channel+cnct: remove preimage from channel and resolution

Now that the success resolver preimage field is always populated by the
incoming contest resolver, preimage lookups earlier in the
process (channel and channel arbitrator) can mostly be removed.

lnwallet/channel.go

@@ -1309,13 +1309,6 @@ type LightningChannel struct {
 	// signatures, of which there may be hundreds.
 	sigPool *SigPool
 
-	// pCache is the global preimage cache shared across all other
-	// LightningChannel instance. We'll use this cache either when we force
-	// close, or we detect that the remote party has force closed. If the
-	// preimage for an incoming HTLC is found in the cache, then we'll try
-	// to claim it on chain.
-	pCache PreimageCache
-
 	// Capacity is the total capacity of this channel.
 	Capacity btcutil.Amount
 
@@ -1368,7 +1361,7 @@ type LightningChannel struct {
 // settled channel state. Throughout state transitions, then channel will
 // automatically persist pertinent state to the database in an efficient
 // manner.
-func NewLightningChannel(signer input.Signer, pCache PreimageCache,
+func NewLightningChannel(signer input.Signer,
 	state *channeldb.OpenChannel,
 	sigPool *SigPool) (*LightningChannel, error) {
 
@@ -1387,7 +1380,6 @@ func NewLightningChannel(signer input.Signer, pCache PreimageCache,
 	lc := &LightningChannel{
 		Signer:            signer,
 		sigPool:           sigPool,
-		pCache:            pCache,
 		currentHeight:     localCommit.CommitHeight,
 		remoteCommitChain: newCommitmentChain(),
 		localCommitChain:  newCommitmentChain(),
@@ -5096,7 +5088,7 @@ type UnilateralCloseSummary struct {
 // which case we will attempt to sweep the non-HTLC output using the passed
 // commitPoint.
 func NewUnilateralCloseSummary(chanState *channeldb.OpenChannel, signer input.Signer,
-	pCache PreimageCache, commitSpend *chainntnfs.SpendDetail,
+	commitSpend *chainntnfs.SpendDetail,
 	remoteCommit channeldb.ChannelCommitment,
 	commitPoint *btcec.PublicKey) (*UnilateralCloseSummary, error) {
 
@@ -5113,7 +5105,6 @@ func NewUnilateralCloseSummary(chanState *channeldb.OpenChannel, signer input.Si
 		SatPerKWeight(remoteCommit.FeePerKw), false, signer,
 		remoteCommit.Htlcs, keyRing, &chanState.LocalChanCfg,
 		&chanState.RemoteChanCfg, *commitSpend.SpenderTxHash,
-		pCache,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("unable to create htlc "+
@@ -5211,11 +5202,11 @@ func NewUnilateralCloseSummary(chanState *channeldb.OpenChannel, signer input.Si
 // using this struct if we need to go on-chain for any reason, or if we detect
 // that the remote party broadcasts their commitment transaction.
 type IncomingHtlcResolution struct {
-	// Preimage is the preimage that will be used to satisfy the contract
-	// of the HTLC.
+	// Preimage is the preimage that will be used to satisfy the contract of
+	// the HTLC.
 	//
-	// NOTE: This field will only be populated if we know the preimage at
-	// the time a unilateral or force close occurs.
+	// NOTE: This field will only be populated in the incoming contest
+	// resolver.
 	Preimage [32]byte
 
 	// SignedSuccessTx is the fully signed HTLC success transaction. This
@@ -5448,7 +5439,7 @@ func newOutgoingHtlcResolution(signer input.Signer, localChanCfg *channeldb.Chan
 func newIncomingHtlcResolution(signer input.Signer, localChanCfg *channeldb.ChannelConfig,
 	commitHash chainhash.Hash, htlc *channeldb.HTLC, keyRing *CommitmentKeyRing,
 	feePerKw SatPerKWeight, dustLimit btcutil.Amount, csvDelay uint32,
-	localCommit bool, preimage [32]byte) (*IncomingHtlcResolution, error) {
+	localCommit bool) (*IncomingHtlcResolution, error) {
 
 	op := wire.OutPoint{
 		Hash:  commitHash,
@@ -5475,7 +5466,6 @@ func newIncomingHtlcResolution(signer input.Signer, localChanCfg *channeldb.Chan
 		// With the script generated, we can completely populated the
 		// SignDescriptor needed to sweep the output.
 		return &IncomingHtlcResolution{
-			Preimage:      preimage,
 			ClaimOutpoint: op,
 			CsvDelay:      csvDelay,
 			SweepSignDesc: input.SignDescriptor{
@@ -5526,10 +5516,12 @@ func newIncomingHtlcResolution(signer input.Signer, localChanCfg *channeldb.Chan
 		InputIndex: 0,
 	}
 
-	// Next, we'll construct the full witness needed to satisfy the input
-	// of the success transaction.
+	// Next, we'll construct the full witness needed to satisfy the input of
+	// the success transaction. Don't specify the preimage yet. The preimage
+	// will be supplied by the contract resolver, either directly or when it
+	// becomes known.
 	successWitness, err := input.ReceiverHtlcSpendRedeem(
-		htlc.Signature, preimage[:], signer, &successSignDesc, successTx,
+		htlc.Signature, nil, signer, &successSignDesc, successTx,
 	)
 	if err != nil {
 		return nil, err
@@ -5554,7 +5546,6 @@ func newIncomingHtlcResolution(signer input.Signer, localChanCfg *channeldb.Chan
 		keyRing.CommitPoint, localChanCfg.DelayBasePoint.PubKey,
 	)
 	return &IncomingHtlcResolution{
-		Preimage:        preimage,
 		SignedSuccessTx: successTx,
 		CsvDelay:        csvDelay,
 		ClaimOutpoint: wire.OutPoint{
@@ -5604,7 +5595,7 @@ func (r *OutgoingHtlcResolution) HtlcPoint() wire.OutPoint {
 func extractHtlcResolutions(feePerKw SatPerKWeight, ourCommit bool,
 	signer input.Signer, htlcs []channeldb.HTLC, keyRing *CommitmentKeyRing,
 	localChanCfg, remoteChanCfg *channeldb.ChannelConfig,
-	commitHash chainhash.Hash, pCache PreimageCache) (*HtlcResolutions, error) {
+	commitHash chainhash.Hash) (*HtlcResolutions, error) {
 
 	// TODO(roasbeef): don't need to swap csv delay?
 	dustLimit := remoteChanCfg.DustLimit
@@ -5628,19 +5619,11 @@ func extractHtlcResolutions(feePerKw SatPerKWeight, ourCommit bool,
 		// If the HTLC is incoming, then we'll attempt to see if we
 		// know the pre-image to the HTLC.
 		if htlc.Incoming {
-			// We'll now query the preimage cache for the preimage
-			// for this HTLC. If it's present then we can fully
-			// populate this resolution.
-			preimage, _ := pCache.LookupPreimage(htlc.RHash)
-
 			// Otherwise, we'll create an incoming HTLC resolution
 			// as we can satisfy the contract.
-			var pre [32]byte
-			copy(pre[:], preimage[:])
 			ihr, err := newIncomingHtlcResolution(
 				signer, localChanCfg, commitHash, &htlc, keyRing,
 				feePerKw, dustLimit, uint32(csvDelay), ourCommit,
-				pre,
 			)
 			if err != nil {
 				return nil, err
@@ -5730,7 +5713,7 @@ func (lc *LightningChannel) ForceClose() (*LocalForceCloseSummary, error) {
 
 	localCommitment := lc.channelState.LocalCommitment
 	summary, err := NewLocalForceCloseSummary(
-		lc.channelState, lc.Signer, lc.pCache, commitTx,
+		lc.channelState, lc.Signer, commitTx,
 		localCommitment,
 	)
 	if err != nil {
@@ -5748,8 +5731,8 @@ func (lc *LightningChannel) ForceClose() (*LocalForceCloseSummary, error) {
 // channel state.  The passed commitTx must be a fully signed commitment
 // transaction corresponding to localCommit.
 func NewLocalForceCloseSummary(chanState *channeldb.OpenChannel, signer input.Signer,
-	pCache PreimageCache, commitTx *wire.MsgTx,
-	localCommit channeldb.ChannelCommitment) (*LocalForceCloseSummary, error) {
+	commitTx *wire.MsgTx, localCommit channeldb.ChannelCommitment) (
+	*LocalForceCloseSummary, error) {
 
 	// Re-derive the original pkScript for to-self output within the
 	// commitment transaction. We'll need this to find the corresponding
@@ -5830,7 +5813,8 @@ func NewLocalForceCloseSummary(chanState *channeldb.OpenChannel, signer input.Si
 	htlcResolutions, err := extractHtlcResolutions(
 		SatPerKWeight(localCommit.FeePerKw), true, signer,
 		localCommit.Htlcs, keyRing, &chanState.LocalChanCfg,
-		&chanState.RemoteChanCfg, txHash, pCache)
+		&chanState.RemoteChanCfg, txHash,
+	)
 	if err != nil {
 		return nil, err
 	}