DBus: Connection was disconnected before a reply was received - c

Question

I want to send notifications to my window manager on linux through the org.freedesktop.Notifications service. In d-feet this works, but in C, I get the error "Connection was disconnected before a reply was received"
#include <stdio.h>
#include <dbus/dbus.h>
int main() {
DBusError error;
DBusConnection *conn;
dbus_uint32_t serial = 0;
char *app_name = "My App";
dbus_uint32_t replaces_id = 0;
char *app_icon = "";
char *summary = "Notification from My App";
char *body = "This is a test notification from My App.";
char **actions = NULL;
dbus_int32_t timeout = -1;
dbus_uint32_t notification_id = 0;
dbus_error_init(&error);
conn = dbus_bus_get(DBUS_BUS_SESSION, &error);
if (dbus_error_is_set(&error)) {
fprintf(stderr, "Error connecting to the D-Bus session bus: %s\n", error.message);
dbus_error_free(&error);
return 1;
}
DBusMessage *message = dbus_message_new_method_call("org.freedesktop.Notifications",
"/org/freedesktop/Notifications",
"org.freedesktop.Notifications",
"Notify");
DBusMessageIter args, array;
dbus_message_iter_init_append(message, &args);
dbus_message_iter_append_basic(&args, DBUS_TYPE_STRING, &app_name);
dbus_message_iter_append_basic(&args, DBUS_TYPE_UINT32, &notification_id);
dbus_message_iter_append_basic(&args, DBUS_TYPE_STRING, &app_icon);
dbus_message_iter_append_basic(&args, DBUS_TYPE_STRING, &summary);
dbus_message_iter_append_basic(&args, DBUS_TYPE_STRING, &body);
dbus_message_iter_open_container(&args, DBUS_TYPE_ARRAY, DBUS_TYPE_STRING_AS_STRING, &array);
dbus_message_iter_close_container(&args, &array);
DBusMessageIter dict_entry;
const char *key = "";
dbus_uint32_t value = 0;
dbus_message_iter_open_container(&args, DBUS_TYPE_DICT_ENTRY, NULL, &dict_entry);
dbus_message_iter_append_basic(&dict_entry, DBUS_TYPE_STRING, &key);
DBusMessageIter variant;
dbus_message_iter_open_container(&dict_entry, DBUS_TYPE_VARIANT, DBUS_TYPE_UINT32_AS_STRING, &variant);
dbus_message_iter_append_basic(&variant, DBUS_TYPE_UINT32, &value);
dbus_message_iter_close_container(&dict_entry, &variant);
dbus_message_iter_close_container(&args, &dict_entry);
dbus_message_iter_append_basic(&args, DBUS_TYPE_INT32, &timeout);
DBusPendingCall* pending;
dbus_connection_send_with_reply(conn, message, &pending, DBUS_TIMEOUT_INFINITE);
dbus_connection_flush(conn);
dbus_message_unref(message);
dbus_pending_call_block(pending);
message = dbus_pending_call_steal_reply(pending);
dbus_pending_call_unref(pending);
DBusMessageIter args2;
int arg, id;
if(!dbus_message_iter_init(message, &args2))
fprintf(stderr, "message has no arugments!\n");
else if (DBUS_TYPE_UINT32 != (arg=dbus_message_iter_get_arg_type(&args2))) {
fprintf(stderr, "Argument is not int!\n");
switch(arg){
case DBUS_TYPE_STRING:
char *string;
dbus_message_iter_get_basic(&args2, &string);
fprintf(stderr, "ITS A STRING: %s\n", string);
break;
}}
else {
dbus_message_iter_get_basic(&args2, &id);
printf("ID: %d\n", id);
}
dbus_message_unref(message);
dbus_connection_close(conn);
return 0;
}
Edit: I fixed the segfaults, but now I get a even more obsucure reply from dbus when reading the reply arguments

Answer 1

While this doesn’t directly answer your question, it will help in the long run: You probably don’t want to use dbus-glib or libdbus to connect to D-Bus. Both are old and have poor API designs which make them hard to use. Using a D-Bus binding with a better-designed API will make your code easier to write and maintain in the long run.
See this answer for a comparison of the D-Bus bindings available to you which are easier to use. It is unfortunately quite confusing that there are so many bindings and that some of them are not recommended.