mysql - erlang-mysql-driver 源代码，为什么小字节序来获取结果

Question

我是 erlang 的新手，正在学习 erlang-mysql-driver .任何人都可以帮助我理解为什么在解析函数“get_lcb”中的二进制文件时这里的字节序很少吗？

以下是mysql_conn.erl中的代码

%%--------------------------------------------------------------------
%% Function: get_query_response(LogFun, RecvPid)
%%           LogFun  = undefined | function() with arity 3
%%           RecvPid = pid(), mysql_recv process
%%           Version = integer(), Representing MySQL version used
%% Descrip.: Wait for frames until we have a complete query response.
%% Returns :   {data, #mysql_result}
%%             {updated, #mysql_result}
%%             {error, #mysql_result}
%%           FieldInfo    = list() of term()
%%           Rows         = list() of [string()]
%%           AffectedRows = int()
%%           Reason       = term()
%%--------------------------------------------------------------------
get_query_response(LogFun, RecvPid, Version) ->
    case do_recv(LogFun, RecvPid, undefined) of
    {ok, Packet, _} ->
        {Fieldcount, Rest} = get_lcb(Packet),
        case Fieldcount of
        0 ->
            %% No Tabular data
            <<AffectedRows:8, Rest2/binary>> = Rest,
            io:format("Rest2=~p~n", [Rest2]),
            {InsertId, _} = get_lcb(Rest2),
            io:format("InsertId=~p~n", [InsertId]),
            {updated, #mysql_result{affectedrows=AffectedRows, insertid=InsertId}};
        255 ->
            <<_Code:16/little, Message/binary>>  = Rest,
            {error, #mysql_result{error=Message}};
        _ ->
            %% Tabular data received
            case get_fields(LogFun, RecvPid, [], Version) of
            {ok, Fields} ->
                case get_rows(Fields, LogFun, RecvPid, []) of
                {ok, Rows} ->
                    {data, #mysql_result{fieldinfo=Fields,
                             rows=Rows}};
                {error, Reason} ->
                    {error, #mysql_result{error=Reason}}
                end;
            {error, Reason} ->
                {error, #mysql_result{error=Reason}}
            end
        end;
    {error, Reason} ->
        {error, #mysql_result{error=Reason}}
    end.


get_lcb(<<251:8, Rest/binary>>) ->
    {null, Rest};
get_lcb(<<252:8, Value:16/little, Rest/binary>>) ->
    io:format("Value=~p~n",[Value]),
    io:format("Rest=~p~n",[Rest]),
    {Value, Rest};
get_lcb(<<253:8, Value:24/little, Rest/binary>>) ->
    {Value, Rest};
get_lcb(<<254:8, Value:32/little, Rest/binary>>) ->
    {Value, Rest};
get_lcb(<<Value:8, Rest/binary>>) when Value < 251 ->
    {Value, Rest};
get_lcb(<<255:8, Rest/binary>>) ->
    {255, Rest}.


%%--------------------------------------------------------------------
%% Function: do_recv(LogFun, RecvPid, SeqNum)
%%           LogFun  = undefined | function() with arity 3
%%           RecvPid = pid(), mysql_recv process
%%           SeqNum  = undefined | integer()
%% Descrip.: Wait for a frame decoded and sent to us by RecvPid.
%%           Either wait for a specific frame if SeqNum is an integer,
%%           or just any frame if SeqNum is undefined.
%% Returns : {ok, Packet, Num} |
%%           {error, Reason}
%%           Reason = term()
%%
%% Note    : Only to be used externally by the 'mysql_auth' module.
%%--------------------------------------------------------------------
do_recv(LogFun, RecvPid, SeqNum)  when is_function(LogFun);
                       LogFun == undefined,
                       SeqNum == undefined ->
    receive
        {mysql_recv, RecvPid, data, Packet, Num} ->
        {ok, Packet, Num};
    {mysql_recv, RecvPid, closed, _E} ->
        {error, "mysql_recv: socket was closed"}
    end;
do_recv(LogFun, RecvPid, SeqNum) when is_function(LogFun);
                      LogFun == undefined,
                      is_integer(SeqNum) ->
    ResponseNum = SeqNum + 1,
    receive
        {mysql_recv, RecvPid, data, Packet, ResponseNum} ->
        {ok, Packet, ResponseNum};
    {mysql_recv, RecvPid, closed, _E} ->
        {error, "mysql_recv: socket was closed"}
    end.

Answer 1

我想你的意思是这些行:Value:16/little、Value:24/little 等等...？好吧，这是因为 MySQL 服务器将始终使用小端值填充响应数据包的这些部分 - 但默认情况下，Erlang 机器将以 CPU 原生的任何字节序运行。