lnwallet: introduce AuxChannelNegotiator interface

We introduce this new interface with the purpose of injecting and
handling custom records on the init message, and also notifying
external components when receiving the ChannelReady or
ChannelReestablish message.

lnwallet/aux_negotiator.go

@@ -0,0 +1,34 @@
+package lnwallet
+
+import (
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/routing/route"
+)
+
+// AuxChannelNegotiator is an interface that allows aux channel implementations
+// to inject or handle custom records in the init message that is used when
+// establishing a connection with a peer. It may also notify the aux channel
+// implementation for the channel ready or channel reestablish events, which
+// mark the channel as ready to use.
+type AuxChannelNegotiator interface {
+	// GetInitRecords is called when sending an init message to a peer.
+	// It returns custom records to include in the init message TLVs. The
+	// implementation can decide which records to include based on the peer
+	// identity.
+	GetInitRecords(peer route.Vertex) (lnwire.CustomRecords, error)
+
+	// ProcessInitRecords handles received init records from a peer. The
+	// implementation can store state internally to affect future
+	// channel operations with this peer.
+	ProcessInitRecords(peer route.Vertex,
+		customRecords lnwire.CustomRecords) error
+
+	// ProcessChannelReady handles the event of marking a channel identified
+	// by its channel ID as ready to use. We also provide the peer the
+	// channel was established with.
+	ProcessChannelReady(cid lnwire.ChannelID, peer route.Vertex)
+
+	// ProcessReestablish handles the received channel_reestablish message
+	// which marks a channel identified by its cid as ready to use again.
+	ProcessReestablish(cid lnwire.ChannelID, peer route.Vertex)
+}