package contractcourt import ( "fmt" "io" "github.com/btcsuite/btcutil" "github.com/lightningnetwork/lnd/channeldb" "github.com/lightningnetwork/lnd/lnwallet" ) // htlcOutgoingContestResolver is a ContractResolver that's able to resolve an // outgoing HTLC that is still contested. An HTLC is still contested, if at the // time that we broadcast the commitment transaction, it isn't able to be fully // resolved. In this case, we'll either wait for the HTLC to timeout, or for // us to learn of the preimage. type htlcOutgoingContestResolver struct { // htlcTimeoutResolver is the inner solver that this resolver may turn // into. This only happens if the HTLC expires on-chain. htlcTimeoutResolver } // newOutgoingContestResolver instantiates a new outgoing contested htlc // resolver. func newOutgoingContestResolver(res lnwallet.OutgoingHtlcResolution, broadcastHeight uint32, htlc channeldb.HTLC, resCfg ResolverConfig) *htlcOutgoingContestResolver { timeout := newTimeoutResolver( res, broadcastHeight, htlc, resCfg, ) return &htlcOutgoingContestResolver{ htlcTimeoutResolver: *timeout, } } // Resolve commences the resolution of this contract. As this contract hasn't // yet timed out, we'll wait for one of two things to happen // // 1. The HTLC expires. In this case, we'll sweep the funds and send a clean // up cancel message to outside sub-systems. // // 2. The remote party sweeps this HTLC on-chain, in which case we'll add the // pre-image to our global cache, then send a clean up settle message // backwards. // // When either of these two things happens, we'll create a new resolver which // is able to handle the final resolution of the contract. We're only the pivot // point. func (h *htlcOutgoingContestResolver) Resolve() (ContractResolver, error) { // If we're already full resolved, then we don't have anything further // to do. if h.resolved { return nil, nil } // Otherwise, we'll watch for two external signals to decide if we'll // morph into another resolver, or fully resolve the contract. // // The output we'll be watching for is the *direct* spend from the HTLC // output. If this isn't our commitment transaction, it'll be right on // the resolution. Otherwise, we fetch this pointer from the input of // the time out transaction. outPointToWatch, scriptToWatch, err := h.chainDetailsToWatch() if err != nil { return nil, err } // First, we'll register for a spend notification for this output. If // the remote party sweeps with the pre-image, we'll be notified. spendNtfn, err := h.Notifier.RegisterSpendNtfn( outPointToWatch, scriptToWatch, h.broadcastHeight, ) if err != nil { return nil, err } // We'll quickly check to see if the output has already been spent. select { // If the output has already been spent, then we can stop early and // sweep the pre-image from the output. case commitSpend, ok := <-spendNtfn.Spend: if !ok { return nil, errResolverShuttingDown } // TODO(roasbeef): Checkpoint? return h.claimCleanUp(commitSpend) // If it hasn't, then we'll watch for both the expiration, and the // sweeping out this output. default: } // If we reach this point, then we can't fully act yet, so we'll await // either of our signals triggering: the HTLC expires, or we learn of // the preimage. blockEpochs, err := h.Notifier.RegisterBlockEpochNtfn(nil) if err != nil { return nil, err } defer blockEpochs.Cancel() for { select { // A new block has arrived, we'll check to see if this leads to // HTLC expiration. case newBlock, ok := <-blockEpochs.Epochs: if !ok { return nil, errResolverShuttingDown } // If the current height is >= expiry-1, then a timeout // path spend will be valid to be included in the next // block, and we can immediately return the resolver. // // TODO(joostjager): Statement above may not be valid. // For CLTV locks, the expiry value is the last // _invalid_ block. The likely reason that this does not // create a problem, is that utxonursery is checking the // expiry again (in the proper way). // // Source: // https://github.com/btcsuite/btcd/blob/991d32e72fe84d5fbf9c47cd604d793a0cd3a072/blockchain/validate.go#L154 newHeight := uint32(newBlock.Height) if newHeight >= h.htlcResolution.Expiry-1 { log.Infof("%T(%v): HTLC has expired "+ "(height=%v, expiry=%v), transforming "+ "into timeout resolver", h, h.htlcResolution.ClaimOutpoint, newHeight, h.htlcResolution.Expiry) return &h.htlcTimeoutResolver, nil } // The output has been spent! This means the preimage has been // revealed on-chain. case commitSpend, ok := <-spendNtfn.Spend: if !ok { return nil, errResolverShuttingDown } // The only way this output can be spent by the remote // party is by revealing the preimage. So we'll perform // our duties to clean up the contract once it has been // claimed. return h.claimCleanUp(commitSpend) case <-h.quit: return nil, fmt.Errorf("resolver canceled") } } } // report returns a report on the resolution state of the contract. func (h *htlcOutgoingContestResolver) report() *ContractReport { // No locking needed as these values are read-only. finalAmt := h.htlc.Amt.ToSatoshis() if h.htlcResolution.SignedTimeoutTx != nil { finalAmt = btcutil.Amount( h.htlcResolution.SignedTimeoutTx.TxOut[0].Value, ) } return &ContractReport{ Outpoint: h.htlcResolution.ClaimOutpoint, Type: ReportOutputOutgoingHtlc, Amount: finalAmt, MaturityHeight: h.htlcResolution.Expiry, LimboBalance: finalAmt, Stage: 1, } } // Stop signals the resolver to cancel any current resolution processes, and // suspend. // // NOTE: Part of the ContractResolver interface. func (h *htlcOutgoingContestResolver) Stop() { close(h.quit) } // IsResolved returns true if the stored state in the resolve is fully // resolved. In this case the target output can be forgotten. // // NOTE: Part of the ContractResolver interface. func (h *htlcOutgoingContestResolver) IsResolved() bool { return h.resolved } // Encode writes an encoded version of the ContractResolver into the passed // Writer. // // NOTE: Part of the ContractResolver interface. func (h *htlcOutgoingContestResolver) Encode(w io.Writer) error { return h.htlcTimeoutResolver.Encode(w) } // newOutgoingContestResolverFromReader attempts to decode an encoded ContractResolver // from the passed Reader instance, returning an active ContractResolver // instance. func newOutgoingContestResolverFromReader(r io.Reader, resCfg ResolverConfig) ( *htlcOutgoingContestResolver, error) { h := &htlcOutgoingContestResolver{} timeoutResolver, err := newTimeoutResolverFromReader(r, resCfg) if err != nil { return nil, err } h.htlcTimeoutResolver = *timeoutResolver return h, nil } // A compile time assertion to ensure htlcOutgoingContestResolver meets the // ContractResolver interface. var _ htlcContractResolver = (*htlcOutgoingContestResolver)(nil)