whhyyyyy.js

  /**
   * Problem:
   *
   * 1. Connect determines whether middleware functions are error handlers by
   *    testing their arity. Not cool.
   * 2. Downstream Express users rely upon being able to introspect on their
   *    middleware functions to find specific functions. Sorta less uncool, but
   *    still a pain.
   * 
   * Solution:
   *
   * Use eval. This once. For this one specific purpose. Not anywhere else for 
   * any reason.
   */
  function wrapHandle(handle) {
    // jshint -W061
    var arglist;

    // reiterated: testing function arity is stupid
    switch (handle.length) {
      case 2:
        arglist = '(req, res)';
        break;

      case 3:
        arglist = '(req, res, next)';
        break;

      // don't break other error handlers
      case 4:
        arglist = '(err, req, res, next)';
        break;

      default:
        arglist = '()';
    }
    // I am a bad person and this makes me feel bad
    var wrapped = eval(
      '(function(){return function ' + (handle.name || '') + arglist +
      '{return agent.tracer.callbackProxy(handle).apply(this,arguments);};}())'
    );
    wrapped[ORIGINAL] = handle;

    return wrapped;
  }