Default user agent string for Node.js http request
$ npm install default-user-agent
var ua = require('default-user-agent');
// darwin
console.log(ua()); // 'Node.js/0.11.15 (OS X Yosemite; x64)'
console.log(ua('urllib', '0.0.1')); // 'urllib/0.0.1 Node.js/0.11.15 (OS X Yosemite; x64)'
// linux
// 'Node.js/0.11.15 (Linux 3.13; x64)'