[Tarantool-patches] [PATCH] iproto: add an empty body to the unprepare response

[Chris Sosnin <k.sosnin@tarantool.org>]

Absence of the body in the unprepare response forces users to perform
additional checks to avoid errors. Adding an empty body fixes this problem.

Closes #4769
---
branch: https://github.com/tarantool/tarantool/commit/970bbec99903c9482b8d3b85040617c4f46a650e
issue: https://github.com/tarantool/tarantool/issues/4769

Yes, I was told that writing tests in python is kind of deprecated thing,
however this test fits here quite well and makes patch much more concise.

 src/box/iproto.cc          | 17 ++++++++++-------
 test/box-py/iproto.test.py | 14 ++++++++++++++
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/src/box/iproto.cc b/src/box/iproto.cc
index f313af6ae..d5891391d 100644
--- a/src/box/iproto.cc
+++ b/src/box/iproto.cc
@@ -1781,20 +1781,23 @@ tx_process_sql(struct cmsg *m)
 	 */
 	out = msg->connection->tx.p_obuf;
 	struct obuf_svp header_svp;
+	if (is_unprepare) {
+		if (iproto_reply_ok(out, msg->header.sync, schema_version) != 0)
+			goto error;
+		iproto_wpos_create(&msg->wpos, out);
+		return;
+	}
 	/* Prepare memory for the iproto header. */
 	if (iproto_prepare_header(out, &header_svp, IPROTO_HEADER_LEN) != 0) {
 		port_destroy(&port);
 		goto error;
 	}
-	/* Nothing to dump in case of UNPREPARE request. */
-	if (!is_unprepare) {
-		if (port_dump_msgpack(&port, out) != 0) {
-			port_destroy(&port);
-			obuf_rollback_to_svp(out, &header_svp);
-			goto error;
-		}
+	if (port_dump_msgpack(&port, out) != 0) {
 		port_destroy(&port);
+		obuf_rollback_to_svp(out, &header_svp);
+		goto error;
 	}
+	port_destroy(&port);
 	iproto_reply_sql(out, &header_svp, msg->header.sync, schema_version);
 	iproto_wpos_create(&msg->wpos, out);
 	return;
diff --git a/test/box-py/iproto.test.py b/test/box-py/iproto.test.py
index 77637d8ed..101e5e913 100644
--- a/test/box-py/iproto.test.py
+++ b/test/box-py/iproto.test.py
@@ -286,6 +286,20 @@ resp = test_request(header, body)
 print 'Schema changed -> error:', resp['header'][0] != 0
 print 'Got another schema_id:', resp['header'][5] != schema_id
 
+#
+# gh-4769 Unprepare response must have a body.
+#
+IPROTO_PREPARE = 13
+IPROTO_SQL_TEXT = 0x40
+IPROTO_STMT_ID = 0x43
+
+header = { IPROTO_CODE : IPROTO_PREPARE }
+body = { IPROTO_SQL_TEXT : 'SELECT 1' }
+resp = test_request(header, body)
+
+body = { IPROTO_STMT_ID : resp['body'][IPROTO_STMT_ID] }
+resp = test_request(header, body)
+
 #
 # gh-2334 Lost SYNC in JOIN response.
 #
-- 
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