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lnwallet: add method to compute output indexes

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This commit adds a new method, findOutputIndexesFromRemote to compute
the our/their output indexes. As we will see in the following commit,
saving these two fields(4+4=8 bytes) will end up saving us some disk
space.
This commit is contained in:
yyforyongyu 2022-04-08 05:37:46 +08:00
parent a129930a95
commit df810114cf
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GPG Key ID: 9BCD95C4FF296868
1 changed files with 75 additions and 0 deletions
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75
lnwallet/commitment.go
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@ -1,11 +1,13 @@
package lnwallet
import (
"bytes"
"fmt"
"github.com/btcsuite/btcd/blockchain"
"github.com/btcsuite/btcd/btcec/v2"
"github.com/btcsuite/btcd/btcutil"
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/btcsuite/btcd/txscript"
"github.com/btcsuite/btcd/wire"
"github.com/lightningnetwork/lnd/channeldb"
@ -960,3 +962,76 @@ func addHTLC(commitTx *wire.MsgTx, ourCommit bool,
return nil
}
// findOutputIndexesFromRemote finds the index of our and their outputs from
// the remote commitment transaction. It derives the key ring to compute the
// output scripts and compares them against the outputs inside the commitment
// to find the match.
func findOutputIndexesFromRemote(revocationPreimage *chainhash.Hash,
chanState *channeldb.OpenChannel) (uint32, uint32, error) {
// Init the output indexes as empty.
ourIndex := uint32(channeldb.OutputIndexEmpty)
theirIndex := uint32(channeldb.OutputIndexEmpty)
chanCommit := chanState.RemoteCommitment
_, commitmentPoint := btcec.PrivKeyFromBytes(revocationPreimage[:])
// With the commitment point generated, we can now derive the king ring
// which will be used to generate the output scripts.
keyRing := DeriveCommitmentKeys(
commitmentPoint, false, chanState.ChanType,
&chanState.LocalChanCfg, &chanState.RemoteChanCfg,
)
// Since it's remote commitment chain, we'd used the mirrored values.
//
// We use the remote's channel config for the csv delay.
theirDelay := uint32(chanState.RemoteChanCfg.CsvDelay)
// If we are the initiator of this channel, then it's be false from the
// remote's PoV.
isRemoteInitiator := !chanState.IsInitiator
var leaseExpiry uint32
if chanState.ChanType.HasLeaseExpiration() {
leaseExpiry = chanState.ThawHeight
}
// Map the scripts from our PoV. When facing a local commitment, the to
// local output belongs to us and the to remote output belongs to them.
// When facing a remote commitment, the to local output belongs to them
// and the to remote output belongs to us.
// Compute the to local script. From our PoV, when facing a remote
// commitment, the to local output belongs to them.
theirScript, err := CommitScriptToSelf(
chanState.ChanType, isRemoteInitiator, keyRing.ToLocalKey,
keyRing.RevocationKey, theirDelay, leaseExpiry,
)
if err != nil {
return ourIndex, theirIndex, err
}
// Compute the to remote script. From our PoV, when facing a remote
// commitment, the to remote output belongs to us.
ourScript, _, err := CommitScriptToRemote(
chanState.ChanType, isRemoteInitiator, keyRing.ToRemoteKey,
leaseExpiry,
)
if err != nil {
return ourIndex, theirIndex, err
}
// Now compare the scripts to find our/their output index.
for i, txOut := range chanCommit.CommitTx.TxOut {
switch {
case bytes.Equal(txOut.PkScript, ourScript.PkScript):
ourIndex = uint32(i)
case bytes.Equal(txOut.PkScript, theirScript.PkScript):
theirIndex = uint32(i)
}
}
return ourIndex, theirIndex, nil
}