package lnwallet import ( "bytes" "container/list" "fmt" "sync" "sync/atomic" "github.com/btcsuite/fastsha256" "github.com/davecgh/go-spew/spew" "github.com/lightningnetwork/lnd/chainntnfs" "github.com/lightningnetwork/lnd/channeldb" "github.com/lightningnetwork/lnd/lnwire" "github.com/roasbeef/btcd/blockchain" "github.com/roasbeef/btcd/chaincfg/chainhash" "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 chainhash.Hash var ( // ErrChanClosing is returned when a caller attempts to close a channel // that has already been closed or is in the process of being closed. ErrChanClosing = fmt.Errorf("channel is being closed, operation disallowed") // ErrNoWindow is returned when revocation window is exausted. ErrNoWindow = fmt.Errorf("unable to sign new commitment, the current" + " revocation window is exhausted") // ErrMaxWeightCost is returned when the cost/weight (see segwit) // exceeds the widely used maximum allowed policy weight limit. In this // case the commitment transaction can't be propagated through the // network. ErrMaxWeightCost = fmt.Errorf("commitment transaction exceed max " + "available cost") // ErrMaxHTLCNumber is returned when a proposed HTLC would exceed the // maximum number of allowed HTLC's if committed in a state transition ErrMaxHTLCNumber = fmt.Errorf("commitment transaction exceed max " + "htlc number") ) const ( // InitialRevocationWindow is the number of revoked commitment // transactions allowed within the commitment chain. This value allows // a greater degree of de-synchronization 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 = 1 ) // 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 = iota // 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 HTLCs 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 // HTLCs 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 is an update type that adds a new HTLC entry into the log. // Either side can add a new penidng HTLC by adding a new Add entry // into their update log. Add updateType = iota // Fail is an update type which removes a prior HTLC entry from the // log. Adding a Fail entry to ones log will modify the _remote_ // parties update log once a new commitment view has been evaluated // which contains the Fail entry. Fail // Settle is an update type which settles a prior HTLC crediting the // balance of the receiving node. Adding a Settle entry to a log will // result in the settle entry being removed on the log as well as the // original add entry from the remote party's log after the next state // transition. Settle ) // PaymentDescriptor represents a commitment state update which either adds, // settles, or removes an HTLC. PaymentDescriptors encapsulate all necessary // metadata w.r.t to an HTLC, and additional data pairing a settle message to // the original added HTLC. // TODO(roasbeef): LogEntry interface?? // * need to separate attrs for cancel/add/settle type PaymentDescriptor struct { 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 // RPreimage is the preimage that settles the HTLC pointed to wthin the // log by the ParentIndex. RPreimage PaymentHash // Timeout is the absolute timeout in blocks, after which this HTLC // expires. Timeout uint32 // Amount is the HTLC amount in satoshis. Amount btcutil.Amount // 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 uint64 // ParentIndex is the index of the log entry that this HTLC update // settles or times out. ParentIndex uint64 // Payload is an opaque blob which is used to complete multi-hop // routing. Payload []byte // EntryType 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 // 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 // pkScript is the raw public key script that encodes the redemption // rules for this particular HTLC. This field will only be populated // iff the EntryType of this PaymentDescriptor is Add. pkScript []byte } // 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 // independently extend the other side's commitment chain, up to a certain // "revocation window", which once reached, disallows 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 independently, 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. ourMessageIndex uint64 theirMessageIndex uint64 // 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 // htlcs is the set of HTLCs which remain unsettled within this // commitment. outgoingHTLCs []*PaymentDescriptor incomingHTLCs []*PaymentDescriptor } // toChannelDelta converts the target commitment into a format suitable to be // written to disk after an accepted state transition. // TODO(roasbeef): properly fill in refund timeouts func (c *commitment) toChannelDelta() (*channeldb.ChannelDelta, error) { numHtlcs := len(c.outgoingHTLCs) + len(c.incomingHTLCs) delta := &channeldb.ChannelDelta{ LocalBalance: c.ourBalance, RemoteBalance: c.theirBalance, UpdateNum: c.height, Htlcs: make([]*channeldb.HTLC, 0, numHtlcs), } // As we also store the output index of the HTLC for continence // purposes, we create a small helper function to locate the output // index of a particular HTLC within the current commitment // transaction. locateOutputIndex := func(p *PaymentDescriptor) uint16 { var idx uint16 for i, txOut := range c.txn.TxOut { // TODO(roasbeef): duplicated payment hashes... if bytes.Equal(txOut.PkScript, p.pkScript) { idx = uint16(i) break } } return idx } for _, htlc := range c.outgoingHTLCs { h := &channeldb.HTLC{ Incoming: false, Amt: htlc.Amount, RHash: htlc.RHash, RefundTimeout: htlc.Timeout, RevocationDelay: 0, OutputIndex: locateOutputIndex(htlc), } delta.Htlcs = append(delta.Htlcs, h) } for _, htlc := range c.incomingHTLCs { h := &channeldb.HTLC{ Incoming: true, Amt: htlc.Amount, RHash: htlc.RHash, RefundTimeout: htlc.Timeout, RevocationDelay: 0, OutputIndex: locateOutputIndex(htlc), } delta.Htlcs = append(delta.Htlcs, h) } return delta, nil } // 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 // commitments 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) } // updateLog is an append-only log that stores updates to a node's commitment // chain. This structure can be seen as the "mempool" within Lightning where // changes are stored before they're committed to the chain. Once an entry has // been committed in both the local and remote commitment chain, then it can be // removed from this log. // // TODO(roasbeef): create lightning package, move commitment and update to // package? // * also move state machine, separate from lnwallet package // * possible embed updateLog within commitmentChain. type updateLog struct { // logIndex is a monotonically increasing integer that tracks the total // number of update entries ever applied to the log. When sending new // commitment states, we include all updates up to this index. logIndex uint64 // ackIndex is a special "pointer" index into the log that tracks the // position which, up to, all changes have been ACK'd by the remote // party. When receiving new commitment states, we include all of our // updates up to this index to restore the commitment view. ackedIndex uint64 // pendingACKIndex is another special "pointer" index into the log that // tracks our logIndex value right before we extend the remote party's // commitment chain. Once we receive an ACK for this changes, then we // set ackedIndex=pendingAckIndex. // // TODO(roasbeef): eventually expand into list when we go back to a // sliding window format pendingAckIndex uint64 // List is the updatelog itself, we embed this value so updateLog has // access to all the method of a list.List. *list.List // updateIndex is an index that maps a particular entries index to the // list element within the list.List above. updateIndex map[uint64]*list.Element } // newUpdateLog creates a new updateLog instance. func newUpdateLog() *updateLog { return &updateLog{ List: list.New(), updateIndex: make(map[uint64]*list.Element), } } // appendUpdate appends a new update to the tip of the updateLog. The entry is // also added to index accordingly. func (u *updateLog) appendUpdate(pd *PaymentDescriptor) { u.updateIndex[u.logIndex] = u.PushBack(pd) u.logIndex++ } // lookup attempts to look up an update entry according to it's index value. In // the case that the entry isn't found, a nil pointer is returned. func (u *updateLog) lookup(i uint64) *PaymentDescriptor { return u.updateIndex[i].Value.(*PaymentDescriptor) } // remove attempts to remove an entry from the update log. If the entry is // found, then the entry will be removed from the update log and index. func (u *updateLog) remove(i uint64) { entry := u.updateIndex[i] u.Remove(entry) delete(u.updateIndex, i) } // initiateTransition marks that the caller has extended the commitment chain // of the remote party with the contents of the updateLog. This function will // mark the log index value at this point so it can later be marked as ACK'd. func (u *updateLog) initiateTransition() { u.pendingAckIndex = u.logIndex } // ackTransition updates the internal indexes of the updateLog to mark that the // last pending state transition has been accepted by the remote party. To do // so, we mark the prior pendingAckIndex as fully ACK'd. func (u *updateLog) ackTransition() { u.ackedIndex = u.pendingAckIndex u.pendingAckIndex = 0 } // compactLogs performs garbage collection within the log removing HTLCs which // have been removed from the point-of-view of the tail of both chains. The // entries which timeout/settle HTLCs are also removed. func compactLogs(ourLog, theirLog *updateLog, localChainTail, remoteChainTail uint64) { compactLog := func(logA, logB *updateLog) { var nextA *list.Element for e := logA.Front(); e != nil; e = nextA { nextA = e.Next() htlc := e.Value.(*PaymentDescriptor) if htlc.EntryType == Add { continue } // If the HTLC hasn't yet been removed from either // chain, the skip it. if htlc.removeCommitHeightRemote == 0 || htlc.removeCommitHeightLocal == 0 { continue } // Otherwise if the height of the tail of both chains // is at least the height in which the HTLC was // removed, then evict the settle/timeout entry along // with the original add entry. if remoteChainTail >= htlc.removeCommitHeightRemote && localChainTail >= htlc.removeCommitHeightLocal { logA.remove(htlc.Index) logB.remove(htlc.ParentIndex) } } } compactLog(ourLog, theirLog) compactLog(theirLog, ourLog) } // 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 { signer Signer signDesc *SignDescriptor channelEvents chainntnfs.ChainNotifier sync.RWMutex pendingACK bool status channelState // Capcity is the total capacity of this channel. Capacity btcutil.Amount // 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 independently // 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.RevokeAndAck // revocationWindow is a window of revocations sent to use by the // remote party, allowing us to create new commitment transactions // until depleted. The revocations don't contain a valid preimage, // 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.RevokeAndAck // 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 // [local|remote]Log 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. localUpdateLog *updateLog remoteUpdateLog *updateLog // rHashMap is a map with PaymentHashes pointing to their respective // PaymentDescriptors. We insert *PaymentDescriptors whenever we // receive HTLCs. When a state transition happens (settling or // canceling the HTLC), rHashMap will provide an efficient // way to lookup the original PaymentDescriptor. rHashMap map[PaymentHash][]*PaymentDescriptor LocalDeliveryScript []byte RemoteDeliveryScript []byte // FundingWitnessScript is the witness script for the 2-of-2 multi-sig // that opened the channel. FundingWitnessScript []byte fundingTxIn *wire.TxIn fundingP2WSH []byte // ForceCloseSignal is a channel that is closed to indicate that a // local system has initiated a force close by broadcasting the current // commitment transaction directly on-chain. ForceCloseSignal chan struct{} // UnilateralCloseSignal is a channel that is closed to indicate that // the remote party has performed a unilateral close by broadcasting // their version of the commitment transaction on-chain. UnilateralCloseSignal chan struct{} // ContractBreach is a channel that is used to communicate the data // necessary to fully resolve the channel in the case that a contract // breach is detected. A contract breach occurs it is detected that the // counterparty has broadcast a prior *revoked* state. ContractBreach chan *BreachRetribution // LocalFundingKey is the public key under control by the wallet that // was used for the 2-of-2 funding output which created this channel. LocalFundingKey *btcec.PublicKey // RemoteFundingKey is the public key for the remote channel counter // party which used for the 2-of-2 funding output which created this // channel. RemoteFundingKey *btcec.PublicKey shutdown int32 quit chan struct{} } // NewLightningChannel creates a new, active payment channel given an // implementation of the 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(signer Signer, events chainntnfs.ChainNotifier, state *channeldb.OpenChannel) (*LightningChannel, error) { lc := &LightningChannel{ signer: signer, channelEvents: events, currentHeight: state.NumUpdates, remoteCommitChain: newCommitmentChain(state.NumUpdates), localCommitChain: newCommitmentChain(state.NumUpdates), channelState: state, revocationWindowEdge: state.NumUpdates, localUpdateLog: newUpdateLog(), remoteUpdateLog: newUpdateLog(), rHashMap: make(map[PaymentHash][]*PaymentDescriptor), Capacity: state.Capacity, LocalDeliveryScript: state.OurDeliveryScript, RemoteDeliveryScript: state.TheirDeliveryScript, FundingWitnessScript: state.FundingWitnessScript, ForceCloseSignal: make(chan struct{}), UnilateralCloseSignal: make(chan struct{}), ContractBreach: make(chan *BreachRetribution, 1), LocalFundingKey: state.OurMultiSigKey, RemoteFundingKey: state.TheirMultiSigKey, quit: make(chan struct{}), } // Initialize both of our chains the current un-revoked commitment for // each side. // TODO(roasbeef): add chnneldb.RevocationLogTail method, then init // their commitment from that as we may be de-synced initialCommitment := &commitment{ height: lc.currentHeight, ourBalance: state.OurBalance, ourMessageIndex: 0, theirBalance: state.TheirBalance, theirMessageIndex: 0, } lc.localCommitChain.addCommitment(initialCommitment) lc.remoteCommitChain.addCommitment(initialCommitment) // If we're restarting from a channel with history, then restore the // update in-memory update logs to that of the prior state. if lc.currentHeight != 0 { lc.restoreStateLogs() } // Create the sign descriptor which we'll be using very frequently to // request a signature for the 2-of-2 multi-sig from the signer in // order to complete channel state transitions. fundingPkScript, err := witnessScriptHash(state.FundingWitnessScript) if err != nil { return nil, err } lc.fundingTxIn = wire.NewTxIn(state.FundingOutpoint, nil, nil) lc.fundingP2WSH = fundingPkScript lc.signDesc = &SignDescriptor{ PubKey: lc.channelState.OurMultiSigKey, WitnessScript: lc.channelState.FundingWitnessScript, Output: &wire.TxOut{ PkScript: lc.fundingP2WSH, Value: int64(lc.channelState.Capacity), }, HashType: txscript.SigHashAll, InputIndex: 0, } // We'll only launch a close observer if the ChainNotifier // implementation is non-nil. Passing a nil value indicates that the // channel shouldn't be actively watched for. if lc.channelEvents != nil { // Register for a notification to be dispatched if the funding // outpoint has been spent. This indicates that either us or // the remote party has broadcasted a commitment transaction // on-chain. fundingOut := &lc.fundingTxIn.PreviousOutPoint channelCloseNtfn, err := lc.channelEvents.RegisterSpendNtfn(fundingOut) if err != nil { return nil, err } // Launch the close observer which will vigilantly watch the // network for any broadcasts the current or prior commitment // transactions, taking action accordingly. go lc.closeObserver(channelCloseNtfn) } return lc, nil } // BreachRetribution contains all the data necessary to bring a channel // counterparty to justice claiming ALL lingering funds within the channel in // the scenario that they broadcast a revoked commitment transaction. A // BreachRetribution is created by the closeObserver if it detects an // uncooperative close of the channel which uses a revoked commitment // transaction. The BreachRetribution is then sent over the ContractBreach // channel in order to allow the subscriber of the channel to dispatch justice. type BreachRetribution struct { // BreachTransaction is the transaction which breached the channel // contract by spending from the funding multi-sig with a revoked // commitment transaction. BreachTransaction *wire.MsgTx // RevokedStateNum is the revoked state number which was broadcast. RevokedStateNum uint64 // PendingHTLCs is a slice of the HTLCs which were pending at this // point within the channel's history transcript. PendingHTLCs []*channeldb.HTLC // LocalOutputSignDesc is a SignDescriptor which is capable of // generating the signature necessary to sweep the output within the // BreachTransaction that pays directly us. LocalOutputSignDesc *SignDescriptor // LocalOutpoint is the outpoint of the output paying to us (the local // party) within the breach transaction. LocalOutpoint wire.OutPoint // RemoteOutputSignDesc is a SignDescriptor which is capable of // generating the signature required to claim the funds as described // within the revocation clause of the remote party's commitment // output. RemoteOutputSignDesc *SignDescriptor // RemoteOutpoint is the output of the output paying to the remote // party within the breach transaction. RemoteOutpoint wire.OutPoint } // newBreachRetribution creates a new fully populated BreachRetribution for the // passed channel, at a particular revoked state number, and one which targets // the passed commitment transaction. func newBreachRetribution(chanState *channeldb.OpenChannel, stateNum uint64, broadcastCommitment *wire.MsgTx) (*BreachRetribution, error) { commitHash := broadcastCommitment.TxHash() // Query the on-disk revocation log for the snapshot which was recorded // at this particular state num. revokedSnapshot, err := chanState.FindPreviousState(stateNum) if err != nil { return nil, err } // With the state number broadcast known, we can now derive/restore the // proper revocation preimage necessary to sweep the remote party's // output. revocationPreimage, err := chanState.RevocationStore.LookUp(stateNum) if err != nil { return nil, err } // Once we derive the revocation leaf, we can then re-create the // revocation public key used within this state. This is needed in // order to create the proper script below. localCommitKey := chanState.OurCommitKey revocationKey := DeriveRevocationPubkey(localCommitKey, revocationPreimage[:]) remoteCommitkey := chanState.TheirCommitKey remoteDelay := chanState.RemoteCsvDelay // Next, reconstruct the scripts as they were present at this state // number so we can have the proper witness script to sign and include // within the final witness. remotePkScript, err := commitScriptToSelf(remoteDelay, remoteCommitkey, revocationKey) if err != nil { return nil, err } remoteWitnessHash, err := witnessScriptHash(remotePkScript) if err != nil { return nil, err } localPkScript, err := commitScriptUnencumbered(localCommitKey) if err != nil { return nil, err } // In order to fully populate the breach retribution struct, we'll need // to find the exact index of the local+remote commitment outputs. localOutpoint := wire.OutPoint{ Hash: commitHash, } remoteOutpoint := wire.OutPoint{ Hash: commitHash, } for i, txOut := range broadcastCommitment.TxOut { switch { case bytes.Equal(txOut.PkScript, localPkScript): localOutpoint.Index = uint32(i) case bytes.Equal(txOut.PkScript, remoteWitnessHash): remoteOutpoint.Index = uint32(i) } } // Finally, with all the necessary data constructed, we can create the // BreachRetribution struct which houses all the data necessary to // swiftly bring justice to the cheating remote party. return &BreachRetribution{ BreachTransaction: broadcastCommitment, RevokedStateNum: stateNum, PendingHTLCs: revokedSnapshot.Htlcs, LocalOutpoint: localOutpoint, LocalOutputSignDesc: &SignDescriptor{ PubKey: localCommitKey, Output: &wire.TxOut{ PkScript: localPkScript, Value: int64(revokedSnapshot.LocalBalance), }, HashType: txscript.SigHashAll, }, RemoteOutpoint: remoteOutpoint, RemoteOutputSignDesc: &SignDescriptor{ PubKey: localCommitKey, PrivateTweak: revocationPreimage[:], WitnessScript: remotePkScript, Output: &wire.TxOut{ PkScript: remoteWitnessHash, Value: int64(revokedSnapshot.RemoteBalance), }, HashType: txscript.SigHashAll, }, }, nil } // closeObserver is a goroutine which watches the network for any spends of the // multi-sig funding output. A spend from the multi-sig output may occur under // the following three scenarios: a cooperative close, a unilateral close, and // a uncooperative contract breaching close. In the case of the last scenario a // BreachRetribution struct is created and sent over the ContractBreach channel // notifying subscribers that the counterparty has violated the condition of // the channel by broadcasting a revoked prior state. // // NOTE: This MUST be run as a goroutine. func (lc *LightningChannel) closeObserver(channelCloseNtfn *chainntnfs.SpendEvent) { walletLog.Infof("Close observer for ChannelPoint(%v) active", lc.channelState.ChanID) var ( commitSpend *chainntnfs.SpendDetail ok bool ) select { // If the daemon is shutting down, then this notification channel will // be closed, so check the second read-value to avoid a false positive. case commitSpend, ok = <-channelCloseNtfn.Spend: if !ok { return } // Otherwise, we've beeen signalled to bail out early by the // caller/maintainer of this channel. case <-lc.quit: // As we're exiting before the spend notification has been // triggered, we'll cancel the notification intent so the // ChainNotiifer can free up the resources. channelCloseNtfn.Cancel() return } // If we've already initiated a local cooperative or unilateral close // locally, then we have nothing more to do. lc.RLock() if lc.status == channelClosed || lc.status == channelDispute || lc.status == channelClosing { lc.RUnlock() return } lc.RUnlock() lc.Lock() defer lc.Unlock() walletLog.Warnf("Unprompted commitment broadcast for ChannelPoint(%v) "+ "detected!", lc.channelState.ChanID) // Otherwise, the remote party might have broadcast a prior revoked // state...!!! commitTxBroadcast := commitSpend.SpendingTx // Decode the state hint encoded within the commitment transaction to // determine if this is a revoked state or not. obsfucator := lc.channelState.StateHintObsfucator broadcastStateNum := GetStateNumHint(commitTxBroadcast, obsfucator) currentStateNum := lc.currentHeight switch { // If state number spending transaction matches the current latest // state, then they've initiated a unilateral close. So we'll trigger // the unilateral close signal so subscribers can clean up the state as // necessary. // // We'll also handle the case of the remote party broadcasting their // commitment transaction which is one height above ours. This case an // arise when we initiate a state transition, but the remote party has // a fail crash _after_ accepting the new state, but _before_ sending // their signature to us. case broadcastStateNum >= currentStateNum: walletLog.Infof("Unilateral close of ChannelPoint(%v) "+ "detected", lc.channelState.ChanID) // As we've deleted that the channel has been closed, // immediately delete the state from disk, creating a close // summary for future usage by related sub-systems. if err := lc.DeleteState(); err != nil { walletLog.Errorf("unable to delete channel state: %v", err) } // Notify any subscribers that we've detected a unilateral // commitment transaction broadcast. close(lc.UnilateralCloseSignal) // If the state number broadcast is lower than the remote node's // current un-revoked height, then THEY'RE ATTEMPTING TO VIOLATE THE // CONTRACT LAID OUT WITHIN THE PAYMENT CHANNEL. Therefore we close // the signal indicating a revoked broadcast to allow subscribers to // swiftly dispatch justice!!! case broadcastStateNum < currentStateNum: walletLog.Warnf("Remote peer has breached the channel "+ "contract for ChannelPoint(%v). Revoked state #%v was "+ "broadcast!!!", lc.channelState.ChanID, broadcastStateNum) // Create a new reach retribution struct which contains all the // data needed to swiftly bring the cheating peer to justice. retribution, err := newBreachRetribution(lc.channelState, broadcastStateNum, commitTxBroadcast) if err != nil { walletLog.Errorf("unable to create breach retribution: %v", err) return } walletLog.Debugf("Punishment breach retribution created: %v", spew.Sdump(retribution)) // Finally, send the retribution struct over the contract beach // channel to allow the observer the use the breach retribution // to sweep ALL funds. lc.ContractBreach <- retribution } } // Stop gracefully shuts down any active goroutines spawned by the // LightningChannel during regular duties. func (lc *LightningChannel) Stop() { if !atomic.CompareAndSwapInt32(&lc.shutdown, 0, 1) { return } close(lc.quit) } // restoreStateLogs runs through the current locked-in HTLCs from the point of // view of the channel and insert corresponding log entries (both local and // remote) for each HTLC read from disk. This method is required sync the // in-memory state of the state machine with that read from persistent storage. func (lc *LightningChannel) restoreStateLogs() error { var pastHeight uint64 if lc.currentHeight > 0 { pastHeight = lc.currentHeight - 1 } var ourCounter, theirCounter uint64 for _, htlc := range lc.channelState.Htlcs { // TODO(roasbeef): set isForwarded to false for all? need to // persist state w.r.t to if forwarded or not, or can // inadvertently trigger replays pd := &PaymentDescriptor{ RHash: htlc.RHash, Timeout: htlc.RefundTimeout, Amount: htlc.Amt, EntryType: Add, addCommitHeightRemote: pastHeight, addCommitHeightLocal: pastHeight, } if !htlc.Incoming { pd.Index = ourCounter lc.localUpdateLog.appendUpdate(pd) ourCounter++ } else { pd.Index = theirCounter lc.remoteUpdateLog.appendUpdate(pd) lc.rHashMap[pd.RHash] = append(lc.rHashMap[pd.RHash], pd) theirCounter++ } } lc.localCommitChain.tail().ourMessageIndex = ourCounter lc.localCommitChain.tail().theirMessageIndex = theirCounter lc.remoteCommitChain.tail().ourMessageIndex = ourCounter lc.remoteCommitChain.tail().theirMessageIndex = theirCounter return nil } // htlcView represents the "active" HTLCs at a particular point within the // history of the HTLC update log. type htlcView struct { ourUpdates []*PaymentDescriptor theirUpdates []*PaymentDescriptor } // 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 uint64) *htlcView { var ourHTLCs []*PaymentDescriptor for e := lc.localUpdateLog.Front(); e != nil; e = e.Next() { htlc := e.Value.(*PaymentDescriptor) // 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. if htlc.Index < ourLogIndex { ourHTLCs = append(ourHTLCs, htlc) } } var theirHTLCs []*PaymentDescriptor for e := lc.remoteUpdateLog.Front(); e != nil; e = e.Next() { htlc := e.Value.(*PaymentDescriptor) // 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. if htlc.Index < theirLogIndex { theirHTLCs = append(theirHTLCs, htlc) } } return &htlcView{ ourUpdates: ourHTLCs, theirUpdates: theirHTLCs, } } // 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 uint64, 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 } nextHeight := commitChain.tip().height + 1 // Run through all the HTLCs 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? htlcView := lc.fetchHTLCView(theirLogIndex, ourLogIndex) filteredHTLCView := lc.evaluateHTLCView(htlcView, &ourBalance, &theirBalance, nextHeight, remoteChain) var selfKey *btcec.PublicKey var remoteKey *btcec.PublicKey var delay uint32 var delayBalance, p2wkhBalance, dustLimit btcutil.Amount if remoteChain { selfKey = lc.channelState.TheirCommitKey remoteKey = lc.channelState.OurCommitKey delay = lc.channelState.RemoteCsvDelay delayBalance = theirBalance p2wkhBalance = ourBalance dustLimit = lc.channelState.TheirDustLimit } else { selfKey = lc.channelState.OurCommitKey remoteKey = lc.channelState.TheirCommitKey delay = lc.channelState.LocalCsvDelay delayBalance = ourBalance p2wkhBalance = theirBalance dustLimit = lc.channelState.OurDustLimit } // Generate a new commitment transaction with all the latest // unsettled/un-timed out HTLCs. ourCommitTx := !remoteChain commitTx, err := CreateCommitTx(lc.fundingTxIn, selfKey, remoteKey, revocationKey, delay, delayBalance, p2wkhBalance, dustLimit) if err != nil { return nil, err } for _, htlc := range filteredHTLCView.ourUpdates { if htlc.Amount < dustLimit { continue } err := lc.addHTLC(commitTx, ourCommitTx, htlc, revocationHash, delay, false) if err != nil { return nil, err } } for _, htlc := range filteredHTLCView.theirUpdates { if htlc.Amount < dustLimit { continue } err := lc.addHTLC(commitTx, ourCommitTx, htlc, revocationHash, delay, true) if err != nil { return nil, err } } // Set the state hint of the commitment transaction to facilitate // quickly recovering the necessary penalty state in the case of an // uncooperative broadcast. obsfucator := lc.channelState.StateHintObsfucator stateNum := nextHeight if err := SetStateNumHint(commitTx, stateNum, obsfucator); err != nil { return nil, err } // Sort the transactions according to the agreed upon canonical // 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, outgoingHTLCs: filteredHTLCView.ourUpdates, incomingHTLCs: filteredHTLCView.theirUpdates, }, nil } // evaluateHTLCView processes all update entries in both HTLC update logs, // producing a final view which is the result of properly applying all adds, // settles, and timeouts found in both logs. The resulting view returned // reflects the current state of HTLCs within the remote or local commitment // chain. func (lc *LightningChannel) evaluateHTLCView(view *htlcView, ourBalance, theirBalance *btcutil.Amount, nextHeight uint64, remoteChain bool) *htlcView { newView := &htlcView{} // We use two maps, one for the local log and one for the remote log to // keep track of which entries we need to skip when creating the final // htlc view. We skip an entry whenever we find a settle or a timeout // modifying an entry. skipUs := make(map[uint64]struct{}) skipThem := make(map[uint64]struct{}) // First we run through non-add entries in both logs, populating the // skip sets and mutating the current chain state (crediting balances, etc) to // reflect the settle/timeout entry encountered. for _, entry := range view.ourUpdates { if entry.EntryType == Add { continue } // If we're settling in inbound HTLC, and it hasn't been // processed, yet, the increment our state tracking the total // number of satoshis we've received within the channel. if entry.EntryType == Settle && !remoteChain && entry.removeCommitHeightLocal == 0 { lc.channelState.TotalSatoshisReceived += uint64(entry.Amount) } addEntry := lc.remoteUpdateLog.lookup(entry.ParentIndex) skipThem[addEntry.Index] = struct{}{} processRemoveEntry(entry, ourBalance, theirBalance, nextHeight, remoteChain, true) } for _, entry := range view.theirUpdates { if entry.EntryType == Add { continue } // If the remote party is settling one of our outbound HTLC's, // and it hasn't been processed, yet, the increment our state // tracking the total number of satoshis we've sent within the // channel. if entry.EntryType == Settle && !remoteChain && entry.removeCommitHeightLocal == 0 { lc.channelState.TotalSatoshisSent += uint64(entry.Amount) } addEntry := lc.localUpdateLog.lookup(entry.ParentIndex) skipUs[addEntry.Index] = struct{}{} processRemoveEntry(entry, ourBalance, theirBalance, nextHeight, remoteChain, false) } // Next we take a second pass through all the log entries, skipping any // settled HTLCs, and debiting the chain state balance due to any // newly added HTLCs. for _, entry := range view.ourUpdates { isAdd := entry.EntryType == Add if _, ok := skipUs[entry.Index]; !isAdd || ok { continue } processAddEntry(entry, ourBalance, theirBalance, nextHeight, remoteChain, false) newView.ourUpdates = append(newView.ourUpdates, entry) } for _, entry := range view.theirUpdates { isAdd := entry.EntryType == Add if _, ok := skipThem[entry.Index]; !isAdd || ok { continue } processAddEntry(entry, ourBalance, theirBalance, nextHeight, remoteChain, true) newView.theirUpdates = append(newView.theirUpdates, entry) } return newView } // processAddEntry evaluates 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 committed 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, remoteChain bool, isIncoming 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 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 an out // 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, remoteChain bool, isIncoming 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 subsystem, or the // upstream peer in the route. Therefore, we increase our balance by // the HTLC amount. case isIncoming && htlc.EntryType == Settle: *ourBalance += htlc.Amount // Otherwise, this HTLC is being failed out, therefore the value of the // HTLC should return to the remote party. case isIncoming && htlc.EntryType == Fail: *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 !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 !isIncoming && htlc.EntryType == Fail: *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, error) { lc.Lock() defer lc.Unlock() // If we're awaiting an ACK to a commitment signature, then we're // unable to create new states as we don't have any revocations we can // use. if lc.pendingACK { return nil, ErrNoWindow } // 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. // TODO(roasbeef): remove now due to above? if len(lc.revocationWindow) == 0 || len(lc.usedRevocations) == InitialRevocationWindow { return nil, ErrNoWindow } // Before we extend this new commitment to the remote commitment chain, // ensure that we aren't violating any of the constraints the remote // party set up when we initially set up the channel. If we are, then // we'll abort this state transition. err := lc.validateCommitmentSanity(lc.remoteUpdateLog.ackedIndex, lc.localUpdateLog.logIndex, false) if err != nil { return nil, err } // 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 // HTLCs. 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. When we creating a new remote view, we include // _all_ of our changes (pending or committed) but only the remote // node's changes up to the last change we've ACK'd. newCommitView, err := lc.fetchCommitmentView(true, lc.localUpdateLog.logIndex, lc.remoteUpdateLog.ackedIndex, remoteRevocationKey, remoteRevocationHash) if err != nil { return nil, err } walletLog.Tracef("ChannelPoint(%v): extending remote chain to height %v", lc.channelState.ChanID, newCommitView.height) walletLog.Tracef("ChannelPoint(%v): remote chain: our_balance=%v, "+ "their_balance=%v, commit_tx: %v", lc.channelState.ChanID, newCommitView.ourBalance, newCommitView.theirBalance, newLogClosure(func() string { return spew.Sdump(newCommitView.txn) })) // Sign their version of the new commitment transaction. lc.signDesc.SigHashes = txscript.NewTxSigHashes(newCommitView.txn) sig, err := lc.signer.SignOutputRaw(newCommitView.txn, lc.signDesc) if err != nil { return nil, 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:] // As we've just created a new update for the remote commitment chain, // we set the bool indicating that we're waiting for an ACK to our new // changes. lc.pendingACK = true // Additionally, we'll remember our log index at this point, so we can // properly track which changes have been ACK'd. lc.localUpdateLog.initiateTransition() return sig, nil } // validateCommitmentSanity is used to validate that on current state the commitment // transaction is valid in terms of propagating it over Bitcoin network, and // also that all outputs are meet Bitcoin spec requirements and they are // spendable. func (lc *LightningChannel) validateCommitmentSanity(theirLogCounter, ourLogCounter uint64, prediction bool) error { htlcCount := 0 if prediction { htlcCount++ } // Run through all the HTLCs that will be covered by this transaction // in order to calculate theirs count. htlcView := lc.fetchHTLCView(theirLogCounter, ourLogCounter) for _, entry := range htlcView.ourUpdates { if entry.EntryType == Add { htlcCount++ } else { htlcCount-- } } for _, entry := range htlcView.theirUpdates { if entry.EntryType == Add { htlcCount++ } else { htlcCount-- } } if htlcCount > MaxHTLCNumber { return ErrMaxHTLCNumber } return nil } // ReceiveNewCommitment process 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 // successfully 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) error { lc.Lock() defer lc.Unlock() // Ensure that this new local update from the remote node respects all // the constraints we specified during initial channel setup. If not, // then we'll abort the channel as they've violated our constraints. err := lc.validateCommitmentSanity(lc.remoteUpdateLog.logIndex, lc.localUpdateLog.ackedIndex, false) if err != nil { return err } theirCommitKey := lc.channelState.TheirCommitKey theirMultiSigKey := lc.channelState.TheirMultiSigKey // We're receiving a new commitment which attempts 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.RevocationProducer.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, lc.localUpdateLog.ackedIndex, lc.remoteUpdateLog.logIndex, revocationKey, revocationHash) if err != nil { return err } walletLog.Tracef("ChannelPoint(%v): extending local chain to height %v", lc.channelState.ChanID, localCommitmentView.height) walletLog.Tracef("ChannelPoint(%v): local chain: our_balance=%v, "+ "their_balance=%v, commit_tx: %v", lc.channelState.ChanID, localCommitmentView.ourBalance, localCommitmentView.theirBalance, newLogClosure(func() string { return spew.Sdump(localCommitmentView.txn) }), ) // Construct the sighash of the commitment transaction corresponding to // this newly proposed state update. localCommitTx := localCommitmentView.txn multiSigScript := lc.channelState.FundingWitnessScript 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 HTLCs... // * need to either roll-back, or make pure return err } // Ensure that the newly constructed commitment state has a valid // signature. theirMultiSigKey.Curve = btcec.S256() 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) // Finally we'll keep track of the current pending index for the remote // party so we can ACK up to this value once we revoke our current // commitment. lc.remoteUpdateLog.initiateTransition() return nil } // PendingUpdates returns a boolean value reflecting if there are any pending // updates which need to be committed. The state machine has pending updates if // the local log index on the local and remote chain tip aren't identical. This // indicates that either we have pending updates they need to commit, or vice // versa. func (lc *LightningChannel) PendingUpdates() bool { lc.RLock() defer lc.RUnlock() // TODO(roasbeef): instead check our current counter? fullySynced := (lc.localCommitChain.tip().ourMessageIndex == lc.remoteCommitChain.tip().ourMessageIndex) return !fullySynced } // 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.RevokeAndAck, error) { lc.Lock() defer lc.Unlock() 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.RevokeAndAck{} currentRevocation, err := lc.channelState.RevocationProducer.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.RevocationProducer.AtIndex(lc.revocationWindowEdge) if err != nil { return nil, err } revocationMsg.NextRevocationKey = DeriveRevocationPubkey(theirCommitKey, revocationEdge[:]) revocationMsg.NextRevocationHash = fastsha256.Sum256(revocationEdge[:]) walletLog.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++ // Additionally, generate a channel delta for this state transition for // persistent storage. tail := lc.localCommitChain.tail() delta, err := tail.toChannelDelta() if err != nil { return nil, err } err = lc.channelState.UpdateCommitment(tail.txn, tail.sig, delta) if err != nil { return nil, err } walletLog.Tracef("ChannelPoint(%v): state transition accepted: "+ "our_balance=%v, their_balance=%v", lc.channelState.ChanID, tail.ourBalance, tail.theirBalance) // In the process of revoking our current commitment, we've also // implicitly ACK'd their set of pending changes that arrived before // the signature the triggered this revocation. So we'll move up their // ACK'd index within the log to right at this set of pending changes. lc.remoteUpdateLog.ackTransition() 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.RevokeAndAck) ([]*PaymentDescriptor, error) { lc.Lock() defer lc.Unlock() // The revocation has a nil (zero) preimage, 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 } // Now that we've received a new revocation from the remote party, // we'll toggle our pendingACk bool to indicate that we can create a // new commitment state after we finish processing this revocation. lc.pendingACK = false ourCommitKey := lc.channelState.OurCommitKey currentRevocationKey := lc.channelState.TheirCurrentRevocation pendingRevocation := chainhash.Hash(revMsg.Revocation) // Ensure that the new pre-image can be placed in preimage store. // TODO(rosbeef): abstract into func store := lc.channelState.RevocationStore if err := store.AddNextEntry(&pendingRevocation); err != nil { return nil, err } // Verify that the revocation public key we can derive using this // preimage and our private key is identical to the revocation key we // were given for their current (prior) commitment transaction. revocationPub := DeriveRevocationPubkey(ourCommitKey, pendingRevocation[:]) if !revocationPub.IsEqual(currentRevocationKey) { return nil, fmt.Errorf("revocation key mismatch") } // Additionally, we need to ensure we were given the proper preimage // to the revocation hash used within any current HTLCs. 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) walletLog.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 revocation producer state is consistent with // the current commitment height. tail := lc.remoteCommitChain.tail() delta, err := tail.toChannelDelta() if err != nil { return nil, err } if err := lc.channelState.AppendToRevocationLog(delta); 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. var htlcsToForward []*PaymentDescriptor for e := lc.remoteUpdateLog.Front(); e != nil; e = e.Next() { htlc := e.Value.(*PaymentDescriptor) if htlc.isForwarded { continue } // TODO(roasbeef): re-visit after adding persistence to HTLCs // * either record add height, or set to N - 1 uncomitted := (htlc.addCommitHeightRemote == 0 || htlc.addCommitHeightLocal == 0) if htlc.EntryType == Add && uncomitted { continue } if htlc.EntryType == Add && remoteChainTail >= htlc.addCommitHeightRemote && localChainTail >= htlc.addCommitHeightLocal { htlc.isForwarded = true htlcsToForward = append(htlcsToForward, htlc) } else if htlc.EntryType != Add && remoteChainTail >= htlc.removeCommitHeightRemote && localChainTail >= htlc.removeCommitHeightLocal { htlc.isForwarded = true htlcsToForward = append(htlcsToForward, htlc) } } // As we've just completed a new state transition, attempt to see if we // can remove any entries from the update log which have been removed // from the PoV of both commitment chains. compactLogs(lc.localUpdateLog, lc.remoteUpdateLog, localChainTail, remoteChainTail) // As a final step, now that we've received an ACK for our last batch // of pending changes, we'll update our local ACK'd index to the now // commitment index, and reset our pendingACKIndex. lc.localUpdateLog.ackTransition() 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.RevokeAndAck, error) { lc.Lock() defer lc.Unlock() /// TODO(roasbeef): error if window edge differs from tail by more than // InitialRevocationWindow revMsg := &lnwire.RevokeAndAck{} revMsg.ChannelPoint = *lc.channelState.ChanID nextHeight := lc.revocationWindowEdge + 1 revocation, err := lc.channelState.RevocationProducer.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 } // NextRevocationkey returns the revocation key for the _next_ commitment // height. The pubkey returned by this function is required by the remote party // to extend our commitment chain with a new commitment. // // TODO(roasbeef): after commitment tx re-write add methdod to ingest // revocation key func (lc *LightningChannel) NextRevocationkey() (*btcec.PublicKey, error) { lc.RLock() defer lc.RUnlock() nextHeight := lc.currentHeight + 1 revocation, err := lc.channelState.RevocationProducer.AtIndex(nextHeight) if err != nil { return nil, err } theirCommitKey := lc.channelState.TheirCommitKey return DeriveRevocationPubkey(theirCommitKey, revocation[:]), nil } // AddHTLC adds an HTLC to the state machine's local update log. This method // should be called when preparing to send an outgoing HTLC. // // TODO(roasbeef): check for duplicates below? edge case during restart w/ HTLC // persistence func (lc *LightningChannel) AddHTLC(htlc *lnwire.UpdateAddHTLC) (uint64, error) { lc.Lock() defer lc.Unlock() if err := lc.validateCommitmentSanity(lc.remoteUpdateLog.logIndex, lc.localUpdateLog.logIndex, true); err != nil { return 0, err } pd := &PaymentDescriptor{ EntryType: Add, RHash: PaymentHash(htlc.PaymentHash), Timeout: htlc.Expiry, Amount: htlc.Amount, Index: lc.localUpdateLog.logIndex, } lc.localUpdateLog.appendUpdate(pd) return pd.Index, nil } // ReceiveHTLC adds an HTLC to the state machine's remote update log. This // method should be called in response to receiving a new HTLC from the remote // party. func (lc *LightningChannel) ReceiveHTLC(htlc *lnwire.UpdateAddHTLC) (uint64, error) { lc.Lock() defer lc.Unlock() if err := lc.validateCommitmentSanity(lc.remoteUpdateLog.logIndex, lc.localUpdateLog.logIndex, true); err != nil { return 0, err } pd := &PaymentDescriptor{ EntryType: Add, RHash: PaymentHash(htlc.PaymentHash), Timeout: htlc.Expiry, Amount: htlc.Amount, Index: lc.remoteUpdateLog.logIndex, } lc.remoteUpdateLog.appendUpdate(pd) lc.rHashMap[pd.RHash] = append(lc.rHashMap[pd.RHash], pd) return pd.Index, nil } // SettleHTLC attempts to settle an existing outstanding received HTLC. The // remote log index of the HTLC settled is returned in order to facilitate // creating the corresponding wire message. In the case the supplied preimage // is invalid, an error is returned. func (lc *LightningChannel) SettleHTLC(preimage [32]byte) (uint64, error) { lc.Lock() defer lc.Unlock() paymentHash := fastsha256.Sum256(preimage[:]) targetHTLCs, ok := lc.rHashMap[paymentHash] if !ok { return 0, fmt.Errorf("invalid payment hash") } targetHTLC := targetHTLCs[0] pd := &PaymentDescriptor{ Amount: targetHTLC.Amount, RPreimage: preimage, Index: lc.localUpdateLog.logIndex, ParentIndex: targetHTLC.Index, EntryType: Settle, } lc.localUpdateLog.appendUpdate(pd) lc.rHashMap[paymentHash][0] = nil lc.rHashMap[paymentHash] = lc.rHashMap[paymentHash][1:] if len(lc.rHashMap[paymentHash]) == 0 { delete(lc.rHashMap, paymentHash) } return targetHTLC.Index, nil } // ReceiveHTLCSettle attempts to settle an existing outgoing HTLC indexed by an // index into the local log. If the specified index doesn't exist within the // log, and error is returned. Similarly if the preimage is invalid w.r.t to // the referenced of then a distinct error is returned. func (lc *LightningChannel) ReceiveHTLCSettle(preimage [32]byte, logIndex uint64) error { lc.Lock() defer lc.Unlock() paymentHash := fastsha256.Sum256(preimage[:]) htlc := lc.localUpdateLog.lookup(logIndex) if htlc == nil { return fmt.Errorf("non existent log entry") } if !bytes.Equal(htlc.RHash[:], paymentHash[:]) { return fmt.Errorf("invalid payment hash") } pd := &PaymentDescriptor{ Amount: htlc.Amount, RPreimage: preimage, ParentIndex: htlc.Index, Index: lc.remoteUpdateLog.logIndex, EntryType: Settle, } lc.remoteUpdateLog.appendUpdate(pd) return nil } // FailHTLC attempts to fail a targeted HTLC by its payment hash, inserting an // entry which will remove the target log entry within the next commitment // update. This method is intended to be called in order to cancel in // _incoming_ HTLC. func (lc *LightningChannel) FailHTLC(rHash [32]byte) (uint64, error) { lc.Lock() defer lc.Unlock() addEntries, ok := lc.rHashMap[rHash] if !ok { return 0, fmt.Errorf("unable to find HTLC to fail") } addEntry := addEntries[0] pd := &PaymentDescriptor{ Amount: addEntry.Amount, RHash: addEntry.RHash, ParentIndex: addEntry.Index, Index: lc.localUpdateLog.logIndex, EntryType: Fail, } lc.localUpdateLog.appendUpdate(pd) lc.rHashMap[rHash][0] = nil lc.rHashMap[rHash] = lc.rHashMap[rHash][1:] if len(lc.rHashMap[rHash]) == 0 { delete(lc.rHashMap, rHash) } return addEntry.Index, nil } // ReceiveFailHTLC attempts to cancel a targeted HTLC by its log index, // inserting an entry which will remove the target log entry within the next // commitment update. This method should be called in response to the upstream // party cancelling an outgoing HTLC. func (lc *LightningChannel) ReceiveFailHTLC(logIndex uint64) error { lc.Lock() defer lc.Unlock() htlc := lc.localUpdateLog.lookup(logIndex) if htlc == nil { return fmt.Errorf("unable to find HTLC to fail") } pd := &PaymentDescriptor{ Amount: htlc.Amount, RHash: htlc.RHash, ParentIndex: htlc.Index, Index: lc.remoteUpdateLog.logIndex, EntryType: Fail, } lc.remoteUpdateLog.appendUpdate(pd) return nil } // ChannelPoint returns the outpoint of the original funding transaction which // created this active channel. This outpoint is used throughout various // subsystems 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. Additionally, in order to be able to efficiently // locate the added HTLC on the commitment transaction from the // PaymentDescriptor that generated it, the generated script is stored within // the descriptor itself. func (lc *LightningChannel) addHTLC(commitTx *wire.MsgTx, ourCommit bool, paymentDesc *PaymentDescriptor, revocation [32]byte, delay uint32, isIncoming bool) error { localKey := lc.channelState.OurCommitKey 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 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 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 !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 !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)) // Store the pkScript of this particular PaymentDescriptor so we can // quickly locate it within the commitment transaction later. paymentDesc.pkScript = htlcP2WSH return nil } // ForceCloseSummary describes the final commitment state before the channel is // locked-down to initiate a force closure by broadcasting the latest state // on-chain. The summary includes all the information required to claim all // rightfully owned outputs. // TODO(roasbeef): generalize, add HTLC info, etc. type ForceCloseSummary struct { // CloseTx is the transaction which closed the channel on-chain. If we // initiate the force close, then this'll be our latest commitment // state. Otherwise, this'll be the state that the remote peer // broadcasted on-chain. CloseTx *wire.MsgTx // SelfOutpoint is the output created by the above close tx which is // spendable by us after a relative time delay. SelfOutpoint wire.OutPoint // SelfOutputMaturity is the relative maturity period before the above // output can be claimed. SelfOutputMaturity uint32 // SelfOutputSignDesc is a fully populated sign descriptor capable of // generating a valid signature to sweep the self output. SelfOutputSignDesc *SignDescriptor } // getSignedCommitTx function take the latest commitment transaction and populate // it with witness data. func (lc *LightningChannel) getSignedCommitTx() (*wire.MsgTx, error) { // Fetch the current commitment transaction, along with their signature // for the transaction. commitTx := lc.channelState.OurCommitTx theirSig := append(lc.channelState.OurCommitSig, byte(txscript.SigHashAll)) // With this, we then generate the full witness so the caller can // broadcast a fully signed transaction. lc.signDesc.SigHashes = txscript.NewTxSigHashes(commitTx) ourSigRaw, err := lc.signer.SignOutputRaw(commitTx, lc.signDesc) if err != nil { return nil, err } ourSig := append(ourSigRaw, byte(txscript.SigHashAll)) // With the final signature generated, create the witness stack // required to spend from the multi-sig output. ourKey := lc.channelState.OurMultiSigKey.SerializeCompressed() theirKey := lc.channelState.TheirMultiSigKey.SerializeCompressed() commitTx.TxIn[0].Witness = SpendMultiSig(lc.FundingWitnessScript, ourKey, ourSig, theirKey, theirSig) return commitTx, nil } // ForceClose executes a unilateral closure of the transaction at the current // lowest commitment height of the channel. Following a force closure, all // state transitions, or modifications to the state update logs will be // rejected. Additionally, this function also returns a ForceCloseSummary which // includes the necessary details required to sweep all the time-locked within // the commitment transaction. // // TODO(roasbeef): all methods need to abort if in dispute state // TODO(roasbeef): method to generate CloseSummaries for when the remote peer // does a unilateral close func (lc *LightningChannel) ForceClose() (*ForceCloseSummary, error) { lc.Lock() defer lc.Unlock() // Set the channel state to indicate that the channel is now in a // contested state. lc.status = channelDispute commitTx, err := lc.getSignedCommitTx() if err != nil { return nil, err } // Re-derive the original pkScript for to-self output within the // commitment transaction. We'll need this to find the corresponding // output in the commitment transaction and potentially for creating // the sign descriptor. csvTimeout := lc.channelState.LocalCsvDelay selfKey := lc.channelState.OurCommitKey producer := lc.channelState.RevocationProducer unusedRevocation, err := producer.AtIndex(lc.currentHeight) if err != nil { return nil, err } revokeKey := DeriveRevocationPubkey(lc.channelState.TheirCommitKey, unusedRevocation[:]) selfScript, err := commitScriptToSelf(csvTimeout, selfKey, revokeKey) if err != nil { return nil, err } payToUsScriptHash, err := witnessScriptHash(selfScript) if err != nil { return nil, err } // Locate the output index of the delayed commitment output back to us. // We'll return the details of this output to the caller so they can // sweep it once it's mature. // TODO(roasbeef): also return HTLC info, assumes only p2wsh is commit // tx var delayIndex uint32 var delayScript []byte var selfSignDesc *SignDescriptor for i, txOut := range commitTx.TxOut { if !bytes.Equal(payToUsScriptHash, txOut.PkScript) { continue } delayIndex = uint32(i) delayScript = txOut.PkScript break } // With the necessary information gathered above, create a new sign // descriptor which is capable of generating the signature the caller // needs to sweep this output. The hash cache, and input index are not // set as the caller will decide these values once sweeping the output. // If the output is non-existant (dust), have the sign descriptor be nil. if len(delayScript) != 0 { selfSignDesc = &SignDescriptor{ PubKey: selfKey, WitnessScript: selfScript, Output: &wire.TxOut{ PkScript: delayScript, Value: int64(lc.channelState.OurBalance), }, HashType: txscript.SigHashAll, } } // Finally, close the channel force close signal which notifies any // subscribers that the channel has now been forcibly closed. This // allows callers to begin to carry out any post channel closure // activities. close(lc.ForceCloseSignal) return &ForceCloseSummary{ CloseTx: commitTx, SelfOutpoint: wire.OutPoint{ Hash: commitTx.TxHash(), Index: delayIndex, }, SelfOutputMaturity: csvTimeout, SelfOutputSignDesc: selfSignDesc, }, 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, *chainhash.Hash, error) { lc.Lock() defer lc.Unlock() // 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 } closeTx := CreateCooperativeCloseTx(lc.fundingTxIn, lc.channelState.OurBalance, lc.channelState.TheirBalance, lc.channelState.OurDeliveryScript, lc.channelState.TheirDeliveryScript, lc.channelState.IsInitiator) // Ensure that the transaction doesn't explicitly validate any // consensus rules such as being too big, or having any value with a // negative output. tx := btcutil.NewTx(closeTx) if err := blockchain.CheckTransactionSanity(tx); err != nil { return nil, nil, err } // Finally, sign the completed cooperative closure transaction. As the // initiator we'll simply send our signature over to the remote party, // using the generated txid to be notified once the closure transaction // has been confirmed. lc.signDesc.SigHashes = txscript.NewTxSigHashes(closeTx) closeSig, err := lc.signer.SignOutputRaw(closeTx, lc.signDesc) if err != nil { return nil, nil, err } // As everything checks out, indicate in the channel status that a // channel closure has been initiated. lc.status = channelClosing closeTxSha := closeTx.TxHash() 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 initiating 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. // // NOTE: The passed remote sig is expected to be a fully complete signature // including the proper sighash byte. func (lc *LightningChannel) CompleteCooperativeClose(remoteSig []byte) (*wire.MsgTx, error) { lc.Lock() defer lc.Unlock() // 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 } // 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, lc.channelState.IsInitiator) // Ensure that the transaction doesn't explicitly validate any // consensus rules such as being too big, or having any value with a // negative output. tx := btcutil.NewTx(closeTx) if err := blockchain.CheckTransactionSanity(tx); err != nil { return nil, err } // With the transaction created, we can finally generate our half of // the 2-of-2 multi-sig needed to redeem the funding output. hashCache := txscript.NewTxSigHashes(closeTx) lc.signDesc.SigHashes = hashCache closeSig, err := lc.signer.SignOutputRaw(closeTx, lc.signDesc) 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.SerializeCompressed() theirKey := lc.channelState.TheirMultiSigKey.SerializeCompressed() ourSig := append(closeSig, byte(txscript.SigHashAll)) witness := SpendMultiSig(lc.signDesc.WitnessScript, ourKey, ourSig, theirKey, remoteSig) closeTx.TxIn[0].Witness = witness // Validate the finalized transaction to ensure the output script is // properly met, and that the remote peer supplied a valid signature. vm, err := txscript.NewEngine(lc.fundingP2WSH, closeTx, 0, txscript.StandardVerifyFlags, nil, hashCache, int64(lc.channelState.Capacity)) if err != nil { return nil, err } if err := vm.Execute(); err != nil { return nil, err } // As the transaction is sane, and the scripts are valid we'll mark the // channel now as closed as the closure transaction should get into the // chain in a timely manner and possibly be re-broadcast by the wallet. lc.status = channelClosed return closeTx, nil } // DeleteState deletes all state concerning the channel from the underlying // database, only leaving a small summary describing metadata of the // channel's lifetime. func (lc *LightningChannel) DeleteState() error { return lc.channelState.CloseChannel() } // StateSnapshot returns a snapshot of the current fully committed state within // the channel. 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 // counterparty within the channel, which can be spent immediately. func CreateCommitTx(fundingOutput *wire.TxIn, selfKey, theirKey *btcec.PublicKey, revokeKey *btcec.PublicKey, csvTimeout uint32, amountToSelf, amountToThem, dustLimit 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 // P2WPKH 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(2) commitTx.AddTxIn(fundingOutput) // Avoid creating dust outputs within the commitment transaction. if amountToSelf >= dustLimit { commitTx.AddTxOut(wire.NewTxOut(int64(amountToSelf), payToUsScriptHash)) } if amountToThem >= dustLimit { 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(2) closeTx.AddTxIn(fundingTxIn) // The initiator of 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 }