lnd.xprv/htlcswitch/circuit.go

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package htlcswitch
import (
"bytes"
"crypto/sha256"
"encoding/hex"
"sync"
"github.com/go-errors/errors"
"github.com/lightningnetwork/lnd/lnwire"
)
// circuitKey uniquely identifies an active circuit between two open channels.
// Currently, the payment hash is used to uniquely identify each circuit.
type circuitKey [sha256.Size]byte
// String represent the circuit key in string format.
func (k *circuitKey) String() string {
return hex.EncodeToString(k[:])
}
// paymentCircuit is used by htlc switch subsystem in order to determine
// backward path for settle/fail htlc messages. A payment circuit will be
// created once a channel link forwards the htlc add request and removed when we
// receive settle/fail htlc message.
//
// NOTE: In current implementation of htlc switch, the payment circuit might be
// uniquely identified by payment hash but in future we implement the payment
// fragmentation which makes possible for number of payments to have
// identical payments hashes, but different source or destination.
//
// For example if Alice(A) want to send 2BTC to Bob(B), then payment will be
// split on two parts and node N3 will have circuit with the same payment hash,
// and destination, but different channel source (N1,N2).
//
// 1BTC N1 1BTC
// + --------- o --------- +
// 2BTC | | 2BTC
// A o ------ o N0 N3 o ------ o B
// | |
// + --------- o --------- +
// 1BTC N2 1BTC
//
type paymentCircuit struct {
// PaymentHash used as unique identifier of payment.
PaymentHash circuitKey
// Src identifies the channel from which add htlc request is came from
// and to which settle/fail htlc request will be returned back. Once the
// switch forwards the settle/fail message to the src the circuit is
// considered to be completed.
// TODO(andrew.shvv) use short channel id instead.
Src lnwire.ChannelID
// Dest identifies the channel to which we propagate the htlc add
// update and from which we are expecting to receive htlc settle/fail
// request back.
// TODO(andrew.shvv) use short channel id instead.
Dest lnwire.ChannelID
// RefCount is used to count the circuits with the same circuit key.
RefCount int
}
// newPaymentCircuit creates new payment circuit instance.
func newPaymentCircuit(src, dest lnwire.ChannelID, key circuitKey) *paymentCircuit {
return &paymentCircuit{
Src: src,
Dest: dest,
PaymentHash: key,
RefCount: 1,
}
}
// isEqual checks the equality of two payment circuits.
func (a *paymentCircuit) isEqual(b *paymentCircuit) bool {
return bytes.Equal(a.PaymentHash[:], b.PaymentHash[:]) &&
a.Src == b.Src &&
a.Dest == b.Dest
}
// circuitMap is a thread safe storage of circuits. Each circuit key (payment
// hash) might have numbers of circuits corresponding to it
// because of future payment fragmentation, now every circuit might be uniquely
// identified by payment hash (1-1 mapping).
//
// NOTE: Also we have the htlc debug mode and in this mode we have the same
// payment hash for all htlcs.
// TODO(andrew.shvv) make it persistent
type circuitMap struct {
mutex sync.RWMutex
circuits map[circuitKey]*paymentCircuit
}
// newCircuitMap initialized circuit map with previously stored circuits and
// return circuit map instance.
func newCircuitMap() *circuitMap {
return &circuitMap{
circuits: make(map[circuitKey]*paymentCircuit),
}
}
// add function adds circuit in circuit map.
func (m *circuitMap) add(circuit *paymentCircuit) error {
m.mutex.Lock()
defer m.mutex.Unlock()
// Examine the circuit map to see if this
// circuit is already in use or not. If so,
// then we'll simply increment the reference
// count. Otherwise, we'll create a new circuit
// from scratch.
// TODO(roasbeef): include dest+src+amt in key
if c, ok := m.circuits[circuit.PaymentHash]; ok {
c.RefCount++
} else {
m.circuits[circuit.PaymentHash] = circuit
}
return nil
}
// remove function removes circuit from map.
func (m *circuitMap) remove(key circuitKey) (
*paymentCircuit, error) {
m.mutex.Lock()
defer m.mutex.Unlock()
if circuit, ok := m.circuits[key]; ok {
if circuit.RefCount--; circuit.RefCount == 0 {
delete(m.circuits, key)
}
return circuit, nil
}
return nil, errors.Errorf("can't find circuit"+
" for key %v", key)
}
// pending returns number of circuits which are waiting for to be completed
// (settle/fail responses to be received)
func (m *circuitMap) pending() int {
m.mutex.RLock()
defer m.mutex.RUnlock()
var length int
for _, circuits := range m.circuits {
length += circuits.RefCount
}
return length
}