tests/qtest: add support for callback to receive QMP events

Currently code must call one of the qtest_qmp_event* functions to
fetch events. These are only usable if the immediate caller knows
the particular event they want to capture, and are only interested
in one specific event type. Adding ability to register an event
callback lets the caller capture a range of events over any period
of time.

Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230601161347.1803440-3-berrange@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

tests/qtest/libqtest.c

@@ -82,6 +82,8 @@ struct QTestState
     GString *rx;
     QTestTransportOps ops;
     GList *pending_events;
+    QTestQMPEventCallback eventCB;
+    void *eventData;
 };
 
 static GHookList abrt_hooks;
@@ -703,8 +705,13 @@ QDict *qtest_qmp_receive(QTestState *s)
         if (!qdict_get_try_str(response, "event")) {
             return response;
         }
-        /* Stash the event for a later consumption */
-        s->pending_events = g_list_append(s->pending_events, response);
+
+        if (!s->eventCB ||
+            !s->eventCB(s, qdict_get_str(response, "event"),
+                        response, s->eventData)) {
+            /* Stash the event for a later consumption */
+            s->pending_events = g_list_append(s->pending_events, response);
+        }
     }
 }
 
@@ -808,6 +815,13 @@ void qtest_qmp_send_raw(QTestState *s, const char *fmt, ...)
     va_end(ap);
 }
 
+void qtest_qmp_set_event_callback(QTestState *s,
+                                  QTestQMPEventCallback cb, void *opaque)
+{
+    s->eventCB = cb;
+    s->eventData = opaque;
+}
+
 QDict *qtest_qmp_event_ref(QTestState *s, const char *event)
 {
     while (s->pending_events) {

tests/qtest/libqtest.h

@@ -238,17 +238,52 @@ QDict *qtest_qmp_receive_dict(QTestState *s);
  * @s: #QTestState instance to operate on.
  *
  * Reads a QMP message from QEMU and returns the response.
- * Buffers all the events received meanwhile, until a
- * call to qtest_qmp_eventwait
+ *
+ * If a callback is registered with qtest_qmp_set_event_callback,
+ * it will be invoked for every event seen, otherwise events
+ * will be buffered until a call to one of the qtest_qmp_eventwait
+ * family of functions.
  */
 QDict *qtest_qmp_receive(QTestState *s);
 
+/*
+ * QTestQMPEventCallback:
+ * @s: #QTestState instance event was received on
+ * @name: name of the event type
+ * @event: #QDict for the event details
+ * @opaque: opaque data from time of callback registration
+ *
+ * This callback will be invoked whenever an event is received.
+ * If the callback returns true the event will be consumed,
+ * otherwise it will be put on the list of pending events.
+ * Pending events can be later handled by calling either
+ * qtest_qmp_eventwait or qtest_qmp_eventwait_ref.
+ *
+ * Return: true to consume the event, false to let it be queued
+ */
+typedef bool (*QTestQMPEventCallback)(QTestState *s, const char *name,
+                                      QDict *event, void *opaque);
+
+/**
+ * qtest_qmp_set_event_callback:
+ * @s: #QTestSTate instance to operate on
+ * @cb: callback to invoke for events
+ * @opaque: data to pass to @cb
+ *
+ * Register a callback to be invoked whenever an event arrives
+ */
+void qtest_qmp_set_event_callback(QTestState *s,
+                                  QTestQMPEventCallback cb, void *opaque);
+
 /**
  * qtest_qmp_eventwait:
  * @s: #QTestState instance to operate on.
  * @event: event to wait for.
  *
  * Continuously polls for QMP responses until it receives the desired event.
+ *
+ * Any callback registered with qtest_qmp_set_event_callback will
+ * be invoked for every event seen.
  */
 void qtest_qmp_eventwait(QTestState *s, const char *event);
 
@@ -258,6 +293,10 @@ void qtest_qmp_eventwait(QTestState *s, const char *event);
  * @event: event to wait for.
  *
  * Continuously polls for QMP responses until it receives the desired event.
+ *
+ * Any callback registered with qtest_qmp_set_event_callback will
+ * be invoked for every event seen.
+ *
  * Returns a copy of the event for further investigation.
  */
 QDict *qtest_qmp_eventwait_ref(QTestState *s, const char *event);