example of how to read a fixed size binary prefix to a pull-stream

box-stream-with-nonce.js

var Reader = require('pull-reader')
var box = require('./')
var pCont = require('pull-cont')
var randomBytes = require('crypto').randomBytes
var pull = require('pull-stream')
var Cat = require('pull-cat')

//key is 32 bytes and nonce is 24 bytes, written to start of stream.

exports.unbox = function UnboxStreamWithNonce (key) {

  var reader = Reader(1000) //timeout, 1 second

  //remember, a through pull-stream is a sink stream (takes a "read", calls it)
  return function (read) {
    reader(read)
    //that returns a source stream, return a "read"
    return pCont(function (cb) {
      reader.read(24, function (err, nonce) {
        if(err) return cb(err)

        var source = function (abort, cb) {
          if(abort) reader.abort(abort, cb)
          else reader.read(null, cb)
        }

        cb(null, pull(source, box.createUnboxStream(key, nonce)))
      })
    })
  }
}


exports.box = function (key) {

  var nonce = randomBytes(24)
  return function (read) {
    return Cat([pull.values([nonce]), pull(read, box.createBoxStream(key, nonce))])
  }

}

if(!module.parent) {
  var crypto = require('crypto')
  var toPull = require('stream-to-pull-stream')
  var key = crypto.createHash('sha256').update(process.argv[3]).digest()

  if(!exports[process.argv[2]]) throw new Error('usage: node example.js box|unbox {passwork}')

  var through = exports[process.argv[2]](key)

  pull(
    toPull.source(process.stdin),
    through,
    toPull.sink(process.stdout)
  )

}