lnd.xprv/elkrem/serdes.go

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package elkrem
import (
"bytes"
"encoding/binary"
"fmt"
"github.com/roasbeef/btcd/chaincfg/chainhash"
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)
/* Serialization and Deserialization methods for the Elkrem structs.
Senders turn into 41 byte long slices. Receivers are variable length,
with 41 bytes for each stored hash, up to a maximum of 48. Receivers are
prepended with the total number of hashes, so the total max size is 1969 bytes.
*/
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// ToBytes turns the Elkrem Receiver into a bunch of bytes in a slice.
// first the number of nodes (1 byte), then a series of 41 byte long
// serialized nodes, which are 1 byte height, 8 byte index, 32 byte hash.
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func (e *ElkremReceiver) ToBytes() ([]byte, error) {
numOfNodes := uint8(len(e.s))
// 0 element receiver also OK. Just an empty slice.
if numOfNodes == 0 {
return nil, nil
}
if numOfNodes > maxHeight+1 {
return nil, fmt.Errorf("Broken ElkremReceiver has %d nodes, max 64",
len(e.s))
}
var buf bytes.Buffer // create buffer
// write number of nodes (1 byte)
err := binary.Write(&buf, binary.BigEndian, numOfNodes)
if err != nil {
return nil, err
}
for _, node := range e.s {
// write 1 byte height
err = binary.Write(&buf, binary.BigEndian, node.h)
if err != nil {
return nil, err
}
// write 8 byte index
err = binary.Write(&buf, binary.BigEndian, node.i)
if err != nil {
return nil, err
}
if node.sha == nil {
return nil, fmt.Errorf("node %d has nil hash", node.i)
}
// write 32 byte sha hash
n, err := buf.Write(node.sha[:])
if err != nil {
return nil, err
}
if n != 32 { // make sure that was 32 bytes
return nil, fmt.Errorf("%d byte hash, expect 32", n)
}
}
if buf.Len() != (int(numOfNodes)*41)+1 {
return nil, fmt.Errorf("Somehow made wrong size buf, got %d expect %d",
buf.Len(), (numOfNodes*41)+1)
}
return buf.Bytes(), nil
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}
func ElkremReceiverFromBytes(b []byte) (*ElkremReceiver, error) {
var e ElkremReceiver
if len(b) == 0 { // empty receiver, which is OK
return &e, nil
}
buf := bytes.NewBuffer(b)
// read 1 byte number of nodes stored in receiver
numOfNodes, err := buf.ReadByte()
if err != nil {
return nil, err
}
if numOfNodes < 1 || numOfNodes > maxHeight+1 {
return nil, fmt.Errorf("Read invalid number of nodes: %d", numOfNodes)
}
if buf.Len() != (int(numOfNodes) * 41) {
return nil, fmt.Errorf("Remaining buf wrong size, expect %d got %d",
(numOfNodes * 41), buf.Len())
}
e.s = make([]ElkremNode, numOfNodes)
for j, _ := range e.s {
e.s[j].sha = new(chainhash.Hash)
// read 1 byte height
err := binary.Read(buf, binary.BigEndian, &e.s[j].h)
if err != nil {
return nil, err
}
// read 8 byte index
err = binary.Read(buf, binary.BigEndian, &e.s[j].i)
if err != nil {
return nil, err
}
// read 32 byte sha hash
err = e.s[j].sha.SetBytes(buf.Next(32))
if err != nil {
return nil, err
}
// sanity check. Note that this doesn't check that index and height
// match. Could add that but it's slow.
if e.s[j].h > maxHeight { // check for super high nodes
return nil, fmt.Errorf("Read invalid node height %d", e.s[j].h)
}
if e.s[j].i > maxIndex { // check for index higher than height allows
return nil, fmt.Errorf("Node claims index %d; %d max at height %d",
e.s[j].i, maxIndex, e.s[j].h)
}
if j > 0 { // check that node heights are descending
if e.s[j-1].h < e.s[j].h {
return nil, fmt.Errorf("Node heights out of order")
}
}
}
return &e, nil
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}
// ToBytes returns the root of the elkrem sender tree as a byte slice. This
// function is in place to allow one to export the root of the tree. However,
// node that if one uses a deterministic procedure to generate the root, then
// serialization isn't necessary as it can simply be re-derived on the fly.
func (e *ElkremSender) ToBytes() []byte {
return e.root[:]
}