lnd.xprv/lnwallet/channel.go

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package lnwallet
import (
"bytes"
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"container/list"
"fmt"
"sync"
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"github.com/btcsuite/fastsha256"
"github.com/davecgh/go-spew/spew"
"github.com/lightningnetwork/lnd/chainntnfs"
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"github.com/lightningnetwork/lnd/channeldb"
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"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"
)
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var zeroHash wire.ShaHash
var (
ErrChanClosing = fmt.Errorf("channel is being closed, operation disallowed")
ErrNoWindow = fmt.Errorf("unable to sign new commitment, the current" +
" revocation window is exhausted")
ErrMaxWeightCost = fmt.Errorf("commitment transaction exceed max " +
"available weight")
ErrMaxHTLCNumber = fmt.Errorf("commitment transaction exceed max " +
"htlc number")
)
const (
// MaxPendingPayments is the max number of pending HTLC's permitted on
// a channel.
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// TODO(roasbeef): make not random value + enforce
// * should be tuned to account for max tx "cost"
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MaxPendingPayments = 100
// 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 = 4
)
// channelState is an enum like type which represents the current state of a
// particular channel.
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// 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 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
)
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// 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
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// 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.
// TODO(roasbeef): LogEntry interface??
// * need to separate attrs for cancel/add/settle
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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
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// 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 uint32
// ParentIndex is the index of the log entry that this HTLC update
// settles or times out.
ParentIndex uint32
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// 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
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// 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
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//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
// 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
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}
// 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
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// independently extend the other side's commitment chain, up to a certain
// "revocation window", which once reached, disallows new commitments until
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// 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
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// to independently, and concurrent send create new commitments. Each
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// 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
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// htlcs is the set of HTLC's 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: uint32(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
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}
// 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
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// commitments we create locally extend the remote node's chain, and vice
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// 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()
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// * 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
bio BlockChainIO
channelEvents chainntnfs.ChainNotifier
sync.RWMutex
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ourLogCounter uint32
theirLogCounter uint32
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status channelState
Capacity btcutil.Amount
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// 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
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// 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 depleted. The revocations don't contain a valid pre-image,
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// 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
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// 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.
ourUpdateLog *list.List
theirUpdateLog *list.List
// logIndex is an index into the above log. This index is used to
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// remove Add state updates, once a timeout/settle is received.
ourLogIndex map[uint32]*list.Element
theirLogIndex map[uint32]*list.Element
LocalDeliveryScript []byte
RemoteDeliveryScript []byte
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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
// counter party has broadcast a prior *revoked* state.
ContractBreach chan *BreachRetribution
started int32
shutdown int32
quit chan struct{}
wg sync.WaitGroup
}
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// 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, bio BlockChainIO,
events chainntnfs.ChainNotifier,
state *channeldb.OpenChannel) (*LightningChannel, error) {
lc := &LightningChannel{
signer: signer,
bio: bio,
channelEvents: events,
currentHeight: state.NumUpdates,
remoteCommitChain: newCommitmentChain(state.NumUpdates),
localCommitChain: newCommitmentChain(state.NumUpdates),
channelState: state,
revocationWindowEdge: state.NumUpdates,
ourUpdateLog: list.New(),
theirUpdateLog: list.New(),
ourLogIndex: make(map[uint32]*list.Element),
theirLogIndex: make(map[uint32]*list.Element),
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),
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}
// 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
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initialCommitment := &commitment{
height: lc.currentHeight,
ourBalance: state.OurBalance,
ourMessageIndex: 0,
theirBalance: state.TheirBalance,
theirMessageIndex: 0,
}
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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)
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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,
}
// 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
// counter-party 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 HTLC's 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.TxSha()
// 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 the proper
// leaf from our revocation tree necessary to sweep the remote party's
// output.
revocationPreimage, err := chanState.RemoteElkrem.AtIndex(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 counter-party 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) {
// If the daemon is shutting down, then this notification channel will
// be closed, so check the second read-value to avoid a false positive.
commitSpend, ok := <-channelCloseNtfn.Spend
if !ok {
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.RUnlock()
return
}
lc.RUnlock()
lc.Lock()
defer lc.Unlock()
// TODO(roasbeef): logs duplicated due to breachArbiter...
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 := uint64(GetStateNumHint(commitTxBroadcast, obsfucator))
currentStateNum, err := lc.channelState.CommitmentHeight()
if err != nil {
walletLog.Errorf("unable to obtain commitment height: %v", err)
return
}
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.
case broadcastStateNum == currentStateNum:
walletLog.Infof("Unilateral close of ChannelPoint(%v) "+
"detected", lc.channelState.ChanID)
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",
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
case broadcastStateNum > currentStateNum:
}
}
// restoreStateLogs runs through the current locked-in HTLC's 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 uint32
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.ourLogIndex[pd.Index] = lc.ourUpdateLog.PushBack(pd)
ourCounter++
} else {
pd.Index = theirCounter
lc.theirLogIndex[pd.Index] = lc.theirUpdateLog.PushBack(pd)
theirCounter++
}
}
lc.ourLogCounter = ourCounter
lc.theirLogCounter = 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" HTLC's at a particular point within the
// history of the HTLC update log.
type htlcView struct {
ourUpdates []*PaymentDescriptor
theirUpdates []*PaymentDescriptor
}
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// 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) *htlcView {
var ourHTLCs []*PaymentDescriptor
for e := lc.ourUpdateLog.Front(); e != nil; e = e.Next() {
htlc := e.Value.(*PaymentDescriptor)
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// 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.theirUpdateLog.Front(); e != nil; e = e.Next() {
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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)
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}
}
return &htlcView{
ourUpdates: ourHTLCs,
theirUpdates: theirHTLCs,
}
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}
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// 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
}
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// 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
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// 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?
htlcView := lc.fetchHTLCView(theirLogIndex, ourLogIndex)
filteredHTLCView := lc.evaluateHTLCView(htlcView, &ourBalance, &theirBalance,
nextHeight, remoteChain)
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var selfKey *btcec.PublicKey
var remoteKey *btcec.PublicKey
var delay uint32
var delayBalance, p2wkhBalance, dustLimit btcutil.Amount
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if remoteChain {
selfKey = lc.channelState.TheirCommitKey
remoteKey = lc.channelState.OurCommitKey
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delay = lc.channelState.RemoteCsvDelay
delayBalance = theirBalance
p2wkhBalance = ourBalance
dustLimit = lc.channelState.TheirDustLimit
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} else {
selfKey = lc.channelState.OurCommitKey
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remoteKey = lc.channelState.TheirCommitKey
delay = lc.channelState.LocalCsvDelay
delayBalance = ourBalance
p2wkhBalance = theirBalance
dustLimit = lc.channelState.OurDustLimit
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}
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// Generate a new commitment transaction with all the latest
// unsettled/un-timed out HTLC's.
ourCommitTx := !remoteChain
commitTx, err := CreateCommitTx(lc.fundingTxIn, selfKey, remoteKey,
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revocationKey, delay, delayBalance, p2wkhBalance)
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 {
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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 := uint32(nextHeight)
if err := SetStateNumHint(commitTx, stateNum, obsfucator); err != nil {
return nil, err
}
// Sort the transactions according to the agreed upon canonical
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// 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,
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}, 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 htlc's 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[uint32]struct{})
skipThem := make(map[uint32]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 entry.EntryType == Settle && !remoteChain {
lc.channelState.TotalSatoshisReceived += uint64(entry.Amount)
}
addEntry := lc.theirLogIndex[entry.ParentIndex].Value.(*PaymentDescriptor)
skipThem[addEntry.Index] = struct{}{}
processRemoveEntry(entry, ourBalance, theirBalance,
nextHeight, remoteChain, true)
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}
for _, entry := range view.theirUpdates {
if entry.EntryType == Add {
continue
}
if entry.EntryType == Settle && !remoteChain {
lc.channelState.TotalSatoshisSent += uint64(entry.Amount)
}
addEntry := lc.ourLogIndex[entry.ParentIndex].Value.(*PaymentDescriptor)
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 HTLC's, and debiting the chain state balance due to any
// newly added HTLC's.
for _, entry := range view.ourUpdates {
isAdd := entry.EntryType == Add
if _, ok := skipUs[entry.Index]; !isAdd || ok {
continue
}
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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
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}
// processAddEntry evaluates the effect of an add entry within the HTLC log.
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// 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
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// 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) {
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// 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
}
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if *addHeight != 0 {
return
}
if isIncoming {
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// 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
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// going HTLC to reflect the pending balance.
*ourBalance -= htlc.Amount
}
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*addHeight = nextHeight
}
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// 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) {
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var removeHeight *uint64
if remoteChain {
removeHeight = &htlc.removeCommitHeightRemote
} else {
removeHeight = &htlc.removeCommitHeightLocal
}
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// Ignore any removal entries which have already been processed.
if *removeHeight != 0 {
return
}
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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 isIncoming && htlc.EntryType == Settle:
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*ourBalance += htlc.Amount
// Otherwise, this HTLC is being timed out, therefore the value of the
// HTLC should return to the remote party.
case isIncoming && htlc.EntryType == Timeout:
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*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:
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*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 == Timeout:
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*ourBalance += htlc.Amount
}
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*removeHeight = nextHeight
}
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// 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) {
lc.Lock()
defer lc.Unlock()
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err := lc.validateCommitmentSanity(lc.theirLogCounter, lc.ourLogCounter, false)
if err != nil {
return nil, 0, err
}
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// 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 {
return nil, 0, ErrNoWindow
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}
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// 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.ourLogCounter,
lc.theirLogCounter, remoteRevocationKey, remoteRevocationHash)
if err != nil {
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return nil, 0, 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)
}))
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// Sign their version of the new commitment transaction.
lc.signDesc.SigHashes = txscript.NewTxSigHashes(newCommitView.txn)
sig, err := lc.signer.SignOutputRaw(newCommitView.txn, lc.signDesc)
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if err != nil {
return nil, 0, err
}
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// Extend the remote commitment chain by one with the addition of our
// latest commitment update.
lc.remoteCommitChain.addCommitment(newCommitView)
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// 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:]
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// Strip off the sighash flag on the signature in order to send it over
// the wire.
return sig, lc.theirLogCounter, nil
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}
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// 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 uint32, prediction bool) error {
htlcCount := 0
if prediction {
htlcCount++
}
// Run through all the HTLC's 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
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// 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
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// 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 {
lc.Lock()
defer lc.Unlock()
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err := lc.validateCommitmentSanity(lc.theirLogCounter, ourLogIndex, false)
if err != nil {
return err
}
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theirCommitKey := lc.channelState.TheirCommitKey
theirMultiSigKey := lc.channelState.TheirMultiSigKey
// We're receiving a new commitment which attempts to extend our local
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// 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[:])
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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.theirLogCounter, revocationKey, revocationHash)
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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)
}))
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// Construct the sighash of the commitment transaction corresponding to
// this newly proposed state update.
localCommitTx := localCommitmentView.txn
multiSigScript := lc.channelState.FundingWitnessScript
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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
}
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// 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")
}
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// 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
}
// 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()
fullySynced := (lc.localCommitChain.tip().ourMessageIndex ==
lc.remoteCommitChain.tip().ourMessageIndex)
return !fullySynced
}
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// 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) {
lc.Lock()
defer lc.Unlock()
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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
}
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copy(revocationMsg.Revocation[:], currentRevocation[:])
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// 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,
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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)
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// 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.
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// TODO(roasbeef): update sent/received.
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
}
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walletLog.Tracef("ChannelPoint(%v): state transition accepted: "+
"our_balance=%v, their_balance=%v", lc.channelState.ChanID,
tail.ourBalance, tail.theirBalance)
revocationMsg.ChannelPoint = lc.channelState.ChanID
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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) {
lc.Lock()
defer lc.Unlock()
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// 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
}
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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
}
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// 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.
revocationPub := DeriveRevocationPubkey(ourCommitKey, pendingRevocation[:])
if !revocationPub.IsEqual(currentRevocationKey) {
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return nil, fmt.Errorf("revocation key mismatch")
}
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// 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")
}
}
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// 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 elkrem receiver 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
}
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// 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.theirUpdateLog.Front(); e != nil; e = e.Next() {
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htlc := e.Value.(*PaymentDescriptor)
if htlc.isForwarded {
continue
}
// TODO(roasbeef): re-visit after adding persistence to HTLC's
// * 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)
}
}
lc.compactLogs(lc.ourUpdateLog, lc.theirUpdateLog,
localChainTail, remoteChainTail)
return htlcsToForward, nil
}
// compactLogs performs garbage collection within the log removing HTLC's which
// have been removed from the point-of-view of the tail of both chains. The
// entries which timeout/settle HTLC's are also removed.
func (lc *LightningChannel) compactLogs(ourLog, theirLog *list.List,
localChainTail, remoteChainTail uint64) {
compactLog := func(logA, logB *list.List, indexB, indexA map[uint32]*list.Element) {
var nextA *list.Element
for e := logA.Front(); e != nil; e = nextA {
nextA = e.Next()
htlc := e.Value.(*PaymentDescriptor)
if htlc.EntryType == Add {
continue
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}
// 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 {
parentLink := indexB[htlc.ParentIndex]
parentIndex := parentLink.Value.(*PaymentDescriptor).Index
logB.Remove(parentLink)
logA.Remove(e)
delete(indexB, parentIndex)
delete(indexA, htlc.Index)
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}
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}
}
compactLog(ourLog, theirLog, lc.theirLogIndex, lc.ourLogIndex)
compactLog(theirLog, ourLog, lc.ourLogIndex, lc.theirLogIndex)
}
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// 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) {
lc.Lock()
defer lc.Unlock()
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/// TODO(roasbeef): error if window edge differs from tail by more than
// InitialRevocationWindow
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revMsg := &lnwire.CommitRevocation{}
revMsg.ChannelPoint = lc.channelState.ChanID
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nextHeight := lc.revocationWindowEdge + 1
revocation, err := lc.channelState.LocalElkrem.AtIndex(nextHeight)
if err != nil {
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return nil, err
}
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theirCommitKey := lc.channelState.TheirCommitKey
revMsg.NextRevocationKey = DeriveRevocationPubkey(theirCommitKey,
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revocation[:])
revMsg.NextRevocationHash = fastsha256.Sum256(revocation[:])
lc.revocationWindowEdge++
return revMsg, 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
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func (lc *LightningChannel) AddHTLC(htlc *lnwire.HTLCAddRequest) (uint32, error) {
lc.Lock()
defer lc.Unlock()
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err := lc.validateCommitmentSanity(lc.theirLogCounter, lc.ourLogCounter, true)
if err != nil {
return 0, err
}
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pd := &PaymentDescriptor{
EntryType: Add,
RHash: PaymentHash(htlc.RedemptionHashes[0]),
Timeout: htlc.Expiry,
Amount: htlc.Amount,
Index: lc.ourLogCounter,
}
lc.ourLogIndex[pd.Index] = lc.ourUpdateLog.PushBack(pd)
lc.ourLogCounter++
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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.
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func (lc *LightningChannel) ReceiveHTLC(htlc *lnwire.HTLCAddRequest) (uint32, error) {
lc.Lock()
defer lc.Unlock()
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err := lc.validateCommitmentSanity(lc.theirLogCounter, lc.ourLogCounter, true)
if err != nil {
return 0, err
}
pd := &PaymentDescriptor{
EntryType: Add,
RHash: PaymentHash(htlc.RedemptionHashes[0]),
Timeout: htlc.Expiry,
Amount: htlc.Amount,
Index: lc.theirLogCounter,
}
lc.theirLogIndex[pd.Index] = lc.theirUpdateLog.PushBack(pd)
lc.theirLogCounter++
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return pd.Index, nil
}
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// 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 pre-image
// is invalid, an error is returned.
func (lc *LightningChannel) SettleHTLC(preimage [32]byte) (uint32, error) {
lc.Lock()
defer lc.Unlock()
var targetHTLC *list.Element
// TODO(roasbeef): optimize
paymentHash := fastsha256.Sum256(preimage[:])
for e := lc.theirUpdateLog.Front(); e != nil; e = e.Next() {
htlc := e.Value.(*PaymentDescriptor)
if htlc.EntryType != Add {
continue
}
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if !htlc.settled && bytes.Equal(htlc.RHash[:], paymentHash[:]) {
htlc.settled = true
targetHTLC = e
break
}
}
if targetHTLC == nil {
return 0, fmt.Errorf("invalid payment hash")
}
parentPd := targetHTLC.Value.(*PaymentDescriptor)
pd := &PaymentDescriptor{
Amount: parentPd.Amount,
RPreimage: preimage,
Index: lc.ourLogCounter,
ParentIndex: parentPd.Index,
EntryType: Settle,
}
lc.ourUpdateLog.PushBack(pd)
lc.ourLogCounter++
return targetHTLC.Value.(*PaymentDescriptor).Index, nil
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}
// 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 uint32) error {
lc.Lock()
defer lc.Unlock()
paymentHash := fastsha256.Sum256(preimage[:])
addEntry, ok := lc.ourLogIndex[logIndex]
if !ok {
return fmt.Errorf("non existant log entry")
}
htlc := addEntry.Value.(*PaymentDescriptor)
if !bytes.Equal(htlc.RHash[:], paymentHash[:]) {
return fmt.Errorf("invalid payment hash")
}
pd := &PaymentDescriptor{
Amount: htlc.Amount,
RPreimage: preimage,
ParentIndex: htlc.Index,
Index: lc.theirLogCounter,
EntryType: Settle,
}
lc.theirUpdateLog.PushBack(pd)
lc.theirLogCounter++
return nil
}
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// 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
}
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// 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.
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func (lc *LightningChannel) addHTLC(commitTx *wire.MsgTx, ourCommit bool,
paymentDesc *PaymentDescriptor, revocation [32]byte, delay uint32,
isIncoming bool) error {
localKey := lc.channelState.OurCommitKey
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remoteKey := lc.channelState.TheirCommitKey
timeout := paymentDesc.Timeout
rHash := paymentDesc.RHash
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// 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:
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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:
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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:
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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:
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pkScript, err = receiverHTLCScript(timeout, delay, localKey,
remoteKey, revocation[:], rHash[:])
}
if err != nil {
return err
}
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// 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
}
// 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
for i, txOut := range commitTx.TxOut {
if !txscript.IsPayToWitnessScriptHash(txOut.PkScript) {
continue
}
delayIndex = uint32(i)
delayScript = txOut.PkScript
}
csvTimeout := lc.channelState.LocalCsvDelay
selfKey := lc.channelState.OurCommitKey
// Re-derive the original pkScript for out to-self output within the
// commitment transaction. We'll need this for the created sign
// descriptor.
elkrem := lc.channelState.LocalElkrem
unusedRevocation, err := elkrem.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
}
// 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.
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.TxSha(),
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, *wire.ShaHash, 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
}
// Otherwise, indicate in the channel status that a channel closure has
// been initiated.
lc.status = channelClosing
closeTx := CreateCooperativeCloseTx(lc.fundingTxIn,
lc.channelState.OurBalance, lc.channelState.TheirBalance,
lc.channelState.OurDeliveryScript, lc.channelState.TheirDeliveryScript,
lc.channelState.IsInitiator)
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.
lc.signDesc.SigHashes = txscript.NewTxSigHashes(closeTx)
closeSig, err := lc.signer.SignOutputRaw(closeTx, lc.signDesc)
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 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
}
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,
lc.channelState.IsInitiator)
// 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
}
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 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
// 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
// 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()
commitTx.Version = 2
commitTx.AddTxIn(fundingOutput)
// Avoid creating zero value outputs within the commitment transaction.
if amountToSelf != 0 {
commitTx.AddTxOut(wire.NewTxOut(int64(amountToSelf), payToUsScriptHash))
}
if amountToThem != 0 {
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
}