Feat(resp): add ResponseBody func to acquire resp body (#356)

* Feat(resp): add ResponseBody func to acquire resp body in middlewares

* add optional field to descide whether wrap the resp body

Co-authored-by: whalecold <zhenglisheng@caicloud.io>

service/context.go

@@ -170,13 +170,19 @@ type ResponseWriter interface {
 	StatusCode() int
 	// ContentLength returns the length of written content.
 	ContentLength() int
+	// ResponseBody returns response body.
+	ResponseBody() []byte
+	// SetWrapRespBodyPolicy set wrap resp body policy.
+	SetWrapRespBodyPolicy(bool)
 }
 
 type response struct {
-	writer        http.ResponseWriter
-	statusCode    int
-	contentLength int
-	hijacked      bool
+	writer         http.ResponseWriter
+	statusCode     int
+	contentLength  int
+	hijacked       bool
+	ifWrapRespBody bool
+	respBody       []byte
 }
 
 // For http.HTTPResponseWriter and HTTPResponseInfo
@@ -191,6 +197,10 @@ func (c *response) Write(data []byte) (int, error) {
 	}
 	length, err := c.writer.Write(data)
 	c.contentLength += length
+	// Append the data to the response cache for the special purpose of users.
+	if c.ifWrapRespBody {
+		c.respBody = append(c.respBody, data[:length]...)
+	}
 	return length, err
 }
 
@@ -241,6 +251,16 @@ func (c *response) HeaderWritable() bool {
 	return !c.hijacked && c.statusCode <= 0
 }
 
+// ResponseBody returns response body.
+func (c *response) ResponseBody() []byte {
+	return c.respBody
+}
+
+// SetWrapRespBodyPolicy set wrap resp body policy.
+func (c *response) SetWrapRespBodyPolicy(v bool) {
+	c.ifWrapRespBody = v
+}
+
 // HTTPContext describes an http context.
 type HTTPContext interface {
 	Request() *http.Request