index.js

var uint64be = require('uint64be')
var lru = require('lru')

module.exports = Tree

function Tree (storage, opts) {
  if (!(this instanceof Tree)) return new Tree(storage, opts)
  if (!opts) opts = {}

  this.storage = storage
  this.live = !!opts.live
  this.cache = lru(opts.cacheSize || 512)
}

Tree.prototype.get = function (i, cb) {
  var k = '' + i
  var val = this.cache.get(k)
  if (val) return cb(null, val)

  var leaf = this.live && !(i & 1)
  var offset = 40 * i + 32 * (this.live ? Math.ceil(i / 2) : 0)
  var length = leaf ? 72 : 40
  var self = this

  this.storage.read(offset, length, function (err, buf) {
    if (err) return cb(err)

    var hash = buf.slice(0, 32)
    var size = uint64be.decode(buf, 32)

    if (!size && isNil(hash)) return cb(new Error('Index not found'))

    val = new Node(i, hash, size, leaf ? buf.slice(40) : null)
    self.cache.set(k, val)
    cb(null, val)
  })
}

Tree.prototype.put = function (i, node, cb) {
  if (!cb) cb = noop

  var leaf = this.live && !(i & 1)
  var length = leaf ? 72 : 40
  var offset = 40 * i + 32 * (this.live ? Math.ceil(i / 2) : 0)
  var buf = Buffer(length)

  node.hash.copy(buf, 0)
  uint64be.encode(node.size, buf, 32)
  if (leaf) node.signature.copy(buf, 40)

  this.cache.set('' + i, new Node(i, node.hash, node.size, node.signature || null))
  this.storage.write(offset, buf, cb)
}

function noop () {}

function Node (i, hash, size, sig) {
  this.index = i
  this.hash = hash
  this.size = size
  this.signature = sig
}

function isNil (buf) {
  for (var i = 0; i < buf.length; i++) {
    if (buf[i]) return false
  }
  return true
}