plugin: Add a status field to htlcs in listpeers

Annotating the htlc in `listpeers` with their current status, and
which plugin is currently holding on to them with their
`htlc_accepted` hook can help us debug where plugins may go wrong.

Changelog-Added: jsonrpc: HTLCs in `listpeers` are now annotated with a status if they are waiting on an `htlc_accepted` hook of a plugin.

lightningd/peer_control.c

@@ -505,6 +505,8 @@ static void json_add_htlcs(struct lightningd *ld,
 				    channel->our_config.dust_limit, LOCAL,
 				    channel->option_anchor_outputs))
 			json_add_bool(response, "local_trimmed", true);
+		if (hin->status != NULL)
+			json_add_string(response, "status", hin->status);
 		json_object_end(response);
 	}
 

lightningd/peer_htlcs.c

@@ -1015,8 +1015,14 @@ static void htlc_accepted_hook_serialize(struct htlc_accepted_hook_payload *p,
 					 struct plugin *plugin)
 {
 	const struct route_step *rs = p->route_step;
-	const struct htlc_in *hin = p->hin;
+	struct htlc_in *hin = p->hin;
 	s32 expiry = hin->cltv_expiry, blockheight = p->ld->topology->tip->height;
+
+	tal_free(hin->status);
+	hin->status =
+	    tal_fmt(hin, "Waiting for the htlc_accepted hook of plugin %s",
+		    plugin->shortname);
+
 	json_object_start(s, "onion");
 
 	json_add_hex_talarr(s, "payload", rs->raw_payload);

tests/test_plugin.py

@@ -1059,6 +1059,13 @@ def test_htlc_accepted_hook_direct_restart(node_factory, executor):
     f1 = executor.submit(l1.rpc.pay, i1)
 
     l2.daemon.wait_for_log(r'Holding onto an incoming htlc for 10 seconds')
+
+    # Check that the status mentions the HTLC being held
+    l2.rpc.listpeers()
+    peers = l2.rpc.listpeers()['peers']
+    htlc_status = peers[0]['channels'][0]['htlcs'][0].get('status', None)
+    assert htlc_status == "Waiting for the htlc_accepted hook of plugin hold_htlcs.py"
+
     needle = l2.daemon.logsearch_start
     l2.restart()