test/be_filter: creating test case for data stuck with active watermarks

v2: fix whitespaces
    s/int/size_t/
    use tt_int_op()
    s/malloc/calloc (to avoid possible false-positive)

test/regress_bufferevent.c

@@ -1227,6 +1227,106 @@ test_bufferevent_pair_flush(void *arg)
 		bufferevent_free(bev2);
 }
 
+struct bufferevent_filter_data_stuck {
+	size_t header_size;
+	size_t total_read;
+};
+
+static void
+bufferevent_filter_data_stuck_readcb(struct bufferevent *bev, void *arg)
+{
+	struct bufferevent_filter_data_stuck *filter_data = arg;
+	struct evbuffer *input = bufferevent_get_input(bev);
+	size_t read_size = evbuffer_get_length(input);
+	evbuffer_drain(input, read_size);
+	filter_data->total_read += read_size;
+}
+
+/**
+ * This filter prepends header once before forwarding data.
+ */
+static enum bufferevent_filter_result
+bufferevent_filter_data_stuck_inputcb(
+    struct evbuffer *src, struct evbuffer *dst, ev_ssize_t dst_limit,
+    enum bufferevent_flush_mode mode, void *ctx)
+{
+	struct bufferevent_filter_data_stuck *filter_data = ctx;
+	static int header_inserted = 0;
+	size_t payload_size;
+	size_t header_size = 0;
+
+	if (!header_inserted) {
+		char *header = calloc(filter_data->header_size, 1);
+		evbuffer_add(dst, header, filter_data->header_size);
+		free(header);
+		header_size = filter_data->header_size;
+		header_inserted = 1;
+	}
+
+	payload_size = evbuffer_get_length(src);
+	if (payload_size > dst_limit - header_size) {
+		payload_size = dst_limit - header_size;
+	}
+
+	tt_int_op(payload_size, ==, evbuffer_remove_buffer(src, dst, payload_size));
+
+end:
+	return BEV_OK;
+}
+
+static void
+test_bufferevent_filter_data_stuck(void *arg)
+{
+	const size_t read_high_wm = 4096;
+	struct bufferevent_filter_data_stuck filter_data;
+	struct basic_test_data *data = arg;
+	struct bufferevent *pair[2];
+	struct bufferevent *filter = NULL;
+
+	int options = BEV_OPT_CLOSE_ON_FREE | BEV_OPT_DEFER_CALLBACKS;
+
+	char payload[4096];
+	int payload_size = sizeof(payload);
+
+	memset(&filter_data, 0, sizeof(filter_data));
+	filter_data.header_size = 20;
+
+	tt_assert(bufferevent_pair_new(data->base, options, pair) == 0);
+
+	bufferevent_setwatermark(pair[0], EV_READ, 0, read_high_wm);
+	bufferevent_setwatermark(pair[1], EV_READ, 0, read_high_wm);
+
+	tt_assert(
+		filter =
+		 bufferevent_filter_new(pair[1],
+		 bufferevent_filter_data_stuck_inputcb,
+		 NULL,
+		 options,
+		 NULL,
+		 &filter_data));
+
+	bufferevent_setcb(filter,
+		bufferevent_filter_data_stuck_readcb,
+		NULL,
+		NULL,
+		&filter_data);
+
+	tt_assert(bufferevent_enable(filter, EV_READ|EV_WRITE) == 0);
+
+	bufferevent_setwatermark(filter, EV_READ, 0, read_high_wm);
+
+	tt_assert(bufferevent_write(pair[0], payload, sizeof(payload)) == 0);
+
+	event_base_dispatch(data->base);
+
+	tt_int_op(filter_data.total_read, ==, payload_size + filter_data.header_size);
+end:
+	if (pair[0])
+		bufferevent_free(pair[0]);
+	if (filter)
+		bufferevent_free(filter);
+}
+
 struct testcase_t bufferevent_testcases[] = {
 
 	LEGACY(bufferevent, TT_ISOLATED),
@@ -1299,6 +1399,9 @@ struct testcase_t bufferevent_testcases[] = {
 	{ "bufferevent_pair_flush",
 	  test_bufferevent_pair_flush,
 	  TT_FORK|TT_NEED_BASE, &basic_setup, NULL },
+	{ "bufferevent_filter_data_stuck",
+	  test_bufferevent_filter_data_stuck,
+	  TT_FORK|TT_NEED_BASE, &basic_setup, NULL },
 
 	END_OF_TESTCASES,
 };