htlcswitch: extend ChannelLink iface with dustHandler iface

This allows the Switch to determine the dust exposure of a certain
channel and allows the link to set the dust limits for its mailbox.

Author: Crypt-iQ

htlcswitch/interfaces.go

@@ -57,6 +57,17 @@ type packetHandler interface {
 	handleLocalAddPacket(*htlcPacket) error
 }
 
+// dustHandler is an interface used exclusively by the Switch to evaluate
+// whether a link has too much dust exposure.
+type dustHandler interface {
+	// getDustSum returns the dust sum on either the local or remote
+	// commitment.
+	getDustSum(remote bool) lnwire.MilliSatoshi
+
+	// getDustLimits returns the underlying channel's dust limits.
+	getDustLimits() (lnwire.MilliSatoshi, lnwire.MilliSatoshi)
+}
+
 // ChannelUpdateHandler is an interface that provides methods that allow
 // sending lnwire.Message to the underlying link as well as querying state.
 type ChannelUpdateHandler interface {
@@ -122,6 +133,9 @@ type ChannelLink interface {
 	// Embed the ChannelUpdateHandler interface.
 	ChannelUpdateHandler
 
+	// Embed the dustHandler interface.
+	dustHandler
+
 	// ChannelPoint returns the channel outpoint for the channel link.
 	ChannelPoint() *wire.OutPoint
 

htlcswitch/link.go

@@ -2192,6 +2192,29 @@ func (l *channelLink) MayAddOutgoingHtlc() error {
 	return l.channel.MayAddOutgoingHtlc()
 }
 
+// getDustSum is a wrapper method that calls the underlying channel's dust sum
+// method.
+//
+// NOTE: Part of the dustHandler interface.
+func (l *channelLink) getDustSum(remote bool) lnwire.MilliSatoshi {
+	return l.channel.GetDustSum(remote)
+}
+
+// getDustLimits returns the local and remote dust limits.
+//
+// NOTE: Part of the dustHandler interface.
+func (l *channelLink) getDustLimits() (lnwire.MilliSatoshi,
+	lnwire.MilliSatoshi) {
+
+	localDustLimit := l.channel.State().LocalChanCfg.DustLimit
+	remoteDustLimit := l.channel.State().RemoteChanCfg.DustLimit
+
+	localMsat := lnwire.NewMSatFromSatoshis(localDustLimit)
+	remoteMsat := lnwire.NewMSatFromSatoshis(remoteDustLimit)
+
+	return localMsat, remoteMsat
+}
+
 // AttachMailBox updates the current mailbox used by this link, and hooks up
 // the mailbox's message and packet outboxes to the link's upstream and
 // downstream chans, respectively.
@@ -2200,6 +2223,11 @@ func (l *channelLink) AttachMailBox(mailbox MailBox) {
 	l.mailBox = mailbox
 	l.upstream = mailbox.MessageOutBox()
 	l.downstream = mailbox.PacketOutBox()
+
+	// Set the mailbox's DustLimit variables if they are not already set.
+	local, remote := l.getDustLimits()
+	l.mailBox.SetDustLimits(local, remote)
+
 	l.Unlock()
 }
 

htlcswitch/mock.go

@@ -716,6 +716,16 @@ func (f *mockChannelLink) handleLocalAddPacket(pkt *htlcPacket) error {
 	return nil
 }
 
+func (f *mockChannelLink) getDustSum(remote bool) lnwire.MilliSatoshi {
+	return 0
+}
+
+func (f *mockChannelLink) getDustLimits() (lnwire.MilliSatoshi,
+	lnwire.MilliSatoshi) {
+
+	return 0, 0
+}
+
 func (f *mockChannelLink) HandleChannelUpdate(lnwire.Message) {
 }