qapi: check invalid arguments on no-args commands

The generated marshal functions do not visit arguments from commands
that take no arguments. Thus they fail to catch invalid
members. Visit the arguments, if provided, to throw an error in case of
invalid members.

Currently, qmp_check_client_args() checks for invalid arguments and
correctly catches this case. When switching to qmp_dispatch() we want to
keep that behaviour. The commands using 'O' may have arbitrary
arguments, and must have 'gen': false in the qapi schema to skip the
generated checks.

Old/new diff:
 void qmp_marshal_stop(QDict *args, QObject **ret, Error **errp)
 {
     Error *err = NULL;
+    Visitor *v = NULL;

-    (void)args;
+    if (args) {
+        v = qmp_input_visitor_new(QOBJECT(args), true);
+        visit_start_struct(v, NULL, NULL, 0, &err);
+        if (err) {
+            goto out;
+        }
+
+        if (!err) {
+            visit_check_struct(v, &err);
+        }
+        visit_end_struct(v, NULL);
+        if (err) {
+            goto out;
+        }
+    }

     qmp_stop(&err);
+
+out:
     error_propagate(errp, err);
+    visit_free(v);
+    if (args) {
+        v = qapi_dealloc_visitor_new();
+        visit_start_struct(v, NULL, NULL, 0, NULL);
+
+        visit_end_struct(v, NULL);
+        visit_free(v);
+    }
 }

The new code closely resembles code for a command with arguments.
Differences:
- the visit of the argument and its cleanup struct don't visit any
  members (because there are none).
- the visit of the argument struct and its cleanup are conditional.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20160912091913.15831-14-marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi-commands.py

@@ -95,6 +95,8 @@ def gen_marshal_decl(name):
 
 
 def gen_marshal(name, arg_type, boxed, ret_type):
+    have_args = arg_type and not arg_type.is_empty()
+
     ret = mcgen('''
 
 %(proto)s
@@ -109,17 +111,31 @@ def gen_marshal(name, arg_type, boxed, ret_type):
 ''',
                      c_type=ret_type.c_type())
 
-    if arg_type and not arg_type.is_empty():
+    if have_args:
+        visit_members = ('visit_type_%s_members(v, &arg, &err);'
+                         % arg_type.c_name())
         ret += mcgen('''
     Visitor *v;
     %(c_name)s arg = {0};
 
+''',
+                     c_name=arg_type.c_name())
+    else:
+        visit_members = ''
+        ret += mcgen('''
+    Visitor *v = NULL;
+
+    if (args) {
+''')
+        push_indent()
+
+    ret += mcgen('''
     v = qmp_input_visitor_new(QOBJECT(args), true);
     visit_start_struct(v, NULL, NULL, 0, &err);
     if (err) {
         goto out;
     }
-    visit_type_%(c_name)s_members(v, &arg, &err);
+    %(visit_members)s
     if (!err) {
         visit_check_struct(v, &err);
     }
@@ -128,35 +144,47 @@ def gen_marshal(name, arg_type, boxed, ret_type):
         goto out;
     }
 ''',
-                     c_name=arg_type.c_name())
+                 visit_members=visit_members)
 
-    else:
+    if not have_args:
+        pop_indent()
         ret += mcgen('''
-
-    (void)args;
+    }
 ''')
 
     ret += gen_call(name, arg_type, boxed, ret_type)
 
-    # 'goto out' produced above for arg_type, and by gen_call() for ret_type
-    if (arg_type and not arg_type.is_empty()) or ret_type:
-        ret += mcgen('''
+    ret += mcgen('''
 
 out:
-''')
-    ret += mcgen('''
     error_propagate(errp, err);
-''')
-    if arg_type and not arg_type.is_empty():
-        ret += mcgen('''
     visit_free(v);
+''')
+
+    if have_args:
+        visit_members = ('visit_type_%s_members(v, &arg, NULL);'
+                         % arg_type.c_name())
+    else:
+        visit_members = ''
+        ret += mcgen('''
+    if (args) {
+''')
+        push_indent()
+
+    ret += mcgen('''
     v = qapi_dealloc_visitor_new();
     visit_start_struct(v, NULL, NULL, 0, NULL);
-    visit_type_%(c_name)s_members(v, &arg, NULL);
+    %(visit_members)s
     visit_end_struct(v, NULL);
     visit_free(v);
 ''',
-                     c_name=arg_type.c_name())
+                 visit_members=visit_members)
+
+    if not have_args:
+        pop_indent()
+        ret += mcgen('''
+    }
+''')
 
     ret += mcgen('''
 }

tests/test-qmp-commands.c

@@ -106,6 +106,7 @@ static void test_dispatch_cmd(void)
 static void test_dispatch_cmd_failure(void)
 {
     QDict *req = qdict_new();
+    QDict *args = qdict_new();
     QObject *resp;
 
     qdict_put_obj(req, "execute", QOBJECT(qstring_from_str("user_def_cmd2")));
@@ -116,6 +117,20 @@ static void test_dispatch_cmd_failure(void)
 
     qobject_decref(resp);
     QDECREF(req);
+
+    /* check that with extra arguments it throws an error */
+    req = qdict_new();
+    qdict_put(args, "a", qint_from_int(66));
+    qdict_put(req, "arguments", args);
+
+    qdict_put_obj(req, "execute", QOBJECT(qstring_from_str("user_def_cmd")));
+
+    resp = qmp_dispatch(QOBJECT(req));
+    assert(resp != NULL);
+    assert(qdict_haskey(qobject_to_qdict(resp), "error"));
+
+    qobject_decref(resp);
+    QDECREF(req);
 }
 
 static QObject *test_qmp_dispatch(QDict *req)