index.js

const assert = require('assert')
const Buffer = require('safe-buffer').Buffer
const Keccak = require('keccakjs')

// NOTE: it only supports 48 bit lengths
function swarmHashBlock (data, totalLength) {
  var hash = new Keccak(256)
  var tmp = Buffer.alloc(8)
  tmp.writeUIntLE(totalLength, 0, 6)
  hash.update(tmp)
  hash.update(data)
  return Buffer.from(hash.digest('bin'), 'binary')
}

function swarmHash (data) {
  assert(Buffer.isBuffer(data))

  const length = data.length

  if (length <= 4096) {
    return swarmHashBlock(data, length)
  }

  var maxSize = 4096
  while ((maxSize * (4096 / 32)) < length) {
    maxSize *= (4096 / 32)
  }

  var innerNodes = []
  for (var i = 0; i < length; i += maxSize) {
    const size = (maxSize < (length - i)) ? maxSize : (length - i)
    innerNodes.push(swarmHash(data.slice(i, i + size)))
  }
  return swarmHashBlock(Buffer.concat(innerNodes), length)
}

module.exports = swarmHash