code: function _bytes (n, fn) {
    assert(!this._parserCallback, 'there is already a "callback" set!');
    assert(isFinite(n) && n > 0, 'can only buffer a finite number of bytes > 0, got "' + n + '"');
    if (!this._parserInit) init(this);
    debug('buffering %o bytes', n);
    this._parserBytesLeft = n;
    this._parserCallback = fn;
    this._parserState = BUFFERING;
  }
docs: Buffers `n` bytes and then invokes `fn` once that amount has been collected.
  
  @param {Number} n the number of bytes to buffer
  @param {Function} fn callback function to invoke when `n` bytes are buffered
  @api public