package lnwallet import ( "bytes" "container/list" "fmt" "sync" "github.com/btcsuite/fastsha256" "github.com/davecgh/go-spew/spew" "github.com/lightningnetwork/lnd/chainntfs" "github.com/lightningnetwork/lnd/channeldb" "github.com/lightningnetwork/lnd/lnwire" "github.com/roasbeef/btcd/btcec" "github.com/roasbeef/btcd/txscript" "github.com/roasbeef/btcd/wire" "github.com/roasbeef/btcutil" "github.com/roasbeef/btcutil/txsort" ) var zeroHash wire.ShaHash var ( ErrChanClosing = fmt.Errorf("channel is being closed, operation disallowed") ) const ( // MaxPendingPayments is the max number of pending HTLC's permitted on // a channel. // TODO(roasbeef): make not random value + enforce // * should be tuned to account for max tx "cost" MaxPendingPayments = 100 // InitialRevocationWindow is the number of unrevoked commitment // transactions allowed within the commitment chain. This value allows // a greater degree of desynchronization by allowing either parties to // extend the other's commitment chain non-interactively, and also // serves as a flow control mechanism to a degree. InitialRevocationWindow = 4 ) // channelState is an enum like type which represents the current state of a // particular channel. // TODO(roasbeef): actually update state type channelState uint8 const ( // channelPending indicates this channel is still going through the // funding workflow, and isn't yet open. channelPending channelState = 1 // channelOpen represents an open, active channel capable of // sending/receiving HTLCs. channelOpen // channelClosing represents a channel which is in the process of being // closed. channelClosing // channelClosed represents a channel which has been fully closed. Note // that before a channel can be closed, ALL pending HTLC's must be // settled/removed. channelClosed // channelDispute indicates that an un-cooperative closure has been // detected within the channel. channelDispute // channelPendingPayment indicates that there a currently outstanding // HTLC's within the channel. channelPendingPayment ) // PaymentHash represents the sha256 of a random value. This hash is used to // uniquely track incoming/outgoing payments within this channel, as well as // payments requested by the wallet/daemon. type PaymentHash [32]byte // UpdateType is the exact type of an entry within the shared HTLC log. type updateType uint8 const ( Add updateType = iota Timeout Settle ) // PaymentDescriptor represents a commitment state update which either adds, // settles, or removes an HTLC. PaymentDescriptors encapsulate all necessary // meta-data w.r.t to an HTLC, and additional data pairing a settle message to // the original added HTLC. type PaymentDescriptor struct { // TODO(roasbeef): LogEntry interface?? sync.RWMutex // RHash is the payment hash for this HTLC. The HTLC can be settled iff // the preimage to this hash is presented. RHash PaymentHash // Timeout is the absolute timeout in blocks, afterwhich this HTLC // expires. Timeout uint32 // Amount is the HTLC amount in satoshis. Amount btcutil.Amount // IsIncoming denotes if this is an incoming HTLC add/settle/timeout. IsIncoming bool // Index is the log entry number that his HTLC update has within the // log. Depending on if IsIncoming is true, this is either an entry the // remote party added, or one that we added locally. Index uint32 // Payload is an opaque blob which is used to complete multi-hop routing. Payload []byte // Type denotes the exact type of the PaymentDescriptor. In the case of // a Timeout, or Settle type, then the Parent field will point into the // log to the HTLC being modified. entryType updateType // Parent is a pointer to the parent HTLC being modified // (timedout/settled) if the Type of this PaymentDescriptor isn't Add. // This pointer is used when determining which HTLC should be included // within a new commitment, and during log compaction to remove the // modified HTLC along with the Timeout/Settle entry. parent *list.Element // addCommitHeight[Remote|Local] encodes the height of the commitment // which included this HTLC on either the remote or local commitment // chain. This value is used to determine when an HTLC is fully // "locked-in". addCommitHeightRemote uint64 addCommitHeightLocal uint64 /// removeCommitHeight[Remote|Local] encodes the height of the //commitment which removed the parent pointer of this PaymentDescriptor //either due to a timeout or a settle. Once both these heights are //above the tail of both chains, the log entries can safely be removed. removeCommitHeightRemote uint64 removeCommitHeightLocal uint64 // isForwarded denotes if an incoming HTLC has been forwarded to any // possible upstream peers in the route. isForwarded bool settled bool } // commitment represents a commitment to a new state within an active channel. // New commitments can be initiated by either side. Commitments are ordered // into a commitment chain, with one existing for both parties. Each side can // independatly extend the other side's commitment chain, up to a certain // "revocation window", which once reached, dissallows new commitments until // the local nodes receives the revocation for the remote node's chain tail. type commitment struct { // height represents the commitment height of this commitment, or the // update number of this commitment. height uint64 // [our|their]MessageIndex are indexes into the HTLC log, up to which // this commitment transaction includes. These indexes allow both sides // to independantly, and concurrent send create new commitments. Each // new commitment sent to the remote party includes an index in the // shared log which details which of their updates we're including in // this new commitment. // TODO(roasbeef): also make uint64? ourMessageIndex uint32 theirMessageIndex uint32 // txn is the commitment transaction generated by including any HTLC // updates whose index are below the two indexes listed above. If this // commitment is being added to the remote chain, then this txn is // their version of the commitment transactions. If the local commit // chain is being modified, the opposite is true. txn *wire.MsgTx // sig is a signature for the above commitment transaction. sig []byte // [our|their]Balance represents the settled balances at this point // within the commitment chain. This balance is computed by properly // evaluating all the add/remove/settle log entries before the listed // indexes. ourBalance btcutil.Amount theirBalance btcutil.Amount } // commitmentChain represents a chain of unrevoked commitments. The tail of the // chain is the latest fully signed, yet unrevoked commitment. Two chains are // tracked, one for the local node, and another for the remote node. New // commitmetns we create locally extend the remote node's chain, and vice // versa. Commitment chains are allowed to grow to a bounded length, after // which the tail needs to be "dropped" before new commitments can be received. // The tail is "dropped" when the owner of the chain sends a revocation for the // previous tail. type commitmentChain struct { // commitments is a linked list of commitments to new states. New // commitments are added to the end of the chain with increase height. // Once a commitment transaction is revoked, the tail is incremented, // freeing up the revocation window for new commitments. commitments *list.List // startingHeight is the starting height of this commitment chain on a // session basis. startingHeight uint64 } // newCommitmentChain creates a new commitment chain from an initial height. func newCommitmentChain(initialHeight uint64) *commitmentChain { return &commitmentChain{ commitments: list.New(), startingHeight: initialHeight, } } // addCommitment extends the commitment chain by a single commitment. This // added commitment represents a state update propsed by either party. Once the // commitment prior to this commitment is revoked, the commitment becomes the // new defacto state within the channel. func (s *commitmentChain) addCommitment(c *commitment) { s.commitments.PushBack(c) } // advanceTail reduces the length of the commitment chain by one. The tail of // the chain should be advanced once a revocation for the lowest unrevoked // commitment in the chain is received. func (s *commitmentChain) advanceTail() { s.commitments.Remove(s.commitments.Front()) } // tip returns the latest commitment added to the chain. func (s *commitmentChain) tip() *commitment { return s.commitments.Back().Value.(*commitment) } // tail returns the lowest unrevoked commitment transaction in the chain. func (s *commitmentChain) tail() *commitment { return s.commitments.Front().Value.(*commitment) } // LightningChannel implements the state machine which corresponds to the // current commitment protocol wire spec. The state machine implemented allows // for asynchronous fully desynchronized, batched+pipelined updates to // commitment transactions allowing for a high degree of non-blocking // bi-directional payment throughput. // // In order to allow updates to be fully non-blocking, either side is able to // create multiple new commitment states up to a pre-determined window size. // This window size is encoded within InitialRevocationWindow. Before the start // of a session, both side should send out revocation messages with nil // preimages in order to populate their revocation window for the remote party. // Ths method .ExtendRevocationWindow() is used to extend the revocation window // by a single revocation. // // The state machine has for main methods: // * .SignNextCommitment() // * Called one one wishes to sign the next commitment, either initiating a // new state update, or responding to a received commitment. /// * .ReceiveNewCommitment() // * Called upon receipt of a new commitment from the remote party. If the // new commitment is valid, then a revocation should immediately be // generated and sent. // * .RevokeCurrentCommitment() // * Revokes the current commitment. Should be called directly after // receiving a new commitment. // * .ReceiveRevocation() // * Processes a revocation from the remote party. If successful creates a // new defacto broadcastable state. // // See the individual comments within the above methods for further details. type LightningChannel struct { // TODO(roasbeef): temporarily replace wallet with either goroutine or // BlockChainIO interface? Later once all signing is done through // wallet can add back. lnwallet *LightningWallet channelEvents chainntnfs.ChainNotifier sync.RWMutex ourLogIndex uint32 theirLogIndex uint32 status channelState // currentHeight is the current height of our local commitment chain. // This is also the same as the number of updates to the channel we've // accepted. currentHeight uint64 // revocationWindowEdge is the edge of the current revocation window. // New revocations for prior states created by this channel extend the // edge of this revocation window. The existence of a revocation window // allows the remote party to initiate new state updates independantly // until the window is exhausted. revocationWindowEdge uint64 // usedRevocations is a slice of revocations given to us by the remote // party that we've used. This slice is extended each time we create a // new commitment. The front of the slice is popped off once we receive // a revocation for a prior state. This head element then becomes the // next set of keys/hashes we expect to be revoked. usedRevocations []*lnwire.CommitRevocation // revocationWindow is a window of revocations sent to use by the // remote party, allowing us to create new commitment transactions // until depleated. The revocations don't contain a valid pre-iamge, // only an additional key/hash allowing us to create a new commitment // transaction for the remote node that they are able to revoke. If // this slice is empty, then we cannot make any new updates to their // commitment chain. revocationWindow []*lnwire.CommitRevocation // remoteCommitChain is the remote node's commitment chain. Any new // commitments we initiate are added to the tip of this chain. remoteCommitChain *commitmentChain // localCommitChain is our local commitment chain. Any new commitments // received are added to the tip of this chain. The tail (or lowest // height) in this chain is our current accepted state, which we are // able to broadcast safely. localCommitChain *commitmentChain // stateMtx protects concurrent access to the state struct. stateMtx sync.RWMutex channelState *channeldb.OpenChannel // stateUpdateLog is a (mostly) append-only log storing all the HTLC // updates to this channel. The log is walked backwards as HTLC updates // are applied in order to re-construct a commitment transaction from a // commitment. The log is compacted once a revocation is received. stateUpdateLog *list.List // logIndex is an index into the above log. This index is used to // remove Add state updates, once a timeout/settle is received. logIndex map[uint32]*list.Element fundingTxIn *wire.TxIn fundingP2WSH []byte channelDB *channeldb.DB started int32 shutdown int32 quit chan struct{} wg sync.WaitGroup } // NewLightningChannel creates a new, active payment channel given an // implementation of the wallet controller, chain notifier, channel database, // and the current settled channel state. Throughout state transitions, then // channel will automatically persist pertinent state to the database in an // efficient manner. func NewLightningChannel(wallet *LightningWallet, events chainntnfs.ChainNotifier, chanDB *channeldb.DB, state *channeldb.OpenChannel) (*LightningChannel, error) { // TODO(roasbeef): remove events+wallet lc := &LightningChannel{ lnwallet: wallet, channelEvents: events, currentHeight: state.NumUpdates, remoteCommitChain: newCommitmentChain(state.NumUpdates), localCommitChain: newCommitmentChain(state.NumUpdates), channelState: state, revocationWindowEdge: state.NumUpdates, stateUpdateLog: list.New(), logIndex: make(map[uint32]*list.Element), channelDB: chanDB, } // Initialize both of our chains the current un-revoked commitment for // each side. initialCommitment := &commitment{ height: lc.currentHeight, ourBalance: state.OurBalance, ourMessageIndex: 0, theirBalance: state.TheirBalance, theirMessageIndex: 0, } lc.localCommitChain.addCommitment(initialCommitment) lc.remoteCommitChain.addCommitment(initialCommitment) // TODO(roasbeef): do a NotifySpent for the funding input, and // NotifyReceived for all commitment outputs. fundingPkScript, err := witnessScriptHash(state.FundingRedeemScript) if err != nil { return nil, err } lc.fundingTxIn = wire.NewTxIn(state.FundingOutpoint, nil, nil) lc.fundingP2WSH = fundingPkScript return lc, nil } // getCommitedHTLCs returns all HTLCs which are currently fully committed, // meaning they are present at the commitment which is at the tip of the // local+remote commitment chains. func (lc *LightningChannel) getCommitedHTLCs() []*PaymentDescriptor { var activeHtlcs []*PaymentDescriptor remoteChainTail := lc.remoteCommitChain.tail().height localChainTail := lc.localCommitChain.tail().height for e := lc.stateUpdateLog.Front(); e != nil; e = e.Next() { htlc := e.Value.(*PaymentDescriptor) // TODO(roasbeef): should only look at the updates in our log? // If the state update isn't a timeout, or settle, then it may // not be considered an active HTLC. if htlc.entryType != Add { continue } // If the height of the tail of both the local, and // remote commitment chains are above the height we // both committed to the HTLC in our chains, then the // HTLC is considered fully active/locked. if remoteChainTail >= htlc.addCommitHeightRemote && localChainTail >= htlc.addCommitHeightLocal { activeHtlcs = append(activeHtlcs, htlc) } } return activeHtlcs } // fetchHTLCView returns all the candidate HTLC updates which should be // considered for inclusion within a commitment based on the passed HTLC log // indexes. func (lc *LightningChannel) fetchHTLCView(theirLogIndex, ourLogIndex uint32) []*PaymentDescriptor { var activeHtlcs []*PaymentDescriptor for e := lc.stateUpdateLog.Front(); e != nil; e = e.Next() { htlc := e.Value.(*PaymentDescriptor) if htlc.IsIncoming && htlc.Index <= theirLogIndex { // If this is an incoming HTLC, then it is only active from // this point-of-view if the index of the HTLC addition in // their log is below the specified view index. activeHtlcs = append(activeHtlcs, htlc) } else if htlc.Index <= ourLogIndex { // Otherwise, this HTLC is active from this // point-of-view iff the log index of the state // update is below the specified index in our // update log. activeHtlcs = append(activeHtlcs, htlc) } } return activeHtlcs } // fetchCommitmentView returns a populated commitment which expresses the state // of the channel from the point of view of a local or remote chain, evaluating // the HTLC log up to the passed indexes. This function is used to construct // both local and remote commitment transactions in order to sign or verify new // commitment updates. A fully populated commitment is returned which reflects // the proper balances for both sides at this point in the commitment chain. func (lc *LightningChannel) fetchCommitmentView(remoteChain bool, ourLogIndex, theirLogIndex uint32, revocationKey *btcec.PublicKey, revocationHash [32]byte) (*commitment, error) { var commitChain *commitmentChain if remoteChain { commitChain = lc.remoteCommitChain } else { commitChain = lc.localCommitChain } // TODO(roasbeef): don't assume view is always fetched from tip? var ourBalance, theirBalance btcutil.Amount if commitChain.tip() == nil { ourBalance = lc.channelState.OurBalance theirBalance = lc.channelState.TheirBalance } else { ourBalance = commitChain.tip().ourBalance theirBalance = commitChain.tip().theirBalance } // Run through all the HTLC's that will be covered by this transaction // in order to update their commitment addition height, and to adjust // the balances on the commitment transaction accordingly. // TODO(roasbeef): error if log empty? skip := make(map[PaymentHash]struct{}) nextHeight := commitChain.tip().height + 1 logViewEntries := lc.fetchHTLCView(theirLogIndex, ourLogIndex) htlcs := make([]*PaymentDescriptor, 0, len(logViewEntries)) for i := len(logViewEntries) - 1; i >= 0; i-- { logEntry := logViewEntries[i] if _, ok := skip[logEntry.RHash]; ok { continue } if processLogEntry(skip, logEntry, &ourBalance, &theirBalance, ourLogIndex, theirLogIndex, nextHeight, remoteChain) { htlcs = append(htlcs, logEntry) } } var selfKey *btcec.PublicKey var remoteKey *btcec.PublicKey var delay uint32 var delayBalance, p2wkhBalance btcutil.Amount if remoteChain { selfKey = lc.channelState.TheirCommitKey remoteKey = lc.channelState.OurCommitKey.PubKey() delay = lc.channelState.RemoteCsvDelay delayBalance = theirBalance p2wkhBalance = ourBalance } else { selfKey = lc.channelState.OurCommitKey.PubKey() remoteKey = lc.channelState.TheirCommitKey delay = lc.channelState.LocalCsvDelay delayBalance = ourBalance p2wkhBalance = theirBalance } // Generate a new commitment transaction with all the latest // unsettled/un-timed out HTLC's. ourCommitTx := !remoteChain commitTx, err := createCommitTx(lc.fundingTxIn, selfKey, remoteKey, revocationKey, delay, delayBalance, p2wkhBalance) if err != nil { return nil, err } for _, htlc := range htlcs { if err := lc.addHTLC(commitTx, ourCommitTx, htlc, revocationHash, delay); err != nil { return nil, err } } // Sort the transactions according to the agreed upon cannonical // ordering. This lets us skip sending the entire transaction over, // instead we'll just send signatures. txsort.InPlaceSort(commitTx) return &commitment{ txn: commitTx, height: nextHeight, ourBalance: ourBalance, ourMessageIndex: ourLogIndex, theirMessageIndex: theirLogIndex, theirBalance: theirBalance, }, nil } // processLogEntry processes a log entry within the HTLC log. Processes entries // either add new HTLCs to the commitment which weren't present in prior // commitments, or remove a commited HTLC which is being settled or timedout. // In either case, the change of balances are applied via the pointers to the // balances passed in. In the case of a removal, the skip map is populated with // the hash of the HTLC which should be excluded from the commitment // transaction. func processLogEntry(skip map[PaymentHash]struct{}, htlc *PaymentDescriptor, ourBalance, theirBalance *btcutil.Amount, ourLogIndex, theirLogIndex uint32, nextHeight uint64, remoteChain bool) bool { if htlc.entryType == Add { processAddEntry(htlc, ourBalance, theirBalance, nextHeight, ourLogIndex, theirLogIndex, remoteChain) return true } // Otherwise, this is a log entry that aims to modify/remove an // existing entry. We add it's "parent" to the skip map since this // entry removes an earlier log entry in order to avoid adding it to // the current commitment transaction. parent := htlc.parent.Value.(*PaymentDescriptor) skip[parent.RHash] = struct{}{} processRemoveEntry(htlc, ourBalance, theirBalance, nextHeight, ourLogIndex, theirLogIndex, remoteChain) return false } // processAddEntry evalualtes the effect of an add entry within the HTLC log. // If the HTLC hasn't yet been committed in either chain, then the height it // was commited is updated. Keeping track of this inclusion height allows us to // later compact the log once the change is fully committed in both chains. func processAddEntry(htlc *PaymentDescriptor, ourBalance, theirBalance *btcutil.Amount, nextHeight uint64, ourLogIndex, theirLogIndex uint32, remoteChain bool) { // If we're evaluating this entry for the remote chain (to create/view // a new commitment), then we'll may be updating the height this entry // was added to the chain. Otherwise, we may be updating the entry's // height w.r.t the local chain. var addHeight *uint64 if remoteChain { addHeight = &htlc.addCommitHeightRemote } else { addHeight = &htlc.addCommitHeightLocal } if *addHeight != 0 { return } if htlc.IsIncoming { // If this is a new incoming (un-committed) HTLC, then we need // to update their balance accordingly by subtracting the // amount of the HTLC that are funds pending. *theirBalance -= htlc.Amount } else { // Similarly, we need to debit our balance if this is anout // going HTLC to reflect the pending balance. *ourBalance -= htlc.Amount } *addHeight = nextHeight } // processRemoveEntry processes a log entry which settles or timesout a // previously added HTLC. If the removal entry has already been processed, it // is skipped. func processRemoveEntry(htlc *PaymentDescriptor, ourBalance, theirBalance *btcutil.Amount, nextHeight uint64, ourLogIndex, theirLogIndex uint32, remoteChain bool) { var removeHeight *uint64 if remoteChain { removeHeight = &htlc.removeCommitHeightRemote } else { removeHeight = &htlc.removeCommitHeightLocal } // Ignore any removal entries which have already been processed. if *removeHeight != 0 { return } switch { // If an incoming HTLC is being settled, then this means that we've // received the preimage either from another sub-system, or the // upstream peer in the route. Therefore, we increase our balance by // the HTLC amount. case htlc.IsIncoming && htlc.entryType == Settle: *ourBalance += htlc.Amount // Otherwise, this HTLC is being timed out, therefore the value of the // HTLC should return to the remote party. case htlc.IsIncoming && htlc.entryType == Timeout: *theirBalance += htlc.Amount // If an outgoing HTLC is being settled, then this means that the // downstream party resented the preimage or learned of it via a // downstream peer. In either case, we credit their settled value with // the value of the HTLC. case !htlc.IsIncoming && htlc.entryType == Settle: *theirBalance += htlc.Amount // Otherwise, one of our outgoing HTLC's has timed out, so the value of // the HTLC should be returned to our settled balance. case !htlc.IsIncoming && htlc.entryType == Timeout: *ourBalance += htlc.Amount } *removeHeight = nextHeight } // SignNextCommitment signs a new commitment which includes any previous // unsettled HTLCs, any new HTLCs, and any modifications to prior HTLCs // committed in previous commitment updates. Signing a new commitment // decrements the available revocation window by 1. After a successful method // call, the remote party's commitment chain is extended by a new commitment // which includes all updates to the HTLC log prior to this method invocation. func (lc *LightningChannel) SignNextCommitment() ([]byte, uint32, error) { // Ensure that we have enough unused revocation hashes given to us by the // remote party. If the set is empty, then we're unable to create a new // state unless they first revoke a prior commitment transaction. if len(lc.revocationWindow) == 0 || len(lc.usedRevocations) == InitialRevocationWindow { // TODO(rosbeef): better error message return nil, 0, fmt.Errorf("unable to sign new commitment, " + "revocation window exausted") } // Grab the next revocation hash and key to use for this new commitment // transaction, if no errors occur then this revocation tuple will be // moved to the used set. nextRevocation := lc.revocationWindow[0] remoteRevocationKey := nextRevocation.NextRevocationKey remoteRevocationHash := nextRevocation.NextRevocationHash // Create a new commitment view which will calculate the evaluated // state of the remote node's new commitment including our latest added // HTLC's. The view includes the latest balances for both sides on the // remote node's chain, and also update the addition height of any new // HTLC log entries. newCommitView, err := lc.fetchCommitmentView(true, lc.ourLogIndex, lc.theirLogIndex, remoteRevocationKey, remoteRevocationHash) if err != nil { return nil, 0, err } log.Tracef("ChannelPoint(%v): extending remote chain to height %v", lc.channelState.ChanID, newCommitView.height) log.Tracef("ChannelPoint(%v): remote chain: our_balance=%v, "+ "their_balance=%v, commit_tx: %v", lc.channelState.ChanID, newCommitView.ourBalance, newCommitView.theirBalance, spew.Sdump(newCommitView.txn)) // Sign their version of the new commitment transaction. hashCache := txscript.NewTxSigHashes(newCommitView.txn) sig, err := txscript.RawTxInWitnessSignature(newCommitView.txn, hashCache, 0, int64(lc.channelState.Capacity), lc.channelState.FundingRedeemScript, txscript.SigHashAll, lc.channelState.OurMultiSigKey) if err != nil { return nil, 0, err } // Extend the remote commitment chain by one with the addition of our // latest commitment update. lc.remoteCommitChain.addCommitment(newCommitView) // Move the now used revocation hash from the unused set to the used set. // We only do this at the end, as we know at this point the procedure will // succeed without any errors. lc.usedRevocations = append(lc.usedRevocations, nextRevocation) lc.revocationWindow[0] = nil // Avoid a GC leak. lc.revocationWindow = lc.revocationWindow[1:] // Strip off the sighash flag on the signature in order to send it over // the wire. return sig[:len(sig)], lc.theirLogIndex, nil } // ReceiveNewCommitment processs a signature for a new commitment state sent by // the remote party. This method will should be called in response to the // remote party initiating a new change, or when the remote party sends a // signature fully accepting a new state we've initiated. If we are able to // succesfully validate the signature, then the generated commitment is added // to our local commitment chain. Once we send a revocation for our prior // state, then this newly added commitment becomes our current accepted channel // state. func (lc *LightningChannel) ReceiveNewCommitment(rawSig []byte, ourLogIndex uint32) error { theirCommitKey := lc.channelState.TheirCommitKey theirMultiSigKey := lc.channelState.TheirMultiSigKey // We're receiving a new commitment which attemps to extend our local // commitment chain height by one, so fetch the proper revocation to // derive the key+hash needed to construct the new commitment view and // state. nextHeight := lc.currentHeight + 1 revocation, err := lc.channelState.LocalElkrem.AtIndex(nextHeight) if err != nil { return err } revocationKey := deriveRevocationPubkey(theirCommitKey, revocation[:]) revocationHash := fastsha256.Sum256(revocation[:]) // With the revocation information calculated, construct the new // commitment view which includes all the entries we know of in their // HTLC log, and up to ourLogIndex in our HTLC log. localCommitmentView, err := lc.fetchCommitmentView(false, ourLogIndex, lc.theirLogIndex, revocationKey, revocationHash) if err != nil { return err } log.Tracef("ChannelPoint(%v): extending local chain to height %v", lc.channelState.ChanID, localCommitmentView.height) log.Tracef("ChannelPoint(%v): local chain: our_balance=%v, "+ "their_balance=%v, commit_tx: %v", lc.channelState.ChanID, localCommitmentView.ourBalance, localCommitmentView.theirBalance, spew.Sdump(localCommitmentView.txn)) // Construct the sighash of the commitment transaction corresponding to // this newly proposed state update. localCommitTx := localCommitmentView.txn multiSigScript := lc.channelState.FundingRedeemScript hashCache := txscript.NewTxSigHashes(localCommitTx) sigHash, err := txscript.CalcWitnessSigHash(multiSigScript, hashCache, txscript.SigHashAll, localCommitTx, 0, int64(lc.channelState.Capacity)) if err != nil { // TODO(roasbeef): fetchview has already mutated the htlc's... // * need to either roll-back, or make pure return err } // Ensure that the newly constructed commitment state has a valid // signature. sig, err := btcec.ParseSignature(rawSig, btcec.S256()) if err != nil { return err } else if !sig.Verify(sigHash, theirMultiSigKey) { return fmt.Errorf("invalid commitment signature") } // The signature checks out, so we can now add the new commitment to // our local commitment chain. localCommitmentView.sig = rawSig lc.localCommitChain.addCommitment(localCommitmentView) return nil } // RevokeCurrentCommitment revokes the next lowest unrevoked commitment // transaction in the local commitment chain. As a result the edge of our // revocation window is extended by one, and the tail of our local commitment // chain is advanced by a single commitment. This now lowest unrevoked // commitment becomes our currently accepted state within the channel. func (lc *LightningChannel) RevokeCurrentCommitment() (*lnwire.CommitRevocation, error) { theirCommitKey := lc.channelState.TheirCommitKey // Now that we've accept a new state transition, we send the remote // party the revocation for our current commitment state. revocationMsg := &lnwire.CommitRevocation{} currentRevocation, err := lc.channelState.LocalElkrem.AtIndex(lc.currentHeight) if err != nil { return nil, err } copy(revocationMsg.Revocation[:], currentRevocation[:]) // Along with this revocation, we'll also send an additional extension // to our revocation window to the remote party. lc.revocationWindowEdge++ revocationEdge, err := lc.channelState.LocalElkrem.AtIndex(lc.revocationWindowEdge) if err != nil { return nil, err } revocationMsg.NextRevocationKey = deriveRevocationPubkey(theirCommitKey, revocationEdge[:]) revocationMsg.NextRevocationHash = fastsha256.Sum256(revocationEdge[:]) log.Tracef("ChannelPoint(%v): revoking height=%v, now at height=%v, window_edge=%v", lc.channelState.ChanID, lc.localCommitChain.tail().height, lc.currentHeight+1, lc.revocationWindowEdge) // Advance our tail, as we've revoked our previous state. lc.localCommitChain.advanceTail() lc.currentHeight++ // TODO(roasbeef): update sent/received. tail := lc.localCommitChain.tail() lc.channelState.OurCommitTx = tail.txn lc.channelState.OurBalance = tail.ourBalance lc.channelState.TheirBalance = tail.theirBalance lc.channelState.OurCommitSig = tail.sig lc.channelState.NumUpdates++ log.Tracef("ChannelPoint(%v): state transition accepted: "+ "our_balance=%v, their_balance=%v", lc.channelState.ChanID, tail.ourBalance, tail.theirBalance) // TODO(roasbeef): use RecordChannelDelta once fin if err := lc.channelState.FullSync(); err != nil { return nil, err } revocationMsg.ChannelPoint = lc.channelState.ChanID return revocationMsg, nil } // ReceiveRevocation processes a revocation sent by the remote party for the // lowest unrevoked commitment within their commitment chain. We receive a // revocation either during the initial session negotiation wherein revocation // windows are extended, or in response to a state update that we initiate. If // successful, then the remote commitment chain is advanced by a single // commitment, and a log compaction is attempted. In addition, a slice of // HTLC's which can be forwarded upstream are returned. func (lc *LightningChannel) ReceiveRevocation(revMsg *lnwire.CommitRevocation) ([]*PaymentDescriptor, error) { // The revocation has a nil (zero) pre-image, then this should simply be // added to the end of the revocation window for the remote node. if bytes.Equal(zeroHash[:], revMsg.Revocation[:]) { lc.revocationWindow = append(lc.revocationWindow, revMsg) return nil, nil } ourCommitKey := lc.channelState.OurCommitKey currentRevocationKey := lc.channelState.TheirCurrentRevocation pendingRevocation := wire.ShaHash(revMsg.Revocation) // Ensure the new pre-image fits in properly within the elkrem receiver // tree. If this fails, then all other checks are skipped. // TODO(rosbeef): abstract into func remoteElkrem := lc.channelState.RemoteElkrem if err := remoteElkrem.AddNext(&pendingRevocation); err != nil { return nil, err } // Verify that the revocation public key we can derive using this // pre-image and our private key is identical to the revocation key we // were given for their current (prior) commitment transaction. revocationPriv := deriveRevocationPrivKey(ourCommitKey, pendingRevocation[:]) if !revocationPriv.PubKey().IsEqual(currentRevocationKey) { return nil, fmt.Errorf("revocation key mismatch") } // Additionally, we need to ensure we were given the proper pre-image // to the revocation hash used within any current HTLC's. if !bytes.Equal(lc.channelState.TheirCurrentRevocationHash[:], zeroHash[:]) { revokeHash := fastsha256.Sum256(pendingRevocation[:]) // TODO(roasbeef): rename to drop the "Their" if !bytes.Equal(lc.channelState.TheirCurrentRevocationHash[:], revokeHash[:]) { return nil, fmt.Errorf("revocation hash mismatch") } } // Advance the head of the revocation queue now that this revocation has // been verified. Additionally, extend the end of our unused revocation // queue with the newly extended revocation window update. nextRevocation := lc.usedRevocations[0] lc.channelState.TheirCurrentRevocation = nextRevocation.NextRevocationKey lc.channelState.TheirCurrentRevocationHash = nextRevocation.NextRevocationHash lc.usedRevocations[0] = nil // Prevent GC leak. lc.usedRevocations = lc.usedRevocations[1:] lc.revocationWindow = append(lc.revocationWindow, revMsg) log.Tracef("ChannelPoint(%v): remote party accepted state transition, "+ "revoked height %v, now at %v", lc.channelState.ChanID, lc.remoteCommitChain.tail().height, lc.remoteCommitChain.tail().height+1) // At this point, the revocation has been accepted, and we've rotated // the current revocation key+hash for the remote party. Therefore we // sync now to ensure the elkrem receiver state is consistent with the // current commitment height. if err := lc.channelState.SyncRevocation(); err != nil { return nil, err } // Since they revoked the current lowest height in their commitment // chain, we can advance their chain by a single commitment. lc.remoteCommitChain.advanceTail() remoteChainTail := lc.remoteCommitChain.tail().height localChainTail := lc.localCommitChain.tail().height // Now that we've verified the revocation update the state of the HTLC // log as we may be able to prune portions of it now, and update their // balance. // TODO(roasbeef): move this out to another func? // * .CompactLog() var next *list.Element var htlcsToForward []*PaymentDescriptor for e := lc.stateUpdateLog.Front(); e != nil; e = next { next = e.Next() htlc := e.Value.(*PaymentDescriptor) if htlc.entryType != Add { // If this entry is either a timeout or settle, then we // can remove it from our log once the update it locked // into both of our chains. if remoteChainTail >= htlc.removeCommitHeightRemote && localChainTail >= htlc.removeCommitHeightLocal { parentLink := htlc.parent lc.stateUpdateLog.Remove(e) lc.stateUpdateLog.Remove(parentLink) } } else if !htlc.isForwarded { // Once an HTLC has been fully locked into both of our // chains, then we can safely forward it to the next // hop. // TODO(roasbeef): only incoming htcls? // * re-visit once multi-hop from jcp if remoteChainTail >= htlc.addCommitHeightRemote && localChainTail >= htlc.addCommitHeightLocal { htlc.isForwarded = true htlcsToForward = append(htlcsToForward, htlc) } } } return htlcsToForward, nil } // ExtendRevocationWindow extends our revocation window by a single revocation, // increasing the number of new commitment updates the remote party can // initiate without our cooperation. func (lc *LightningChannel) ExtendRevocationWindow() (*lnwire.CommitRevocation, error) { /// TODO(roasbeef): error if window edge differs from tail by more than // InitialRevocationWindow revMsg := &lnwire.CommitRevocation{} revMsg.ChannelPoint = lc.channelState.ChanID nextHeight := lc.revocationWindowEdge + 1 revocation, err := lc.channelState.LocalElkrem.AtIndex(nextHeight) if err != nil { return nil, err } theirCommitKey := lc.channelState.TheirCommitKey revMsg.NextRevocationKey = deriveRevocationPubkey(theirCommitKey, revocation[:]) revMsg.NextRevocationHash = fastsha256.Sum256(revocation[:]) lc.revocationWindowEdge++ return revMsg, nil } // AddPayment adds a new HTLC to either the local or remote HTLC log depending // on the value of 'incoming'. func (lc *LightningChannel) AddHTLC(htlc *lnwire.HTLCAddRequest, incoming bool) error { pd := &PaymentDescriptor{ entryType: Add, RHash: PaymentHash(htlc.RedemptionHashes[0]), Timeout: htlc.Expiry, Amount: btcutil.Amount(htlc.Amount), IsIncoming: incoming, } var index uint32 if !incoming { index = lc.ourLogIndex lc.ourLogIndex++ } else { index = lc.theirLogIndex lc.theirLogIndex++ } pd.Index = index lc.stateUpdateLog.PushBack(pd) return nil } // SettleHTLC attempts to settle an existing outstanding HTLC with an htlc // settle request. When settling incoming HTLC's the value of incoming should // be false, when receiving a settlement to a previously outgoing HTLC, then // the value of incoming should be true. If the settlement fails due to an // invalid preimage, then an error is returned. func (lc *LightningChannel) SettleHTLC(preimage [32]byte, incoming bool) (uint32, error) { var targetHTLC *list.Element // TODO(roasbeef): optimize paymentHash := fastsha256.Sum256(preimage[:]) for e := lc.stateUpdateLog.Back(); e != nil; e = e.Next() { htlc := e.Value.(*PaymentDescriptor) if htlc.entryType != Add { continue } if bytes.Equal(htlc.RHash[:], paymentHash[:]) && !htlc.settled { htlc.settled = true targetHTLC = e break } } if targetHTLC == nil { return 0, fmt.Errorf("invalid payment hash") } parentPd := targetHTLC.Value.(*PaymentDescriptor) // TODO(roasbeef): maybe make the log entries an interface? pd := &PaymentDescriptor{} pd.IsIncoming = parentPd.IsIncoming pd.Amount = parentPd.Amount pd.parent = targetHTLC pd.entryType = Settle var index uint32 if !incoming { index = lc.ourLogIndex lc.ourLogIndex++ } else { index = lc.theirLogIndex lc.theirLogIndex++ } pd.Index = index lc.stateUpdateLog.PushBack(pd) return targetHTLC.Value.(*PaymentDescriptor).Index, nil } // TimeoutHTLC... func (lc *LightningChannel) TimeoutHTLC() error { return nil } // ChannelPoint returns the outpoint of the original funding transaction which // created this active channel. This outpoint is used throughout various // sub-systems to uniquely identify an open channel. func (lc *LightningChannel) ChannelPoint() *wire.OutPoint { return lc.channelState.ChanID } // addHTLC adds a new HTLC to the passed commitment transaction. One of four // full scripts will be generated for the HTLC output depending on if the HTLC // is incoming and if it's being applied to our commitment transaction or that // of the remote node's. func (lc *LightningChannel) addHTLC(commitTx *wire.MsgTx, ourCommit bool, paymentDesc *PaymentDescriptor, revocation [32]byte, delay uint32) error { localKey := lc.channelState.OurCommitKey.PubKey() remoteKey := lc.channelState.TheirCommitKey timeout := paymentDesc.Timeout rHash := paymentDesc.RHash // Generate the proper redeem scripts for the HTLC output modified by // two-bits denoting if this is an incoming HTLC, and if the HTLC is // being applied to their commitment transaction or ours. var pkScript []byte var err error switch { // The HTLC is paying to us, and being applied to our commitment // transaction. So we need to use the receiver's version of HTLC the // script. case paymentDesc.IsIncoming && ourCommit: pkScript, err = receiverHTLCScript(timeout, delay, remoteKey, localKey, revocation[:], rHash[:]) // We're being paid via an HTLC by the remote party, and the HTLC is // being added to their commitment transaction, so we use the sender's // version of the HTLC script. case paymentDesc.IsIncoming && !ourCommit: pkScript, err = senderHTLCScript(timeout, delay, remoteKey, localKey, revocation[:], rHash[:]) // We're sending an HTLC which is being added to our commitment // transaction. Therefore, we need to use the sender's version of the // HTLC script. case !paymentDesc.IsIncoming && ourCommit: pkScript, err = senderHTLCScript(timeout, delay, localKey, remoteKey, revocation[:], rHash[:]) // Finally, we're paying the remote party via an HTLC, which is being // added to their commitment transaction. Therefore, we use the // receiver's version of the HTLC script. case !paymentDesc.IsIncoming && !ourCommit: pkScript, err = receiverHTLCScript(timeout, delay, localKey, remoteKey, revocation[:], rHash[:]) } if err != nil { return err } // Now that we have the redeem scripts, create the P2WSH public key // script for the output itself. htlcP2WSH, err := witnessScriptHash(pkScript) if err != nil { return err } // Add the new HTLC outputs to the respective commitment transactions. amountPending := int64(paymentDesc.Amount) commitTx.AddTxOut(wire.NewTxOut(amountPending, htlcP2WSH)) return nil } // ForceClose... func (lc *LightningChannel) ForceClose() error { return nil } // InitCooperativeClose initiates a cooperative closure of an active lightning // channel. This method should only be executed once all pending HTLCs (if any) // on the channel have been cleared/removed. Upon completion, the source channel // will shift into the "closing" state, which indicates that all incoming/outgoing // HTLC requests should be rejected. A signature for the closing transaction, // and the txid of the closing transaction are returned. The initiator of the // channel closure should then watch the blockchain for a confirmation of the // closing transaction before considering the channel terminated. In the case // of an unresponsive remote party, the initiator can either choose to execute // a force closure, or backoff for a period of time, and retry the cooperative // closure. // TODO(roasbeef): caller should initiate signal to reject all incoming HTLCs, // settle any inflight. func (lc *LightningChannel) InitCooperativeClose() ([]byte, *wire.ShaHash, error) { lc.Lock() defer lc.Unlock() // TODO(roasbeef): coarser graiend locking // If we're already closing the channel, then ignore this request. if lc.status == channelClosing || lc.status == channelClosed { // TODO(roasbeef): check to ensure no pending payments return nil, nil, ErrChanClosing } // Otherwise, indicate in the channel status that a channel closure has // been initiated. lc.status = channelClosing // TODO(roasbeef): assumes initiator pays fees closeTx := createCooperativeCloseTx(lc.fundingTxIn, lc.channelState.OurBalance, lc.channelState.TheirBalance, lc.channelState.OurDeliveryScript, lc.channelState.TheirDeliveryScript, true) closeTxSha := closeTx.TxSha() // Finally, sign the completed cooperative closure transaction. As the // initiator we'll simply send our signature over the the remote party, // using the generated txid to be notified once the closure transaction // has been confirmed. hashCache := txscript.NewTxSigHashes(closeTx) closeSig, err := txscript.RawTxInWitnessSignature(closeTx, hashCache, 0, int64(lc.channelState.Capacity), lc.channelState.FundingRedeemScript, txscript.SigHashAll, lc.channelState.OurMultiSigKey) if err != nil { return nil, nil, err } return closeSig, &closeTxSha, nil } // CompleteCooperativeClose completes the cooperative closure of the target // active lightning channel. This method should be called in response to the // remote node initating a cooperative channel closure. A fully signed closure // transaction is returned. It is the duty of the responding node to broadcast // a signed+valid closure transaction to the network. func (lc *LightningChannel) CompleteCooperativeClose(remoteSig []byte) (*wire.MsgTx, error) { lc.Lock() defer lc.Unlock() // TODO(roasbeef): coarser graiend locking // If we're already closing the channel, then ignore this request. if lc.status == channelClosing || lc.status == channelClosed { // TODO(roasbeef): check to ensure no pending payments return nil, ErrChanClosing } lc.status = channelClosed // Create the transaction used to return the current settled balance // on this active channel back to both parties. In this current model, // the initiator pays full fees for the cooperative close transaction. closeTx := createCooperativeCloseTx(lc.fundingTxIn, lc.channelState.OurBalance, lc.channelState.TheirBalance, lc.channelState.OurDeliveryScript, lc.channelState.TheirDeliveryScript, false) // With the transaction created, we can finally generate our half of // the 2-of-2 multi-sig needed to redeem the funding output. redeemScript := lc.channelState.FundingRedeemScript hashCache := txscript.NewTxSigHashes(closeTx) closeSig, err := txscript.RawTxInWitnessSignature(closeTx, hashCache, 0, int64(lc.channelState.Capacity), redeemScript, txscript.SigHashAll, lc.channelState.OurMultiSigKey) if err != nil { return nil, err } // Finally, construct the witness stack minding the order of the // pubkeys+sigs on the stack. ourKey := lc.channelState.OurMultiSigKey.PubKey().SerializeCompressed() theirKey := lc.channelState.TheirMultiSigKey.SerializeCompressed() witness := spendMultiSig(redeemScript, ourKey, closeSig, theirKey, remoteSig) closeTx.TxIn[0].Witness = witness // TODO(roasbeef): VALIDATE return closeTx, nil } // DeleteState deletes all state concerning the channel from the underlying // database, only leaving a small summary describing meta-data of the // channel's lifetime. func (lc *LightningChannel) DeleteState() error { return lc.channelState.CloseChannel() } // StateSnapshot returns a snapshot b func (lc *LightningChannel) StateSnapshot() *channeldb.ChannelSnapshot { lc.stateMtx.RLock() defer lc.stateMtx.RUnlock() return lc.channelState.Snapshot() } // createCommitTx creates a commitment transaction, spending from specified // funding output. The commitment transaction contains two outputs: one paying // to the "owner" of the commitment transaction which can be spent after a // relative block delay or revocation event, and the other paying the the // counter-party within the channel, which can be spent immediately. func createCommitTx(fundingOutput *wire.TxIn, selfKey, theirKey *btcec.PublicKey, revokeKey *btcec.PublicKey, csvTimeout uint32, amountToSelf, amountToThem btcutil.Amount) (*wire.MsgTx, error) { // First, we create the script for the delayed "pay-to-self" output. // This output has 2 main redemption clauses: either we can redeem the // output after a relative block delay, or the remote node can claim // the funds with the revocation key if we broadcast a revoked // commitment transaction. ourRedeemScript, err := commitScriptToSelf(csvTimeout, selfKey, revokeKey) if err != nil { return nil, err } payToUsScriptHash, err := witnessScriptHash(ourRedeemScript) if err != nil { return nil, err } // Next, we create the script paying to them. This is just a regular // P2WKH output, without any added CSV delay. theirWitnessKeyHash, err := commitScriptUnencumbered(theirKey) if err != nil { return nil, err } // Now that both output scripts have been created, we can finally create // the transaction itself. We use a transaction version of 2 since CSV // will fail unless the tx version is >= 2. commitTx := wire.NewMsgTx() commitTx.Version = 2 commitTx.AddTxIn(fundingOutput) // TODO(roasbeef): don't make 0 BTC output... commitTx.AddTxOut(wire.NewTxOut(int64(amountToSelf), payToUsScriptHash)) commitTx.AddTxOut(wire.NewTxOut(int64(amountToThem), theirWitnessKeyHash)) return commitTx, nil } // createCooperativeCloseTx creates a transaction which if signed by both // parties, then broadcast cooperatively closes an active channel. The creation // of the closure transaction is modified by a boolean indicating if the party // constructing the channel is the initiator of the closure. Currently it is // expected that the initiator pays the transaction fees for the closing // transaction in full. func createCooperativeCloseTx(fundingTxIn *wire.TxIn, ourBalance, theirBalance btcutil.Amount, ourDeliveryScript, theirDeliveryScript []byte, initiator bool) *wire.MsgTx { // Construct the transaction to perform a cooperative closure of the // channel. In the event that one side doesn't have any settled funds // within the channel then a refund output for that particular side can // be omitted. closeTx := wire.NewMsgTx() closeTx.AddTxIn(fundingTxIn) // The initiator the a cooperative closure pays the fee in entirety. // Determine if we're the initiator so we can compute fees properly. if initiator { // TODO(roasbeef): take sat/byte here instead of properly calc ourBalance -= 5000 } else { theirBalance -= 5000 } // TODO(roasbeef): dust check... // * although upper layers should prevent if ourBalance != 0 { closeTx.AddTxOut(&wire.TxOut{ PkScript: ourDeliveryScript, Value: int64(ourBalance), }) } if theirBalance != 0 { closeTx.AddTxOut(&wire.TxOut{ PkScript: theirDeliveryScript, Value: int64(theirBalance), }) } txsort.InPlaceSort(closeTx) return closeTx }