lsps2: framework for scid management

There's a background watcher that scans the lightning node for in-use scids. These scids are cached in memory.
There's a table containing the scids in use for the LSP.

`ScidService.ReserveNewScid` attempts to reserve an unused scid. It tries a few times, just in case it runs into a collision.

To tie this PR together into something working:
- Initialize a `lightning.ScidCache`
- Run `LightningClient.WatchScids` on either the CLN or LND client
- Initialize a `jit.ScidCleaner` and start it
- Initialize a `jit.ScidService`
- Call `ScidService.ReserveNewScid` to reserve a scid

cln/cln_client.go

@@ -1,6 +1,7 @@
 package cln
 
 import (
+	"context"
 	"encoding/hex"
 	"fmt"
 	"log"
@@ -259,7 +260,7 @@ func (c *ClnClient) GetPeerId(scid *basetypes.ShortChannelID) ([]byte, error) {
 	return hex.DecodeString(*dest)
 }
 
-var pollingInterval = 400 * time.Millisecond
+var onlinePollingInterval = 400 * time.Millisecond
 
 func (c *ClnClient) WaitOnline(peerID []byte, deadline time.Time) error {
 	peerIDStr := hex.EncodeToString(peerID)
@@ -272,11 +273,73 @@ func (c *ClnClient) WaitOnline(peerID []byte, deadline time.Time) error {
 		select {
 		case <-time.After(time.Until(deadline)):
 			return fmt.Errorf("timeout")
-		case <-time.After(pollingInterval):
+		case <-time.After(onlinePollingInterval):
 		}
 	}
 }
 
 func (c *ClnClient) WaitChannelActive(peerID []byte, deadline time.Time) error {
 	return nil
 }
+
+const scidPollingInterval = time.Second * 10
+
+func (c *ClnClient) WatchScids(
+	ctx context.Context,
+	cache lightning.ScidCacheWriter,
+) error {
+	ticker := time.NewTicker(scidPollingInterval)
+	defer ticker.Stop()
+
+	err := c.updateScids(cache)
+	if err != nil {
+		return err
+	}
+
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-ticker.C:
+			err = c.updateScids(cache)
+			if err != nil {
+				return err
+			}
+		}
+	}
+}
+
+func (c *ClnClient) updateScids(cache lightning.ScidCacheWriter) error {
+	peers, err := c.client.ListPeers()
+	if err != nil {
+		return err
+	}
+
+	var scids []basetypes.ShortChannelID
+	for _, peer := range peers {
+		for _, ch := range peer.Channels {
+			s, err := mapToScids(ch.Alias.Local, ch.ShortChannelId)
+			if err != nil {
+				return err
+			}
+
+			scids = append(scids, s...)
+		}
+	}
+
+	cache.ReplaceScids(scids)
+	return nil
+}
+
+func mapToScids(scids ...string) ([]basetypes.ShortChannelID, error) {
+	var result []basetypes.ShortChannelID
+	for _, scid := range scids {
+		s, err := basetypes.NewShortChannelIDFromString(scid)
+		if err != nil {
+			return nil, err
+		}
+		result = append(result, *s)
+	}
+
+	return result, nil
+}

lightning/client.go

@@ -1,6 +1,7 @@
 package lightning
 
 import (
+	"context"
 	"time"
 
 	"github.com/breez/lspd/basetypes"
@@ -38,4 +39,5 @@ type Client interface {
 	GetClosedChannels(nodeID string, channelPoints map[string]uint64) (map[string]uint64, error)
 	WaitOnline(peerID []byte, deadline time.Time) error
 	WaitChannelActive(peerID []byte, deadline time.Time) error
+	WatchScids(ctx context.Context, cache ScidCacheWriter) error
 }

lightning/scid_cache.go

@@ -0,0 +1,72 @@
+package lightning
+
+import (
+	"sync"
+
+	"github.com/breez/lspd/basetypes"
+)
+
+type ScidCacheReader interface {
+	ContainsScid(scid basetypes.ShortChannelID) bool
+}
+
+type ScidCacheWriter interface {
+	AddScids(scids ...basetypes.ShortChannelID)
+	RemoveScids(scids ...basetypes.ShortChannelID)
+	ReplaceScids(scids []basetypes.ShortChannelID)
+}
+
+type ScidCache struct {
+	activeScids map[uint64]bool
+	mtx         sync.RWMutex
+}
+
+func NewScidCache() *ScidCache {
+	return &ScidCache{
+		activeScids: make(map[uint64]bool),
+	}
+}
+
+func (s *ScidCache) ContainsScid(
+	scid basetypes.ShortChannelID,
+) bool {
+	s.mtx.RLock()
+	defer s.mtx.RUnlock()
+
+	_, ok := s.activeScids[uint64(scid)]
+	return ok
+}
+
+func (s *ScidCache) AddScids(
+	scids ...basetypes.ShortChannelID,
+) {
+	s.mtx.Lock()
+	defer s.mtx.Unlock()
+
+	for _, scid := range scids {
+		s.activeScids[uint64(scid)] = true
+	}
+}
+
+func (s *ScidCache) RemoveScids(
+	scids ...basetypes.ShortChannelID,
+) {
+	s.mtx.Lock()
+	defer s.mtx.Unlock()
+
+	for _, scid := range scids {
+		delete(s.activeScids, uint64(scid))
+	}
+}
+
+func (s *ScidCache) ReplaceScids(
+	scids []basetypes.ShortChannelID,
+) {
+	s.mtx.Lock()
+	defer s.mtx.Unlock()
+
+	s.activeScids = make(map[uint64]bool)
+	for _, scid := range scids {
+		s.activeScids[uint64(scid)] = true
+	}
+}

lnd/client.go

@@ -365,6 +365,72 @@ func (c *LndClient) GetClosedChannels(nodeID string, channelPoints map[string]ui
 	return r, nil
 }
 
+func (c *LndClient) WatchScids(
+	ctx context.Context,
+	cache lightning.ScidCacheWriter,
+) error {
+	stream, err := c.client.SubscribeChannelEvents(
+		ctx,
+		&lnrpc.ChannelEventSubscription{},
+	)
+	if err != nil {
+		return err
+	}
+
+	// Sync current scids first
+	chans, err := c.client.ListChannels(
+		context.Background(),
+		&lnrpc.ListChannelsRequest{},
+	)
+	if err != nil {
+		return err
+	}
+
+	var initialScids []basetypes.ShortChannelID
+	for _, ch := range chans.Channels {
+		initialScids = append(
+			initialScids,
+			mapToScids(append(ch.AliasScids, ch.ChanId, ch.ZeroConfConfirmedScid)...)...)
+	}
+	cache.ReplaceScids(initialScids)
+
+	// Watch channels for changes
+	for {
+		upd, err := stream.Recv()
+		if err != nil {
+			return err
+		}
+
+		switch upd.Type {
+		case lnrpc.ChannelEventUpdate_OPEN_CHANNEL:
+			ch := upd.GetOpenChannel()
+			if ch == nil {
+				continue
+			}
+
+			scids := mapToScids(append(ch.AliasScids, ch.ChanId, ch.ZeroConfConfirmedScid)...)
+			cache.AddScids(scids...)
+		case lnrpc.ChannelEventUpdate_CLOSED_CHANNEL:
+			ch := upd.GetClosedChannel()
+			if ch == nil {
+				continue
+			}
+
+			scids := mapToScids(append(ch.AliasScids, ch.ChanId, ch.ZeroConfConfirmedScid)...)
+			cache.RemoveScids(scids...)
+		}
+	}
+}
+
+func mapToScids(scids ...uint64) []basetypes.ShortChannelID {
+	var result []basetypes.ShortChannelID
+	for _, scid := range scids {
+		result = append(result, basetypes.ShortChannelID(scid))
+	}
+
+	return result
+}
+
 func (c *LndClient) getWaitingCloseChannels(nodeID string) ([]*lnrpc.PendingChannelsResponse_WaitingCloseChannel, error) {
 	pendingResponse, err := c.client.PendingChannels(context.Background(), &lnrpc.PendingChannelsRequest{})
 	if err != nil {

lsps2/scid_cleaner.go

@@ -0,0 +1,39 @@
+package lsps2
+
+import (
+	"context"
+	"log"
+	"time"
+)
+
+type ScidCleaner struct {
+	interval time.Duration
+	store    ScidStore
+}
+
+func NewScidCleaner(
+	store ScidStore,
+	interval time.Duration,
+) *ScidCleaner {
+	return &ScidCleaner{
+		interval: interval,
+		store:    store,
+	}
+}
+
+func (s *ScidCleaner) Start(ctx context.Context) error {
+	ticker := time.NewTicker(s.interval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case t := <-ticker.C:
+			err := s.store.RemoveExpired(ctx, t)
+			if err != nil {
+				log.Printf("Failed to remove expired scids: %v", err)
+			}
+		}
+	}
+}

lsps2/scid_service.go

@@ -0,0 +1,82 @@
+package lsps2
+
+import (
+	"context"
+	"crypto/rand"
+	"fmt"
+	"log"
+	"math/big"
+	"time"
+
+	"github.com/breez/lspd/basetypes"
+	"github.com/breez/lspd/lightning"
+)
+
+const maxScidAttempts = 5
+
+var two = big.NewInt(2)
+var sixtyfour = big.NewInt(64)
+var maxUint64 = two.Exp(two, sixtyfour, nil)
+
+func newScid() (*basetypes.ShortChannelID, error) {
+	s, err := rand.Int(rand.Reader, maxUint64)
+	if err != nil {
+		return nil, err
+	}
+
+	scid := basetypes.ShortChannelID(s.Uint64())
+	return &scid, nil
+}
+
+type ScidService struct {
+	store ScidStore
+	cache lightning.ScidCacheReader
+}
+
+func NewScidService(
+	store ScidStore,
+	cache lightning.ScidCacheReader,
+) *ScidService {
+	return &ScidService{store: store, cache: cache}
+}
+
+func (s *ScidService) ReserveNewScid(
+	ctx context.Context,
+	expiry time.Time,
+) (*basetypes.ShortChannelID, error) {
+	for attempts := 0; attempts < maxScidAttempts; attempts++ {
+		scid, err := newScid()
+		if err != nil {
+			log.Printf("NewScid() error: %v", err)
+			continue
+		}
+
+		if s.cache.ContainsScid(*scid) {
+			log.Printf(
+				"Collision with existing channel when generating new scid %s",
+				scid.ToString(),
+			)
+			continue
+		}
+
+		err = s.store.AddScid(ctx, *scid, expiry)
+		if err == ErrScidExists {
+			log.Printf(
+				"Collision on inserting random new scid %s",
+				scid.ToString(),
+			)
+			continue
+		}
+
+		if err != nil {
+			return nil, fmt.Errorf("failed to insert scid reservation: %w", err)
+		}
+
+		return scid, nil
+	}
+
+	return nil, fmt.Errorf(
+		"failed to reserve scid after %v attempts",
+		maxScidAttempts,
+	)
+}

lsps2/scid_store.go

@@ -0,0 +1,20 @@
+package lsps2
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/breez/lspd/basetypes"
+)
+
+var ErrScidExists = fmt.Errorf("scid already exists")
+
+type ScidStore interface {
+	AddScid(
+		ctx context.Context,
+		scid basetypes.ShortChannelID,
+		expiry time.Time,
+	) error
+	RemoveExpired(ctx context.Context, before time.Time) error
+}

postgresql/migrations/000014_lsps2.down.sql

@@ -0,0 +1,2 @@
+DROP INDEX scid_reservations_expiry_idx;
+DROP TABLE public.scid_reservations;