AWS Lambda script:: Compiling JavaScript files which are triggered by s3 events.

s3-compile-js.js

var AWS   = require('aws-sdk');
var async = require('async');
var path  = require("path");
var mkdir = require("mkdirp");
var fs    = require('fs');
var spawn = require('child_process').spawn;

exports.handler = function (event, context) {
  // console.log('Event: '+JSON.stringify(event, true, ' '));
  var key = event.Records[0].s3.object.key;
  if (! /\.js$/.test(key)) {
    context.done(null, '');
  }
  if (/\.min\.js$/.test(key)) {
    context.done(null, '');
  }
  
  AWS.config.region = event.Records[0].awsRegion;
  var s3 = new AWS.S3(),
      bucket = event.Records[0].s3.bucket.name,
      min = key.replace(/\.js$/, '.min.js');

  async.series([
    function (callback) {
      _get(s3, bucket, key, function () {
        callback(null, 'get');
      });
    },

    /**
     * using google closure-compiler
     */
    // function (callback) {
    //   _get(bucket, 'compiler.jar', function () {
    //     callback(null, 'jar');
    //   });
    // },
    // function (callback) {
    //   var command = 'java',
    //       args = ['-Xms6m', '-Xmx128m', '-jar', '/tmp/compiler.jar',
    //               '--compilation_level', 'SIMPLE_OPTIMIZATIONS',
    //               '--charset', 'UTF-8', '--js', '/tmp/'+key,
    //               '--js_output_file', '/tmp/'+min
    //       ];
    //   _command(command, args, null, function () {
    //     callback(null, 'java');
    //   });
    // },

    /**
     * using yui compressor
     */
    function (callback) {
      _get(s3, bucket, 'yuicompressor-2.4.8.jar', function () {
        callback(null, 'jar');
      });
    },
    function (callback) {
      var command = 'java',
          args = ['-Xms6m', '-Xmx128m', '-jar', '/tmp/yuicompressor-2.4.8.jar',
                  '/tmp/'+key, '-o', '/tmp/'+min, '--charset', 'UTF-8'
          ];
      _command(command, args, null, function () {
        callback(null, 'java');
      });
    },

    function (callback) {
      _put(s3, bucket, min, function () {
        callback(null, 'post');
      });
    }
  ], function (err) {
    context.done(null, '');
  });
};


function _get(s3, bucket, key, callback) {
  mkdir(path.dirname('/tmp/'+key), function (err) {
    if (err) throw err;
    var file = fs.createWriteStream('/tmp/'+key);
    s3.getObject({Bucket: bucket, Key: key}).on('error', function (err) {
      throw err;
    }).createReadStream().pipe(file).on('close', function () {
      callback();
    });
  });
}

function _put(s3, bucket, key, callback) {
  var stream = fs.createReadStream('/tmp/'+key);
  s3.putObject({Bucket: bucket, Key: key, Body: stream}, function (err) {
    if (err) throw err;
    callback();
  });
}

function _command(command, args, options, callback) {
  var child = spawn(command, args, options);
  child.stdout.on('data', function (data) {
    console.log('stdout: ' + data);
  });
  child.stderr.on('data', function (data) {
    console.log('stderr: ' + data);
  });
  child.on('close', function (code) {
    if (code !== 0) {
      throw new Error("Process exited with non-zero status code");
    }
    callback();
  });
}