, ok := w.ResponseWriter.(http.Hijacker); ok {
+		return hijacker.Hijack()
+	}
+	return nil, nil, errHijackNotSupported
 }
 
 // CloseNotify implements the http.CloseNotifier interface.
+//
+// If the underlying ResponseWriter doesn't implement http.CloseNotifier
+// (e.g. httptest.NewRecorder), the returned channel will never fire.
+// Use Request.Context().Done() to observe client disconnects instead.
+//
+// Deprecated: the CloseNotifier interface predates Go's context package.
+// New code should use Request.Context instead.
 func (w *responseWriter) CloseNotify() <-chan bool {
-	return w.ResponseWriter.(http.CloseNotifier).CloseNotify()
+	if cn, ok := w.ResponseWriter.(http.CloseNotifier); ok {
+		return cn.CloseNotify()
+	}
+	return make(chan bool)
 }
 
 // Flush implements the http.Flusher interface.

response_writer_test.go

@@ -113,15 +113,12 @@ func TestResponseWriterHijack(t *testing.T) {
 	writer.reset(testWriter)
 	w := ResponseWriter(writer)
 
-	assert.Panics(t, func() {
-		_, _, err := w.Hijack()
-		require.NoError(t, err)
-	})
+	_, _, err := w.Hijack()
+	require.ErrorIs(t, err, errHijackNotSupported)
 	assert.True(t, w.Written())
 
-	assert.Panics(t, func() {
-		w.CloseNotify()
-	})
+	ch := w.CloseNotify()
+	assert.NotNil(t, ch)
 
 	w.Flush()
 }
@@ -315,3 +312,48 @@ func TestPusherWithoutPusher(t *testing.T) {
 	pusher := w.Pusher()
 	assert.Nil(t, pusher, "Expected pusher to be nil")
 }
+
+// mockCloseNotifier is an http.ResponseWriter that implements http.CloseNotifier.
+type mockCloseNotifier struct {
+	*httptest.ResponseRecorder
+}
+
+func (m *mockCloseNotifier) CloseNotify() <-chan bool {
+	return make(chan bool)
+}
+
+func TestCloseNotifyWithCloseNotifier(t *testing.T) {
+	rw := &mockCloseNotifier{ResponseRecorder: httptest.NewRecorder()}
+	w := &responseWriter{}
+	w.reset(rw)
+
+	ch := w.CloseNotify()
+	assert.NotNil(t, ch, "Expected CloseNotify channel to be non-nil")
+}
+
+func TestCloseNotifyWithoutCloseNotifier(t *testing.T) {
+	// httptest.NewRecorder does not implement http.CloseNotifier
+	rw := httptest.NewRecorder()
+	w := &responseWriter{}
+	w.reset(rw)
+
+	ch := w.CloseNotify()
+	assert.NotNil(t, ch, "Expected non-nil channel when CloseNotifier is not supported")
+	select {
+	case <-ch:
+		t.Fatal("channel should never fire when CloseNotifier is not supported")
+	default:
+	}
+}
+
+func TestHijackWithoutHijacker(t *testing.T) {
+	// httptest.NewRecorder does not implement http.Hijacker
+	rw := httptest.NewRecorder()
+	w := &responseWriter{}
+	w.reset(rw)
+
+	conn, buf, err := w.Hijack()
+	assert.Nil(t, conn)
+	assert.Nil(t, buf)
+	require.ErrorIs(t, err, errHijackNotSupported)
+}