Simple go proxy, copying body

main.go

package main

import (
	"bytes"
	"io/ioutil"
	"log"
	"net/http"
	"net/http/httputil"
	"net/url"
)

func main() {
	log.Printf("Starting...")
	http.HandleFunc("/", someFunc)
	log.Fatal(http.ListenAndServe(":8080", nil))
}

func someFunc(w http.ResponseWriter, r *http.Request) {
	// change the request host to match the target
	r.Host = "localhost:3000"
	u, _ := url.Parse("http://localhost:3000")
	proxy := httputil.NewSingleHostReverseProxy(u)

	proxy.Transport = &myTransport{}

	proxy.ServeHTTP(w, r)
}

type myTransport struct{}

func (t *myTransport) RoundTrip(request *http.Request) (*http.Response, error) {
	response, err := http.DefaultTransport.RoundTrip(request)

	bodyBytes, err := ioutil.ReadAll(response.Body)
	if err != nil {
		// err
	} else {
		response.Body.Close()

		// Restore the io.ReadCloser to its original state
		// This is causing huge increases in memory usage.
		response.Body = ioutil.NopCloser(bytes.NewBuffer(bodyBytes))
	}

	// Another way to do it, with httputil.. same result, lots of memory.
	// The httputil package provides a DumpResponse() func that will copy the
	// contents of the body into a []byte and return it. It also wraps it in an
	// ioutil.NopCloser and sets up the response to be passed on to the client.
	// _, err = httputil.DumpResponse(response, true)
	// if err != nil {
	// 	return nil, err
	// }

	return response, err
}