absoluteUrl middleware in express

origin-middleware.js

/**
 *
 * @description
 * adds an <code>absoluteUrl</code> function on request
 *
 * <pre>
 *    var absoluteUrl = req.absoluteUrl('/myRelativeUrl'); //==> http://my.domain/myRelativeUrl
 * </pre>
 *
 * and variable <code>origin</code> on request which will be equals to <code>http://my.domain</code>
 *
 * @param {object}   req the request
 * @param {object}   res the response
 * @param {function} next next middleware to operate
 */
exports.origin = function origin( req, res, next){
    var _origin = req.protocol + '://' +req.get('Host')  ;
    req.origin = _origin;

    // expects a URL from root "/some/page" which will result in "protocol://host:port/some/page"
    req.absoluteUrl = function( relativeUrl ){
        return _origin + relativeUrl;
    };
    next();
};