Fix for CONC-566:

If cursor type is set to read only, and SERVER_STATUS_CURSOR_EXISTS
flag was not set in the server_status of EOF packet, the assumption
was made that a single result set will follow which will be stored
by a call to mysql_stmt_store_result().

As the example in the bug report shows, this is not always the case,
since a stored procedure call might also unset the CURSOR flag and
will always return multiple result sets. In this case it will be
handled now as "normal" unbuffered result set.

libmariadb/mariadb_stmt.c

@@ -1961,7 +1961,8 @@ int stmt_read_execute_response(MYSQL_STMT *stmt)
       /* Only cursor read */
       stmt->default_rset_handler = _mysql_stmt_use_result;
 
-    } else if (stmt->flags & CURSOR_TYPE_READ_ONLY)
+    } else if (stmt->flags & CURSOR_TYPE_READ_ONLY &&
+               !(stmt->upsert_status.server_status & SERVER_MORE_RESULTS_EXIST))
     {
       /*
          We have asked for CURSOR but got no cursor, because the condition

unittest/libmariadb/ps_bugs.c

@@ -5319,7 +5319,34 @@ static int test_conc512(MYSQL *mysql)
   return OK;
 }
 
+static int test_conc566(MYSQL *mysql)
+{
+  int rc;
+  MYSQL_STMT *stmt = mysql_stmt_init(mysql);
+  unsigned long cursor = CURSOR_TYPE_READ_ONLY;
+  const char* query= "call sp()";
+
+  rc= mysql_query(mysql,"drop procedure if exists sp");
+  check_mysql_rc(rc, mysql);
+
+  rc= mysql_query(mysql,"create procedure sp() select 1");
+  check_mysql_rc(rc, mysql);
+
+  rc= mysql_stmt_prepare(stmt,query,-1);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_attr_set(stmt, STMT_ATTR_CURSOR_TYPE, &cursor);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  check_stmt_rc(rc, stmt);
+
+  mysql_stmt_close(stmt);
+  return OK;
+}
+
 struct my_tests_st my_tests[] = {
+  {"test_conc566", test_conc566, TEST_CONNECTION_DEFAULT, 0, NULL, NULL},
   {"test_conc512", test_conc512, TEST_CONNECTION_DEFAULT, 0, NULL, NULL},
   {"test_conc504", test_conc504, TEST_CONNECTION_DEFAULT, 0, NULL, NULL},
   {"test_returning", test_returning, TEST_CONNECTION_DEFAULT, 0, NULL, NULL},