package loop import ( "bytes" "context" "fmt" "strconv" "strings" "github.com/btcsuite/btcd/btcec/v2" "github.com/btcsuite/btcd/btcutil" "github.com/btcsuite/btcd/chaincfg/chainhash" "github.com/btcsuite/btcd/wire" "github.com/lightninglabs/lndclient" "github.com/lightningnetwork/lnd/channeldb" "github.com/lightningnetwork/lnd/lnwire" "github.com/lightningnetwork/lnd/routing/route" "github.com/lightningnetwork/lnd/zpay32" ) var ( // DefaultMaxHopHints is set to 20 as that is the default set in LND. DefaultMaxHopHints = 20 // hopHintFactor is factor by which we scale the total amount of // inbound capacity we want our hop hints to represent, allowing us to // have some leeway if peers go offline. hopHintFactor = 2 ) // isPublicNode checks if a node is public, by simply checking if there's any // channels reported to the node. func isPublicNode(ctx context.Context, lnd *lndclient.LndServices, pubKey [33]byte) (bool, error) { // GetNodeInfo doesn't report our private channels with the queried node // so we can use it to determine if the node is considered public. nodeInfo, err := lnd.Client.GetNodeInfo( ctx, pubKey, true, ) if err != nil { return false, err } return (nodeInfo.ChannelCount > 0), nil } // fetchChannelEdgesByID fetches the edge info for the passed channel and // returns the channeldb structs filled with the data that is needed for // LND's SelectHopHints implementation. func fetchChannelEdgesByID(ctx context.Context, lnd *lndclient.LndServices, chanID uint64) (*channeldb.ChannelEdgeInfo, *channeldb.ChannelEdgePolicy, *channeldb.ChannelEdgePolicy, error) { chanInfo, err := lnd.Client.GetChanInfo(ctx, chanID) if err != nil { return nil, nil, nil, err } edgeInfo := &channeldb.ChannelEdgeInfo{ ChannelID: chanID, NodeKey1Bytes: chanInfo.Node1, NodeKey2Bytes: chanInfo.Node2, } policy1 := &channeldb.ChannelEdgePolicy{ FeeBaseMSat: lnwire.MilliSatoshi( chanInfo.Node1Policy.FeeBaseMsat, ), FeeProportionalMillionths: lnwire.MilliSatoshi( chanInfo.Node1Policy.FeeRateMilliMsat, ), TimeLockDelta: uint16(chanInfo.Node1Policy.TimeLockDelta), } policy2 := &channeldb.ChannelEdgePolicy{ FeeBaseMSat: lnwire.MilliSatoshi( chanInfo.Node2Policy.FeeBaseMsat, ), FeeProportionalMillionths: lnwire.MilliSatoshi( chanInfo.Node2Policy.FeeRateMilliMsat, ), TimeLockDelta: uint16(chanInfo.Node2Policy.TimeLockDelta), } return edgeInfo, policy1, policy2, nil } // parseOutPoint attempts to parse an outpoint from the passed in string. func parseOutPoint(s string) (*wire.OutPoint, error) { split := strings.Split(s, ":") if len(split) != 2 { return nil, fmt.Errorf("expecting outpoint to be in format "+ "of txid:index: %s", s) } index, err := strconv.ParseInt(split[1], 10, 32) if err != nil { return nil, fmt.Errorf("unable to decode output index: %v", err) } txid, err := chainhash.NewHashFromStr(split[0]) if err != nil { return nil, fmt.Errorf("unable to parse hex string: %v", err) } return &wire.OutPoint{ Hash: *txid, Index: uint32(index), }, nil } // getAlias tries to get the ShortChannelId from the passed ChannelId and // aliasCache. func getAlias(aliasCache map[lnwire.ChannelID]lnwire.ShortChannelID, channelID lnwire.ChannelID) (lnwire.ShortChannelID, error) { if channelID, ok := aliasCache[channelID]; ok { return channelID, nil } return lnwire.ShortChannelID{}, fmt.Errorf("can't find channelId") } // SelectHopHints calls into LND's exposed SelectHopHints prefiltered to the // includeNodes map (unless it's empty). func SelectHopHints(ctx context.Context, lnd *lndclient.LndServices, amt btcutil.Amount, numMaxHophints int, includeNodes map[route.Vertex]struct{}) ([][]zpay32.HopHint, error) { aliasCache := make(map[lnwire.ChannelID]lnwire.ShortChannelID) // Fetch all active and public channels. channels, err := lnd.Client.ListChannels(ctx, false, false) if err != nil { return nil, err } openChannels := []*HopHintInfo{} for _, channel := range channels { if len(includeNodes) > 0 { if _, ok := includeNodes[channel.PubKeyBytes]; !ok { continue } } outPoint, err := parseOutPoint(channel.ChannelPoint) if err != nil { return nil, err } remotePubkey, err := btcec.ParsePubKey(channel.PubKeyBytes[:]) if err != nil { return nil, err } openChannels = append( openChannels, &HopHintInfo{ IsPublic: !channel.Private, IsActive: channel.Active, FundingOutpoint: *outPoint, RemotePubkey: remotePubkey, RemoteBalance: lnwire.MilliSatoshi( channel.RemoteBalance * 1000, ), ShortChannelID: channel.ChannelID, }, ) channelID := lnwire.NewChanIDFromOutPoint(outPoint) scID := lnwire.NewShortChanIDFromInt(channel.ChannelID) aliasCache[channelID] = scID } cfg := &SelectHopHintsCfg{ IsPublicNode: func(pubKey [33]byte) (bool, error) { return isPublicNode(ctx, lnd, pubKey) }, FetchChannelEdgesByID: func(chanID uint64) ( *channeldb.ChannelEdgeInfo, *channeldb.ChannelEdgePolicy, *channeldb.ChannelEdgePolicy, error) { return fetchChannelEdgesByID(ctx, lnd, chanID) }, GetAlias: func(id lnwire.ChannelID) ( lnwire.ShortChannelID, error) { return getAlias(aliasCache, id) }, } routeHints := invoicesrpcSelectHopHints( lnwire.MilliSatoshi(amt*1000), cfg, openChannels, numMaxHophints, ) return routeHints, nil } // chanCanBeHopHint returns true if the target channel is eligible to be a hop // hint. func chanCanBeHopHint(channel *HopHintInfo, cfg *SelectHopHintsCfg) ( *channeldb.ChannelEdgePolicy, bool) { // Since we're only interested in our private channels, we'll skip // public ones. if channel.IsPublic { return nil, false } // Make sure the channel is active. if !channel.IsActive { log.Debugf("Skipping channel %v due to not "+ "being eligible to forward payments", channel.ShortChannelID) return nil, false } // To ensure we don't leak unadvertised nodes, we'll make sure our // counterparty is publicly advertised within the network. Otherwise, // we'll end up leaking information about nodes that intend to stay // unadvertised, like in the case of a node only having private // channels. var remotePub [33]byte copy(remotePub[:], channel.RemotePubkey.SerializeCompressed()) isRemoteNodePublic, err := cfg.IsPublicNode(remotePub) if err != nil { log.Errorf("Unable to determine if node %x "+ "is advertised: %v", remotePub, err) return nil, false } if !isRemoteNodePublic { log.Debugf("Skipping channel %v due to "+ "counterparty %x being unadvertised", channel.ShortChannelID, remotePub) return nil, false } // Fetch the policies for each end of the channel. info, p1, p2, err := cfg.FetchChannelEdgesByID(channel.ShortChannelID) if err != nil { // In the case of zero-conf channels, it may be the case that // the alias SCID was deleted from the graph, and replaced by // the confirmed SCID. Check the Graph for the confirmed SCID. confirmedScid := channel.ConfirmedScidZC info, p1, p2, err = cfg.FetchChannelEdgesByID(confirmedScid) if err != nil { log.Errorf("Unable to fetch the routing policies for "+ "the edges of the channel %v: %v", channel.ShortChannelID, err) return nil, false } } // Now, we'll need to determine which is the correct policy for HTLCs // being sent from the remote node. var remotePolicy *channeldb.ChannelEdgePolicy if bytes.Equal(remotePub[:], info.NodeKey1Bytes[:]) { remotePolicy = p1 } else { remotePolicy = p2 } return remotePolicy, true } // addHopHint creates a hop hint out of the passed channel and channel policy. // The new hop hint is appended to the passed slice. func addHopHint(hopHints *[][]zpay32.HopHint, channel *HopHintInfo, chanPolicy *channeldb.ChannelEdgePolicy, aliasScid lnwire.ShortChannelID) { hopHint := zpay32.HopHint{ NodeID: channel.RemotePubkey, ChannelID: channel.ShortChannelID, FeeBaseMSat: uint32(chanPolicy.FeeBaseMSat), FeeProportionalMillionths: uint32( chanPolicy.FeeProportionalMillionths, ), CLTVExpiryDelta: chanPolicy.TimeLockDelta, } var defaultScid lnwire.ShortChannelID if aliasScid != defaultScid { hopHint.ChannelID = aliasScid.ToUint64() } *hopHints = append(*hopHints, []zpay32.HopHint{hopHint}) } // HopHintInfo contains the channel information required to create a hop hint. type HopHintInfo struct { // IsPublic indicates whether a channel is advertised to the network. IsPublic bool // IsActive indicates whether the channel is online and available for // use. IsActive bool // FundingOutpoint is the funding txid:index for the channel. FundingOutpoint wire.OutPoint // RemotePubkey is the public key of the remote party that this channel // is in. RemotePubkey *btcec.PublicKey // RemoteBalance is the remote party's balance (our current incoming // capacity). RemoteBalance lnwire.MilliSatoshi // ShortChannelID is the short channel ID of the channel. ShortChannelID uint64 // ConfirmedScidZC is the confirmed SCID of a zero-conf channel. This // may be used for looking up a channel in the graph. ConfirmedScidZC uint64 // ScidAliasFeature denotes whether the channel has negotiated the // option-scid-alias feature bit. ScidAliasFeature bool } // SelectHopHintsCfg contains the dependencies required to obtain hop hints // for an invoice. type SelectHopHintsCfg struct { // IsPublicNode is returns a bool indicating whether the node with the // given public key is seen as a public node in the graph from the // graph's source node's point of view. IsPublicNode func(pubKey [33]byte) (bool, error) // FetchChannelEdgesByID attempts to lookup the two directed edges for // the channel identified by the channel ID. FetchChannelEdgesByID func(chanID uint64) (*channeldb.ChannelEdgeInfo, *channeldb.ChannelEdgePolicy, *channeldb.ChannelEdgePolicy, error) // GetAlias allows the peer's alias SCID to be retrieved for private // option_scid_alias channels. GetAlias func(lnwire.ChannelID) (lnwire.ShortChannelID, error) } // sufficientHints checks whether we have sufficient hop hints, based on the // following criteria: // - Hop hint count: limit to a set number of hop hints, regardless of whether // we've reached our invoice amount or not. // - Total incoming capacity: limit to our invoice amount * scaling factor to // allow for some of our links going offline. // // We limit our number of hop hints like this to keep our invoice size down, // and to avoid leaking all our private channels when we don't need to. func sufficientHints(numHints, maxHints, scalingFactor int, amount, totalHintAmount lnwire.MilliSatoshi) bool { if numHints >= maxHints { log.Debug("Reached maximum number of hop hints") return true } requiredAmount := amount * lnwire.MilliSatoshi(scalingFactor) if totalHintAmount >= requiredAmount { log.Debugf("Total hint amount: %v has reached target hint "+ "bandwidth: %v (invoice amount: %v * factor: %v)", totalHintAmount, requiredAmount, amount, scalingFactor) return true } return false } // SelectHopHints will select up to numMaxHophints from the set of passed open // channels. The set of hop hints will be returned as a slice of functional // options that'll append the route hint to the set of all route hints. // // TODO(sputn1ck): remove when https://github.com/lightningnetwork/lnd/pull/7065 // is merged to a new lnd release. func invoicesrpcSelectHopHints(amtMSat lnwire.MilliSatoshi, cfg *SelectHopHintsCfg, openChannels []*HopHintInfo, numMaxHophints int) [][]zpay32.HopHint { // We'll add our hop hints in two passes, first we'll add all channels // that are eligible to be hop hints, and also have a local balance // above the payment amount. var totalHintBandwidth lnwire.MilliSatoshi hopHintChans := make(map[wire.OutPoint]struct{}) hopHints := make([][]zpay32.HopHint, 0, numMaxHophints) for _, channel := range openChannels { enoughHopHints := sufficientHints( len(hopHints), numMaxHophints, hopHintFactor, amtMSat, totalHintBandwidth, ) if enoughHopHints { log.Debugf("First pass of hop selection has " + "sufficient hints") return hopHints } // If this channel can't be a hop hint, then skip it. edgePolicy, canBeHopHint := chanCanBeHopHint(channel, cfg) if edgePolicy == nil || !canBeHopHint { continue } // Similarly, in this first pass, we'll ignore all channels in // isolation can't satisfy this payment. if channel.RemoteBalance < amtMSat { continue } // Lookup and see if there is an alias SCID that exists. chanID := lnwire.NewChanIDFromOutPoint( &channel.FundingOutpoint, ) alias, _ := cfg.GetAlias(chanID) // If this is a channel where the option-scid-alias feature bit // was negotiated and the alias is not yet assigned, we cannot // issue an invoice. Doing so might expose the confirmed SCID // of a private channel. if channel.ScidAliasFeature { var defaultScid lnwire.ShortChannelID if alias == defaultScid { continue } } // Now that we now this channel use usable, add it as a hop // hint and the indexes we'll use later. addHopHint(&hopHints, channel, edgePolicy, alias) hopHintChans[channel.FundingOutpoint] = struct{}{} totalHintBandwidth += channel.RemoteBalance } // In this second pass we'll add channels, and we'll either stop when // we have 20 hop hints, we've run through all the available channels, // or if the sum of available bandwidth in the routing hints exceeds 2x // the payment amount. We do 2x here to account for a margin of error // if some of the selected channels no longer become operable. for i := 0; i < len(openChannels); i++ { enoughHopHints := sufficientHints( len(hopHints), numMaxHophints, hopHintFactor, amtMSat, totalHintBandwidth, ) if enoughHopHints { log.Debugf("Second pass of hop selection has " + "sufficient hints") return hopHints } channel := openChannels[i] // Skip the channel if we already selected it. if _, ok := hopHintChans[channel.FundingOutpoint]; ok { continue } // If the channel can't be a hop hint, then we'll skip it. // Otherwise, we'll use the policy information to populate the // hop hint. remotePolicy, canBeHopHint := chanCanBeHopHint(channel, cfg) if !canBeHopHint || remotePolicy == nil { continue } // Lookup and see if there's an alias SCID that exists. chanID := lnwire.NewChanIDFromOutPoint( &channel.FundingOutpoint, ) alias, _ := cfg.GetAlias(chanID) // If this is a channel where the option-scid-alias feature bit // was negotiated and the alias is not yet assigned, we cannot // issue an invoice. Doing so might expose the confirmed SCID // of a private channel. if channel.ScidAliasFeature { var defaultScid lnwire.ShortChannelID if alias == defaultScid { continue } } // Include the route hint in our set of options that will be // used when creating the invoice. addHopHint(&hopHints, channel, remotePolicy, alias) // As we've just added a new hop hint, we'll accumulate it's // available balance now to update our tally. // // TODO(roasbeef): have a cut off based on min bandwidth? totalHintBandwidth += channel.RemoteBalance } return hopHints }