lightningd: create --list-features-only which lists what features we support.

This allows the lightning-rfc protocol tests to automatically query what
features we support.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/features.c

@@ -1,6 +1,7 @@
 #include "features.h"
 #include <assert.h>
 #include <ccan/array_size/array_size.h>
+#include <common/utils.h>
 #include <wire/peer_wire.h>
 
 static const u32 our_localfeatures[] = {
@@ -150,3 +151,30 @@ bool global_feature_negotiated(const u8 *gfeatures, size_t f)
 	return feature_supported(f, our_globalfeatures,
 				 ARRAY_SIZE(our_globalfeatures));
 }
+
+static const char *feature_name(const tal_t *ctx, size_t f)
+{
+	static const char *fnames[] = {
+		"option_data_loss_protect",
+		"option_initial_routing_sync",
+		"option_upfront_shutdown_script",
+		"option_gossip_queries",
+		"option_var_onion_optin",
+		"option_gossip_queries_ex" };
+
+	assert(f / 2 < ARRAY_SIZE(fnames));
+	return tal_fmt(ctx, "%s/%s",
+		       fnames[f / 2], (f & 1) ? "odd" : "even");
+}
+
+const char **list_supported_features(const tal_t *ctx)
+{
+	const char **list = tal_arr(ctx, const char *, 0);
+
+	/* The local/global number spaces are to be distinct, so this works */
+	for (size_t i = 0; i < ARRAY_SIZE(our_localfeatures); i++)
+		tal_arr_expand(&list, feature_name(list, our_localfeatures[i]));
+	for (size_t i = 0; i < ARRAY_SIZE(our_globalfeatures); i++)
+		tal_arr_expand(&list, feature_name(list, our_globalfeatures[i]));
+	return list;
+}

common/features.h

@@ -18,6 +18,9 @@ bool feature_offered(const u8 *features, size_t f);
 bool local_feature_negotiated(const u8 *lfeatures, size_t f);
 bool global_feature_negotiated(const u8 *gfeatures, size_t f);
 
+/* Return a list of what features we advertize. */
+const char **list_supported_features(const tal_t *ctx);
+
 /* BOLT #9:
  *
  * Flags are numbered from the least-significant bit, at bit 0 (i.e. 0x1,

lightningd/options.c

@@ -13,6 +13,7 @@
 #include <ccan/tal/str/str.h>
 #include <common/configdir.h>
 #include <common/derive_basepoints.h>
+#include <common/features.h>
 #include <common/json_command.h>
 #include <common/jsonrpc_errors.h>
 #include <common/memleak.h>
@@ -723,6 +724,14 @@ static char *test_subdaemons_and_exit(struct lightningd *ld)
 	return NULL;
 }
 
+static char *list_features_and_exit(struct lightningd *ld)
+{
+	const char **features = list_supported_features(ld);
+	for (size_t i = 0; i < tal_count(features); i++)
+		printf("%s\n", features[i]);
+	exit(0);
+}
+
 static char *opt_lightningd_usage(struct lightningd *ld)
 {
 	/* Reload config so that --help has the correct network defaults
@@ -783,7 +792,8 @@ static char *opt_set_conf(const char *arg, struct lightningd *ld)
 	return NULL;
 }
 
-/* Just enough parsing to find config file. */
+/* Just enough parsing to find config file, and other maintenance options
+ * which don't want us to create the lightning dir */
 static void handle_minimal_config_opts(struct lightningd *ld,
 				       int argc, char *argv[])
 {
@@ -796,6 +806,9 @@ static void handle_minimal_config_opts(struct lightningd *ld,
 			       opt_set_talstr, opt_show_charp,
 			       &ld->config_dir,
 			       "Set working directory. All other files are relative to this");
+	opt_register_early_noarg("--list-features-only",
+				 list_features_and_exit,
+				 ld, opt_hidden);
 
 	/* Handle --version (and exit) here too: don't create lightning-dir for this */
 	opt_register_version();
@@ -1133,7 +1146,9 @@ static void add_config(struct lightningd *ld,
 	const char *answer = NULL;
 
 	if (opt->type & OPT_NOARG) {
-		if (opt->cb == (void *)opt_usage_and_exit
+		if (opt->desc == opt_hidden) {
+			/* Ignore hidden options (deprecated) */
+		} else if (opt->cb == (void *)opt_usage_and_exit
 		    || opt->cb == (void *)version_and_exit
 		    /* These two show up as --network= */
 		    || opt->cb == (void *)opt_set_testnet

tests/test_misc.py

@@ -3,7 +3,7 @@ from fixtures import *  # noqa: F401,F403
 from flaky import flaky  # noqa: F401
 from lightning import RpcError
 from threading import Event
-from utils import DEVELOPER, TIMEOUT, VALGRIND, sync_blockheight, only_one, wait_for, TailableProc
+from utils import DEVELOPER, TIMEOUT, VALGRIND, sync_blockheight, only_one, wait_for, TailableProc, EXPERIMENTAL_FEATURES
 from ephemeral_port_reserve import reserve
 
 import json
@@ -1435,3 +1435,15 @@ def test_dev_demux(node_factory):
 
     with pytest.raises(RpcError):
         l1.rpc.call('dev', {'subcommand': 'crash'})
+
+
+def test_list_features_only(node_factory):
+    features = subprocess.check_output(['lightningd/lightningd',
+                                        '--list-features-only']).decode('utf-8').splitlines()
+    expected = ['option_data_loss_protect/odd',
+                'option_initial_routing_sync/odd',
+                'option_upfront_shutdown_script/odd',
+                'option_gossip_queries/odd']
+    if EXPERIMENTAL_FEATURES:
+        expected.append('option_gossip_queries_ex/odd')
+    assert features == expected