koa-lite/examples/streams-pipe.js

var zlib = require('zlib');
var koa = require('..');
var fs = require('fs');
var app = koa();

// ignore favicons

app.use(function *(next){
  if ('/favicon.ico' == this.path) this.status = 404;
  yield next;
});

// logger

app.use(function *(next){
  console.log('%s %s', this.method, this.url);
  yield next;
});

// stream a file

app.use(function *(next){
  var path = __dirname + this.path;
  var exists = yield isFile(path);

  if (!exists) return yield next;

  this.body = fs.createReadStream(path);
  yield next;
});

// gzip the response

app.use(function *(next){
  var body = this.body;

  if (!body || !body.readable) return yield next;

  var gzip = zlib.createGzip();
  this.set('Content-Encoding', 'gzip');
  this.body = gzip;
  body.pipe(gzip);

  yield next;
});

app.listen(3000);

/**
 * Stat regular file helper.
 */

function isFile(file) {
  return function(done){
    fs.stat(file, function(err, stat){
      if (err && 'ENOENT' == err.code) return done(null, false);
      if (err) return done(err);
      done(null, stat.isFile());
    });
  }
}