webp.js

var path = require('path');
var http = require('http');
var fs   = require('fs');
var spawn = require('child_process').spawn;

function safe_path(request_url) {
  var cwd = path.resolve(path.dirname());
  var target = path.resolve(request_url.slice(1));
  if (target.indexOf(cwd) !== 0)
    return;

  return target;
}

http.createServer(function(req, res) {
  var image_path = safe_path(req.url);
  if (!image_path) {
    res.writeHead(500);
    return res.end();
  }

  if (!fs.existsSync(image_path) || req.url == '/') {
    res.writeHead(404);
    return res.end();
  }

  var webp = spawn('cwebp', [image_path, '-o', '-']);

  webp.stderr.on('data', function(data) {
    console.log(data.toString('utf8'));
  });

  webp.stdout.pipe(res);

  res.writeHead(200, {
    'Content-Type': 'image/webp',
  });
}).listen(4000, '127.0.0.1');

console.log('http://127.0.0.1:4000');