Merge bc46a095350725318e46839b7cd2ac4ae10d25c7 into 5c00df8afadd06cc5be530dde00fe6d9fa4a2e4a

* init test

* fix test

* fix assert.EqualValues usage

---------

Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>

context.go

@@ -1157,6 +1157,15 @@ func (c *Context) Render(code int, r render.Render) {
 		return
 	}
 
+	if c.Writer.Written() && IsDebugging() {
+		// Skip warning for SSE and streaming responses (status code -1)
+		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

@@ -1396,6 +1396,43 @@ 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 := os.Getenv("GIN_MODE")
+	defer os.Setenv("GIN_MODE", 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 := os.Getenv("GIN_MODE")
+	defer os.Setenv("GIN_MODE", 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)

render/data.go

@@ -4,7 +4,10 @@
 
 package render
 
-import "net/http"
+import (
+	"net/http"
+	"strconv"
+)
 
 // Data contains ContentType and bytes data.
 type Data struct {
@@ -15,6 +18,9 @@ type Data struct {
 // Render (Data) writes data with custom ContentType.
 func (r Data) Render(w http.ResponseWriter) (err error) {
 	r.WriteContentType(w)
+	if len(r.Data) > 0 {
+		w.Header().Set("Content-Length", strconv.Itoa(len(r.Data)))
+	}
 	_, err = w.Write(r.Data)
 	return
 }

render/render_test.go

@@ -8,6 +8,7 @@ import (
 	"encoding/xml"
 	"errors"
 	"html/template"
+	"io"
 	"net"
 	"net/http"
 	"net/http/httptest"
@@ -453,6 +454,36 @@ func TestRenderData(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "#!PNG some raw data", w.Body.String())
 	assert.Equal(t, "image/png", w.Header().Get("Content-Type"))
+	assert.Equal(t, "19", w.Header().Get("Content-Length"))
+}
+
+func TestRenderDataContentLength(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		size, err := strconv.Atoi(r.URL.Query().Get("size"))
+		assert.NoError(t, err)
+
+		data := Data{
+			ContentType: "application/octet-stream",
+			Data:        make([]byte, size),
+		}
+		assert.NoError(t, data.Render(w))
+	}))
+	t.Cleanup(srv.Close)
+
+	for _, size := range []int{0, 1, 100, 100_000} {
+		t.Run(strconv.Itoa(size), func(t *testing.T) {
+			resp, err := http.Get(srv.URL + "?size=" + strconv.Itoa(size))
+			require.NoError(t, err)
+			defer resp.Body.Close()
+
+			assert.Equal(t, "application/octet-stream", resp.Header.Get("Content-Type"))
+			assert.Equal(t, strconv.Itoa(size), resp.Header.Get("Content-Length"))
+
+			actual, err := io.Copy(io.Discard, resp.Body)
+			require.NoError(t, err)
+			assert.EqualValues(t, size, actual)
+		})
+	}
 }
 
 func TestRenderString(t *testing.T) {