plugins: add `feature_set` to init object.

Shows what features we use in various contexts, including those added
by plugins in getmanifest.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Added: Plugin: `feature_set` object added to `init`

lightningd/plugin.c

@@ -1169,6 +1169,15 @@ plugin_populate_init_request(struct plugin *plugin, struct jsonrpc_request *req)
 	json_add_string(req->stream, "rpc-file", ld->rpc_filename);
 	json_add_bool(req->stream, "startup", plugin->plugins->startup);
 	json_add_string(req->stream, "network", chainparams->network_name);
+	json_object_start(req->stream, "feature_set");
+	for (enum feature_place fp = 0; fp < NUM_FEATURE_PLACE; fp++) {
+		if (plugin_feature_place_names[fp]) {
+			json_add_hex_talarr(req->stream,
+					    plugin_feature_place_names[fp],
+					    ld->feature_set->bits[fp]);
+		}
+	}
+	json_object_end(req->stream);
 	json_object_end(req->stream);
 }
 

tests/plugins/show_feature_set.py

@@ -0,0 +1,17 @@
+#!/usr/bin/env python3
+from pyln.client import Plugin
+
+plugin = Plugin()
+
+
+@plugin.init()
+def init(options, configuration, plugin):
+    plugin.feature_set = configuration['feature_set']
+
+
+@plugin.method('getfeatureset')
+def getfeatureset(plugin):
+    return plugin.feature_set
+
+
+plugin.run()

tests/test_plugin.py

@@ -1153,3 +1153,14 @@ def test_hook_crash(node_factory, executor, bitcoind):
 
     # Collect the results:
     [f.result(TIMEOUT) for f in futures]
+
+
+def test_feature_set(node_factory):
+    plugin = os.path.join(os.path.dirname(__file__), 'plugins/show_feature_set.py')
+    l1 = node_factory.get_node(options={"plugin": plugin})
+
+    fs = l1.rpc.call('getfeatureset')
+    assert fs['init'] == expected_features()
+    assert fs['node'] == expected_features()
+    assert fs['channel'] == ''
+    assert 'invoice' in fs