lnrpc: Update SubscribeOnionMessages

With this Update we change the SubscribeOnionMessages RPC to return a
stream of OnionMessageUpdate messages instead of OnionMessage. This way
we also send back the decrypted payload if any, so we can inspect that
in itests.

Author: gijswijs

itest/lnd_onion_message_test.go

@@ -20,7 +20,7 @@ func testOnionMessage(ht *lntest.HarnessTest) {
 	defer cancel()
 
 	// Create a channel to receive onion messages on.
-	messages := make(chan *lnrpc.OnionMessage)
+	messages := make(chan *lnrpc.OnionMessageUpdate)
 	go func() {
 		for {
 			// If we fail to receive, just exit. The test should

lnrpc/lightning.pb.go

@@ -607,7 +607,7 @@ service Lightning {
     SubscribeOnionMessages subscribes to a stream of incoming onion messages.
     */
     rpc SubscribeOnionMessages (SubscribeOnionMessagesRequest)
-        returns (stream OnionMessage);
+        returns (stream OnionMessageUpdate);
 
     /* lncli: `listaliases`
     ListAliases returns the set of all aliases that have ever existed with
@@ -676,7 +676,7 @@ message SendCustomMessageResponse {
 message SubscribeOnionMessagesRequest {
 }
 
-message OnionMessage {
+message OnionMessageUpdate {
     // Peer from which this message originates. Represented as a byte-encoded
     // public key.
     bytes peer = 1;
@@ -694,6 +694,20 @@ message OnionMessage {
     // encrypted payloads and routing instructions used to forward this message
     // along its designated path.
     bytes onion = 3;
+
+    // reply_path is the blinded path that should be used when replying to a
+    // received message.
+    BlindedPath reply_path = 4;
+
+    // encrypted_recipient_data is the encrypted data that contains the
+    // forwarding information for an onion message. It contains either
+    // next_node_id or short_channel_id for each non-final node. It MAY contain
+    // the path_id for the final node.
+    bytes encrypted_recipient_data = 5;
+
+    // Custom onion message tlv records. These are customized fields that are
+    // not defined by LND and cannot be extracted.
+    map<uint64, bytes> custom_records = 6;
 }
 
 message SendOnionMessageRequest {

lnrpc/lightning.proto

@@ -2308,13 +2308,13 @@
               "type": "object",
               "properties": {
                 "result": {
-                  "$ref": "#/definitions/lnrpcOnionMessage"
+                  "$ref": "#/definitions/lnrpcOnionMessageUpdate"
                 },
                 "error": {
                   "$ref": "#/definitions/rpcStatus"
                 }
               },
-              "title": "Stream result of lnrpcOnionMessage"
+              "title": "Stream result of lnrpcOnionMessageUpdate"
             }
           },
           "default": {
@@ -6542,7 +6542,7 @@
         }
       }
     },
-    "lnrpcOnionMessage": {
+    "lnrpcOnionMessageUpdate": {
       "type": "object",
       "properties": {
         "peer": {
@@ -6559,6 +6559,23 @@
           "type": "string",
           "format": "byte",
           "description": "Serialized Sphinx onion packet (BOLT 4) containing the layered, per-hop\nencrypted payloads and routing instructions used to forward this message\nalong its designated path."
+        },
+        "reply_path": {
+          "$ref": "#/definitions/lnrpcBlindedPath",
+          "description": "reply_path is the blinded path that should be used when replying to a\nreceived message."
+        },
+        "encrypted_recipient_data": {
+          "type": "string",
+          "format": "byte",
+          "description": "encrypted_recipient_data is the encrypted data that contains the\nforwarding information for an onion message. It contains either\nnext_node_id or short_channel_id for each non-final node. It MAY contain\nthe path_id for the final node."
+        },
+        "custom_records": {
+          "type": "object",
+          "additionalProperties": {
+            "type": "string",
+            "format": "byte"
+          },
+          "description": "Custom onion message tlv records. These are customized fields that are\nnot defined by LND and cannot be extracted."
         }
       }
     },

lnrpc/lightning.swagger.json

@@ -9368,10 +9368,30 @@ func (r *rpcServer) SubscribeOnionMessages(
 					"failed type assertion: %T", update)
 			}
 
-			err := server.Send(&lnrpc.OnionMessage{
-				Peer:    oMsg.Peer[:],
-				PathKey: oMsg.PathKey[:],
-				Onion:   oMsg.OnionBlob,
+			bp := &lnrpc.BlindedPath{}
+
+			//nolint:ll
+			if oMsg.ReplyPath != nil {
+				bp.IntroductionNode = oMsg.ReplyPath.FirstNodeID.SerializeCompressed()
+				bp.BlindingPoint = oMsg.ReplyPath.BlindingPoint.SerializeCompressed()
+
+				for _, hop := range oMsg.ReplyPath.Hops {
+					rpcHop := &lnrpc.BlindedHop{
+						BlindedNode:   hop.BlindedNodeID.SerializeCompressed(),
+						EncryptedData: hop.EncryptedData,
+					}
+					bp.BlindedHops = append(bp.BlindedHops, rpcHop)
+				}
+			}
+
+			//nolint:ll
+			err := server.Send(&lnrpc.OnionMessageUpdate{
+				Peer:                   oMsg.Peer[:],
+				PathKey:                oMsg.PathKey[:],
+				Onion:                  oMsg.OnionBlob,
+				ReplyPath:              bp,
+				EncryptedRecipientData: oMsg.EncryptedRecipientData,
+				CustomRecords:          oMsg.CustomRecords,
 			})
 			if err != nil {
 				return err