bmt: Binary Merkle Tree Hash (#14334)
bmt is a new package that provides hashers for binary merkle tree hashes on size-limited chunks. the main motivation is that using BMT hash as the chunk hash of the swarm hash offers logsize inclusion proofs for arbitrary files on a 32-byte resolution completely viable to use in challenges on the blockchain.
This commit is contained in:
Viktor Trón
Felix Lange
562
bmt/bmt.go
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562
bmt/bmt.go
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@ -0,0 +1,562 @@
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// Copyright 2017 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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// Package bmt provides a binary merkle tree implementation
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package bmt
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import (
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"fmt"
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"hash"
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"io"
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"strings"
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"sync"
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"sync/atomic"
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)
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/*
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Binary Merkle Tree Hash is a hash function over arbitrary datachunks of limited size
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It is defined as the root hash of the binary merkle tree built over fixed size segments
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of the underlying chunk using any base hash function (e.g keccak 256 SHA3)
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It is used as the chunk hash function in swarm which in turn is the basis for the
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128 branching swarm hash http://swarm-guide.readthedocs.io/en/latest/architecture.html#swarm-hash
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The BMT is optimal for providing compact inclusion proofs, i.e. prove that a
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segment is a substring of a chunk starting at a particular offset
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The size of the underlying segments is fixed at 32 bytes (called the resolution
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of the BMT hash), the EVM word size to optimize for on-chain BMT verification
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as well as the hash size optimal for inclusion proofs in the merkle tree of the swarm hash.
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Two implementations are provided:
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* RefHasher is optimized for code simplicity and meant as a reference implementation
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* Hasher is optimized for speed taking advantage of concurrency with minimalistic
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control structure to coordinate the concurrent routines
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It implements the ChunkHash interface as well as the go standard hash.Hash interface
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*/
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const (
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// DefaultSegmentCount is the maximum number of segments of the underlying chunk
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DefaultSegmentCount = 128 // Should be equal to storage.DefaultBranches
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// DefaultPoolSize is the maximum number of bmt trees used by the hashers, i.e,
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// the maximum number of concurrent BMT hashing operations performed by the same hasher
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DefaultPoolSize = 8
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)
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// BaseHasher is a hash.Hash constructor function used for the base hash of the BMT.
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type BaseHasher func() hash.Hash
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// Hasher a reusable hasher for fixed maximum size chunks representing a BMT
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// implements the hash.Hash interface
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// reuse pool of Tree-s for amortised memory allocation and resource control
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// supports order-agnostic concurrent segment writes
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// as well as sequential read and write
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// can not be called concurrently on more than one chunk
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// can be further appended after Sum
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// Reset gives back the Tree to the pool and guaranteed to leave
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// the tree and itself in a state reusable for hashing a new chunk
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type Hasher struct {
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pool *TreePool // BMT resource pool
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bmt *Tree // prebuilt BMT resource for flowcontrol and proofs
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blocksize int // segment size (size of hash) also for hash.Hash
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count int // segment count
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size int // for hash.Hash same as hashsize
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cur int // cursor position for righmost currently open chunk
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segment []byte // the rightmost open segment (not complete)
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depth int // index of last level
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result chan []byte // result channel
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hash []byte // to record the result
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max int32 // max segments for SegmentWriter interface
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blockLength []byte // The block length that needes to be added in Sum
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}
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// New creates a reusable Hasher
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// implements the hash.Hash interface
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// pulls a new Tree from a resource pool for hashing each chunk
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func New(p *TreePool) *Hasher {
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return &Hasher{
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pool: p,
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depth: depth(p.SegmentCount),
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size: p.SegmentSize,
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blocksize: p.SegmentSize,
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count: p.SegmentCount,
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result: make(chan []byte),
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}
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}
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// Node is a reuseable segment hasher representing a node in a BMT
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// it allows for continued writes after a Sum
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// and is left in completely reusable state after Reset
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type Node struct {
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level, index int // position of node for information/logging only
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initial bool // first and last node
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root bool // whether the node is root to a smaller BMT
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isLeft bool // whether it is left side of the parent double segment
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unbalanced bool // indicates if a node has only the left segment
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parent *Node // BMT connections
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state int32 // atomic increment impl concurrent boolean toggle
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left, right []byte
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}
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// NewNode constructor for segment hasher nodes in the BMT
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func NewNode(level, index int, parent *Node) *Node {
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return &Node{
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parent: parent,
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level: level,
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index: index,
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initial: index == 0,
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isLeft: index%2 == 0,
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}
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}
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// TreePool provides a pool of Trees used as resources by Hasher
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// a Tree popped from the pool is guaranteed to have clean state
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// for hashing a new chunk
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// Hasher Reset releases the Tree to the pool
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type TreePool struct {
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lock sync.Mutex
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c chan *Tree
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hasher BaseHasher
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SegmentSize int
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SegmentCount int
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Capacity int
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count int
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}
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// NewTreePool creates a Tree pool with hasher, segment size, segment count and capacity
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// on GetTree it reuses free Trees or creates a new one if size is not reached
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func NewTreePool(hasher BaseHasher, segmentCount, capacity int) *TreePool {
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return &TreePool{
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c: make(chan *Tree, capacity),
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hasher: hasher,
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SegmentSize: hasher().Size(),
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SegmentCount: segmentCount,
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Capacity: capacity,
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}
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}
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// Drain drains the pool uptil it has no more than n resources
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func (self *TreePool) Drain(n int) {
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self.lock.Lock()
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defer self.lock.Unlock()
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for len(self.c) > n {
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<-self.c
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self.count--
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}
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}
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// Reserve is blocking until it returns an available Tree
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// it reuses free Trees or creates a new one if size is not reached
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func (self *TreePool) Reserve() *Tree {
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self.lock.Lock()
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defer self.lock.Unlock()
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var t *Tree
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if self.count == self.Capacity {
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return <-self.c
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}
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select {
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case t = <-self.c:
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default:
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t = NewTree(self.hasher, self.SegmentSize, self.SegmentCount)
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self.count++
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}
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return t
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}
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// Release gives back a Tree to the pool.
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// This Tree is guaranteed to be in reusable state
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// does not need locking
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func (self *TreePool) Release(t *Tree) {
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self.c <- t // can never fail but...
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}
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// Tree is a reusable control structure representing a BMT
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// organised in a binary tree
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// Hasher uses a TreePool to pick one for each chunk hash
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// the Tree is 'locked' while not in the pool
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type Tree struct {
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leaves []*Node
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}
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// Draw draws the BMT (badly)
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func (self *Tree) Draw(hash []byte, d int) string {
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var left, right []string
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var anc []*Node
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for i, n := range self.leaves {
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left = append(left, fmt.Sprintf("%v", hashstr(n.left)))
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if i%2 == 0 {
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anc = append(anc, n.parent)
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}
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right = append(right, fmt.Sprintf("%v", hashstr(n.right)))
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}
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anc = self.leaves
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var hashes [][]string
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for l := 0; len(anc) > 0; l++ {
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var nodes []*Node
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hash := []string{""}
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for i, n := range anc {
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hash = append(hash, fmt.Sprintf("%v|%v", hashstr(n.left), hashstr(n.right)))
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if i%2 == 0 && n.parent != nil {
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nodes = append(nodes, n.parent)
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}
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}
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hash = append(hash, "")
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hashes = append(hashes, hash)
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anc = nodes
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}
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hashes = append(hashes, []string{"", fmt.Sprintf("%v", hashstr(hash)), ""})
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total := 60
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del := " "
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var rows []string
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for i := len(hashes) - 1; i >= 0; i-- {
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var textlen int
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hash := hashes[i]
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for _, s := range hash {
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textlen += len(s)
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}
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if total < textlen {
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total = textlen + len(hash)
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}
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delsize := (total - textlen) / (len(hash) - 1)
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if delsize > len(del) {
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delsize = len(del)
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}
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row := fmt.Sprintf("%v: %v", len(hashes)-i-1, strings.Join(hash, del[:delsize]))
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rows = append(rows, row)
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}
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rows = append(rows, strings.Join(left, " "))
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rows = append(rows, strings.Join(right, " "))
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return strings.Join(rows, "\n") + "\n"
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}
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// NewTree initialises the Tree by building up the nodes of a BMT
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// segment size is stipulated to be the size of the hash
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// segmentCount needs to be positive integer and does not need to be
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// a power of two and can even be an odd number
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// segmentSize * segmentCount determines the maximum chunk size
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// hashed using the tree
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func NewTree(hasher BaseHasher, segmentSize, segmentCount int) *Tree {
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n := NewNode(0, 0, nil)
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n.root = true
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prevlevel := []*Node{n}
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// iterate over levels and creates 2^level nodes
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level := 1
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count := 2
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for d := 1; d <= depth(segmentCount); d++ {
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nodes := make([]*Node, count)
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for i := 0; i < len(nodes); i++ {
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var parent *Node
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parent = prevlevel[i/2]
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t := NewNode(level, i, parent)
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nodes[i] = t
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}
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prevlevel = nodes
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level++
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count *= 2
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}
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// the datanode level is the nodes on the last level where
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return &Tree{
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leaves: prevlevel,
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}
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}
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// methods needed by hash.Hash
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// Size returns the size
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func (self *Hasher) Size() int {
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return self.size
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}
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// BlockSize returns the block size
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func (self *Hasher) BlockSize() int {
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return self.blocksize
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}
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// Sum returns the hash of the buffer
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// hash.Hash interface Sum method appends the byte slice to the underlying
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// data before it calculates and returns the hash of the chunk
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func (self *Hasher) Sum(b []byte) (r []byte) {
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t := self.bmt
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i := self.cur
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n := t.leaves[i]
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j := i
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// must run strictly before all nodes calculate
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// datanodes are guaranteed to have a parent
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if len(self.segment) > self.size && i > 0 && n.parent != nil {
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n = n.parent
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} else {
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i *= 2
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}
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d := self.finalise(n, i)
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self.writeSegment(j, self.segment, d)
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c := <-self.result
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self.releaseTree()
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// sha3(length + BMT(pure_chunk))
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if self.blockLength == nil {
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return c
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}
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res := self.pool.hasher()
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res.Reset()
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res.Write(self.blockLength)
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res.Write(c)
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return res.Sum(nil)
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}
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// Hasher implements the SwarmHash interface
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// Hash waits for the hasher result and returns it
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// caller must call this on a BMT Hasher being written to
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func (self *Hasher) Hash() []byte {
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return <-self.result
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}
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// Hasher implements the io.Writer interface
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// Write fills the buffer to hash
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// with every full segment complete launches a hasher go routine
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// that shoots up the BMT
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func (self *Hasher) Write(b []byte) (int, error) {
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l := len(b)
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if l <= 0 {
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return 0, nil
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}
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s := self.segment
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i := self.cur
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count := (self.count + 1) / 2
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need := self.count*self.size - self.cur*2*self.size
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size := self.size
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if need > size {
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size *= 2
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}
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if l < need {
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need = l
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}
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// calculate missing bit to complete current open segment
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rest := size - len(s)
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if need < rest {
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rest = need
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}
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s = append(s, b[:rest]...)
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need -= rest
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// read full segments and the last possibly partial segment
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for need > 0 && i < count-1 {
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// push all finished chunks we read
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self.writeSegment(i, s, self.depth)
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need -= size
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if need < 0 {
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size += need
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}
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s = b[rest : rest+size]
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rest += size
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i++
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}
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self.segment = s
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self.cur = i
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// otherwise, we can assume len(s) == 0, so all buffer is read and chunk is not yet full
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return l, nil
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}
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// Hasher implements the io.ReaderFrom interface
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// ReadFrom reads from io.Reader and appends to the data to hash using Write
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// it reads so that chunk to hash is maximum length or reader reaches EOF
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// caller must Reset the hasher prior to call
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func (self *Hasher) ReadFrom(r io.Reader) (m int64, err error) {
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bufsize := self.size*self.count - self.size*self.cur - len(self.segment)
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buf := make([]byte, bufsize)
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var read int
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for {
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var n int
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n, err = r.Read(buf)
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read += n
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if err == io.EOF || read == len(buf) {
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hash := self.Sum(buf[:n])
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if read == len(buf) {
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err = NewEOC(hash)
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}
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break
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}
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if err != nil {
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break
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}
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n, err = self.Write(buf[:n])
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if err != nil {
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break
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}
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}
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return int64(read), err
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}
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// Reset needs to be called before writing to the hasher
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func (self *Hasher) Reset() {
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self.getTree()
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self.blockLength = nil
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}
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// Hasher implements the SwarmHash interface
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// ResetWithLength needs to be called before writing to the hasher
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// the argument is supposed to be the byte slice binary representation of
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// the legth of the data subsumed under the hash
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func (self *Hasher) ResetWithLength(l []byte) {
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self.Reset()
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self.blockLength = l
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}
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// Release gives back the Tree to the pool whereby it unlocks
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// it resets tree, segment and index
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func (self *Hasher) releaseTree() {
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if self.bmt != nil {
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n := self.bmt.leaves[self.cur]
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for ; n != nil; n = n.parent {
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n.unbalanced = false
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if n.parent != nil {
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n.root = false
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}
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}
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self.pool.Release(self.bmt)
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self.bmt = nil
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}
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self.cur = 0
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self.segment = nil
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}
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func (self *Hasher) writeSegment(i int, s []byte, d int) {
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h := self.pool.hasher()
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n := self.bmt.leaves[i]
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if len(s) > self.size && n.parent != nil {
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go func() {
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h.Reset()
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h.Write(s)
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s = h.Sum(nil)
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if n.root {
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self.result <- s
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return
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}
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self.run(n.parent, h, d, n.index, s)
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}()
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return
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}
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go self.run(n, h, d, i*2, s)
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}
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func (self *Hasher) run(n *Node, h hash.Hash, d int, i int, s []byte) {
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isLeft := i%2 == 0
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for {
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if isLeft {
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n.left = s
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} else {
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n.right = s
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}
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if !n.unbalanced && n.toggle() {
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return
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}
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if !n.unbalanced || !isLeft || i == 0 && d == 0 {
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h.Reset()
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h.Write(n.left)
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h.Write(n.right)
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s = h.Sum(nil)
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} else {
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s = append(n.left, n.right...)
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}
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self.hash = s
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if n.root {
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self.result <- s
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return
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}
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isLeft = n.isLeft
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n = n.parent
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i++
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}
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}
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// getTree obtains a BMT resource by reserving one from the pool
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func (self *Hasher) getTree() *Tree {
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if self.bmt != nil {
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return self.bmt
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}
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t := self.pool.Reserve()
|
||||
self.bmt = t
|
||||
return t
|
||||
}
|
||||
|
||||
// atomic bool toggle implementing a concurrent reusable 2-state object
|
||||
// atomic addint with %2 implements atomic bool toggle
|
||||
// it returns true if the toggler just put it in the active/waiting state
|
||||
func (self *Node) toggle() bool {
|
||||
return atomic.AddInt32(&self.state, 1)%2 == 1
|
||||
}
|
||||
|
||||
func hashstr(b []byte) string {
|
||||
end := len(b)
|
||||
if end > 4 {
|
||||
end = 4
|
||||
}
|
||||
return fmt.Sprintf("%x", b[:end])
|
||||
}
|
||||
|
||||
func depth(n int) (d int) {
|
||||
for l := (n - 1) / 2; l > 0; l /= 2 {
|
||||
d++
|
||||
}
|
||||
return d
|
||||
}
|
||||
|
||||
// finalise is following the zigzags on the tree belonging
|
||||
// to the final datasegment
|
||||
func (self *Hasher) finalise(n *Node, i int) (d int) {
|
||||
isLeft := i%2 == 0
|
||||
for {
|
||||
// when the final segment's path is going via left segments
|
||||
// the incoming data is pushed to the parent upon pulling the left
|
||||
// we do not need toogle the state since this condition is
|
||||
// detectable
|
||||
n.unbalanced = isLeft
|
||||
n.right = nil
|
||||
if n.initial {
|
||||
n.root = true
|
||||
return d
|
||||
}
|
||||
isLeft = n.isLeft
|
||||
n = n.parent
|
||||
d++
|
||||
}
|
||||
}
|
||||
|
||||
// EOC (end of chunk) implements the error interface
|
||||
type EOC struct {
|
||||
Hash []byte // read the hash of the chunk off the error
|
||||
}
|
||||
|
||||
// Error returns the error string
|
||||
func (self *EOC) Error() string {
|
||||
return fmt.Sprintf("hasher limit reached, chunk hash: %x", self.Hash)
|
||||
}
|
||||
|
||||
// NewEOC creates new end of chunk error with the hash
|
||||
func NewEOC(hash []byte) *EOC {
|
||||
return &EOC{hash}
|
||||
}
|
||||
Reference in New Issue
Block a user