merkle-tree-stream

A stream that generates a merkle tree based on the incoming data.

npm install merkle-tree-stream

Usage

var MerkleTreeStream = require('merkle-tree-stream')
var crypto = require('crypto')

var stream = new MerkleTreeStream({
  leaf: function (leaf, roots) {
    // this function should hash incoming data
    // roots in the current partial roots of the merkle tree
    return crypto.createHash('sha256').update(leaf.data).digest()
  },
  parent: function (a, b) {
    // hash two merkle tree node hashes into a new parent hash
    return crypto.createHash('sha256').update(a.hash).update(b.hash).digest()
  }
})

stream.write('hello')
stream.write('hashed')
stream.write('world')

stream.on('data', function (data) {
  console.log(data)
})

Running the above will print

{ index: 0,
  parent: 1,
  hash: ,
  data:  } // 'hello' as buffer
{ index: 2,
  parent: 1,
  hash: ,
  data:  } // 'hashed' as buffer
{ index: 1,
  parent: 3,
  hash: ,
  data: null }
{ index: 4,
  parent: 5,
  hash: ,
  data:  } // 'world' as buffer

index is the tree node index. all even numbers are data nodes (will have a non-null data property).

parent is the index of a tree node's parent node.

hash is the hash of a tree node.

You can always access the current partial roots of the merkle tree by accessing stream.roots. If the number of nodes written to the stream is not a power of 2 then stream.roots will contain more than 1 node (at most log2(number-of-nodes-written)). Otherwise it will contain just a single root.

Optionally you can also pass in an array of roots in the options map as {roots: roots} to continue adding data to a previously generated merkle tree.

Low-level interface

A non stream low-level interface can required by doing require('merkle-tree-stream/generator').

var MerkleGenerator = require('merkle-tree-stream/generator')
var gen = new MerkleGenerator({leaf: ..., parent: ...}) // same options as above

var nodes = gen.next('some data')
console.log(nodes) // returns the tree nodes generated, similar to the stream output
console.log(gen.roots) // contains the current roots nodes

Related

See mafintosh/flat-tree for more information about how node/parent indexes are calculated.

License

MIT