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lnwallet/commit_sort: add commit sorting with htlc tie breaker

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This commit is contained in:
Conner Fromknecht 2019-06-05 08:34:45 +02:00
parent e6c0ddc825
commit a627c65d65
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GPG Key ID: E7D737B67FA592C7
2 changed files with 367 additions and 0 deletions
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114
lnwallet/commit_sort.go Normal file
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package lnwallet
import (
"bytes"
"sort"
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/btcsuite/btcd/wire"
)
// InPlaceCommitSort performs an in-place sort of a commitment transaction,
// given an unsorted transaction and a list of CLTV values for the HTLCs.
//
// The sort applied is a modified BIP69 sort, that uses the CLTV values of HTLCs
// as a tie breaker in case two HTLC outputs have an identical amount and
// pkscript. The pkscripts can be the same if they share the same payment hash,
// but since the CLTV is enforced via the nLockTime of the second-layer
// transactions, the script does not directly commit to them. Instead, the CLTVs
// must be supplied separately to act as a tie-breaker, otherwise we may produce
// invalid HTLC signatures if the receiver produces an alternative ordering
// during verification.
//
// NOTE: Commitment outputs should have a 0 CLTV corresponding to their index on
// the unsorted commitment transaction.
func InPlaceCommitSort(tx *wire.MsgTx, cltvs []uint32) {
if len(tx.TxOut) != len(cltvs) {
panic("output and cltv list size mismatch")
}
sort.Sort(sortableInputSlice(tx.TxIn))
sort.Sort(sortableCommitOutputSlice{tx.TxOut, cltvs})
}
// sortableInputSlice is a slice of transaction inputs that supports sorting via
// BIP69.
type sortableInputSlice []*wire.TxIn
// Len returns the length of the sortableInputSlice.
//
// NOTE: Part of the sort.Interface interface.
func (s sortableInputSlice) Len() int { return len(s) }
// Swap exchanges the position of inputs i and j.
//
// NOTE: Part of the sort.Interface interface.
func (s sortableInputSlice) Swap(i, j int) {
s[i], s[j] = s[j], s[i]
}
// Less is the BIP69 input comparison function. The sort is first applied on
// input hash (reversed / rpc-style), then index. This logic is copied from
// btcutil/txsort.
//
// NOTE: Part of the sort.Interface interface.
func (s sortableInputSlice) Less(i, j int) bool {
// Input hashes are the same, so compare the index.
ihash := s[i].PreviousOutPoint.Hash
jhash := s[j].PreviousOutPoint.Hash
if ihash == jhash {
return s[i].PreviousOutPoint.Index < s[j].PreviousOutPoint.Index
}
// At this point, the hashes are not equal, so reverse them to
// big-endian and return the result of the comparison.
const hashSize = chainhash.HashSize
for b := 0; b < hashSize/2; b++ {
ihash[b], ihash[hashSize-1-b] = ihash[hashSize-1-b], ihash[b]
jhash[b], jhash[hashSize-1-b] = jhash[hashSize-1-b], jhash[b]
}
return bytes.Compare(ihash[:], jhash[:]) == -1
}
// sortableCommitOutputSlice is a slice of transaction outputs on a commitment
// transaction and the corresponding CLTV values of any HTLCs. Commitment
// outputs should have a CLTV of 0 and the same index in cltvs.
type sortableCommitOutputSlice struct {
txouts []*wire.TxOut
cltvs []uint32
}
// Len returns the length of the sortableCommitOutputSlice.
//
// NOTE: Part of the sort.Interface interface.
func (s sortableCommitOutputSlice) Len() int {
return len(s.txouts)
}
// Swap exchanges the position of outputs i and j, as well as their
// corresponding CLTV values.
//
// NOTE: Part of the sort.Interface interface.
func (s sortableCommitOutputSlice) Swap(i, j int) {
s.txouts[i], s.txouts[j] = s.txouts[j], s.txouts[i]
s.cltvs[i], s.cltvs[j] = s.cltvs[j], s.cltvs[i]
}
// Less is a modified BIP69 output comparison, that sorts based on value, then
// pkscript, then CLTV value.
//
// NOTE: Part of the sort.Interface interface.
func (s sortableCommitOutputSlice) Less(i, j int) bool {
outi, outj := s.txouts[i], s.txouts[j]
if outi.Value != outj.Value {
return outi.Value < outj.Value
}
pkScriptCmp := bytes.Compare(outi.PkScript, outj.PkScript)
if pkScriptCmp != 0 {
return pkScriptCmp < 0
}
return s.cltvs[i] < s.cltvs[j]
}

253
lnwallet/commit_sort_test.go Normal file
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package lnwallet_test
import (
"reflect"
"testing"
"github.com/btcsuite/btcd/wire"
"github.com/lightningnetwork/lnd/lnwallet"
)
type commitSortTest struct {
name string
tx *wire.MsgTx
cltvs []uint32
intrans map[int]int // input transformation
outtrans map[int]int // output transformation
}
func (t *commitSortTest) expTxIns() []*wire.TxIn {
if len(t.intrans) == 0 {
return nil
}
expTxIns := make([]*wire.TxIn, len(t.intrans))
for start, end := range t.intrans {
expTxIns[end] = t.tx.TxIn[start]
}
return expTxIns
}
func (t *commitSortTest) expTxOuts() []*wire.TxOut {
if len(t.outtrans) == 0 {
return nil
}
expTxOuts := make([]*wire.TxOut, len(t.outtrans))
for start, end := range t.outtrans {
expTxOuts[end] = t.tx.TxOut[start]
}
return expTxOuts
}
var commitSortTests = []commitSortTest{
{
name: "sort inputs on prevoutpoint txid",
tx: &wire.MsgTx{
TxIn: []*wire.TxIn{
{
PreviousOutPoint: wire.OutPoint{
Hash: [32]byte{0x01},
},
},
{
PreviousOutPoint: wire.OutPoint{
Hash: [32]byte{0x00},
},
},
},
},
intrans: map[int]int{
0: 1,
1: 0,
},
},
{
name: "sort inputs on prevoutpoint index",
tx: &wire.MsgTx{
TxIn: []*wire.TxIn{
{
PreviousOutPoint: wire.OutPoint{
Index: 1,
},
},
{
PreviousOutPoint: wire.OutPoint{
Index: 0,
},
},
},
},
intrans: map[int]int{
0: 1,
1: 0,
},
},
{
name: "inputs already sorted",
tx: &wire.MsgTx{
TxIn: []*wire.TxIn{
{
PreviousOutPoint: wire.OutPoint{
Index: 0,
},
},
{
PreviousOutPoint: wire.OutPoint{
Index: 1,
},
},
},
},
intrans: map[int]int{
0: 0,
1: 1,
},
},
{
name: "sort outputs on value",
tx: &wire.MsgTx{
TxOut: []*wire.TxOut{
{
Value: 2,
PkScript: []byte{0x0},
},
{
Value: 1,
PkScript: []byte{0x0},
},
},
},
cltvs: []uint32{0, 0},
outtrans: map[int]int{
0: 1,
1: 0,
},
},
{
name: "sort outputs on pkscript",
tx: &wire.MsgTx{
TxOut: []*wire.TxOut{
{
Value: 1,
PkScript: []byte{0x2},
},
{
Value: 1,
PkScript: []byte{0x1},
},
},
},
cltvs: []uint32{0, 0},
outtrans: map[int]int{
0: 1,
1: 0,
},
},
{
name: "sort outputs on cltv",
tx: &wire.MsgTx{
TxOut: []*wire.TxOut{
{
Value: 1,
PkScript: []byte{0x1},
},
{
Value: 1,
PkScript: []byte{0x1},
},
},
},
cltvs: []uint32{2, 1},
outtrans: map[int]int{
0: 1,
1: 0,
},
},
{
name: "sort complex outputs",
tx: &wire.MsgTx{
TxOut: []*wire.TxOut{
{
Value: 100000,
PkScript: []byte{0x01, 0x02},
},
{
Value: 200000,
PkScript: []byte{0x03, 0x02},
},
{
Value: 1000,
PkScript: []byte{0x03},
},
{
Value: 1000,
PkScript: []byte{0x02},
},
{
Value: 1000,
PkScript: []byte{0x1},
},
{
Value: 1000,
PkScript: []byte{0x1},
},
},
},
cltvs: []uint32{0, 0, 100, 90, 70, 80},
outtrans: map[int]int{
0: 4,
1: 5,
2: 3,
3: 2,
4: 0,
5: 1,
},
},
{
name: "outputs already sorted",
tx: &wire.MsgTx{
TxOut: []*wire.TxOut{
{
Value: 1,
PkScript: []byte{0x1},
},
{
Value: 1,
PkScript: []byte{0x1},
},
},
},
cltvs: []uint32{1, 2},
outtrans: map[int]int{
0: 0,
1: 1,
},
},
}
// TestCommitSort asserts that the outputs of a transaction are properly sorted
// using InPlaceCommitSort. The outputs should always be sorted by value, then
// lexicographically by pkscript, and then CLTV value.
func TestCommitSort(t *testing.T) {
for _, test := range commitSortTests {
t.Run(test.name, func(t *testing.T) {
expTxIns := test.expTxIns()
expTxOuts := test.expTxOuts()
lnwallet.InPlaceCommitSort(test.tx, test.cltvs)
if !reflect.DeepEqual(test.tx.TxIn, expTxIns) {
t.Fatalf("commit inputs mismatch, want: %v, "+
"got: %v", expTxIns, test.tx.TxIn)
}
if !reflect.DeepEqual(test.tx.TxOut, expTxOuts) {
t.Fatalf("commit outputs mismatch, want: %v, "+
"got: %v", expTxOuts, test.tx.TxOut)
}
})
}
}