package htlcswitch import ( "sync" "sync/atomic" "time" "crypto/sha256" "github.com/davecgh/go-spew/spew" "github.com/go-errors/errors" "github.com/lightningnetwork/lnd/lnrpc" "github.com/lightningnetwork/lnd/lnwallet" "github.com/lightningnetwork/lnd/lnwire" "github.com/roasbeef/btcd/wire" "github.com/roasbeef/btcutil" ) var ( // ErrChannelLinkNotFound is used when channel link hasn't been found. ErrChannelLinkNotFound = errors.New("channel link not found") // zeroPreimage is the empty preimage which is returned when we have // some errors. zeroPreimage [sha256.Size]byte ) // pendingPayment represents the payment which made by user and waits for // updates to be received whether the payment has been rejected or proceed // successfully. type pendingPayment struct { paymentHash lnwallet.PaymentHash amount btcutil.Amount preimage chan [sha256.Size]byte err chan error // deobfuscator is an serializable entity which is used if we received // an error, it deobfuscates the onion failure blob, and extracts the // exact error from it. deobfuscator Deobfuscator } // plexPacket encapsulates switch packet and adds error channel to receive // error from request handler. type plexPacket struct { pkt *htlcPacket err chan error } // ChannelCloseType is a enum which signals the type of channel closure the // peer should execute. type ChannelCloseType uint8 const ( // CloseRegular indicates a regular cooperative channel closure // should be attempted. CloseRegular ChannelCloseType = iota // CloseBreach indicates that a channel breach has been dtected, and // the link should immediately be marked as unavailable. CloseBreach ) // ChanClose represents a request which close a particular channel specified by // its id. type ChanClose struct { // CloseType is a variable which signals the type of channel closure the // peer should execute. CloseType ChannelCloseType // ChanPoint represent the id of the channel which should be closed. ChanPoint *wire.OutPoint // Updates is used by request creator to receive the notifications about // execution of the close channel request. Updates chan *lnrpc.CloseStatusUpdate // Err is used by request creator to receive request execution error. Err chan error } // Config defines the configuration for the service. ALL elements within the // configuration MUST be non-nil for the service to carry out its duties. type Config struct { // LocalChannelClose kicks-off the workflow to execute a cooperative // or forced unilateral closure of the channel initiated by a local // subsystem. LocalChannelClose func(pubKey []byte, request *ChanClose) // UpdateTopology sends the onion error failure topology update to router // subsystem. UpdateTopology func(msg *lnwire.ChannelUpdate) error } // Switch is the central messaging bus for all incoming/outgoing HTLCs. // Connected peers with active channels are treated as named interfaces which // refer to active channels as links. A link is the switch's message // communication point with the goroutine that manages an active channel. New // links are registered each time a channel is created, and unregistered once // the channel is closed. The switch manages the hand-off process for multi-hop // HTLCs, forwarding HTLCs initiated from within the daemon, and finally // notifies users local-systems concerning their outstanding payment requests. type Switch struct { started int32 shutdown int32 wg sync.WaitGroup quit chan struct{} // cfg is a copy of the configuration struct that the htlc switch // service was initialized with. cfg *Config // pendingPayments is correspondence of user payments and its hashes, // which is used to save the payments which made by user and notify // them about result later. pendingPayments map[lnwallet.PaymentHash][]*pendingPayment pendingMutex sync.RWMutex // circuits is storage for payment circuits which are used to // forward the settle/fail htlc updates back to the add htlc initiator. circuits *circuitMap // links is a map of channel id and channel link which manages // this channel. linkIndex map[lnwire.ChannelID]ChannelLink // forwardingIndex is an index which is consulted by the switch when it // needs to locate the next hop to forward an incoming/outgoing HTLC // update to/from. // // TODO(roasbeef): eventually add a NetworkHop mapping before the // ChannelLink forwardingIndex map[lnwire.ShortChannelID]ChannelLink // interfaceIndex maps the compressed public key of a peer to all the // channels that the switch maintains iwht that peer. interfaceIndex map[[33]byte]map[ChannelLink]struct{} // htlcPlex is the channel which all connected links use to coordinate // the setup/teardown of Sphinx (onion routing) payment circuits. // Active links forward any add/settle messages over this channel each // state transition, sending new adds/settles which are fully locked // in. htlcPlex chan *plexPacket // chanCloseRequests is used to transfer the channel close request to // the channel close handler. chanCloseRequests chan *ChanClose // linkControl is a channel used to propogate add/remove/get htlc // switch handler commands. linkControl chan interface{} } // New creates the new instance of htlc switch. func New(cfg Config) *Switch { return &Switch{ cfg: &cfg, circuits: newCircuitMap(), linkIndex: make(map[lnwire.ChannelID]ChannelLink), forwardingIndex: make(map[lnwire.ShortChannelID]ChannelLink), interfaceIndex: make(map[[33]byte]map[ChannelLink]struct{}), pendingPayments: make(map[lnwallet.PaymentHash][]*pendingPayment), htlcPlex: make(chan *plexPacket), chanCloseRequests: make(chan *ChanClose), linkControl: make(chan interface{}), quit: make(chan struct{}), } } // SendHTLC is used by other subsystems which aren't belong to htlc switch // package in order to send the htlc update. func (s *Switch) SendHTLC(nextNode [33]byte, htlc *lnwire.UpdateAddHTLC, deobfuscator Deobfuscator) ([sha256.Size]byte, error) { // Create payment and add to the map of payment in order later to be // able to retrieve it and return response to the user. payment := &pendingPayment{ err: make(chan error, 1), preimage: make(chan [sha256.Size]byte, 1), paymentHash: htlc.PaymentHash, amount: htlc.Amount, deobfuscator: deobfuscator, } s.pendingMutex.Lock() s.pendingPayments[htlc.PaymentHash] = append( s.pendingPayments[htlc.PaymentHash], payment) s.pendingMutex.Unlock() // Generate and send new update packet, if error will be received on // this stage it means that packet haven't left boundaries of our // system and something wrong happened. packet := newInitPacket(nextNode, htlc) if err := s.forward(packet); err != nil { s.removePendingPayment(payment.amount, payment.paymentHash) return zeroPreimage, err } // Returns channels so that other subsystem might wait/skip the // waiting of handling of payment. var preimage [sha256.Size]byte var err error select { case e := <-payment.err: err = e case <-s.quit: return zeroPreimage, errors.New("service is shutdown") } select { case p := <-payment.preimage: preimage = p case <-s.quit: return zeroPreimage, errors.New("service is shutdown") } return preimage, err } // forward is used in order to find next channel link and apply htlc // update. Also this function is used by channel links itself in order to // forward the update after it has been included in the channel. func (s *Switch) forward(packet *htlcPacket) error { command := &plexPacket{ pkt: packet, err: make(chan error, 1), } select { case s.htlcPlex <- command: case <-s.quit: return errors.New("Htlc Switch was stopped") } select { case err := <-command.err: return err case <-s.quit: return errors.New("Htlc Switch was stopped") } } // handleLocalDispatch is used at the start/end of the htlc update life // cycle. At the start (1) it is used to send the htlc to the channel link // without creation of circuit. At the end (2) it is used to notify the user // about the result of his payment is it was successful or not. // // Alice Bob Carol // o --add----> o ---add----> o // (1) // // (2) // o <-settle-- o <--settle-- o // Alice Bob Carol // func (s *Switch) handleLocalDispatch(payment *pendingPayment, packet *htlcPacket) error { switch htlc := packet.htlc.(type) { // User have created the htlc update therefore we should find the // appropriate channel link and send the payment over this link. case *lnwire.UpdateAddHTLC: // Try to find links by node destination. links, err := s.getLinks(packet.destNode) if err != nil { log.Errorf("unable to find links by "+ "destination %v", err) return errors.New(lnwire.CodeUnknownNextPeer) } // Try to find destination channel link with appropriate // bandwidth. var destination ChannelLink for _, link := range links { if link.Bandwidth() >= htlc.Amount { destination = link break } } // If the channel link we're attempting to forward the update // over has insufficient capacity, then we'll cancel the HTLC // as the payment cannot succeed. if destination == nil { log.Errorf("unable to find appropriate channel link "+ "insufficient capacity, need %v", htlc.Amount) return errors.New(lnwire.CodeTemporaryChannelFailure) } // Send the packet to the destination channel link which // manages then channel. destination.HandleSwitchPacket(packet) return nil // We've just received a settle update which means we can finalize // the user payment and return successful response. case *lnwire.UpdateFufillHTLC: // Notify the user that his payment was // successfully proceed. payment.err <- nil payment.preimage <- htlc.PaymentPreimage s.removePendingPayment(payment.amount, payment.paymentHash) // We've just received a fail update which means we can finalize the // user payment and return fail response. case *lnwire.UpdateFailHTLC: var userErr error // We'll attempt to fully decrypt the onion encrypted error. If // we're unable to then we'll bail early. failure, err := payment.deobfuscator.Deobfuscate(htlc.Reason) if err != nil { userErr = errors.Errorf("unable to de-obfuscate "+ "onion failure, htlc with hash(%v): %v", payment.paymentHash[:], err) log.Error(userErr) } else { // Process payment failure by updating the lightning // network topology by using router subsystem handler. var update *lnwire.ChannelUpdate // Only a few error message actually contain a channel // update message, so we'll filter out for those that // do. switch failure := failure.(type) { case *lnwire.FailTemporaryChannelFailure: update = failure.Update case *lnwire.FailAmountBelowMinimum: update = &failure.Update case *lnwire.FailFeeInsufficient: update = &failure.Update case *lnwire.FailIncorrectCltvExpiry: update = &failure.Update case *lnwire.FailExpiryTooSoon: update = &failure.Update case *lnwire.FailChannelDisabled: update = &failure.Update } // If we've been sent an error that includes an update, // then we'll apply it to the local graph. // // TODO(roasbeef): instead, make all onion errors the // error interface, and handle this within the router. // Will allow us more flexibility w.r.t how we handle // the error. if update != nil { log.Info("Received payment failure(%v), "+ "applying lightning network topology update", failure.Code()) if err := s.cfg.UpdateTopology(update); err != nil { log.Errorf("unable to update topology: %v", err) } } userErr = errors.New(failure.Code()) } // Notify user that his payment was discarded. payment.err <- userErr payment.preimage <- zeroPreimage s.removePendingPayment(payment.amount, payment.paymentHash) default: return errors.New("wrong update type") } return nil } // handlePacketForward is used in cases when we need forward the htlc update // from one channel link to another and be able to propagate the settle/fail // updates back. This behaviour is achieved by creation of payment circuits. func (s *Switch) handlePacketForward(packet *htlcPacket) error { switch htlc := packet.htlc.(type) { // Channel link forwarded us a new htlc, therefore we initiate the // payment circuit within our internal state so we can properly forward // the ultimate settle message back latter. case *lnwire.UpdateAddHTLC: source, err := s.getLinkByShortID(packet.src) if err != nil { err := errors.Errorf("unable to find channel link "+ "by channel point (%v): %v", packet.src, err) log.Error(err) return err } targetLink, err := s.getLinkByShortID(packet.dest) if err != nil { // If packet was forwarded from another channel link // than we should notify this link that some error // occurred. failure := lnwire.FailUnknownNextPeer{} reason, err := packet.obfuscator.InitialObfuscate(failure) if err != nil { err := errors.Errorf("unable to obfuscate "+ "error: %v", err) log.Error(err) return err } go source.HandleSwitchPacket(newFailPacket( packet.src, &lnwire.UpdateFailHTLC{ Reason: reason, }, htlc.PaymentHash, 0, true, )) err = errors.Errorf("unable to find link with "+ "destination %v", packet.dest) log.Error(err) return err } interfaceLinks, _ := s.getLinks(targetLink.Peer().PubKey()) // Try to find destination channel link with appropriate // bandwidth. var destination ChannelLink for _, link := range interfaceLinks { if link.Bandwidth() >= htlc.Amount { destination = link break } } // If the channel link we're attempting to forward the update // over has insufficient capacity, then we'll cancel the htlc // as the payment cannot succeed. if destination == nil { // If packet was forwarded from another // channel link than we should notify this // link that some error occurred. failure := lnwire.NewTemporaryChannelFailure(nil) reason, err := packet.obfuscator.InitialObfuscate(failure) if err != nil { err := errors.Errorf("unable to obfuscate "+ "error: %v", err) log.Error(err) return err } go source.HandleSwitchPacket(newFailPacket( packet.src, &lnwire.UpdateFailHTLC{ Reason: reason, }, htlc.PaymentHash, 0, true, )) err = errors.Errorf("unable to find appropriate "+ "channel link insufficient capacity, need "+ "%v", htlc.Amount) log.Error(err) return err } // If packet was forwarded from another channel link than we // should create circuit (remember the path) in order to // forward settle/fail packet back. if err := s.circuits.add(newPaymentCircuit( source.ShortChanID(), destination.ShortChanID(), htlc.PaymentHash, packet.obfuscator, )); err != nil { failure := lnwire.NewTemporaryChannelFailure(nil) reason, err := packet.obfuscator.InitialObfuscate(failure) if err != nil { err := errors.Errorf("unable to obfuscate "+ "error: %v", err) log.Error(err) return err } go source.HandleSwitchPacket(newFailPacket( packet.src, &lnwire.UpdateFailHTLC{ Reason: reason, }, htlc.PaymentHash, 0, true, )) err = errors.Errorf("unable to add circuit: "+ "%v", err) log.Error(err) return err } // Send the packet to the destination channel link which // manages the channel. destination.HandleSwitchPacket(packet) return nil // We've just received a settle packet which means we can finalize the // payment circuit by forwarding the settle msg to the channel from // which htlc add packet was initially received. case *lnwire.UpdateFufillHTLC, *lnwire.UpdateFailHTLC: // Exit if we can't find and remove the active circuit to // continue propagating the fail over. circuit, err := s.circuits.remove(packet.payHash) if err != nil { err := errors.Errorf("unable to remove "+ "circuit for payment hash: %v", packet.payHash) log.Error(err) return err } // If this is failure than we need to obfuscate the error. if htlc, ok := htlc.(*lnwire.UpdateFailHTLC); ok && !packet.isObfuscated { htlc.Reason = circuit.Obfuscator.BackwardObfuscate(htlc.Reason) } // Propagating settle/fail htlc back to src of add htlc packet. source, err := s.getLinkByShortID(circuit.Src) if err != nil { err := errors.Errorf("unable to get source "+ "channel link to forward settle/fail htlc: %v", err) log.Error(err) return err } log.Debugf("Closing completed onion "+ "circuit for %x: %v<->%v", packet.payHash[:], circuit.Src, circuit.Dest) source.HandleSwitchPacket(packet) return nil default: return errors.New("wrong update type") } } // CloseLink creates and sends the close channel command. func (s *Switch) CloseLink(chanPoint *wire.OutPoint, closeType ChannelCloseType) (chan *lnrpc.CloseStatusUpdate, chan error) { // TODO(roasbeef) abstract out the close updates. updateChan := make(chan *lnrpc.CloseStatusUpdate, 1) errChan := make(chan error, 1) command := &ChanClose{ CloseType: closeType, ChanPoint: chanPoint, Updates: updateChan, Err: errChan, } select { case s.chanCloseRequests <- command: return updateChan, errChan case <-s.quit: errChan <- errors.New("unable close channel link, htlc " + "switch already stopped") close(updateChan) return updateChan, errChan } } // handleCloseLink sends a message to the peer responsible for the target // channel point, instructing it to initiate a cooperative channel closure. func (s *Switch) handleChanelClose(req *ChanClose) { targetChanID := lnwire.NewChanIDFromOutPoint(req.ChanPoint) var link ChannelLink for chanID, l := range s.linkIndex { if chanID == targetChanID { link = l } } if link == nil { req.Err <- errors.Errorf("channel with ChannelID(%v) not "+ "found", targetChanID) return } log.Debugf("requesting local channel close, peer(%v) channel(%v)", link.Peer(), targetChanID) // TODO(roasbeef): if type was CloseBreach initiate force closure with // all other channels (if any) we have with the remote peer. peerPub := link.Peer().PubKey() s.cfg.LocalChannelClose(peerPub[:], req) return } // htlcForwarder is responsible for optimally forwarding (and possibly // fragmenting) incoming/outgoing HTLCs amongst all active interfaces and their // links. The duties of the forwarder are similar to that of a network switch, // in that it facilitates multi-hop payments by acting as a central messaging // bus. The switch communicates will active links to create, manage, and tear // down active onion routed payments. Each active channel is modeled as // networked device with metadata such as the available payment bandwidth, and // total link capacity. // // NOTE: This MUST be run as a goroutine. func (s *Switch) htlcForwarder() { defer s.wg.Done() // Remove all links once we've been signalled for shutdown. defer func() { for _, link := range s.linkIndex { if err := s.removeLink(link.ChanID()); err != nil { log.Errorf("unable to remove "+ "channel link on stop: %v", err) } } }() // TODO(roasbeef): cleared vs settled distinction var ( totalNumUpdates uint64 totalSatSent btcutil.Amount totalSatRecv btcutil.Amount ) logTicker := time.NewTicker(10 * time.Second) defer logTicker.Stop() for { select { // A local close request has arrived, we'll forward this to the // relevant link (if it exists) so the channel can be // cooperatively closed (if possible). case req := <-s.chanCloseRequests: s.handleChanelClose(req) // A new packet has arrived for forwarding, we'll interpret the // packet concretely, then either forward it along, or // interpret a return packet to a locally initialized one. case cmd := <-s.htlcPlex: var ( paymentHash lnwallet.PaymentHash amount btcutil.Amount ) // Only three types of message should be forwarded: // add, fails, and settles. Anything else is an error. switch m := cmd.pkt.htlc.(type) { case *lnwire.UpdateAddHTLC: paymentHash = m.PaymentHash amount = m.Amount case *lnwire.UpdateFufillHTLC, *lnwire.UpdateFailHTLC: paymentHash = cmd.pkt.payHash amount = cmd.pkt.amount default: cmd.err <- errors.New("wrong type of update") return } // If we can locate this packet in our local records, // then this means a local sub-system initiated it. // Otherwise, this is just a packet to be forwarded, so // we'll treat it as so. // // TODO(roasbeef): can fast path this payment, err := s.findPayment(amount, paymentHash) if err != nil { cmd.err <- s.handlePacketForward(cmd.pkt) } else { cmd.err <- s.handleLocalDispatch(payment, cmd.pkt) } // The log ticker has fired, so we'll calculate some forwarding // stats for the last 10 seconds to display within the logs to // users. case <-logTicker.C: // First, we'll collate the current running tally of // our forwarding stats. prevSatSent := totalSatSent prevSatRecv := totalSatRecv prevNumUpdates := totalNumUpdates var ( newNumUpdates uint64 newSatSent btcutil.Amount newSatRecv btcutil.Amount ) // Next, we'll run through all the registered links and // compute their up-to-date forwarding stats. for _, link := range s.linkIndex { // TODO(roasbeef): when links first registered // stats printed. updates, sent, recv := link.Stats() newNumUpdates += updates newSatSent += sent newSatRecv += recv } var ( diffNumUpdates uint64 diffSatSent btcutil.Amount diffSatRecv btcutil.Amount ) // If this is the first time we're computing these // stats, then the diff is just the new value. We do // this in order to avoid integer underflow issues. if prevNumUpdates == 0 { diffNumUpdates = newNumUpdates diffSatSent = newSatSent diffSatRecv = newSatRecv } else { diffNumUpdates = newNumUpdates - prevNumUpdates diffSatSent = newSatSent - prevSatSent diffSatRecv = newSatRecv - prevSatRecv } // If the diff of num updates is zero, then we haven't // forwarded anything in the last 10 seconds, so we can // skip this update. if diffNumUpdates == 0 { continue } // Otherwise, we'll log this diff, then accumulate the // new stats into the running total. log.Infof("Sent %v satoshis received %v satoshi "+ "in the last 10 seconds (%v tx/sec)", diffSatSent, diffSatRecv, float64(diffNumUpdates)/10) totalNumUpdates += diffNumUpdates totalSatSent += diffSatSent totalSatRecv += diffSatRecv case req := <-s.linkControl: switch cmd := req.(type) { case *addLinkCmd: cmd.err <- s.addLink(cmd.link) case *removeLinkCmd: cmd.err <- s.removeLink(cmd.chanID) case *getLinkCmd: link, err := s.getLink(cmd.chanID) cmd.done <- link cmd.err <- err case *getLinksCmd: links, err := s.getLinks(cmd.peer) cmd.done <- links cmd.err <- err } case <-s.quit: return } } } // Start starts all helper goroutines required for the operation of the switch. func (s *Switch) Start() error { if !atomic.CompareAndSwapInt32(&s.started, 0, 1) { log.Warn("Htlc Switch already started") return nil } log.Infof("Starting HTLC Switch") s.wg.Add(1) go s.htlcForwarder() return nil } // Stop gracefully stops all active helper goroutines, then waits until they've // exited. func (s *Switch) Stop() error { if !atomic.CompareAndSwapInt32(&s.shutdown, 0, 1) { log.Warn("Htlc Switch already stopped") return nil } log.Infof("HLTC Switch shutting down") close(s.quit) s.wg.Wait() return nil } // addLinkCmd is a add link command wrapper, it is used to propagate handler // parameters and return handler error. type addLinkCmd struct { link ChannelLink err chan error } // AddLink is used to initiate the handling of the add link command. The // request will be propagated and handled in the main goroutine. func (s *Switch) AddLink(link ChannelLink) error { command := &addLinkCmd{ link: link, err: make(chan error, 1), } select { case s.linkControl <- command: return <-command.err case <-s.quit: return errors.New("Htlc Switch was stopped") } } // addLink is used to add the newly created channel link and start // use it to handle the channel updates. func (s *Switch) addLink(link ChannelLink) error { // First we'll add the link to the linkIndex which lets us quickly look // up a channel when we need to close or register it, and the // forwarding index which'll be used when forwarding HTLC's in the // multi-hop setting. s.linkIndex[link.ChanID()] = link s.forwardingIndex[link.ShortChanID()] = link // Next we'll add the link to the interface index so we can quickly // look up all the channels for a particular node. peerPub := link.Peer().PubKey() if _, ok := s.interfaceIndex[peerPub]; !ok { s.interfaceIndex[peerPub] = make(map[ChannelLink]struct{}) } s.interfaceIndex[peerPub][link] = struct{}{} if err := link.Start(); err != nil { return err } log.Infof("Added channel link with chan_id=%v, short_chan_id=(%v), "+ "bandwidth=%v", link.ChanID(), spew.Sdump(link.ShortChanID()), link.Bandwidth()) return nil } // getLinkCmd is a get link command wrapper, it is used to propagate handler // parameters and return handler error. type getLinkCmd struct { chanID lnwire.ChannelID err chan error done chan ChannelLink } // GetLink is used to initiate the handling of the get link command. The // request will be propagated/handled to/in the main goroutine. func (s *Switch) GetLink(chanID lnwire.ChannelID) (ChannelLink, error) { command := &getLinkCmd{ chanID: chanID, err: make(chan error, 1), done: make(chan ChannelLink, 1), } select { case s.linkControl <- command: return <-command.done, <-command.err case <-s.quit: return nil, errors.New("Htlc Switch was stopped") } } // getLink attempts to return the link that has the specified channel ID. func (s *Switch) getLink(chanID lnwire.ChannelID) (ChannelLink, error) { link, ok := s.linkIndex[chanID] if !ok { return nil, ErrChannelLinkNotFound } return link, nil } // getLinkByShortID attempts to return the link which possesses the target // short channel ID. func (s *Switch) getLinkByShortID(chanID lnwire.ShortChannelID) (ChannelLink, error) { link, ok := s.forwardingIndex[chanID] if !ok { return nil, ErrChannelLinkNotFound } return link, nil } // removeLinkCmd is a get link command wrapper, it is used to propagate handler // parameters and return handler error. type removeLinkCmd struct { chanID lnwire.ChannelID err chan error } // RemoveLink is used to initiate the handling of the remove link command. The // request will be propagated/handled to/in the main goroutine. func (s *Switch) RemoveLink(chanID lnwire.ChannelID) error { command := &removeLinkCmd{ chanID: chanID, err: make(chan error, 1), } select { case s.linkControl <- command: return <-command.err case <-s.quit: return errors.New("Htlc Switch was stopped") } } // removeLink is used to remove and stop the channel link. func (s *Switch) removeLink(chanID lnwire.ChannelID) error { log.Infof("Removing channel link with ChannelID(%v)", chanID) link, ok := s.linkIndex[chanID] if !ok { return ErrChannelLinkNotFound } // Remove the channel from channel map. delete(s.linkIndex, chanID) delete(s.forwardingIndex, link.ShortChanID()) // Remove the channel from channel index. peerPub := link.Peer().PubKey() delete(s.interfaceIndex, peerPub) go link.Stop() return nil } // getLinksCmd is a get links command wrapper, it is used to propagate handler // parameters and return handler error. type getLinksCmd struct { peer [33]byte err chan error done chan []ChannelLink } // GetLinksByInterface fetches all the links connected to a particular node // identified by the serialized compressed form of its public key. func (s *Switch) GetLinksByInterface(hop [33]byte) ([]ChannelLink, error) { command := &getLinksCmd{ peer: hop, err: make(chan error, 1), done: make(chan []ChannelLink, 1), } select { case s.linkControl <- command: return <-command.done, <-command.err case <-s.quit: return nil, errors.New("Htlc Switch was stopped") } } // getLinks is function which returns the channel links of the peer by hop // destination id. func (s *Switch) getLinks(destination [33]byte) ([]ChannelLink, error) { links, ok := s.interfaceIndex[destination] if !ok { return nil, errors.Errorf("unable to locate channel link by"+ "destination hop id %v", destination) } channelLinks := make([]ChannelLink, 0, len(links)) for link := range links { channelLinks = append(channelLinks, link) } return channelLinks, nil } // removePendingPayment is the helper function which removes the pending user // payment. func (s *Switch) removePendingPayment(amount btcutil.Amount, hash lnwallet.PaymentHash) error { s.pendingMutex.Lock() defer s.pendingMutex.Unlock() payments, ok := s.pendingPayments[hash] if ok { for i, payment := range payments { if payment.amount == amount { // Delete without preserving order // Google: Golang slice tricks payments[i] = payments[len(payments)-1] payments[len(payments)-1] = nil s.pendingPayments[hash] = payments[:len(payments)-1] if len(s.pendingPayments[hash]) == 0 { delete(s.pendingPayments, hash) } return nil } } } return errors.Errorf("unable to remove pending payment with "+ "hash(%v) and amount(%v)", hash, amount) } // findPayment is the helper function which find the payment. func (s *Switch) findPayment(amount btcutil.Amount, hash lnwallet.PaymentHash) (*pendingPayment, error) { s.pendingMutex.RLock() defer s.pendingMutex.RUnlock() payments, ok := s.pendingPayments[hash] if ok { for _, payment := range payments { if payment.amount == amount { return payment, nil } } } return nil, errors.Errorf("unable to remove pending payment with "+ "hash(%v) and amount(%v)", hash, amount) } // numPendingPayments is helper function which returns the overall number of // pending user payments. func (s *Switch) numPendingPayments() int { var l int for _, payments := range s.pendingPayments { l += len(payments) } return l }