lnwallet/chancloser: create a MsgMapper for the protofsm rbf close

This'll allow us to treat the state machine as a MsgEndpoint, and have
the readHandler in the peer automatically send new messages to it.

lnwallet/chancloser/rbf_coop_msg_mapper.go

@@ -0,0 +1,77 @@
+package chancloser
+
+import (
+	"github.com/lightningnetwork/lnd/fn/v2"
+	"github.com/lightningnetwork/lnd/lnwire"
+)
+
+// RbfMsgMapper is a struct that implements the MsgMapper interface for the
+// rbf-coop close state machine. This enables the state machine to be used with
+// protofsm.
+type RbfMsgMapper struct {
+	// blockHeight is the height of the block when the co-op close request
+	// was initiated. This is used to validate conditions related to the
+	// thaw height.
+	blockHeight uint32
+
+	// chanID is the channel ID of the channel being closed.
+	chanID lnwire.ChannelID
+}
+
+// NewRbfMsgMapper creates a new RbfMsgMapper instance given the current block
+// height when the co-op close request was initiated.
+func NewRbfMsgMapper(blockHeight uint32,
+	chanID lnwire.ChannelID) *RbfMsgMapper {
+
+	return &RbfMsgMapper{
+		blockHeight: blockHeight,
+		chanID:      chanID,
+	}
+}
+
+// someEvent returns the target type as a protocol event option.
+func someEvent[T ProtocolEvent](m T) fn.Option[ProtocolEvent] {
+	return fn.Some(ProtocolEvent(m))
+}
+
+// isExpectedChanID returns true if the channel ID of the message matches the
+// bound instance.
+func (r *RbfMsgMapper) isExpectedChanID(chanID lnwire.ChannelID) bool {
+	return r.chanID == chanID
+}
+
+// MapMsg maps a wire message into a FSM event. If the message is not mappable,
+// then an error is returned.
+func (r *RbfMsgMapper) MapMsg(wireMsg lnwire.Message) fn.Option[ProtocolEvent] {
+	switch msg := wireMsg.(type) {
+	case *lnwire.Shutdown:
+		if !r.isExpectedChanID(msg.ChannelID) {
+			return fn.None[ProtocolEvent]()
+		}
+
+		return someEvent(&ShutdownReceived{
+			BlockHeight:    r.blockHeight,
+			ShutdownScript: msg.Address,
+		})
+
+	case *lnwire.ClosingComplete:
+		if !r.isExpectedChanID(msg.ChannelID) {
+			return fn.None[ProtocolEvent]()
+		}
+
+		return someEvent(&OfferReceivedEvent{
+			SigMsg: *msg,
+		})
+
+	case *lnwire.ClosingSig:
+		if !r.isExpectedChanID(msg.ChannelID) {
+			return fn.None[ProtocolEvent]()
+		}
+
+		return someEvent(&LocalSigReceived{
+			SigMsg: *msg,
+		})
+	}
+
+	return fn.None[ProtocolEvent]()
+}