link: increase expiry grace delta

This commit increase the expiry grace delta to a value above the
broadcast delta. This prevents htlcs from being accepted that would
immediately trigger a channel force close.

A correct delta is generated in server.go where there is access to
the broadcast delta and passed via the peer to the links.

Co-authored-by: Jim Posen <jim.posen@gmail.com>

peer.go

@@ -58,6 +58,13 @@ const (
 	// messages to be sent across the wire, requested by objects outside
 	// this struct.
 	outgoingQueueLen = 50
+
+	// extraExpiryGraceDelta is the additional number of blocks required by
+	// the ExpiryGraceDelta of the forwarding policy beyond the maximum
+	// broadcast delta. This is the minimum number of blocks between the
+	// expiry on an accepted or offered HTLC and the block height at which
+	// we will go to chain.
+	extraExpiryGraceDelta = 3
 )
 
 // outgoingMsg packages an lnwire.Message to be sent out on the wire, along with
@@ -199,6 +206,12 @@ type peer struct {
 	// remote node.
 	localFeatures *lnwire.RawFeatureVector
 
+	// expiryGraceDelta is the block time allowance for HTLCs offered and
+	// received on channels with this peer. The parameter is used to
+	// configure links with the peer. See ExpiryGraceDelta on
+	// ChannelLinkConfig for more information.
+	expiryGraceDelta uint32
+
 	// remoteLocalFeatures is the local feature vector received from the
 	// peer during the connection handshake.
 	remoteLocalFeatures *lnwire.FeatureVector
@@ -236,7 +249,8 @@ var _ lnpeer.Peer = (*peer)(nil)
 func newPeer(conn net.Conn, connReq *connmgr.ConnReq, server *server,
 	addr *lnwire.NetAddress, inbound bool,
 	localFeatures *lnwire.RawFeatureVector,
-	chanActiveTimeout time.Duration) (*peer, error) {
+	chanActiveTimeout time.Duration, expiryGraceDelta uint32) (
+	*peer, error) {
 
 	nodePub := addr.IdentityKey
 
@@ -249,7 +263,8 @@ func newPeer(conn net.Conn, connReq *connmgr.ConnReq, server *server,
 
 		server: server,
 
-		localFeatures: localFeatures,
+		localFeatures:    localFeatures,
+		expiryGraceDelta: expiryGraceDelta,
 
 		sendQueue:     make(chan outgoingMsg),
 		outgoingQueue: make(chan outgoingMsg),
@@ -587,6 +602,7 @@ func (p *peer) addLink(chanPoint *wire.OutPoint,
 		UnsafeReplay:        cfg.UnsafeReplay,
 		MinFeeUpdateTimeout: htlcswitch.DefaultMinLinkFeeUpdateTimeout,
 		MaxFeeUpdateTimeout: htlcswitch.DefaultMaxLinkFeeUpdateTimeout,
+		ExpiryGraceDelta:    p.expiryGraceDelta,
 	}
 
 	link := htlcswitch.NewChannelLink(linkCfg, lnChan)