From 781c6e5bea78bb9d5c650f5d52e8c5017646d7e9 Mon Sep 17 00:00:00 2001
From: Conner Fromknecht <conner@lightning.engineering>
Date: Wed, 25 Nov 2020 15:05:36 -0800
Subject: [PATCH] wtclient: add anchor-aware session negotiation and filtering

---
 watchtower/wtclient/client.go             | 17 +++++++++++------
 watchtower/wtclient/session_negotiator.go | 13 ++++++++++++-
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/watchtower/wtclient/client.go b/watchtower/wtclient/client.go
index d0cb4283..36f36d19 100644
--- a/watchtower/wtclient/client.go
+++ b/watchtower/wtclient/client.go
@@ -41,13 +41,14 @@ const (
 	DefaultForceQuitDelay = 10 * time.Second
 )
 
-var (
-	// activeSessionFilter is a filter that ignored any sessions which are
-	// not active.
-	activeSessionFilter = func(s *wtdb.ClientSession) bool {
-		return s.Status == wtdb.CSessionActive
+// genActiveSessionFilter generates a filter that selects active sessions that
+// also match the desired channel type, either legacy or anchor.
+func genActiveSessionFilter(anchor bool) func(*wtdb.ClientSession) bool {
+	return func(s *wtdb.ClientSession) bool {
+		return s.Status == wtdb.CSessionActive &&
+			anchor == s.Policy.IsAnchorChannel()
 	}
-)
+}
 
 // RegisteredTower encompasses information about a registered watchtower with
 // the client.
@@ -280,6 +281,8 @@ func New(config *Config) (*TowerClient, error) {
 	// the client. We will use any of these session if their policies match
 	// the current policy of the client, otherwise they will be ignored and
 	// new sessions will be requested.
+	isAnchorClient := cfg.Policy.IsAnchorChannel()
+	activeSessionFilter := genActiveSessionFilter(isAnchorClient)
 	candidateSessions, err := getClientSessions(
 		cfg.DB, cfg.SecretKeyRing, nil, activeSessionFilter,
 	)
@@ -1068,6 +1071,8 @@ func (c *TowerClient) handleNewTower(msg *newTowerMsg) error {
 	c.candidateTowers.AddCandidate(tower)
 
 	// Include all of its corresponding sessions to our set of candidates.
+	isAnchorClient := c.cfg.Policy.IsAnchorChannel()
+	activeSessionFilter := genActiveSessionFilter(isAnchorClient)
 	sessions, err := getClientSessions(
 		c.cfg.DB, c.cfg.SecretKeyRing, &tower.ID, activeSessionFilter,
 	)
diff --git a/watchtower/wtclient/session_negotiator.go b/watchtower/wtclient/session_negotiator.go
index 67be526d..59ad59f3 100644
--- a/watchtower/wtclient/session_negotiator.go
+++ b/watchtower/wtclient/session_negotiator.go
@@ -112,8 +112,19 @@ var _ SessionNegotiator = (*sessionNegotiator)(nil)
 
 // newSessionNegotiator initializes a fresh sessionNegotiator instance.
 func newSessionNegotiator(cfg *NegotiatorConfig) *sessionNegotiator {
+	// Generate the set of features the negitator will present to the tower
+	// upon connection. For anchor channels, we'll conditionally signal that
+	// we require support for anchor channels depdening on the requested
+	// policy.
+	features := []lnwire.FeatureBit{
+		wtwire.AltruistSessionsRequired,
+	}
+	if cfg.Policy.IsAnchorChannel() {
+		features = append(features, wtwire.AnchorCommitRequired)
+	}
+
 	localInit := wtwire.NewInitMessage(
-		lnwire.NewRawFeatureVector(wtwire.AltruistSessionsRequired),
+		lnwire.NewRawFeatureVector(features...),
 		cfg.ChainHash,
 	)