mysql_stmt_fetch_column does not respect 'offset' parameter for blob fields

static int test_fetch_offset(MYSQL *mysql)

{

  MYSQL_STMT *stmt;

  MYSQL_BIND my_bind[2];

  char       data[11], chunk[5];

  ulong      length[2];

  int        rc;

  my_bool    is_null[2];

  char       *query = "SELECT * FROM t1";

  rc= mysql_query(mysql, "drop table if exists t1");

  check_mysql_rc(rc, mysql);

  rc= mysql_query(mysql, "create table t1(a char(10), b mediumblob)");

  check_mysql_rc(rc, mysql);

  rc= mysql_query(mysql, "insert into t1 values('abcdefghij', 'klmnopqrstzy'), (null, null)");

  check_mysql_rc(rc, mysql);

  stmt= mysql_stmt_init(mysql);

  FAIL_IF(!stmt, mysql_error(mysql));

  rc= mysql_stmt_prepare(stmt, query, (unsigned long)strlen(query));

  check_stmt_rc(rc,stmt);

  memset(my_bind, '\0', sizeof(my_bind));

  my_bind[0].buffer_type= MYSQL_TYPE_STRING;

  my_bind[0].buffer= (void *)data;

  my_bind[0].buffer_length= 11;

  my_bind[0].is_null= &is_null[0];

  my_bind[0].length= &length[0];

  my_bind[1].buffer_type= MYSQL_TYPE_STRING;

  my_bind[1].buffer= NULL;

  my_bind[1].buffer_length= 0;

  my_bind[1].is_null= &is_null[1];

  my_bind[1].length= &length[1];

  rc= mysql_stmt_execute(stmt);

  check_stmt_rc(rc,stmt);

  rc= mysql_stmt_fetch_column(stmt, my_bind, 0, 0);

  FAIL_IF(!rc, "Error expected");

  rc= mysql_stmt_execute(stmt);

  check_stmt_rc(rc,stmt);

  rc= mysql_stmt_bind_result(stmt, my_bind);

  check_stmt_rc(rc,stmt);

  rc= mysql_stmt_store_result(stmt);

  check_stmt_rc(rc,stmt);

  rc= mysql_stmt_fetch(stmt);

  FAIL_UNLESS(rc == MYSQL_DATA_TRUNCATED, "rc != MYSQL_DATA_TRUNCATED");

  data[0]= '\0';

  rc= mysql_stmt_fetch_column(stmt, &my_bind[0], 0, 0);

  check_stmt_rc(rc,stmt);

  FAIL_IF(!(strncmp(data, "abcd", 4) == 0 && length[0] == 10), "Wrong value");

  rc= mysql_stmt_fetch_column(stmt, &my_bind[0], 0, 5);

  check_stmt_rc(rc,stmt);

  FAIL_IF(!(strncmp(data, "fg", 2) == 0 && length[0] == 10), "Wrong value");

  rc= mysql_stmt_fetch_column(stmt, &my_bind[0], 0, 9);

  check_stmt_rc(rc,stmt);

  FAIL_IF(!(strncmp(data, "j", 1) == 0 && length[0] == 10), "Wrong value");

  /* Now blob field */

  my_bind[1].buffer= chunk;

  my_bind[1].buffer_length= sizeof(chunk);

  rc= mysql_stmt_fetch_column(stmt, &my_bind[1], 1, 0);

  check_stmt_rc(rc,stmt);

  FAIL_IF(!(strncmp(chunk, "klmno", 5) == 0 && length[1] == 12), "Wrong value");

  rc= mysql_stmt_fetch_column(stmt, &my_bind[1], 1, 5);

  check_stmt_rc(rc,stmt);

  FAIL_IF(!(strncmp(chunk, "pqrst", 5) == 0 && length[1] == 12), "Wrong value");

  rc= mysql_stmt_fetch_column(stmt, &my_bind[1], 1, 10);

  check_stmt_rc(rc,stmt);

  FAIL_IF(!(strncmp(chunk, "zy", 2) == 0 && length[1] == 12), "Wrong value");

  rc= mysql_stmt_fetch(stmt);

  check_stmt_rc(rc,stmt);

  memset(is_null, 0, sizeof(is_null));

  rc= mysql_stmt_fetch_column(stmt, &my_bind[0], 0, 0);

  check_stmt_rc(rc,stmt);

  FAIL_IF(is_null[0] != 1, "Null flag not set");

  rc= mysql_stmt_fetch_column(stmt, &my_bind[1], 1, 0);

  check_stmt_rc(rc,stmt);

  FAIL_IF(is_null[1] != 1, "Null flag not set");

  rc= mysql_stmt_fetch(stmt);

  FAIL_IF(rc != MYSQL_NO_DATA, "Expected MYSQL_NO_DATA");

  rc= mysql_stmt_fetch_column(stmt, my_bind, 1, 0);

  FAIL_IF(!rc, "Error expected");

  mysql_stmt_close(stmt);

  rc= mysql_query(mysql, "drop table t1");

  check_mysql_rc(rc, mysql);

  return OK;

}

diff --git a/libmariadb/my_stmt_codec.c b/libmariadb/my_stmt_codec.c

index 7d90151..6e9dee2 100644

--- a/libmariadb/my_stmt_codec.c

+++ b/libmariadb/my_stmt_codec.c

@@ -925,8 +925,9 @@ void ps_fetch_bin(MYSQL_BIND *r_param, const MYSQL_FIELD *field,

   if (!(field->flags & BINARY_FLAG) && r_param->buffer_type == MYSQL_TYPE_STRING)

     field_length++;

-  copylen= MIN(field_length, r_param->buffer_length);

-  memcpy(r_param->buffer, *row, copylen);

+  /* Making sure that we do not copy past the field. e.g. if offset >= field_length, copylen is 0 */

+  copylen= MIN(field_length - MIN(r_param->offset, field_length), r_param->buffer_length);

+  memcpy(r_param->buffer, *row + MIN(r_param->offset, field_length), copylen);

   *r_param->error= copylen < field_length;

   /* don't count trailing zero if we fetch into string */

@@ -934,9 +935,9 @@ void ps_fetch_bin(MYSQL_BIND *r_param, const MYSQL_FIELD *field,

       !*r_param->error)

     field_length--;

-  *r_param->length= field_length;

+  *r_param->length= field_length; /*copylen;*/

-  (*row) += field_length;

+  (*row) += copylen/*field_length*/;

 }

 /* }}} */