eis: implement eis_peek_event() and eis_next_event_type()

Motivation for peek is the same as for libei - the upcoming test suite needs
to check a few things before actually dequeuing the event.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

src/libeis.c

@@ -315,3 +315,22 @@ eis_get_event(struct eis *eis)
 
 	return e;
 }
+
+_public_ struct eis_event *
+eis_peek_event(struct eis *eis)
+{
+	if (list_empty(&eis->event_queue))
+		return NULL;
+
+	struct eis_event *e = list_first_entry(&eis->event_queue, e, link);
+	return eis_event_ref(e);
+}
+
+_public_ enum eis_event_type
+eis_next_event_type(struct eis *eis)
+{
+	if (list_empty(&eis->event_queue))
+		return EIS_EVENT_NONE;
+	struct eis_event *e = list_first_entry(&eis->event_queue, e, link);
+	return e->type;
+}

src/libeis.h

@@ -149,9 +149,38 @@ eis_get_fd(struct eis *eis);
 void
 eis_dispatch(struct eis *eis);
 
+/**
+ * Returns the next event in the internal event queue (or NULL) and removes
+ * it from the queue.
+ *
+ * The returned event is refcounted, use eis_event_unref() to drop the
+ * reference.
+ *
+ * You must not call this function while holding a reference to an event
+ * returned by eis_peek_event().
+ */
 struct eis_event *
 eis_get_event(struct eis *eis);
 
+/**
+ * Returns the next event in the internal event queue (or NULL) without
+ * removing that event from the queue, i.e. the next call to eis_get_event()
+ * will return that same event.
+ *
+ * This call is useful for checking whether there is an event and/or what
+ * type of event it is.
+ *
+ * Repeated calls to eis_peek_event() return the same event.
+ *
+ * The returned event is refcounted, use eis_event_unref() to drop the
+ * reference.
+ *
+ * A caller must not call eis_get_event() while holding a ref to an event
+ * returned by eis_peek_event().
+ */
+struct eis_event *
+eis_peek_event(struct eis *eis);
+
 struct eis_event *
 eis_event_unref(struct eis_event *event);