multi: add custom message overrides to protocol config options

config.go

@@ -39,6 +39,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/signrpc"
 	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/routing"
 	"github.com/lightningnetwork/lnd/signal"
 	"github.com/lightningnetwork/lnd/sweep"
@@ -1656,6 +1657,17 @@ func ValidateConfig(cfg Config, interceptor signal.Interceptor, fileParser,
 			lncfg.DefaultIncomingBroadcastDelta)
 	}
 
+	// If the experimental protocol options specify any protocol messages
+	// that we want to handle as custom messages, set them now.
+	//nolint:lll
+	customMsg := cfg.ProtocolOptions.ExperimentalProtocol.CustomMessageOverrides()
+
+	// We can safely set our custom override values during startup because
+	// startup is blocked on config parsing.
+	if err := lnwire.SetCustomOverrides(customMsg); err != nil {
+		return nil, mkErr("custom-message: %v", err)
+	}
+
 	// Validate the subconfigs for workers, caches, and the tower client.
 	err = lncfg.Validate(
 		cfg.Workers,

lncfg/protocol_experimental_off.go

@@ -7,3 +7,9 @@ package lncfg
 // features that also require a build-tag to activate.
 type ExperimentalProtocol struct {
 }
+
+// CustomMessageOverrides returns the set of protocol messages that we override
+// to allow custom handling.
+func (p ExperimentalProtocol) CustomMessageOverrides() []uint16 {
+	return nil
+}

lncfg/protocol_experimental_on.go

@@ -5,5 +5,14 @@ package lncfg
 
 // ExperimentalProtocol is a sub-config that houses any experimental protocol
 // features that also require a build-tag to activate.
+//
+//nolint:lll
 type ExperimentalProtocol struct {
+	CustomMessage []uint16 `long:"custom-message" description:"allows the custom message apis to send and report messages with the protocol number provided that fall outside of the custom message number range."`
+}
+
+// CustomMessageOverrides returns the set of protocol messages that we override
+// to allow custom handling.
+func (p ExperimentalProtocol) CustomMessageOverrides() []uint16 {
+	return p.CustomMessage
 }