proxy.go

package main

import (
	"bytes"
	"io"
	"io/ioutil"
	"log"
	"strings"

	"github.com/go-macaron/binding"
	"gopkg.in/macaron.v1"
	"net/http"
	"net/http/httputil"
)

type RenderRequest struct {
	Targets       []string `json:"target" form:"target"`
	MaxDataPoints int      `json:"maxDataPoints" form:"maxDataPoints"`
	Format        string   `json:"format" form:"format"`
}

func ProxyHandeler(ctx *macaron.Context, request RenderRequest, body OriginalBody) {
	needProxy := false
	for _, target := range request.Targets {
		// if target is wrapped in a function
		if strings.HasSuffix(target, ")") {
			needProxy = true
		}
	}

	if !needProxy {
		log.Printf("request can be handled locally.")
		render(ctx, request)
		return
	}

	log.Printf("request needs to be proxied.")

	director := func(req *http.Request) {
		req.URL.Scheme = "http"
		req.URL.Host = "localhost:4000"
		req.URL.Path = "/proxy" + req.URL.Path
		req.Body = body.ReadCloser
	}

	proxy := httputil.ReverseProxy{Director: director}
	proxy.ServeHTTP(ctx.Resp, ctx.Req.Request)
}

func render(ctx *macaron.Context, request RenderRequest) {
	ctx.JSON(200, request)
}

func logProxy(ctx *macaron.Context, request RenderRequest) {
	log.Printf("request being handled by proxy")
	return
}

type OriginalBody struct {
	ReadCloser io.ReadCloser
}

func captureBody(ctx *macaron.Context) {
	buf, _ := ioutil.ReadAll(ctx.Req.Body().ReadCloser())
	rdr1 := ioutil.NopCloser(bytes.NewBuffer(buf))
	rdr2 := ioutil.NopCloser(bytes.NewBuffer(buf))
	ctx.Req.Request.Body = rdr2

	ctx.Map(OriginalBody{
		ReadCloser: rdr1,
	})
}

func main() {
	bind := binding.Bind
	m := macaron.Classic()
	m.Use(macaron.Renderer())
	m.Combo("/render", captureBody, bind(RenderRequest{})).Get(ProxyHandeler).Post(ProxyHandeler)
	m.Combo("/proxy/render", bind(RenderRequest{}), logProxy).Get(render).Post(render)
	m.Run()
}