server+netann+peer: put peer's alias in Update, proper config for link

This commit modifies the netann subsystem to use the peer's alias
for ChannelUpdates where appropriate (i.e. in case we are sending
the alias to the peer). It also modifies the loadActiveChannels
function in the peer package to handle upgrading a channel when the
scid-alias feature bit is turned on.

peer/brontide.go

@@ -330,6 +330,18 @@ type Config struct {
 	// from the peer.
 	HandleCustomMessage func(peer [33]byte, msg *lnwire.Custom) error
 
+	// GetAliases is passed to created links so the Switch and link can be
+	// aware of the channel's aliases.
+	GetAliases func(base lnwire.ShortChannelID) []lnwire.ShortChannelID
+
+	// RequestAlias allows the Brontide struct to request an alias to send
+	// to the peer.
+	RequestAlias func() (lnwire.ShortChannelID, error)
+
+	// AddLocalAlias persists an alias to an underlying alias store.
+	AddLocalAlias func(alias, base lnwire.ShortChannelID,
+		gossip bool) error
+
 	// PongBuf is a slice we'll reuse instead of allocating memory on the
 	// heap. Since only reads will occur and no writes, there is no need
 	// for any synchronization primitives. As a result, it's safe to share
@@ -666,7 +678,65 @@ func (p *Brontide) loadActiveChannels(chans []*channeldb.OpenChannel) (
 	// cannot be loaded normally.
 	var msgs []lnwire.Message
 
+	scidAliasNegotiated := p.hasNegotiatedScidAlias()
+
 	for _, dbChan := range chans {
+		hasScidFeature := dbChan.ChanType.HasScidAliasFeature()
+		if scidAliasNegotiated && !hasScidFeature {
+			// We'll request and store an alias, making sure that a
+			// gossiper mapping is not created for the alias to the
+			// real SCID. This is done because the peer and funding
+			// manager are not aware of each other's states and if
+			// we did not do this, we would accept alias channel
+			// updates after 6 confirmations, which would be buggy.
+			// We'll queue a funding_locked message with the new
+			// alias. This should technically be done *after* the
+			// reestablish, but this behavior is pre-existing since
+			// the funding manager may already queue a
+			// funding_locked before the channel_reestablish.
+			if !dbChan.IsPending {
+				aliasScid, err := p.cfg.RequestAlias()
+				if err != nil {
+					return nil, err
+				}
+
+				err = p.cfg.AddLocalAlias(
+					aliasScid, dbChan.ShortChanID(), false,
+				)
+				if err != nil {
+					return nil, err
+				}
+
+				chanID := lnwire.NewChanIDFromOutPoint(
+					&dbChan.FundingOutpoint,
+				)
+
+				// Fetch the second commitment point to send in
+				// the funding_locked message.
+				second, err := dbChan.SecondCommitmentPoint()
+				if err != nil {
+					return nil, err
+				}
+
+				fundingLockedMsg := lnwire.NewFundingLocked(
+					chanID, second,
+				)
+				fundingLockedMsg.AliasScid = &aliasScid
+
+				msgs = append(msgs, fundingLockedMsg)
+			}
+
+			// If we've negotiated the option-scid-alias feature
+			// and this channel does not have ScidAliasFeature set
+			// to true due to an upgrade where the feature bit was
+			// turned on, we'll update the channel's database
+			// state.
+			err := dbChan.MarkScidAliasNegotiated()
+			if err != nil {
+				return nil, err
+			}
+		}
+
 		lnChan, err := lnwallet.NewLightningChannel(
 			p.cfg.Signer, dbChan, p.cfg.SigPool,
 		)
@@ -900,6 +970,7 @@ func (p *Brontide) addLink(chanPoint *wire.OutPoint,
 		NotifyActiveChannel:     p.cfg.ChannelNotifier.NotifyActiveChannelEvent,
 		NotifyInactiveChannel:   p.cfg.ChannelNotifier.NotifyInactiveChannelEvent,
 		HtlcNotifier:            p.cfg.HtlcNotifier,
+		GetAliases:              p.cfg.GetAliases,
 	}
 
 	// Before adding our new link, purge the switch of any pending or live
@@ -3054,6 +3125,14 @@ func (p *Brontide) RemoteFeatures() *lnwire.FeatureVector {
 	return p.remoteFeatures
 }
 
+// hasNegotiatedScidAlias returns true if we've negotiated the
+// option-scid-alias feature bit with the peer.
+func (p *Brontide) hasNegotiatedScidAlias() bool {
+	peerHas := p.remoteFeatures.HasFeature(lnwire.ScidAliasOptional)
+	localHas := p.cfg.Features.HasFeature(lnwire.ScidAliasOptional)
+	return peerHas && localHas
+}
+
 // sendInitMsg sends the Init message to the remote peer. This message contains
 // our currently supported local and global features.
 func (p *Brontide) sendInitMsg(legacyChan bool) error {

peer/test_utils.go

@@ -340,7 +340,11 @@ func createTestPeer(notifier chainntnfs.ChainNotifier,
 		OurPubKey:                aliceKeyPub,
 		OurKeyLoc:                testKeyLoc,
 		IsChannelActive:          func(lnwire.ChannelID) bool { return true },
-		ApplyChannelUpdate:       func(*lnwire.ChannelUpdate) error { return nil },
+		ApplyChannelUpdate: func(*lnwire.ChannelUpdate,
+			*wire.OutPoint, bool) error {
+
+			return nil
+		},
 	})
 	if err != nil {
 		return nil, nil, nil, err