Go proxy middleware and modify response

Question

I'm trying to proxy a request from a Go backend to a microservice and modify the response before it is sent to the client. The request chain is: Client -> Go backend -> microservice -> Go backend -> client

I'm using the Go Gin framework. The working middleware:

func ReverseProxy(target string) gin.HandlerFunc {
    log.Println(target)
    url, err := url.Parse(target)
    if err != nil {
        log.Fatal(err)
    }
    proxy := httputil.NewSingleHostReverseProxy(url)
    return func(c *gin.Context) {
        proxy.ServeHTTP(c.Writer, c.Request)
    }
}

Now my question is: How can I receive and modify the response sent by the microservice?

Answer 1

How about using ReverseProxy.ModifyResponse?

For example, this will add a custom header to the response.

func addCustomHeader(r *http.Response) error {
    r.Header["Hello"] = []string{"World"}
    return nil
}

proxy.ModifyResponse = addCustomHeader