lnrpc: receive custom message

cmd/lncli/cmd_custom.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"encoding/hex"
+	"fmt"
 
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/urfave/cli"
@@ -51,3 +52,32 @@ func sendCustom(ctx *cli.Context) error {
 
 	return err
 }
+
+var subscribeCustomCommand = cli.Command{
+	Name:   "subscribecustom",
+	Action: actionDecorator(subscribeCustom),
+}
+
+func subscribeCustom(ctx *cli.Context) error {
+	ctxc := getContext()
+	client, cleanUp := getClient(ctx)
+	defer cleanUp()
+
+	stream, err := client.SubscribeCustomMessages(
+		ctxc,
+		&lnrpc.SubscribeCustomMessagesRequest{},
+	)
+	if err != nil {
+		return err
+	}
+
+	for {
+		msg, err := stream.Recv()
+		if err != nil {
+			return err
+		}
+
+		fmt.Printf("Received from peer %x: type=%d, data=%x\n",
+			msg.Peer, msg.Type, msg.Data)
+	}
+}

cmd/lncli/main.go

@@ -380,6 +380,7 @@ func main() {
 		profileSubCommand,
 		getStateCommand,
 		sendCustomCommand,
+		subscribeCustomCommand,
 	}
 
 	// Add any extra commands determined by build flags.

docs/release-notes/release-notes-0.14.0.md

@@ -41,6 +41,22 @@ you.
 * [Makes publishtransaction, in the wallet sub-server, reachable through 
   lncli](https://github.com/lightningnetwork/lnd/pull/5460).
 
+## Custom peer messages
+
+Lightning nodes have a connection to each of their peers for exchanging
+messages. In regular operation, these messages coordinate processes such as
+channel opening and payment forwarding.
+
+The lightning spec however also defines a custom range (>= 32768) for
+experimental and application-specific peer messages.
+
+With this release, [custom peer message
+exchange](https://github.com/lightningnetwork/lnd/pull/5346) is added to open up
+a range of new possibilities. Custom peer messages allow the lightning protocol
+with its transport mechanisms (including tor) and public key authentication to
+be leveraged for application-level communication. Note that peers exchange these
+messages directly. There is no routing/path finding involved.
+
 # Safety
 
 * Locally force closed channels are now [kept in the channel.backup file until
@@ -152,6 +168,7 @@ change](https://github.com/lightningnetwork/lnd/pull/5613).
 * Andras Banki-Horvath
 * ErikEk
 * Eugene Siegel
+* Joost Jager
 * Martin Habovstiak
 * Zero-1729
 * Oliver Gugger