-- Copyright (C) 2012 Yichun Zhang (agentzh)
-- Copyright (C) 2014 Chang Feng
-- This file is modified version from https://github.com/openresty/lua-resty-mysql
-- The license is under the BSD license.
-- Modified by Cloud Wu (remove bit32 for lua 5.3)

local socketchannel = require "skynet.socketchannel"
local crypt = require "skynet.crypt"

local sub = string.sub
local strgsub = string.gsub
local strformat = string.format
local strbyte = string.byte
local strchar = string.char
local strrep = string.rep
local strunpack = string.unpack
local strpack = string.pack
local sha1 = crypt.sha1
local setmetatable = setmetatable
local error = error
local tonumber = tonumber
local tointeger = math.tointeger

local _M = {_VERSION = "0.14"}

-- constants
local COM_QUERY = "\x03"
local COM_PING = "\x0e"
local COM_STMT_PREPARE = "\x16"
local COM_STMT_EXECUTE = "\x17"
local COM_STMT_CLOSE = "\x19"
local COM_STMT_RESET = "\x1a"
local CURSOR_TYPE_NO_CURSOR = 0x00
local SERVER_MORE_RESULTS_EXISTS = 8

local mt = {__index = _M}

-- mysql field value type converters
local converters = {}

for i = 0x01, 0x05 do
    -- tiny, short, long, float, double
    converters[i] = tonumber
end
converters[0x08] = tonumber -- long long
converters[0x09] = tonumber -- int24
converters[0x0d] = tonumber -- year
converters[0xf6] = tonumber -- newdecimal

local function _get_byte1(data, i)
    return strbyte(data, i), i + 1
end

local function _get_byte2(data, i)
    return strunpack("<I2", data, i)
end

local function _get_byte3(data, i)
    return strunpack("<I3", data, i)
end

local function _get_byte4(data, i)
    return strunpack("<I4", data, i)
end

local function _get_byte8(data, i)
    return strunpack("<I8", data, i)
end

local function _get_float(data, i)
    return strunpack("<f", data, i)
end

local function _get_double(data, i)
    return strunpack("<d", data, i)
end

local function _set_byte2(n)
    return strpack("<I2", n)
end

local function _set_byte3(n)
    return strpack("<I3", n)
end

local function _set_byte4(n)
    return strpack("<I4", n)
end

local function _set_byte8(n)
    return strpack("<I8", n)
end

local function _set_float(n)
    return strpack("<f", n)
end

local function _set_double(n)
    return strpack("<d", n)
end

local function _from_cstring(data, i)
    return strunpack("z", data, i)
end

local function _dumphex(bytes)
    return strgsub(bytes, ".",
        function(x)
            return strformat("%02x ", strbyte(x))
        end)
end

local function _compute_token(password, scramble)
    if password == "" then
        return ""
    end
    --_dumphex(scramble)

    local stage1 = sha1(password)
    --print("stage1:", _dumphex(stage1) )
    local stage2 = sha1(stage1)
    local stage3 = sha1(scramble .. stage2)

    local i = 0
    return strgsub(stage3, ".",
        function(x)
            i = i + 1
            -- ~ is xor in lua 5.3
            return strchar(strbyte(x) ~ strbyte(stage1, i))
        end
    )
end

local function _compose_packet(self, req)
    self.packet_no = self.packet_no + 1
    local size = #req
    return strpack("<I3Bc" .. size, size, self.packet_no, req)
end

local function _recv_packet(self, sock)
    local data = sock:read(4)
    if not data then
        return nil, nil, "failed to receive packet header: "
    end

    local len, pos = _get_byte3(data, 1)
    if len == 0 then
        return nil, nil, "empty packet"
    end

    self.packet_no = strbyte(data, pos)

    data = sock:read(len)
    if not data then
        return nil, nil, "failed to read packet content: "
    end

    local field_count = strbyte(data, 1)
    local typ
    if field_count == 0x00 then
        typ = "OK"
    elseif field_count == 0xff then
        typ = "ERR"
    elseif field_count == 0xfe then
        typ = "EOF"
    else
        typ = "DATA"
    end

    return data, typ
end

local function _from_length_coded_bin(data, pos)
    local first = strbyte(data, pos)

    if not first then
        return nil, pos
    end

    if first >= 0 and first <= 250 then
        return first, pos + 1
    end

    if first == 251 then
        return nil, pos + 1
    end

    if first == 252 then
        pos = pos + 1
        return _get_byte2(data, pos)
    end

    if first == 253 then
        pos = pos + 1
        return _get_byte3(data, pos)
    end

    if first == 254 then
        pos = pos + 1
        return _get_byte8(data, pos)
    end

    return false, pos + 1
end

local function _set_length_coded_bin(n)
    if n < 251 then
        return strchar(n)
    end

    if n < (1 << 16) then
        return strpack("<BI2", 0xfc, n)
    end

    if n < (1 << 24) then
        return strpack("<BI3", 0xfd, n)
    end

    return strpack("<BI8", 0xfe, n)
end

local function _from_length_coded_str(data, pos)
    local len
    len, pos = _from_length_coded_bin(data, pos)
    if len == nil then
        return nil, pos
    end
    return sub(data, pos, pos + len - 1), pos + len
end

local function _parse_ok_packet(packet)
    local res = {}
    local pos

    res.affected_rows, pos = _from_length_coded_bin(packet, 2)
    res.insert_id, pos = _from_length_coded_bin(packet, pos)
    res.server_status, pos = _get_byte2(packet, pos)
    res.warning_count, pos = _get_byte2(packet, pos)

    local message = sub(packet, pos)
    if message and message ~= "" then
        res.message = message
    end
    return res
end

local function _parse_eof_packet(packet)
    local pos = 2
    local warning_count, pos = _get_byte2(packet, pos)
    local status_flags = _get_byte2(packet, pos)
    return warning_count, status_flags
end

local function _parse_err_packet(packet)
    local errno, pos = _get_byte2(packet, 2)
    local marker = sub(packet, pos, pos)
    local sqlstate
    if marker == '#' then
        -- with sqlstate
        pos = pos + 1
        sqlstate = sub(packet, pos, pos + 5 - 1)
        pos = pos + 5
    end
    local message = sub(packet, pos)
    return errno, message, sqlstate
end

local function _parse_result_set_header_packet(packet)
    local field_count, pos = _from_length_coded_bin(packet, 1)
    return field_count, _from_length_coded_bin(packet, pos)
end

local function _parse_field_packet(data)
    local col = {}
    local catalog, db, table, orig_table, orig_name, charsetnr, length
    local pos

    catalog, pos = _from_length_coded_str(data, 1)
    db, pos = _from_length_coded_str(data, pos)
    table, pos = _from_length_coded_str(data, pos)
    orig_table, pos = _from_length_coded_str(data, pos)
    col.name, pos = _from_length_coded_str(data, pos)
    orig_name, pos = _from_length_coded_str(data, pos)
    pos = pos + 1 -- ignore the filler
    charsetnr, pos = _get_byte2(data, pos)
    length, pos = _get_byte4(data, pos)
    col.type = strbyte(data, pos)

    --[[
    pos = pos + 1
    col.flags, pos = _get_byte2(data, pos)
    col.decimals = strbyte(data, pos)
    pos = pos + 1
    local default = sub(data, pos + 2)
    if default and default ~= "" then
        col.default = default
    end
    --]]
    return col
end

local function _parse_row_data_packet(data, cols, compact)
    local value, col, conv
    local pos = 1
    local ncols = #cols
    local row = {}

    for i = 1, ncols do
        value, pos = _from_length_coded_str(data, pos)
        col = cols[i]

        if value ~= nil then
            conv = converters[col.type]
            if conv then
                value = conv(value)
            end
        end

        if compact then
            row[i] = value
        else
            row[col.name] = value
        end
    end

    return row
end

local function _recv_field_packet(self, sock)
    local packet, typ, err = _recv_packet(self, sock)
    if not packet then
        return nil, err
    end

    if typ == "ERR" then
        local errno, msg, sqlstate = _parse_err_packet(packet)
        return nil, msg, errno, sqlstate
    end

    if typ ~= "DATA" then
        return nil, "bad field packet type: " .. typ
    end

    -- typ == 'DATA'

    return _parse_field_packet(packet)
end

local function _recv_decode_packet_resp(self)
    return function(sock)
        local packet, typ, err = _recv_packet(self, sock)
        if not packet then
            return false, "failed to receive the result packet" .. err
        end

        if typ == "ERR" then
            local errno, msg, sqlstate = _parse_err_packet(packet)
            return false, strformat("errno:%d, msg:%s,sqlstate:%s", errno, msg, sqlstate)
        end

        if typ == "EOF" then
            return false, "old pre-4.1 authentication protocol not supported"
        end

        return true, packet
    end
end

local function _mysql_login(self, user, password, database, on_connect)
    return function(sockchannel)
        local dispatch_resp = _recv_decode_packet_resp(self)
        local packet = sockchannel:response(dispatch_resp)

        self.protocol_ver = strbyte(packet)

        local server_ver, pos = _from_cstring(packet, 2)
        if not server_ver then
            error "bad handshake initialization packet: bad server version"
        end

        self._server_ver = server_ver

        local thread_id, pos = _get_byte4(packet, pos)
        local scramble1 = sub(packet, pos, pos + 8 - 1)
        if not scramble1 then
            error "1st part of scramble not found"
        end

        pos = pos + 9 -- skip filler

        -- two lower bytes
        self._server_capabilities, pos = _get_byte2(packet, pos)
        self._server_lang = strbyte(packet, pos)
        pos = pos + 1
        self._server_status, pos = _get_byte2(packet, pos)

        local more_capabilities
        more_capabilities, pos = _get_byte2(packet, pos)

        self._server_capabilities = self._server_capabilities | more_capabilities << 16

        local len = 21 - 8 - 1
        pos = pos + 1 + 10

        local scramble_part2 = sub(packet, pos, pos + len - 1)
        if not scramble_part2 then
            error "2nd part of scramble not found"
        end

        local scramble = scramble1 .. scramble_part2
        local token = _compute_token(password, scramble)
        local client_flags = 260047
        local req = strpack("<I4I4c24zs1z",
            client_flags,
            self._max_packet_size,
            strrep("\0", 24), -- TODO: add support for charset encoding
            user,
            token,
            database
        )
        local authpacket = _compose_packet(self, req)
        sockchannel:request(authpacket, dispatch_resp)
        if on_connect then
            on_connect(self)
        end
    end
end

-- 构造ping数据包
local function _compose_ping(self)
    self.packet_no = -1
    return _compose_packet(self, COM_PING)
end

local function _compose_query(self, query)
    self.packet_no = -1
    local cmd_packet = COM_QUERY .. query
    return _compose_packet(self, cmd_packet)
end

local function _compose_stmt_prepare(self, query)
    self.packet_no = -1
    local cmd_packet = COM_STMT_PREPARE .. query
    return _compose_packet(self, cmd_packet)
end

--参数字段类型转换
local store_types = {
    number = function(v)
        if not tointeger(v) then
            return _set_byte2(0x05), _set_double(v)
        else
            return _set_byte2(0x08), _set_byte8(v)
        end
    end,
    string = function(v)
        return _set_byte2(0x0f), _set_length_coded_bin(#v) .. v
    end,
    --bool转换为0,1
    boolean = function(v)
        if v then
            return _set_byte2(0x01), strchar(1)
        else
            return _set_byte2(0x01), strchar(0)
        end
    end
}

local function _compose_stmt_execute(self, stmt, cursor_type, args)
    local arg_num = #args
    if arg_num ~= stmt.param_count then
        error("require stmt.param_count " .. stmt.param_count .. " get arg_num " .. arg_num)
    end

    self.packet_no = -1

    local cmd_packet = strpack("<c1I4BI4", COM_STMT_EXECUTE, stmt.prepare_id, cursor_type, 0x01)
    if arg_num > 0 then
        local null_count = (arg_num + 7) // 8
        local f, ts, vs
        local types_buf = ""
        local values_buf = ""
        for _, v in pairs(args) do
            f = store_types[type(v)]
            if not f then
                error("invalid parameter type", type(v))
            end
            ts, vs = f(v)
            types_buf = types_buf .. ts
            values_buf = values_buf .. vs
        end
        cmd_packet = cmd_packet .. strrep("\0", null_count) .. strchar(0x01) .. types_buf .. values_buf
    end

    return _compose_packet(self, cmd_packet)
end

local function read_result(self, sock)
    local packet, typ, err = _recv_packet(self, sock)
    if not packet then
        return nil, err
        --error( err )
    end

    if typ == "ERR" then
        local errno, msg, sqlstate = _parse_err_packet(packet)
        return nil, msg, errno, sqlstate
        --error( strformat("errno:%d, msg:%s,sqlstate:%s",errno,msg,sqlstate))
    end

    if typ == "OK" then
        local res = _parse_ok_packet(packet)
        if res and res.server_status & SERVER_MORE_RESULTS_EXISTS ~= 0 then
            return res, "again"
        end
        return res
    end

    if typ ~= "DATA" then
        return nil, "packet type " .. typ .. " not supported"
        --error( "packet type " .. typ .. " not supported" )
    end

    -- typ == 'DATA'

    local field_count, extra = _parse_result_set_header_packet(packet)
    local cols = {}
    for i = 1, field_count do
        local col, err, errno, sqlstate = _recv_field_packet(self, sock)
        if not col then
            return nil, err, errno, sqlstate
            --error( strformat("errno:%d, msg:%s,sqlstate:%s",errno,msg,sqlstate))
        end
        cols[i] = col
    end

    local packet, typ, err = _recv_packet(self, sock)
    if not packet then
        --error( err)
        return nil, err
    end

    if typ ~= "EOF" then
        --error ( "unexpected packet type " .. typ .. " while eof packet is ".. "expected" )
        return nil, "unexpected packet type " .. typ .. " while eof packet is " .. "expected"
    end

    -- typ == 'EOF'

    local compact = self.compact
    local rows = {}
    local i = 0
    while true do
        packet, typ, err = _recv_packet(self, sock)
        if not packet then
            --error (err)
            return nil, err
        end

        if typ == "EOF" then
            local warning_count, status_flags = _parse_eof_packet(packet)
            if status_flags & SERVER_MORE_RESULTS_EXISTS ~= 0 then
                return rows, "again"
            end
            break
        end

        -- if typ ~= 'DATA' then
        --     return nil, 'bad row packet type: ' .. typ
        -- end

        -- typ == 'DATA'

        i = i + 1
        rows[i] = _parse_row_data_packet(packet, cols, compact)
    end

    return rows
end

local function _query_resp(self)
    return function(sock)
        local res, err, errno, sqlstate = read_result(self, sock)
        if not res then
            local badresult = {}
            badresult.badresult = true
            badresult.err = err
            badresult.errno = errno
            badresult.sqlstate = sqlstate
            return true, badresult
        end
        if err ~= "again" then
            return true, res
        end
        local multiresultset = {res}
        multiresultset.multiresultset = true
        local i = 2
        while err == "again" do
            res, err, errno, sqlstate = read_result(self, sock)
            if not res then
                multiresultset.badresult = true
                multiresultset.err = err
                multiresultset.errno = errno
                multiresultset.sqlstate = sqlstate
                return true, multiresultset
            end
            multiresultset[i] = res
            i = i + 1
        end
        return true, multiresultset
    end
end

function _M.connect(opts)
    local self = setmetatable({}, mt)

    local max_packet_size = opts.max_packet_size
    if not max_packet_size then
        max_packet_size = 1024 * 1024 -- default 1 MB
    end
    self._max_packet_size = max_packet_size
    self.compact = opts.compact_arrays

    local database = opts.database or ""
    local user = opts.user or ""
    local password = opts.password or ""

    local channel =
        socketchannel.channel {
        host = opts.host,
        port = opts.port or 3306,
        auth = _mysql_login(self, user, password, database, opts.on_connect),
        overload = opts.overload
    }
    self.sockchannel = channel
    -- try connect first only once
    channel:connect(true)

    return self
end

function _M.disconnect(self)
    self.sockchannel:close()
    setmetatable(self, nil)
end

function _M.query(self, query)
    local querypacket = _compose_query(self, query)
    local sockchannel = self.sockchannel
    if not self.query_resp then
        self.query_resp = _query_resp(self)
    end
    return sockchannel:request(querypacket, self.query_resp)
end

local function read_prepare_result(self, sock)
    local resp = {}
    local packet, typ, err = _recv_packet(self, sock)
    if not packet then
        resp.badresult = true
        resp.errno = 300101
        resp.err = err
        return false, resp
    end

    if typ == "ERR" then
        local errno, msg, sqlstate = _parse_err_packet(packet)
        resp.badresult = true
        resp.errno = errno
        resp.err = msg
        resp.sqlstate = sqlstate
        return true, resp
    end

    --第一节只能是OK
    if typ ~= "OK" then
        resp.badresult = true
        resp.errno = 300201
        resp.err = "first typ must be OK,now" .. typ
        return false, resp
    end
    resp.prepare_id, resp.field_count, resp.param_count, resp.warning_count = strunpack("<I4I2I2xI2", packet, 2)

    resp.params = {}
    resp.fields = {}

    if resp.param_count > 0 then
        local param = _recv_field_packet(self, sock)
        while param do
            table.insert(resp.params, param)
            param = _recv_field_packet(self, sock)
        end
    end
    if resp.field_count > 0 then
        local field = _recv_field_packet(self, sock)
        while field do
            table.insert(resp.fields, field)
            field = _recv_field_packet(self, sock)
        end
    end

    return true, resp
end

local function _prepare_resp(self, sql)
    return function(sock)
        return read_prepare_result(self, sock, sql)
    end
end

-- 注册预处理语句
function _M.prepare(self, sql)
    local querypacket = _compose_stmt_prepare(self, sql)
    local sockchannel = self.sockchannel
    if not self.prepare_resp then
        self.prepare_resp = _prepare_resp(self)
    end
    return sockchannel:request(querypacket, self.prepare_resp)
end

local function _get_datetime(data, pos)
    local len, year, month, day, hour, minute, second
    local value
    len, pos = _from_length_coded_bin(data, pos)
    if len == 7 then
        year, month, day, hour, minute, second, pos = string.unpack("<I2BBBBB", data, pos)
        value = strformat("%04d-%02d-%02d %02d:%02d:%02d", year, month, day, hour, minute, second)
    else
        value = "2017-09-09 20:08:09"
        --unsupported format
        pos = pos + len
    end
    return value, pos
end

local _binary_parser = {
    [0x01] = _get_byte1,
    [0x02] = _get_byte2,
    [0x03] = _get_byte4,
    [0x04] = _get_float,
    [0x05] = _get_double,
    [0x07] = _get_datetime,
    [0x08] = _get_byte8,
    [0x0c] = _get_datetime,
    [0x0f] = _from_length_coded_str,
    [0x10] = _from_length_coded_str,
    [0xf9] = _from_length_coded_str,
    [0xfa] = _from_length_coded_str,
    [0xfb] = _from_length_coded_str,
    [0xfc] = _from_length_coded_str,
    [0xfd] = _from_length_coded_str,
    [0xfe] = _from_length_coded_str
}

local function _parse_row_data_binary(data, cols, compact)
    local ncols = #cols
    -- 空位图,前两个bit系统保留 (列数量 + 7 + 2) / 8
    local null_count = (ncols + 9) // 8
    local pos = 2 + null_count
    local value

    --空字段表
    local null_fields = {}
    local field_index = 1
    local byte
    for i = 2, pos - 1 do
        byte = strbyte(data, i)
        for j = 0, 7 do
            if field_index > 2 then
                if byte & (1 << j) == 0 then
                    null_fields[field_index - 2] = false
                else
                    null_fields[field_index - 2] = true
                end
            end
            field_index = field_index + 1
        end
    end

    local row = {}
    local parser
    for i = 1, ncols do
        local col = cols[i]
        local typ = col.type
        local name = col.name
        if not null_fields[i] then
            parser = _binary_parser[typ]
            if not parser then
                error("_parse_row_data_binary()error,unsupported field type " .. typ)
            end
            value, pos = parser(data, pos)
            if compact then
                row[i] = value
            else
                row[name] = value
            end
        end
    end

    return row
end

local function read_execute_result(self, sock)
    local packet, typ, err = _recv_packet(self, sock)
    if not packet then
        return nil, err
        --error( err )
    end

    if typ == "ERR" then
        local errno, msg, sqlstate = _parse_err_packet(packet)
        return nil, msg, errno, sqlstate
        --error( strformat("errno:%d, msg:%s,sqlstate:%s",errno,msg,sqlstate))
    end

    if typ == "OK" then
        local res = _parse_ok_packet(packet)
        if res and res.server_status & SERVER_MORE_RESULTS_EXISTS ~= 0 then
            return res, "again"
        end
        return res
    end

    if typ ~= "DATA" then
        return nil, "packet type " .. typ .. " not supported"
        --error( "packet type " .. typ .. " not supported" )
    end

    -- typ == 'DATA'

    local field_count, extra = _parse_result_set_header_packet(packet)

    local cols = {}
    local col
    while true do
        packet, typ, err = _recv_packet(self, sock)
        if typ == "EOF" then
            local warning_count, status_flags = _parse_eof_packet(packet)
            break
        end
        col = _parse_field_packet(packet)
        if not col then
            break
            --error( strformat("errno:%d, msg:%s,sqlstate:%s",errno,msg,sqlstate))
        end
        table.insert(cols, col)
    end

    --没有记录集返回
    if #cols < 1 then
        return {}
    end

    local compact = self.compact
    local rows = {}
    local row
    while true do
        packet, typ, err = _recv_packet(self, sock)
        if typ == "EOF" then
            local warning_count, status_flags = _parse_eof_packet(packet)
            if status_flags & SERVER_MORE_RESULTS_EXISTS ~= 0 then
                return rows, "again"
            end
            break
        end
        row = _parse_row_data_binary(packet, cols, compact)
        if not col then
            break
        end
        table.insert(rows, row)
    end

    return rows
end

local function _execute_resp(self)
    return function(sock)
        local res, err, errno, sqlstate = read_execute_result(self, sock)
        if not res then
            local badresult = {}
            badresult.badresult = true
            badresult.err = err
            badresult.errno = errno
            badresult.sqlstate = sqlstate
            return true, badresult
        end
        if err ~= "again" then
            return true, res
        end
        local mulitresultset = {res}
        mulitresultset.mulitresultset = true
        local i = 2
        while err == "again" do
            res, err, errno, sqlstate = read_execute_result(self, sock)
            if not res then
                mulitresultset.badresult = true
                mulitresultset.err = err
                mulitresultset.errno = errno
                mulitresultset.sqlstate = sqlstate
                return true, mulitresultset
            end
            mulitresultset[i] = res
            i = i + 1
        end
        return true, mulitresultset
    end
end

--[[
    执行预处理语句
    失败返回字段
        errno
        badresult
        sqlstate
        err
]]
function _M.execute(self, stmt, ...)
    -- 检查参数，不能为nil
    local p_n = select('#', ...)
    local p_v
    for i = 1, p_n do
        p_v = select(i, ...)
        if p_v == nil then
            return {
                badresult = true,
                errno = 30902,
                err = "parameter " .. i .. " is nil"
            }
        end
    end

    local querypacket, er = _compose_stmt_execute(self, stmt, CURSOR_TYPE_NO_CURSOR, {...})
    if not querypacket then
        return {
            badresult = true,
            errno = 30902,
            err = er
        }
    end
    local sockchannel = self.sockchannel
    if not self.execute_resp then
        self.execute_resp = _execute_resp(self)
    end
    return sockchannel:request(querypacket, self.execute_resp)
end

local function _compose_stmt_reset(self, stmt)
	self.packet_no = -1

	local cmd_packet = strpack("c1<I4", COM_STMT_RESET, stmt.prepare_id)
	return _compose_packet(self, cmd_packet)
end

--重置预处理句柄
function _M.stmt_reset(self, stmt)
	local querypacket = _compose_stmt_reset(self, stmt)
	local sockchannel = self.sockchannel
		if not self.query_resp then
		self.query_resp = _query_resp(self)
	end
	return sockchannel:request(querypacket, self.query_resp)
end

local function _compose_stmt_close(self, stmt)
	self.packet_no = -1

	local cmd_packet = strpack("c1<I4", COM_STMT_CLOSE, stmt.prepare_id)
	return _compose_packet(self, cmd_packet)
end

--关闭预处理句柄
function _M.stmt_close(self, stmt)
	local querypacket = _compose_stmt_close(self, stmt)
	local sockchannel = self.sockchannel
	return sockchannel:request(querypacket)
end


function _M.ping(self)
    local querypacket, er = _compose_ping(self)
    if not querypacket then
        return {
            badresult = true,
            errno = 30902,
            err = er
        }
    end
    local sockchannel = self.sockchannel
    if not self.query_resp then
        self.query_resp = _query_resp(self)
    end
    return sockchannel:request(querypacket, self.query_resp)
end

function _M.server_ver(self)
    return self._server_ver
end

local escape_map = {
    ['\0'] = "\\0",
    ['\b'] = "\\b",
    ['\n'] = "\\n",
    ['\r'] = "\\r",
    ['\t'] = "\\t",
    ['\26'] = "\\Z",
    ['\\'] = "\\\\",
    ["'"] = "\\'",
    ['"'] = '\\"',
}

function _M.quote_sql_str( str)
    return strformat("'%s'", strgsub(str, "[\0\b\n\r\t\26\\\'\"]", escape_map))
end

function _M.set_compact_arrays(self, value)
    self.compact = value
end

return _M