pull-peek/index.js

module.exports = function (first) {

  var end, data, waiting, peeked = false

  return function (read) {

    read(null, function (_end, _data) {
      end = _end; data = _data
      if(first) first(end, data)
      if(waiting) {
        var cb = waiting
        waiting = null
        peeked = true
        cb(end, data)
      }
    })

    return function (_abort, cb) {
      //if the peekahead hasn't returned key.
      if(!(end || data)) {
        abort = _abort
        waiting = cb
      }
      //if it has, but we havn't called back yet.
      else if(!peeked) {
        peeked = true
        cb(end, data)
      }
      //if we are streaming as normal.
      else
        read(_abort, cb)
    }
  }
}