Fix plugin startup crash

lightningd/plugin.c

@@ -875,14 +875,24 @@ static struct io_plan *plugin_write_json(struct io_conn *conn,
 /* This catches the case where their stdout closes (usually they're dead). */
 static void plugin_conn_finish(struct io_conn *conn, struct plugin *plugin)
 {
-	struct db *db = plugin->plugins->ld->wallet->db;
-	db_begin_transaction(db);
+	struct db *db;
+
+	/* If they die during startup (plugins_init) wallet is NULL
+	 * (but there are also no plugin commands to kill, so nothing
+	 * would ever try to access db */
+	if (plugin->plugins->ld->wallet) {
+		db = plugin->plugins->ld->wallet->db;
+		db_begin_transaction(db);
+	} else
+		db = NULL;
+
 	/* This is expected at shutdown of course. */
 	plugin_kill(plugin,
 		    plugin->plugins->ld->state == LD_STATE_SHUTDOWN
 		    ? LOG_DBG : LOG_INFORM,
 		    "exited %s", state_desc(plugin));
-	db_commit_transaction(db);
+	if (db)
+		db_commit_transaction(db);
 }
 
 struct io_plan *plugin_stdin_conn_init(struct io_conn *conn,

tests/plugins/broken.py

@@ -2,18 +2,27 @@
 """Simple plugin to test that lightningd doesnt crash if it starts a
 misbehaving plugin via RPC.
 """
-
 from pyln.client import Plugin
-import an_unexistent_module_that_will_make_me_crash
-
-plugin = Plugin(dynamic=False)
+import os
+plugin = Plugin()
+crash_at = os.environ.get("BROKEN_CRASH", "before_start")
 
 
 @plugin.init()
 def init(options, configuration, plugin):
     plugin.log("broken.py initializing {}".format(configuration))
-    # We need to actually use the import to pass source checks..
-    an_unexistent_module_that_will_make_me_crash.hello()
+    assert crash_at == "during_init"
+    plugin.does_not_exist()
+
+
+@plugin.method("test_broken")
+def test_broken():
+    return {}
+
 
+if crash_at == "before_start":
+    assert False
+elif crash_at == "during_getmanifest":
+    del plugin.methods['getmanifest']
 
 plugin.run()

tests/test_plugin.py

@@ -300,6 +300,18 @@ def test_plugin_command(node_factory):
     n.rpc.stop()
 
 
+def test_plugin_fail_on_startup(node_factory):
+    for crash in ('during_init', 'before_start', 'during_getmanifest'):
+        os.environ['BROKEN_CRASH'] = crash
+        n = node_factory.get_node(options={'plugin': os.path.join(os.getcwd(), "tests/plugins/broken.py")})
+        # This can happen before 'Server started with public key' msg
+        n.daemon.logsearch_start = 0
+        n.daemon.wait_for_log('plugin-broken.py: Traceback')
+
+    # Make sure they don't die *after* the message!
+    time.sleep(30)
+
+
 def test_plugin_disable(node_factory):
     """--disable-plugin works"""
     plugin_dir = os.path.join(os.getcwd(), 'contrib/plugins')