File ead038d.patch of Package mariadb-connector-c

From ead038dc8a2b3d7819f87af33e14f105325f8cf9 Mon Sep 17 00:00:00 2001
From: Georg Richter <georg@mariadb.com>
Date: Thu, 3 Sep 2026 11:58:38 +0200
Subject: [PATCH] CONC-821: Avoid resetting length pointer for variable-length
 types in mysql_stmt_bind_result

Prior fix for CONC-821 initialized the length pointer (*bind->length)
to 0 during mysql_stmt_bind_result() for variable-length types (strings,
blobs, etc.).

This broke third-party drivers and applications (e.g. Perl DBD::MariaDB,
Qt, and others) that perform a re-bind step after fetching data but prior
to reading/copying the bind buffer, as re-binding zeroed out the fetched
length prematurely.

Fix this regression by leaving the length pointer untouched during result
binding for non-fixed-sized types.
---
 libmariadb/mariadb_stmt.c     |  10 ++--
 unittest/libmariadb/ps_bugs.c | 106 ++++++++++++++++++++--------------
 2 files changed, 69 insertions(+), 47 deletions(-)

Index: mariadb-connector-c-3.4.9-src/libmariadb/mariadb_stmt.c
===================================================================
--- mariadb-connector-c-3.4.9-src.orig/libmariadb/mariadb_stmt.c
+++ mariadb-connector-c-3.4.9-src/libmariadb/mariadb_stmt.c
@@ -1442,7 +1442,9 @@ my_bool STDCALL mysql_stmt_bind_result(M
     {
       *stmt->bind[i].length= stmt->bind[i].length_value= mysql_ps_fetch_functions[stmt->bind[i].buffer_type].pack_len;
     } else {
-      *stmt->bind[i].length= stmt->bind[i].length_value= 0;
+    /* CONC-821: We don't initialize length for variable length types to avoid
+                 problems with applications which rebind before storing/copying retrieved
+                 values from bind buffer */
     }
 
     /* set length values for numeric types */
Index: mariadb-connector-c-3.4.9-src/unittest/libmariadb/ps_bugs.c
===================================================================
--- mariadb-connector-c-3.4.9-src.orig/unittest/libmariadb/ps_bugs.c
+++ mariadb-connector-c-3.4.9-src/unittest/libmariadb/ps_bugs.c
@@ -6035,7 +6035,7 @@ static int test_conc762(MYSQL *mysql)
   mysql_stmt_fetch(stmt);
   FAIL_IF(is_null[0]==0, "Expected NULL value");
   FAIL_IF(is_null[1]==1, "Expected non-NULL value");
-  FAIL_IF(length[0]!=0, "Expected length=0");
+  FAIL_IF(length[0]!=1, "Expected length=1 (unchanged)");
   FAIL_IF(length[1]!=3, "Expected length=3");
 
   mysql_stmt_fetch(stmt);
@@ -6063,7 +6063,8 @@ static int test_conc762(MYSQL *mysql)
   check_stmt_rc(rc, stmt);
 
   mysql_stmt_fetch(stmt);
-  FAIL_IF(length[0]!=0, "Expected length=0");
+  FAIL_IF(length[0]==0, "Expected length>0 (untouched)");
+  FAIL_IF(is_null[0]==0, "Expected null indicator");
 
   mysql_stmt_close(stmt);
   return OK;