download.js

var Url = require('url'),
    Http = require('http'),
    Fs = require('fs');


function download(url, filename, cb) {
  var urlObject = Url.parse(url),
      file;
    
  var request = Http.get(urlObject, function(res) {
    if (res.statusCode != 200) {
      makeCallback(new Error("HTTP Error: " + res.statusCode));
      return;
    }
    
    file = Fs.createWriteStream(filename);
    res.pipe(file);
    
    file.on('error', function() {
      file.destroy();
    });  
    
    file.on('close', function() {
      file = null;
      makeCallback(); 
    });
  });

  request.on('error', function(err) {
    if (file) file.destroy();
    makeCallback(err);
  });
  
  function makeCallback(err) {
    if (!cb) return;
    cb(err);
    cb = null;
  }
}

function test_download(url, filename) {
  download(url, filename, function(err) {
    console.log("url:", url);
    console.log("filename:", filename);
    console.log("result", err || 'success');
    console.log("");
  });
}

// Should succeed:
test_download('http://www.google.com/images/srpr/logo3w.png', 'google.png');

// Should fail with HTTP 4xx or 5xx status
test_download('http://www.google.com/does not exists', 'fail1.png');

// Should fail with a DNS error
test_download('http://324579jhfsdlflkdsf/', 'fail2.png');

// Should fail with an ECONNREFUSED or ETIMEDOUT error
test_download('http://www.google.com:9876/test.png', 'fail3.png');

// Should fail with an ECONNREFUSED or ETIMEDOUT error
test_download('http://www.c9.io:81/test.png', 'fail4.png');

// Should fail with ENOENT because the target filename is invalid
test_download('http://www.google.com/images/srpr/logo3w.png', '');