Merge f9beb8845190b8d6acb5edf928e040a520c46f01 into d75fcd4c9ab260e5225de590f1f0f8c0e0e12d11

context.go

@@ -1185,6 +1185,18 @@ func (c *Context) Render(code int, r render.Render) {
 		return
 	}
 
+	if c.Writer.Size() > 0 && IsDebugging() {
+		// Skip this warning when:
+		//   - status code is -1, which is used for special/streaming-style renders (including some
+		//     non-streaming helpers like redirects) where multiple writes are expected, and
+		//   - the renderer is an SSE event, since Server-Sent Events are sent as a stream.
+		if code != -1 {
+			if _, ok := r.(sse.Event); !ok {
+				debugPrint("[WARNING] Response body already written. Attempting to write again with status code %d", code)
+			}
+		}
+	}
+
 	if err := r.Render(c.Writer); err != nil {
 		// Pushing error to c.Errors
 		_ = c.Error(err)

context_test.go

@@ -1425,6 +1425,43 @@ func TestContextRenderNoContentData(t *testing.T) {
 	assert.Equal(t, "text/csv", w.Header().Get("Content-Type"))
 }
 
+// Test multiple JSON writes in debug mode
+func TestContextRenderMultipleJSON(t *testing.T) {
+	w := httptest.NewRecorder()
+	c, _ := CreateTestContext(w)
+
+	oldMode := Mode()
+	defer SetMode(oldMode)
+	SetMode(DebugMode)
+
+	output := captureOutput(t, func() {
+		c.JSON(http.StatusOK, H{"foo": "bar"})
+		c.JSON(http.StatusOK, H{"baz": "qux"})
+	})
+
+	assert.Equal(t, http.StatusOK, w.Code)
+	assert.Contains(t, output, "[WARNING] Response body already written")
+	assert.Contains(t, output, "status code 200")
+}
+
+// Test multiple SSE writes in debug mode
+func TestContextRenderMultipleSSE(t *testing.T) {
+	w := httptest.NewRecorder()
+	c, _ := CreateTestContext(w)
+
+	oldMode := Mode()
+	defer SetMode(oldMode)
+	SetMode(DebugMode)
+
+	output := captureOutput(t, func() {
+		c.SSEvent("message", "test1")
+		c.SSEvent("message", "test2")
+	})
+
+	assert.Equal(t, http.StatusOK, w.Code)
+	assert.NotContains(t, output, "[WARNING] Response body already written")
+}
+
 func TestContextRenderSSE(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := CreateTestContext(w)