adjusted negotiation logic so that it is possible to add or overwrite…

context.go

@@ -1264,32 +1264,64 @@ type Negotiate struct {
 	TOMLData any
 }
 
-// Negotiate calls different Render according to acceptable Accept format.
-func (c *Context) Negotiate(code int, config Negotiate) {
-	switch c.NegotiateFormat(config.Offered...) {
-	case binding.MIMEJSON:
+func NewNegotiate(offered []string) Negotiate {
+	return Negotiate{Offered: offered}
+}
+func (receiver Negotiate) WithData(data any) Negotiate {
+	receiver.Data = data
+	return receiver
+}
+
+// NegotiationRenderFunc is responsible for rendering data in a specific format.
+type NegotiationRenderFunc func(status int, config Negotiate, c *Context)
+
+func AddNegotiationRenderMapping(mimeType string, binding NegotiationRenderFunc) {
+	negotiationRenderMappings[mimeType] = binding
+}
+
+// All predefined negotiationRenderMappings - associate a content type
+// with a NegotiationRenderFunc, which is responsible for rendering
+// data in a specific format.
+var negotiationRenderMappings = map[string]NegotiationRenderFunc{
+	binding.MIMEJSON: func(code int, config Negotiate, c *Context) {
 		data := chooseData(config.JSONData, config.Data)
 		c.JSON(code, data)
-
-	case binding.MIMEHTML:
+	},
+	binding.MIMEHTML: func(code int, config Negotiate, c *Context) {
 		data := chooseData(config.HTMLData, config.Data)
 		c.HTML(code, config.HTMLName, data)
-
-	case binding.MIMEXML:
+	},
+	binding.MIMEXML: func(code int, config Negotiate, c *Context) {
 		data := chooseData(config.XMLData, config.Data)
 		c.XML(code, data)
-
-	case binding.MIMEYAML, binding.MIMEYAML2:
+	},
+	binding.MIMEYAML: func(code int, config Negotiate, c *Context) {
 		data := chooseData(config.YAMLData, config.Data)
 		c.YAML(code, data)
-
-	case binding.MIMETOML:
+	},
+	binding.MIMEYAML2: func(code int, config Negotiate, c *Context) {
+		data := chooseData(config.YAMLData, config.Data)
+		c.YAML(code, data)
+	},
+	binding.MIMETOML: func(code int, config Negotiate, c *Context) {
 		data := chooseData(config.TOMLData, config.Data)
 		c.TOML(code, data)
+	},
+	binding.MIMEPROTOBUF: func(code int, config Negotiate, c *Context) {
+		c.ProtoBuf(code, config.Data)
+	},
+}
 
-	default:
-		c.AbortWithError(http.StatusNotAcceptable, errors.New("the accepted formats are not offered by the server")) //nolint: errcheck
+// Negotiate calls different Render according to acceptable Accept format.
+func (c *Context) Negotiate(code int, config Negotiate) {
+
+	accepted := c.NegotiateFormat(config.Offered...)
+	if fn, ok := negotiationRenderMappings[accepted]; ok {
+		fn(code, config, c)
+		return
 	}
+	c.AbortWithError(http.StatusNotAcceptable, errors.New("the accepted formats are not offered by the server")) //nolint: errcheck
+
 }
 
 // NegotiateFormat returns an acceptable Accept format.

context_test.go

@@ -1542,6 +1542,44 @@ func TestContextNegotiationWithHTML(t *testing.T) {
 	assert.Equal(t, "text/html; charset=utf-8", w.Header().Get("Content-Type"))
 }
 
+func TestContextNegotiationWithProto(t *testing.T) {
+	w := httptest.NewRecorder()
+	c, _ := CreateTestContext(w)
+	c.Request, _ = http.NewRequest(http.MethodPost, "", nil)
+
+	c.Negotiate(http.StatusOK, Negotiate{
+		Offered: []string{binding.MIMEPROTOBUF},
+		Data:    &testdata.Test{},
+	})
+
+	assert.Equal(t, http.StatusOK, w.Code)
+	assert.Equal(t, 0, w.Body.Len())
+	assert.Equal(t, "application/x-protobuf", w.Header().Get("Content-Type"))
+}
+
+func TestContextNegotiationWithCustom(t *testing.T) {
+
+	contentType := "application/whatever"
+
+	w := httptest.NewRecorder()
+	c, _ := CreateTestContext(w)
+	c.Request, _ = http.NewRequest(http.MethodPost, "", nil)
+
+	AddNegotiationRenderMapping(contentType, func(status int, config Negotiate, c *Context) {
+		data := config.Data.([]byte)
+		c.Data(status, contentType, data)
+	})
+
+	c.Negotiate(http.StatusOK, Negotiate{
+		Offered: []string{contentType},
+		Data:    []byte("Hello World"),
+	})
+
+	assert.Equal(t, http.StatusOK, w.Code)
+	assert.Equal(t, "Hello World", w.Body.String())
+	assert.Equal(t, contentType, w.Header().Get("Content-Type"))
+}
+
 func TestContextNegotiationNotSupport(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := CreateTestContext(w)