plugins: get usage from plugins (required unless deprecated_apis == True).

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

doc/PLUGINS.md

@@ -70,10 +70,12 @@ this example:
 	"rpcmethods": [
 		{
 			"name": "hello",
+			"usage": "[name]",
 			"description": "Returns a personalized greeting for {greeting} (set via options)."
 		},
 		{
 			"name": "gettime",
+			"usage": "",
 			"description": "Returns the current time in {timezone}",
 			"long_description": "Returns the current time in the timezone that is given as the only parameter.\nThis description may be quite long and is allowed to span multiple lines."
 		}
@@ -93,9 +95,10 @@ currently only string options are supported.*
 The `rpcmethods` are methods that will be exposed via `lightningd`'s
 JSON-RPC over Unix-Socket interface, just like the builtin
 commands. Any parameters given to the JSON-RPC calls will be passed
-through verbatim. Notice that the `name` and the `description` fields
+through verbatim. Notice that the `name`, `description` and `usage` fields
 are mandatory, while the `long_description` can be omitted (it'll be
-set to `description` if it was not provided).
+set to `description` if it was not provided). `usage` should surround optional
+parameter names in `[]`.
 
 Plugins are free to register any `name` for their `rpcmethod` as long
 as the name was not previously registered. This includes both built-in
@@ -149,11 +152,13 @@ called `hello` and `gettime`:
 	"rpcmethods": [
 		{
 			"name": "hello",
+			"usage": "[name]",
 			"description": "Returns a personalized greeting for {greeting} (set via options)."
 		},
 		{
 			"name": "gettime",
 			"description": "Returns the current time in {timezone}",
+			"usage": "",
 			"long_description": "Returns the current time in the timezone that is given as the only parameter.\nThis description may be quite long and is allowed to span multiple lines."
 		}
 	],

lightningd/plugin.c

@@ -19,6 +19,7 @@
 #include <lightningd/json.h>
 #include <lightningd/lightningd.h>
 #include <lightningd/notification.h>
+#include <lightningd/options.h>
 #include <lightningd/plugin_hook.h>
 #include <signal.h>
 #include <sys/stat.h>
@@ -633,12 +634,14 @@ static bool plugin_rpcmethod_add(struct plugin *plugin,
 				 const char *buffer,
 				 const jsmntok_t *meth)
 {
-	const jsmntok_t *nametok, *desctok, *longdesctok;
+	const jsmntok_t *nametok, *desctok, *longdesctok, *usagetok;
 	struct json_command *cmd;
+	const char *usage;
 
 	nametok = json_get_member(buffer, meth, "name");
 	desctok = json_get_member(buffer, meth, "description");
 	longdesctok = json_get_member(buffer, meth, "long_description");
+	usagetok = json_get_member(buffer, meth, "usage");
 
 	if (!nametok || nametok->type != JSMN_STRING) {
 		plugin_kill(plugin,
@@ -662,6 +665,13 @@ static bool plugin_rpcmethod_add(struct plugin *plugin,
 		return false;
 	}
 
+	if (usagetok && usagetok->type != JSMN_STRING) {
+		plugin_kill(plugin,
+			    "\"usage\" is not a string: %.*s",
+			    meth->end - meth->start, buffer + meth->start);
+		return false;
+	}
+
 	cmd = notleak(tal(plugin, struct json_command));
 	cmd->name = json_strdup(cmd, buffer, nametok);
 	cmd->description = json_strdup(cmd, buffer, desctok);
@@ -669,12 +679,18 @@ static bool plugin_rpcmethod_add(struct plugin *plugin,
 		cmd->verbose = json_strdup(cmd, buffer, longdesctok);
 	else
 		cmd->verbose = cmd->description;
+	if (usagetok)
+		usage = json_strdup(tmpctx, buffer, usagetok);
+	else if (!deprecated_apis) {
+		plugin_kill(plugin,
+			    "\"usage\" not provided by plugin");
+		return false;
+	} else
+		usage = "[params]";
 
 	cmd->deprecated = false;
 	cmd->dispatch = plugin_rpcmethod_dispatch;
-	if (!jsonrpc_command_add(plugin->plugins->ld->jsonrpc, cmd,
-				 /* FIXME */
-				 "[params]")) {
+	if (!jsonrpc_command_add(plugin->plugins->ld->jsonrpc, cmd, usage)) {
 		log_broken(plugin->log,
 			   "Could not register method \"%s\", a method with "
 			   "that name is already registered",

tests/test_plugin.py

@@ -1,6 +1,7 @@
 from collections import OrderedDict
 from fixtures import *  # noqa: F401,F403
 from lightning import RpcError
+from utils import only_one
 
 import pytest
 import subprocess
@@ -47,6 +48,8 @@ def test_rpc_passthrough(node_factory):
     cmd = [hlp for hlp in n.rpc.help()['help'] if 'hello' in hlp['command']]
     assert(len(cmd) == 1)
 
+    # Make sure usage message is present.
+    assert only_one(n.rpc.help('hello')['help'])['command'] == 'hello [name]'
     # While we're at it, let's check that helloworld.py is logging
     # correctly via the notifications plugin->lightningd
     assert n.daemon.is_in_log('Plugin helloworld.py initialized')
@@ -119,3 +122,7 @@ def test_pay_plugin(node_factory):
 
     with pytest.raises(RpcError, match=r'missing required parameter'):
         l1.rpc.call('pay')
+
+    # Make sure usage messages are present.
+    assert only_one(l1.rpc.help('pay')['help'])['command'] == 'pay bolt11 [msatoshi] [description] [riskfactor] [maxfeepercent] [retry_for] [maxdelay] [exemptfee]'
+    assert only_one(l1.rpc.help('paystatus')['help'])['command'] == 'paystatus [bolt11]'