node/doc/vendor/path-to-regexp/index.js

var isArray = Array.isArray || function (arr) {
  return Object.prototype.toString.call(arr) == '[object Array]';
};

/**
 * Expose `pathToRegexp`.
 */
// module.exports = pathToRegexp

/**
 * The main path matching regexp utility.
 *
 * @type {RegExp}
 */
var PATH_REGEXP = new RegExp([
  // Match escaped characters that would otherwise appear in future matches.
  // This allows the user to escape special characters that won't transform.
  '(\\\\.)',
  // Match Express-style parameters and un-named parameters with a prefix
  // and optional suffixes. Matches appear as:
  //
  // "/:test(\\d+)?" => ["/", "test", "\d+", undefined, "?"]
  // "/route(\\d+)" => [undefined, undefined, undefined, "\d+", undefined]
  '([\\/.])?(?:\\:(\\w+)(?:\\(((?:\\\\.|[^)])*)\\))?|\\(((?:\\\\.|[^)])*)\\))([+*?])?',
  // Match regexp special characters that are always escaped.
  '([.+*?=^!:${}()[\\]|\\/])'
].join('|'), 'g');

/**
 * Escape the capturing group by escaping special characters and meaning.
 *
 * @param  {String} group
 * @return {String}
 */
function escapeGroup (group) {
  return group.replace(/([=!:$\/()])/g, '\\$1');
}

/**
 * Attach the keys as a property of the regexp.
 *
 * @param  {RegExp} re
 * @param  {Array}  keys
 * @return {RegExp}
 */
function attachKeys (re, keys) {
  re.keys = keys;
  return re;
}

/**
 * Get the flags for a regexp from the options.
 *
 * @param  {Object} options
 * @return {String}
 */
function flags (options) {
  return options.sensitive ? '' : 'i';
}

/**
 * Pull out keys from a regexp.
 *
 * @param  {RegExp} path
 * @param  {Array}  keys
 * @return {RegExp}
 */
function regexpToRegexp (path, keys) {
  // Use a negative lookahead to match only capturing groups.
  var groups = path.source.match(/\((?!\?)/g);

  if (groups) {
    for (var i = 0; i < groups.length; i++) {
      keys.push({
        name:      i,
        delimiter: null,
        optional:  false,
        repeat:    false
      });
    }
  }

  return attachKeys(path, keys);
}

/**
 * Transform an array into a regexp.
 *
 * @param  {Array}  path
 * @param  {Array}  keys
 * @param  {Object} options
 * @return {RegExp}
 */
function arrayToRegexp (path, keys, options) {
  var parts = [];

  for (var i = 0; i < path.length; i++) {
    parts.push(pathToRegexp(path[i], keys, options).source);
  }

  var regexp = new RegExp('(?:' + parts.join('|') + ')', flags(options));
  return attachKeys(regexp, keys);
}

/**
 * Replace the specific tags with regexp strings.
 *
 * @param  {String} path
 * @param  {Array}  keys
 * @return {String}
 */
function replacePath (path, keys) {
  var index = 0;

  function replace (_, escaped, prefix, key, capture, group, suffix, escape) {
    if (escaped) {
      return escaped;
    }

    if (escape) {
      return '\\' + escape;
    }

    var repeat   = suffix === '+' || suffix === '*';
    var optional = suffix === '?' || suffix === '*';

    keys.push({
      name:      key || index++,
      delimiter: prefix || '/',
      optional:  optional,
      repeat:    repeat
    });

    prefix = prefix ? ('\\' + prefix) : '';
    capture = escapeGroup(capture || group || '[^' + (prefix || '\\/') + ']+?');

    if (repeat) {
      capture = capture + '(?:' + prefix + capture + ')*';
    }

    if (optional) {
      return '(?:' + prefix + '(' + capture + '))?';
    }

    // Basic parameter support.
    return prefix + '(' + capture + ')';
  }

  return path.replace(PATH_REGEXP, replace);
}

/**
 * Normalize the given path string, returning a regular expression.
 *
 * An empty array can be passed in for the keys, which will hold the
 * placeholder key descriptions. For example, using `/user/:id`, `keys` will
 * contain `[{ name: 'id', delimiter: '/', optional: false, repeat: false }]`.
 *
 * @param  {(String|RegExp|Array)} path
 * @param  {Array}                 [keys]
 * @param  {Object}                [options]
 * @return {RegExp}
 */
function pathToRegexp (path, keys, options) {
  keys = keys || [];

  if (!isArray(keys)) {
    options = keys;
    keys = [];
  } else if (!options) {
    options = {};
  }

  if (path instanceof RegExp) {
    return regexpToRegexp(path, keys, options);
  }

  if (isArray(path)) {
    return arrayToRegexp(path, keys, options);
  }

  var strict = options.strict;
  var end = options.end !== false;
  var route = replacePath(path, keys);
  var endsWithSlash = path.charAt(path.length - 1) === '/';

  // In non-strict mode we allow a slash at the end of match. If the path to
  // match already ends with a slash, we remove it for consistency. The slash
  // is valid at the end of a path match, not in the middle. This is important
  // in non-ending mode, where "/test/" shouldn't match "/test//route".
  if (!strict) {
    route = (endsWithSlash ? route.slice(0, -2) : route) + '(?:\\/(?=$))?';
  }

  if (end) {
    route += '$';
  } else {
    // In non-ending mode, we need the capturing groups to match as much as
    // possible by using a positive lookahead to the end or next path segment.
    route += strict && endsWithSlash ? '' : '(?=\\/|$)';
  }

  return attachKeys(new RegExp('^' + route, flags(options)), keys);
}