Need help in rewriting the response

[palashjain95]

I want to hijack and rewrite the response after the api call has been serviced by the business logic.
Kind like making use of modify response function in body dump middleware. Struggling on it for some time. Can some please help with this.

func CusstomMiddleware() echo.MiddlewareFunc {
	return middleware.BodyDump(func(c echo.Context, reqBody, resBody []byte) {
		if c.Response().Status >= 200 && c.Response().Status < 300 && c.QueryParam("keyFilter") != "" {
			var inputJson interface{}
			_ = json.Unmarshal(resBody, &inputJson)
			/*
                        result : modify response
                        */
			b, _ := json.Marshal(result)
			if _, err := io.Copy(c.Response().Writer, bytes.NewBuffer(b)); err != nil {
				return
			}
		}
	})
}

Original Response

{
    "name": "test-group-magnetism",
    "description": "Test-Group-magnetism",
    "isGlobal": false,
    "tags": {
        "key": "value"
    }
}

Expected Response

{
    "tags": {
        "key": "value"
    }
}

Actual Response

{
    "name": "test-group-magnetism",
    "description": "Test-Group-magnetism",
    "isGlobal": false,
    "tags": {
        "key": "value"
    }
}{
    "tags": {
        "key": "value"
    }
}

Tried with proxy middleware

url, _ := url.Parse("http://localhost:8080/")
	target := middleware.ProxyTarget{
		URL: url,
	}
	rb := middleware.NewRandomBalancer([]*middleware.ProxyTarget{&target})
	proxyConfig := middleware.ProxyConfig{
		Balancer: rb,
		ModifyResponse: func(res *http.Response) error {
			res.Body = ioutil.NopCloser(bytes.NewBuffer([]byte("modified")))
			res.Header.Set("X-Modified", "1")
			return nil
		},
	}

In this I am getting gateway timeout with multiple calls to my server. Can't understand how the proxy middleware works

[aldas]

rewrite the response after the api call has been serviced by the business logic

Are you trying to change external service (out of this go process) response inside Echo or you want to change some (wrapped) handler response before it is served to the client?

If you want to replace/modify proxied request response body then this will help you https://stackoverflow.com/questions/31535569/how-to-read-response-body-of-reverseproxy

Proxy middleware supports providing your own ModifyResponse callback

echo/middleware/proxy.go

Lines 57 to 58 in c6f0c66

	// ModifyResponse defines function to modify response from ProxyTarget.
	ModifyResponse func(*http.Response) error

Middleware definition would be something like that if we combine StackOverflow example:

	url1, _ := url.Parse("http://target:80")

	e.Use(ProxyWithConfig(ProxyConfig{
		Balancer: NewRoundRobinBalancer([]*ProxyTarget{
			{
				Name: "target 1",
				URL:  url1,
			},
		}),
		ModifyResponse: func(resp *http.Response) error {
			b, err := ioutil.ReadAll(resp.Body)
			if err != nil {
				return  err
			}
			err = resp.Body.Close()
			if err != nil {
				return err
			}
			b = bytes.Replace(b, []byte("server"), []byte("schmerver"), -1)
			body := ioutil.NopCloser(bytes.NewReader(b))
			resp.Body = body
			resp.ContentLength = int64(len(b))
			resp.Header.Set("Content-Length", strconv.Itoa(len(b)))
			return nil
		},
	}))