funding: create new AuxFundingController interface

In this commit, we make a new `AuxFundingController` interface capable of processing messages off the wire. In addition, we can use it to abstract away details w.r.t how we obtain a `AuxFundingDesc` for a given channel.

We'll now use this whenever we get a channel funding request, to make sure we pass along the custom state that a channel may require.

Author: Roasbeef

funding/aux_funding.go

@@ -0,0 +1,26 @@
+package funding
+
+import (
+	"github.com/lightningnetwork/lnd/fn"
+	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/protofsm"
+)
+
+// AuxFundingController permits the implementation of the funding of custom
+// channels types. The controller serves as a MsgEndpoint which allows it to
+// intercept custom messages, or even the regular funding messages. The
+// controller might also pass along an aux funding desc based on an existing
+// pending channel ID.
+type AuxFundingController interface {
+	// The controller is also a message endpoint. This'll allow it to
+	// handle custom messages specific to the funding type.
+	protofsm.MsgEndpoint
+
+	// DescPendingChanID takes a pending channel ID, that may already be
+	// known due to prior custom channel messages, and maybe returns an aux
+	// funding desc which can be used to modify how a channel is funded.
+	//
+	// TODO(roasbeef): erorr on validation if fail due to invalid root
+	// match?
+	DescFromPendingChanID(PendingChanID) fn.Option[lnwallet.AuxFundingDesc]
+}

funding/manager.go

@@ -539,6 +539,12 @@ type Config struct {
 	// AliasManager is an implementation of the aliasHandler interface that
 	// abstracts away the handling of many alias functions.
 	AliasManager aliasHandler
+
+	// AuxFundingController is an optional controller that can be used to
+	// modify the way we handle certain custom chanenl types. It's also
+	// able to automatically handle new custom protocol messages related to
+	// the funding process.
+	AuxFundingController fn.Option[AuxFundingController]
 }
 
 // Manager acts as an orchestrator/bridge between the wallet's
@@ -1604,6 +1610,15 @@ func (f *Manager) fundeeProcessOpenChannel(peer lnpeer.Peer,
 		return
 	}
 
+	// At this point, if we have an AuxFundingController active, we'll
+	// check to see if we have any aux info that we should carry along for
+	// this pid.
+	auxFundingDesc := fn.MapOption(
+		func(a AuxFundingController) fn.Option[lnwallet.AuxFundingDesc] {
+			return a.DescFromPendingChanID(msg.PendingChannelID)
+		},
+	)(f.cfg.AuxFundingController)
+
 	req := &lnwallet.InitFundingReserveMsg{
 		ChainHash:        &msg.ChainHash,
 		PendingChanID:    msg.PendingChannelID,
@@ -1620,6 +1635,7 @@ func (f *Manager) fundeeProcessOpenChannel(peer lnpeer.Peer,
 		ZeroConf:         zeroConf,
 		OptionScidAlias:  scid,
 		ScidAliasFeature: scidFeatureVal,
+		AuxFundingDesc:   fn.FlattenOption(auxFundingDesc),
 	}
 
 	reservation, err := f.cfg.Wallet.InitChannelReservation(req)
@@ -4594,6 +4610,15 @@ func (f *Manager) handleInitFundingMsg(msg *InitFundingMsg) {
 		scidFeatureVal = true
 	}
 
+	// At this point, if we have an AuxFundingController active, we'll
+	// check to see if we have any aux info that we should carry along for
+	// this pid.
+	auxFundingDesc := fn.MapOption(
+		func(a AuxFundingController) fn.Option[lnwallet.AuxFundingDesc] {
+			return a.DescFromPendingChanID(chanID)
+		},
+	)(f.cfg.AuxFundingController)
+
 	req := &lnwallet.InitFundingReserveMsg{
 		ChainHash:         &msg.ChainHash,
 		PendingChanID:     chanID,
@@ -4617,6 +4642,7 @@ func (f *Manager) handleInitFundingMsg(msg *InitFundingMsg) {
 		OptionScidAlias:   scid,
 		ScidAliasFeature:  scidFeatureVal,
 		Memo:              msg.Memo,
+		AuxFundingDesc:    fn.FlattenOption(auxFundingDesc),
 	}
 
 	reservation, err := f.cfg.Wallet.InitChannelReservation(req)