MaxScale/server/modules/routing/readwritesplit/rwsplit_session_cmd.cc

/*
 * Copyright (c) 2016 MariaDB Corporation Ab
 *
 * Use of this software is governed by the Business Source License included
 * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
 *
 * Change Date: 2022-01-01
 *
 * On the date above, in accordance with the Business Source License, use
 * of this software will be governed by version 2 or later of the General
 * Public License.
 */

#include "readwritesplit.hh"
#include "rwsplitsession.hh"

#include <stdio.h>
#include <strings.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>

#include <maxscale/router.h>

using namespace maxscale;

/**
 * Functions for session command handling
 */


std::string extract_error(GWBUF* buffer)
{
    std::string rval;

    if (MYSQL_IS_ERROR_PACKET(((uint8_t*)GWBUF_DATA(buffer))))
    {
        size_t replylen = MYSQL_GET_PAYLOAD_LEN(GWBUF_DATA(buffer)) + MYSQL_HEADER_LEN;
        char replybuf[replylen];
        gwbuf_copy_data(buffer, 0, sizeof(replybuf), (uint8_t*)replybuf);
        std::string err;
        std::string msg;

        /**
         * The payload starts with a one byte command followed by a two byte error code, a six byte state and
         * a human-readable string that spans the rest of the packet.
         */
        err.append(replybuf + MYSQL_HEADER_LEN + 3, 6);
        msg.append(replybuf + MYSQL_HEADER_LEN + 3 + 6, replylen - MYSQL_HEADER_LEN - 3 - 6);
        rval = err + ": " + msg;
    }

    return rval;
}

/**
 * Discards the slave connection if its response differs from the master's response
 *
 * @param backend    The slave Backend
 * @param master_cmd Master's reply
 * @param slave_cmd  Slave's reply
 */
static void discard_if_response_differs(SRWBackend backend,
                                        uint8_t master_response,
                                        uint8_t slave_response,
                                        SSessionCommand sescmd)
{
    if (master_response != slave_response)
    {
        uint8_t cmd = sescmd->get_command();
        std::string query = sescmd->to_string();
        MXS_WARNING("Slave server '%s': response (0x%02hhx) differs "
                    "from master's response (0x%02hhx) to %s: `%s`. "
                    "Closing slave connection due to inconsistent session state.",
                    backend->name(),
                    slave_response,
                    master_response,
                    STRPACKETTYPE(cmd),
                    query.empty() ? "<no query>" : query.c_str());
        backend->close(mxs::Backend::CLOSE_FATAL);
        backend->set_close_reason("Invalid response to: " + query);
    }
}

void RWSplitSession::process_sescmd_response(SRWBackend& backend, GWBUF** ppPacket)
{
    if (backend->has_session_commands())
    {
        mxb_assert(GWBUF_IS_COLLECTED_RESULT(*ppPacket));
        uint8_t cmd;
        gwbuf_copy_data(*ppPacket, MYSQL_HEADER_LEN, 1, &cmd);
        uint8_t command = backend->next_session_command()->get_command();
        mxs::SSessionCommand sescmd = backend->next_session_command();
        uint64_t id = backend->complete_session_command();
        MXS_PS_RESPONSE resp = {};
        bool discard = true;

        if (command == MXS_COM_STMT_PREPARE && cmd != MYSQL_REPLY_ERR)
        {
            // This should never fail or the backend protocol is broken
            MXB_AT_DEBUG(bool b = ) mxs_mysql_extract_ps_response(*ppPacket, &resp);
            mxb_assert(b);
            backend->add_ps_handle(id, resp.id);
        }

        if (m_recv_sescmd < m_sent_sescmd && id == m_recv_sescmd + 1)
        {
            if (!m_current_master || !m_current_master->in_use()// Session doesn't have a master
                || m_current_master == backend)                 // This is the master's response
            {
                /** First reply to this session command, route it to the client */
                ++m_recv_sescmd;
                discard = false;

                /** Store the master's response so that the slave responses can
                 * be compared to it */
                m_sescmd_responses[id] = cmd;

                if (cmd == MYSQL_REPLY_ERR)
                {
                    MXS_INFO("Session command no. %lu failed: %s",
                             id,
                             extract_error(*ppPacket).c_str());
                }
                else if (command == MXS_COM_STMT_PREPARE)
                {
                    /** Map the returned response to the internal ID */
                    MXS_INFO("PS ID %u maps to internal ID %lu", resp.id, id);
                    m_qc.ps_store_response(id, *ppPacket);
                }

                // Discard any slave connections that did not return the same result
                for (SlaveResponseList::iterator it = m_slave_responses.begin();
                     it != m_slave_responses.end(); it++)
                {
                    discard_if_response_differs(it->first, cmd, it->second, sescmd);
                }

                m_slave_responses.clear();
            }
            else
            {
                /** Record slave command so that the response can be validated
                 * against the master's response when it arrives. */
                m_slave_responses.push_back(std::make_pair(backend, cmd));
            }
        }
        else
        {
            if (cmd == MYSQL_REPLY_ERR && m_sescmd_responses[id] != MYSQL_REPLY_ERR)
            {
                MXS_WARNING("Session command failed on slave '%s': %s",
                            backend->name(), extract_error(*ppPacket).c_str());
            }

            discard_if_response_differs(backend, m_sescmd_responses[id], cmd, sescmd);
        }

        if (discard)
        {
            gwbuf_free(*ppPacket);
            *ppPacket = NULL;
        }

        if (m_expected_responses == 0 && !m_config.disable_sescmd_history
            && (command == MXS_COM_CHANGE_USER || command == MXS_COM_RESET_CONNECTION))
        {
            mxb_assert_message(!m_sescmd_list.empty(), "Must have stored session commands");
            mxb_assert_message(m_slave_responses.empty(), "All responses should've been processed");
            // This is the last session command to finish that resets the session state, reset the history
            MXS_INFO("Resetting session command history (length: %lu)", m_sescmd_list.size());

            /**
             * Since new connections need to perform the COM_CHANGE_USER, pop it off the list along
             * with the expected response to it.
             */
            SSessionCommand latest = m_sescmd_list.back();
            cmd = m_sescmd_responses[latest->get_position()];

            m_sescmd_list.clear();
            m_sescmd_responses.clear();

            // Push the response back as the first executed session command
            m_sescmd_list.push_back(latest);
            m_sescmd_responses[latest->get_position()] = cmd;

            // Adjust counters to match the number of stored session commands
            m_recv_sescmd = 1;
            m_sent_sescmd = 1;
            m_sescmd_count = 2;
        }
    }
}