I’ll make a short walk thru how I’ve built a simple Web-service (proxy) with Node.js that might be usefull for developers who are started playing with it.

The source code for the app is available on xslim/img.mrt.io

Hello world? No, dump Readme

We’ll use Express.js for our routes. Check that your package.json contains express as a dependency in dependencies section and install them with npm install. Create README.md file with some content. Next, create an app.js and fill with usefull code:

var express = require('express'),
    app = express(),
    http = require('http'),
    fs = require('fs');

app.get("/", function(req, res, next) {
  fs.readFile('README.md', function(err, data) {
    res.writeHead(200, {"Content-Type": "text/plain"});
    res.end(data);
  });
});

app.listen(process.env.PORT || 3000);

Now after running node app.js and visiting the http://localhost:3000/ will give you a dump of your README.md file (Real example). Cool, huh?

Coffeescript

I prefer having a simpler and cleaner code. Thus, I use Coffee script. To use it, add coffee-script npm dependency. The filenames should be changed from .js to .coffee, and the code should be changed as well. You can use js2coffee.org for converting the code. So our app.coffee will be changed to this:

express = require('express')
app = express()
http = require('http')
fs = require('fs')

app.get "/", (req, res, next) ->
  fs.readFile 'README.md', (err, data) ->
    res.writeHead 200, "Content-Type": "text/plain"
    res.end data

app.listen process.env.PORT or 3000

To run it, use coffee app.coffee.

Watch it!

It might be quite boring to restart the Node every time you make a change to a file. We can automate this using Grunt and nodemon.

Create a section devDependencies in package.json and add grunt, grunt-contrib-watch, load-grunt-tasks and grunt-nodemon. Create Gruntfile.js with contents:

module.exports = function (grunt) {
    require('load-grunt-tasks')(grunt);
    grunt.initConfig({
        nodemon: {
          dev: {
            script: 'app.coffee'
          }
        }
      });
};

Now the only thing you need to run is grunt nodemon and enjoy. For a more crazy automation, ther’s an awesome blog post Continuous Development in Node.js.

Let’s make a proxy

Say we want to show our avatar calling /avatar.jpg by streaming the actual data from Gravatar. Can be done!

First, create a proxy method

proxyTo = (url, response) ->
  try
    http.get url, (res) ->
      res.pipe response

  catch _error
    response.writeHead 500, "Content-Type": "text/html"
    response.end url, _error.message

And the endpoint:

app.get "/avatar.jpg", (req, res) ->
  proxyTo "http://gravatar.com/avatar/4374a44a5a6642a24ac2975b9aa2dfe7", res

Real example

More advanced proxy

How do we deal with a variables? Let’s make a proxy for google static maps. As opposed to Google API which is not that clean, we want a simple clean one. For example, we want /map/{lat},{lon},{zoom}/{size}:

app.get "/map/:lat,:lon,:zoom/:size", (req, res) ->
  lat = req.param("lat")
  lon = req.param("lon")
  zoom = req.param("zoom")

  size = req.param("size")
  size = size.split("x")
  w = size[0]
  h = size[1]

  url = "http://maps.googleapis.com"
  url += "/maps/api/staticmap?center=" + lat + "," + lon + "&zoom=" + zoom + "&size=" + w + "x" + h + "&sensor=false"

  proxyTo url, res

Real example

Refactor & Extract

Going with a best practice of not having all the code in one file, let’s refactor the map url generation in a separate “module”. Create maps.coffee that exports the function:

exports.static_link = (lat, lon, zoom, size, provider) ->
  size = size.split("x")
  url = ""
  w = size[0]
  h = size[1]
  provider = "google" unless provider
  switch provider
    when "google"
      key = process.env.KEY_GOOGLE
      url = "http://maps.googleapis.com"
      url += "/maps/api/staticmap?center=" + lat + "," + lon + "&zoom=" + zoom + "&size=" + w + "x" + h + "&sensor=false"
      if (key.length > 0)
        url += "&key="+key
    when "here"
      url = "http://m.nok.it"
      url += "?w=" + w + "&h=" + h + "&ml=eng&nord&nodot&pip&c=" + lat + "," + lon + "&z=" + zoom + "&f=0"
  url

Use it in app.coffee:

maps = require('./maps')

app.get "/map/:lat,:lon,:zoom/:size", (req, res) ->
  url = maps.static_link(req.param("lat"), req.param("lon"), req.param("zoom"), req.param("size"), req.query.t)
  proxyTo url, res

Deploy to Heroku

Well, Heroku have a nice write-up on how to do this. The only thing to know is that we’r using Coffee script, so we need to change Procfile to this:

web: coffee app.coffee