feat(context): add Protocol Buffers support to content negotiation (#4423)

Co-authored-by: 1911860538 <alxps1911@gmail.com>

context.go

@@ -39,6 +39,7 @@ const (
 	MIMEYAML              = binding.MIMEYAML
 	MIMEYAML2             = binding.MIMEYAML2
 	MIMETOML              = binding.MIMETOML
+	MIMEPROTOBUF          = binding.MIMEPROTOBUF
 )
 
 // BodyBytesKey indicates a default body bytes key.
@@ -1280,14 +1281,15 @@ func (c *Context) Stream(step func(w io.Writer) bool) bool {
 
 // Negotiate contains all negotiations data.
 type Negotiate struct {
-	Offered  []string
-	HTMLName string
-	HTMLData any
-	JSONData any
-	XMLData  any
-	YAMLData any
-	Data     any
-	TOMLData any
+	Offered      []string
+	HTMLName     string
+	HTMLData     any
+	JSONData     any
+	XMLData      any
+	YAMLData     any
+	Data         any
+	TOMLData     any
+	PROTOBUFData any
 }
 
 // Negotiate calls different Render according to acceptable Accept format.
@@ -1313,6 +1315,10 @@ func (c *Context) Negotiate(code int, config Negotiate) {
 		data := chooseData(config.TOMLData, config.Data)
 		c.TOML(code, data)
 
+	case binding.MIMEPROTOBUF:
+		data := chooseData(config.PROTOBUFData, config.Data)
+		c.ProtoBuf(code, data)
+
 	default:
 		c.AbortWithError(http.StatusNotAcceptable, errors.New("the accepted formats are not offered by the server")) //nolint: errcheck
 	}

context_test.go

@@ -1628,6 +1628,32 @@ func TestContextNegotiationWithHTML(t *testing.T) {
 	assert.Equal(t, "text/html; charset=utf-8", w.Header().Get("Content-Type"))
 }
 
+func TestContextNegotiationWithPROTOBUF(t *testing.T) {
+	w := httptest.NewRecorder()
+	c, _ := CreateTestContext(w)
+	c.Request = httptest.NewRequest(http.MethodPost, "/", nil)
+
+	reps := []int64{int64(1), int64(2)}
+	label := "test"
+	data := &testdata.Test{
+		Label: &label,
+		Reps:  reps,
+	}
+
+	c.Negotiate(http.StatusCreated, Negotiate{
+		Offered: []string{MIMEPROTOBUF, MIMEJSON, MIMEXML},
+		Data:    data,
+	})
+
+	// Marshal original data for comparison
+	protoData, err := proto.Marshal(data)
+	require.NoError(t, err)
+
+	assert.Equal(t, http.StatusCreated, w.Code)
+	assert.Equal(t, string(protoData), w.Body.String())
+	assert.Equal(t, "application/x-protobuf", w.Header().Get("Content-Type"))
+}
+
 func TestContextNegotiationNotSupport(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := CreateTestContext(w)