impressionist.go

package main

import (
	"bytes"
	"flag"
	"fmt"
	"github.com/elazarl/goproxy"
	"github.com/robertkrimen/otto"
	"io"
	"io/ioutil"
	"log"
	. "net/http"
)

type nopCloser struct {
	io.Reader
}

func (nopCloser) Close() error { return nil }

func main() {
	verbose := flag.Bool("v", false, "should every proxy request be logged to stdout")
	addr := flag.String("addr", ":8080", "proxy listen address")
	flag.Parse()

	proxy := goproxy.NewProxyHttpServer()
	proxy.OnRequest().HandleConnect(goproxy.AlwaysMitm)

	proxy.OnRequest().DoFunc(func(r *Request, ctx *goproxy.ProxyCtx) (*Request, *Response) {
		fmt.Println(r.URL.Host + r.URL.Path)
		return r, nil
	})

	proxy.OnResponse(goproxy.UrlIs("example.com:8001/endpoint/")).DoFunc(func(response *Response, context *goproxy.ProxyCtx) *Response {
		defer response.Body.Close()
		contents, _ := ioutil.ReadAll(response.Body)
		data := string(contents)
		vm := otto.New()
		vm.Set("body", data)
		vm.Run(`
			var data;

			data = JSON.parse(body);
      data.message = "Hello";

			body = JSON.stringify(data);
		`)

		newContents, _ := vm.Get("body")
		{
			newContents, _ := newContents.ToString()
			response.Body = nopCloser{bytes.NewBufferString(newContents)}
		}
		return response
	})

	proxy.Verbose = *verbose
	log.Fatal(ListenAndServe(*addr, proxy))
}