A Golang server to proxy XML requests, parse them to JSON, and add CORS headers.

app.yaml

application: scenic-cedar-88515
version: 1
runtime: go
api_version: go1

handlers:
- url: /.*
  script: _go_app

main.go

package instaql

import (
	"appengine"
	"appengine/urlfetch"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"strconv"
)

func init() {
	log.SetFlags(log.LstdFlags | log.Lshortfile)

	http.HandleFunc("/", CorsMiddleware(proxy))
}

func proxy(w http.ResponseWriter, r *http.Request) {
	vals := r.URL.Query()
	url := vals.Get("url")
	if url == "" {
		w.Write([]byte("No url provided"))
		return
	}

	log.Println(url)
	c := appengine.NewContext(r)
	client := urlfetch.Client(c)
	res, err := client.Get(url)
	if err != nil {
		http.Error(w, fmt.Sprintf("Error making request to %s: %s", url, err.Error()), http.StatusInternalServerError)
		return
	}
	body, err := ioutil.ReadAll(res.Body)
	if err != nil {
		http.Error(w, "Error reading body from requested URL", http.StatusInternalServerError)
		return
	}
	json, err := NextbusToJSON(body)
	if err != nil {
		http.Error(w, fmt.Sprintf("Error marshaling XML to JSON: %s", err.Error()), http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	w.Write(json)
	return
}

func CorsMiddleware(fn func(http.ResponseWriter, *http.Request)) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method == "OPTIONS" {
			w.Header().Set("Access-Control-Allow-Methods", "GET, POST")
			w.Header().Set("Access-Control-Max-Age", strconv.Itoa(60*60*6))
			w.Header().Set("Access-Control-Allow-Headers", "CONTENT-TYPE, ACCEPT")
			return
		}
		w.Header().Set("Access-Control-Allow-Origin", "*")
		fn(w, r)
	}
}

nextbus.go

package instaql

import (
	"encoding/json"
	"encoding/xml"
	"log"
)

type RunsData struct {
	Runs []Run `xml:"Body>Nextbus2Response>Runs>Run" json:"runs"`
}

type Run struct {
	Route         string `json:"route"`
	Sign          string `json:"sign"`
	Direction     string `json:"direction"`
	TripTime      string `xml:"Triptime" json:"trip_time"`
	TripID        string `xml:"Tripid" json:"trip_id"`
	Adherence     string `json:"adherence"`
	RealtimeValid string `xml:"Realtime>Valid" json:"valid"`
	EstimatedTime string `xml:"Realtime>Estimatedtime" json:"estimated_time"`
	PollTime      string `xml:"Realtime>Polltime" json:"poll_time"`
	VehicleID     string `xml:"Realtime>Vehicleid" json:"vehicle_id"`
	VehicleLon    string `xml:"Realtime>Long" json:"vehicle_lon"`
	VehicleLat    string `xml:"Realtime>Lat" json:"vehicle_lat"`
	Block         string `json:"block"`
	StopID        string `xml:"Stopid" json:"stop_id"`
}

func NextbusToJSON(data []byte) ([]byte, error) {
	xmlData := new(RunsData)
	err := xml.Unmarshal(data, xmlData)
	if err != nil {
		log.Println(err)
		return nil, err
	}
	res, err := json.Marshal(xmlData)
	return res, err
}