reckless: catch and raise usage errors

While the reckless utility provided usage hints, the rpc plugin
would simply exit with an unhelpful:
{
   "code": -3,
   "message": "the reckless process has crashed"
}

This captures the usage hint from the utility and reports it
from the plugin as well.

Changelog-Fixed: reckless-rpc plugin now raises incorrect usage from the reckless utility.

Author: endothermicdev

plugins/recklessrpc.c

@@ -200,6 +200,23 @@ static struct command_result *reckless_fail(struct reckless *reckless,
 	return command_finished(reckless->cmd, resp);
 }
 
+/* Regurgitates the syntax error reported by the utility */
+static struct command_result *fail_bad_usage(struct reckless *reckless)
+{
+	char **lines;
+	lines = tal_strsplit(reckless, reckless->stderrbuf, "\n", STR_EMPTY_OK);
+	if (lines != NULL)
+	{
+		/* The last line of reckless output contains the usage error.
+		 * Capture it for the user. */
+		int i = 0;
+		while (lines[i + 1] != NULL)
+			i++;
+		return reckless_fail(reckless, lines[i]);
+	}
+	return reckless_fail(reckless, "the reckless process has crashed");
+}
+
 static void reckless_conn_finish(struct io_conn *conn,
 				 struct reckless *reckless)
 {
@@ -239,14 +256,18 @@ static void reckless_conn_finish(struct io_conn *conn,
 				   "Reckless process has crashed (%i).",
 				   WEXITSTATUS(status));
 			char * err;
-			if (reckless->process_failed)
-				err = reckless->process_failed;
-			else
-				err = tal_strdup(tmpctx, "the reckless process "
-						 "has crashed");
-			reckless_fail(reckless, err);
-			plugin_log(plugin, LOG_UNUSUAL,
-				   "The reckless subprocess has failed.");
+			if (WEXITSTATUS(status) == 2)
+				fail_bad_usage(reckless);
+			else {
+				if (reckless->process_failed)
+					err = reckless->process_failed;
+				else
+					err = tal_strdup(tmpctx, "the reckless process "
+							 "has crashed");
+				reckless_fail(reckless, err);
+				plugin_log(plugin, LOG_UNUSUAL,
+					   "The reckless subprocess has failed.");
+			}
 		}
 	}
 	tal_free(reckless);

tests/test_reckless.py

@@ -6,6 +6,7 @@
 import time
 import unittest
 from fixtures import *  # noqa: F401,F403
+from pyln.client import lightning
 from pyln.testing.utils import VALGRIND
 import pytest
 
@@ -481,3 +482,21 @@ def test_reckless_notifications(node_factory):
     listconfig_log.pop(1)
     for log in listconfig_log:
         assert node.daemon.is_in_log(f"reckless_log: {{'reckless_log': {{'log': '{log}'", start=0)
+
+
+def test_reckless_usage(node_factory):
+    """The reckless rpc response is more useful if it can pass back incorrect
+    usage errors."""
+    node = node_factory.get_node(options={}, may_fail=True, start=False)
+    node.start(stderr_redir=True)
+    r = reckless(['searhc', 'testplugpass'],
+                 dir=node.lightning_dir)
+    # The reckless utility should fail and argparse should provide a usage hint
+    # as the line of output.
+    assert r.returncode == 2
+    assert "reckless: error: argument cmd1: invalid choice: 'searhc' (choose from " in r.stderr[-1]
+
+    # The rpc plugin should capture and raise this usage error
+    with pytest.raises(lightning.RpcError,
+                       match="reckless: error: argument cmd1: invalid choice: 'saerch'"):
+        node.rpc.reckless('saerch', 'testplugpass')