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package main
import (
"encoding/binary"
"os"
"golang.org/x/crypto/sha3"
)
const hashSize int64 = 32
type Merkle interface {
Build() []byte
Put(id int64, data []byte)
Read(buf []byte, id int64)
Size() int64
Proof(id int64) [][]byte
}
func NewMerkle(mtype string, height int64, fname string) Merkle {
var m Merkle
switch mtype {
case "bfs":
m = NewBFSMerkle(height, fname)
case "post":
m = NewPostMerkle(height, fname)
}
return m
}
func ChildrenId(m Merkle, id int64) (id1, id2 int64) {
id2 = (id + 1) * 2
id1 = id2 - 1
return id1, id2
}
func Children(child1, child2 []byte, id int64, m Merkle) {
id1, id2 := ChildrenId(m, id)
m.Read(child1, id1)
m.Read(child2, id2)
}
func Init(m Merkle) {
h := sha3.New256()
hsize := h.Size()
buf := make([]byte, hsize)
for id := m.Size() / 2; id <= m.Size(); id++ {
h.Reset()
binary.Write(h, binary.LittleEndian, id)
buf = h.Sum(buf[:0])
m.Put(id, buf)
}
}
// nodes are stored in BFS order, root node first
type BFSMerkle struct {
height int64
file *os.File
size int64
}
func NewBFSMerkle(height int64, fname string) *BFSMerkle {
file, err := os.Create(fname)
if err != nil {
panic(err)
}
size := int64(1)<<uint64(height) - 2
return &BFSMerkle{height: height, file: file, size: size}
}
func (m *BFSMerkle) Size() int64 {
return m.size
}
func (m *BFSMerkle) Put(id int64, data []byte) {
m.file.WriteAt(data, id*hashSize)
}
func (m *BFSMerkle) Read(buf []byte, id int64) {
m.file.ReadAt(buf, id*hashSize)
}
// disk access is sequential and mostly backward
func (m *BFSMerkle) Build() []byte {
Init(m)
size := m.Size()
h := sha3.New256()
hsize := h.Size()
child1 := make([]byte, hsize)
child2 := make([]byte, hsize)
buf := make([]byte, hsize)
for id := size/2 - 1; id >= 0; id-- {
Children(child1, child2, id, m)
h.Reset()
h.Write(child1)
h.Write(child2)
buf = h.Sum(buf[:0])
m.Put(id, buf)
}
return buf
}
func (m *BFSMerkle) Proof(id int64) [][]byte {
proof := make([][]byte, m.height)
proof[0] = make([]byte, hashSize)
m.Read(proof[0], id)
for i := 1; id > 0; i++ {
proof[i] = make([]byte, hashSize)
if id&1 == 0 {
m.Read(proof[i], id-1)
} else {
m.Read(proof[i], id+1)
}
id = (id - 1) >> 1
}
return proof
}
// nodes are stored in depth-first post order
type PostMerkle struct {
height int64
file *os.File
size int64
}
func NewPostMerkle(height int64, fname string) *PostMerkle {
file, err := os.Create(fname)
if err != nil {
panic(err)
}
size := int64(1)<<uint64(height) - 2
return &PostMerkle{height: height, file: file, size: size}
}
func (m *PostMerkle) Size() int64 {
return m.size
}
func (m *PostMerkle) Put(id int64, data []byte) {
pos := Post(m.size, m.height, id)
m.file.WriteAt(data, pos*hashSize)
}
func (m *PostMerkle) Read(buf []byte, id int64) {
pos := Post(m.size, m.height, id)
m.file.ReadAt(buf, pos*hashSize)
}
// Iterative post-order depth-first construction of the Merkle tree
// disk access is optimal and forward
func (m *PostMerkle) Build() []byte {
size := m.Size()
h := sha3.New256()
hsize := int64(h.Size())
// pre-allocating the hash stack
stack := make([][]byte, m.height)
for i := 0; i < len(stack); i++ {
stack[i] = make([]byte, hsize)
}
var cur int64 = size / 2 // current node (bfs id)
var count int64 = 0 // post-order id of current node
var l = 0 // length of the stack
for count < size {
if cur >= size/2 { // leaf node
l++
h.Reset()
binary.Write(h, binary.LittleEndian, cur)
h.Sum(stack[l-1][:0])
m.file.WriteAt(stack[l-1], count*hsize)
for cur&1 == 0 && count < size {
// we just completed a right node, moving up to the parent
cur = (cur - 1) >> 1
count++
h.Reset()
h.Write(stack[l-2])
h.Write(stack[l-1])
l-- // pop two items, add one item
h.Sum(stack[l-1][:0])
m.file.WriteAt(stack[l-1], count*hsize)
}
// we just completed a left node, moving to its sibling
cur++
count++
} else {
cur = (cur << 1) + 1 // moving to the left child
}
}
return stack[0]
}
func (m *PostMerkle) Proof(id int64) [][]byte {
// traversing the tree from the root to the leaf reading the siblings along
// the path and filling the proof from right to left
proof := make([][]byte, m.height)
cur := int64(1)<<uint64(m.height) - 2 // post-order id of the current node along the path, starting from the root
size := int64(1) << uint64(m.height-1) // size of a subtree of the current node
mask := size >> 1
id += 1
for i := len(proof) - 1; mask > 0; i-- {
proof[i] = make([]byte, hashSize)
if mask&id > 0 { // leaf is in the right subtree of current node
m.file.ReadAt(proof[i], (cur-size)*hashSize) // reading the left child
cur -= 1 // moving to the right subtree
} else { // left is in the left subtree of current node
m.file.ReadAt(proof[i], (cur-1)*hashSize) // reading the right child
cur -= size // moving the left subtree
}
size = mask
mask >>= 1
}
proof[0] = make([]byte, hashSize)
m.file.ReadAt(proof[0], cur*hashSize)
return proof
}
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