qmp: De-duplicate error response building

All callers of qmp_build_error_object() duplicate the code to wrap it
in a response object.  Replace it by qmp_error_response() that
captures the duplicated code, including error_free().
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-Id: <20180703085358.13941-23-armbru@redhat.com>

include/qapi/qmp/dispatch.h

@@ -47,7 +47,7 @@ void qmp_enable_command(QmpCommandList *cmds, const char *name);
 bool qmp_command_is_enabled(const QmpCommand *cmd);
 const char *qmp_command_name(const QmpCommand *cmd);
 bool qmp_has_success_response(const QmpCommand *cmd);
-QObject *qmp_build_error_object(Error *err);
+QDict *qmp_error_response(Error *err);
 QObject *qmp_dispatch(QmpCommandList *cmds, QObject *request,
                       bool allow_oob);
 bool qmp_is_oob(QDict *dict);

monitor.c

@@ -4107,14 +4107,9 @@ static int monitor_can_read(void *opaque)
 static void monitor_qmp_respond(Monitor *mon, QObject *rsp,
                                 Error *err, QObject *id)
 {
-    QDict *qdict = NULL;
-
     if (err) {
         assert(!rsp);
-        qdict = qdict_new();
-        qdict_put_obj(qdict, "error", qmp_build_error_object(err));
-        error_free(err);
-        rsp = QOBJECT(qdict);
+        rsp = QOBJECT(qmp_error_response(err));
     }
 
     if (rsp) {

qapi/qmp-dispatch.c

@@ -141,11 +141,15 @@ static QObject *do_qmp_dispatch(QmpCommandList *cmds, QObject *request,
     return ret;
 }
 
-QObject *qmp_build_error_object(Error *err)
+QDict *qmp_error_response(Error *err)
 {
-    return qobject_from_jsonf("{ 'class': %s, 'desc': %s }",
-                              QapiErrorClass_str(error_get_class(err)),
-                              error_get_pretty(err));
+    QDict *rsp;
+
+    rsp = qdict_from_jsonf_nofail("{ 'error': { 'class': %s, 'desc': %s } }",
+                                  QapiErrorClass_str(error_get_class(err)),
+                                  error_get_pretty(err));
+    error_free(err);
+    return rsp;
 }
 
 /*
@@ -166,15 +170,13 @@ QObject *qmp_dispatch(QmpCommandList *cmds, QObject *request,
 
     ret = do_qmp_dispatch(cmds, request, allow_oob, &err);
 
-    rsp = qdict_new();
     if (err) {
-        qdict_put_obj(rsp, "error", qmp_build_error_object(err));
-        error_free(err);
+        rsp = qmp_error_response(err);
     } else if (ret) {
+        rsp = qdict_new();
         qdict_put_obj(rsp, "return", ret);
     } else {
-        qobject_unref(rsp);
-        return NULL;
+        rsp = NULL;
     }
 
     return QOBJECT(rsp);

qga/main.c

@@ -610,15 +610,13 @@ static void process_event(JSONMessageParser *parser, GQueue *tokens)
     qdict = qobject_to(QDict, json_parser_parse_err(tokens, NULL, &err));
     if (err || !qdict) {
         qobject_unref(qdict);
-        qdict = qdict_new();
         if (!err) {
             g_warning("failed to parse event: unknown error");
             error_setg(&err, QERR_JSON_PARSING);
         } else {
             g_warning("failed to parse event: %s", error_get_pretty(err));
         }
-        qdict_put_obj(qdict, "error", qmp_build_error_object(err));
-        error_free(err);
+        qdict = qmp_error_response(err);
     }
 
     /* handle host->guest commands */
@@ -627,11 +625,9 @@ static void process_event(JSONMessageParser *parser, GQueue *tokens)
     } else {
         if (!qdict_haskey(qdict, "error")) {
             qobject_unref(qdict);
-            qdict = qdict_new();
             g_warning("unrecognized payload format");
             error_setg(&err, QERR_UNSUPPORTED);
-            qdict_put_obj(qdict, "error", qmp_build_error_object(err));
-            error_free(err);
+            qdict = qmp_error_response(err);
         }
         ret = send_response(s, QOBJECT(qdict));
         if (ret < 0) {