parse-headers.js

var trim = function(string) {
  return string.replace(/^\s+|\s+$/g, '');
}
  , isArray = function(arg) {
      return Object.prototype.toString.call(arg) === '[object Array]';
    }

module.exports = function (headers) {
  if (!headers)
    return {}

  var result = {}

  var headersArr = trim(headers).split('\n')

  for (var i = 0; i < headersArr.length; i++) {
    var row = headersArr[i]
    var index = row.indexOf(':')
    , key = trim(row.slice(0, index)).toLowerCase()
    , value = trim(row.slice(index + 1))

    if (typeof(result[key]) === 'undefined') {
      result[key] = value
    } else if (isArray(result[key])) {
      result[key].push(value)
    } else {
      result[key] = [ result[key], value ]
    }
  }

  return result
}