Workaround/Fix for CONC-424:

1) In case a cursor is used in a stored procedure server sends a SERVER_STATUS_CURSOR_EXISTS flag,
even if the client didn't open a cursor via mysql_stmt_attr_set. This ends in a "comands out of sync" error,
since the client is sending a COM_STMT_FETCH command while the result sets were not read before.
We check now in case server sends a SERVER_STATUS_CURSOR_EXIST flag, if the client opened a cursor before.

2) The stmt error codes weren't update for all COM_STMT* commands correctly, e.g. COM_STMT_FETCH didn't show an error even if it failed.

libmariadb/mariadb_stmt.c

@@ -56,6 +56,9 @@
 #include <mysql/client_plugin.h>
 #include <ma_common.h>
 
+#define UPDATE_STMT_ERROR(stmt)\
+SET_CLIENT_STMT_ERROR((stmt), (stmt)->mysql->net.last_errno, (stmt)->mysql->net.sqlstate, (stmt)->mysql->net.last_error)
+
 #define STMT_NUM_OFS(type, a,r) ((type *)(a))[r]
 #define MADB_RESET_ERROR     1
 #define MADB_RESET_LONGDATA  2
@@ -310,7 +313,10 @@ static int stmt_cursor_fetch(MYSQL_STMT *stmt, uchar **row)
     int4store(buf + STMT_ID_LENGTH, stmt->prefetch_rows);
 
     if (stmt->mysql->methods->db_command(stmt->mysql, COM_STMT_FETCH, (char *)buf, sizeof(buf), 1, stmt))
+    {
+      UPDATE_STMT_ERROR(stmt);
       return(1);
+    }
 
     /* free previously allocated buffer */
     ma_free_root(&result->alloc, MYF(MY_KEEP_PREALLOC));
@@ -1327,7 +1333,7 @@ static my_bool net_stmt_close(MYSQL_STMT *stmt, my_bool remove)
       if (stmt->mysql->methods->db_command(stmt->mysql,COM_STMT_CLOSE, stmt_id,
                                            sizeof(stmt_id), 1, stmt))
       {
-        SET_CLIENT_STMT_ERROR(stmt, stmt->mysql->net.last_errno, stmt->mysql->net.sqlstate, stmt->mysql->net.last_error);
+        UPDATE_STMT_ERROR(stmt);
         return 1;
       }
     }
@@ -1671,8 +1677,7 @@ int STDCALL mysql_stmt_prepare(MYSQL_STMT *stmt, const char *query, unsigned lon
 
 fail:
   stmt->state= MYSQL_STMT_INITTED;
-  SET_CLIENT_STMT_ERROR(stmt, mysql->net.last_errno, mysql->net.sqlstate,
+  UPDATE_STMT_ERROR(stmt);
-      mysql->net.last_error);
   return(rc);
 }
 
@@ -1886,7 +1891,8 @@ int stmt_read_execute_response(MYSQL_STMT *stmt)
       }
     }
 
-    if (stmt->upsert_status.server_status & SERVER_STATUS_CURSOR_EXISTS)
+    if ((stmt->upsert_status.server_status & SERVER_STATUS_CURSOR_EXISTS) &&
+        (stmt->flags & CURSOR_TYPE_READ_ONLY))
     {
       stmt->cursor_exists = TRUE;
       mysql->status = MYSQL_STATUS_READY;
@@ -2006,8 +2012,7 @@ int STDCALL mysql_stmt_execute(MYSQL_STMT *stmt)
 
   if (ret)
   {
-    SET_CLIENT_STMT_ERROR(stmt, mysql->net.last_errno, mysql->net.sqlstate,
+    UPDATE_STMT_ERROR(stmt);
-    mysql->net.last_error);
     return(1);
   }
 
@@ -2078,8 +2083,7 @@ static my_bool madb_reset_stmt(MYSQL_STMT *stmt, unsigned int flags)
         if ((ret= stmt->mysql->methods->db_command(mysql,COM_STMT_RESET, (char *)cmd_buf,
                                                    sizeof(cmd_buf), 0, stmt)))
         {
-          SET_CLIENT_STMT_ERROR(stmt, mysql->net.last_errno, mysql->net.sqlstate,
+          UPDATE_STMT_ERROR(stmt);
-              mysql->net.last_error);
           return(ret);
         }
       }
@@ -2231,6 +2235,8 @@ my_bool STDCALL mysql_stmt_send_long_data(MYSQL_STMT *stmt, uint param_number,
     stmt->params[param_number].long_data_used= 1;
     ret= stmt->mysql->methods->db_command(stmt->mysql, COM_STMT_SEND_LONG_DATA,
                                          (char *)cmd_buff, packet_len, 1, stmt);
+    if (ret)
+      UPDATE_STMT_ERROR(stmt);
     free(cmd_buff);
     return(ret);
   }
@@ -2441,8 +2447,7 @@ int STDCALL mariadb_stmt_execute_direct(MYSQL_STMT *stmt,
 fail:
   /* check if we need to set error message */
   if (!mysql_stmt_errno(stmt))
-    SET_CLIENT_STMT_ERROR(stmt, mysql->net.last_errno, mysql->net.sqlstate,
+    UPDATE_STMT_ERROR(stmt);
-        mysql->net.last_error);
   do {
     stmt->mysql->methods->db_stmt_flush_unbuffered(stmt);
   } while(mysql_stmt_more_results(stmt));

unittest/libmariadb/ps_bugs.c

@@ -5042,8 +5042,77 @@ static int test_zerofill_1byte(MYSQL *mysql)
   return OK;
 }
 
+static int test_conc424(MYSQL *mysql)
+{
+  int rc;
+  MYSQL_STMT *stmt;
+  my_bool max_len= 1;
+
+  rc= mysql_query(mysql, "DROP TABLE IF EXISTS test_table1");
+  check_mysql_rc(rc, mysql);
+  rc= mysql_query(mysql, "CREATE TABLE test_table1 (test_int INT, b int)");
+  check_mysql_rc(rc, mysql);
+  rc= mysql_query(mysql, "INSERT INTO test_table1 values(10,11),(11,12)");
+  check_mysql_rc(rc, mysql);
+
+  rc= mysql_query(mysql, "DROP PROCEDURE IF EXISTS testCursor");
+  check_mysql_rc(rc, mysql);
+
+  rc= mysql_query(mysql, "CREATE PROCEDURE testCursor()\n"
+                  "BEGIN\n"
+                  "DECLARE test_int INT;\n"
+                  "DECLARE b INT;\n"
+                  "DECLARE done INT DEFAULT FALSE;\n"
+                  "DECLARE testCursor CURSOR\n"
+                  "FOR\n"
+                  "SELECT test_int,b FROM test_table1;\n"
+                  "DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;\n"
+                  "OPEN testCursor;\n"
+
+                  " read_loop: LOOP\n"
+                  "   FETCH testCursor INTO test_int, b;\n"
+                  "   IF done THEN\n"
+                  "     LEAVE read_loop;\n"
+                  "   END IF;\n"
+                  "   SELECT test_int,b;"
+                  " END LOOP;\n"
+                  "CLOSE testCursor;\n"
+                  "END");
+  check_mysql_rc(rc, mysql);
+
+  stmt= mysql_stmt_init(mysql);
+  rc= mysql_stmt_prepare(stmt, SL("CALL testCursor()"));
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_attr_set(stmt, STMT_ATTR_UPDATE_MAX_LENGTH, &max_len);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  check_stmt_rc(rc, stmt);
+
+  do {
+    if (mysql_stmt_field_count(stmt))
+    {
+      MYSQL_RES *res= mysql_stmt_result_metadata(stmt);
+      rc= mysql_stmt_fetch(stmt);
+      FAIL_IF(rc, "Wrong return code");
+      mysql_free_result(res);
+    }
+    rc= mysql_stmt_next_result(stmt);
+    
+  } while (!rc);
+
+  rc= mysql_query(mysql, "DROP PROCEDURE testCursor");
+  check_mysql_rc(rc, mysql);
+
+  rc= mysql_query(mysql, "DROP TABLE test_table1");
+  check_mysql_rc(rc, mysql);
+
+  return OK;
+} 
 
 struct my_tests_st my_tests[] = {
+  {"test_conc424", test_conc424, TEST_CONNECTION_NEW, 0, NULL, NULL},
   {"test_conc344", test_conc344, TEST_CONNECTION_NEW, 0, NULL, NULL},
   {"test_conc334", test_conc334, TEST_CONNECTION_NEW, 0, NULL, NULL},
   {"test_compress", test_compress, TEST_CONNECTION_NEW, CLIENT_COMPRESS, NULL, NULL},