Invertible Bloom Filter-based set reconciliation as described by Eppstein et al. in What's the Difference? Efficient Set Reconciliation without Prior Context.

Implemented over duplex Node.js streams. JavaScript Standard Style.

The example in this README is run as the package's test suite.

var assert = require('assert')
var crypto = require('crypto')
var fromArray = require('from2-array')
var net = require('net') // Over TCP
var reconcile = require('reconcile-sets')

// Create a small data set.
var keys = [
  'January', 'February', 'March', 'April', 'May', 'June',
  'July', 'August', 'September', 'October', 'November', 'December'
]

// The server has some keys, the client has others, and the two share a
// few keys in common.
var serverHas = keys.slice(0, 5)
var bothHave = keys.slice(5, 7)
var clientHas = keys.slice(7)

// Create factory functions that create streams of keys that the server
// and client have.
var streamServerKeys = stream(bothHave.concat(serverHas))
var streamClientKeys = stream(bothHave.concat(clientHas))

// Create a TCP server that responds to reconciliation requests.
var server = net.createServer({allowHalfOpen: true}, function (socket) {
  reconcile.respond(streamServerKeys, socket)
})

// Start the server on a random high port.
server.listen(0, function () {
  var port = this.address().port
  // Connect to the server.
  var options = {port: port, allowHalfOpen: true}
  var socket = net.connect(options, function () {
    // Issue a reconciliation request.
    reconcile.request(
      streamClientKeys, socket,
      function (error, difference) {
        assert.ifError(error)
        assert.deepEqual(
          difference.missing
            .map(arrayBufferToHex)
            .sort(),
          serverHas
            .map(hexDigest)
            .sort(),
          'difference shows keys only server has'
        )
        assert.deepEqual(
          difference.additional
            .map(arrayBufferToHex)
            .sort(),
          clientHas
            .map(hexDigest)
            .sort(),
          'difference shows keys only client has'
        )
        server.close()
      }
    )
  })
})

// Helper Functions

// Turn an array into a stream of ArrayBuffer digests.
function stream (arrayOfStrings) {
  return function () {
    return fromArray.obj(arrayOfStrings.map(binaryDigest))
  }
}

function binaryDigest (string) {
  return digest(string).buffer
}

function hexDigest (string) {
  return digest(string).toString('hex')
}

function arrayBufferToHex (arrayBuffer) {
  return new Buffer(arrayBuffer).toString('hex')
}

function digest (string) {
  return crypto.createHash('sha256')
    .update(string)
    .digest()
}