作者：ani_di 
版權所有，轉載務必保留此鏈接 http://blog.csdn.net/ani_di

Lua獲取網絡時間

網絡授時服務是一些網絡上的時間服務器提供的時間，一般用於本地時鍾同步。 授時服務有很多種，一般我們選擇RFC-868。這個協議的工作流程是：（S代表Server，C代表Client）

1. S: 檢測端口37
2. U: 連接到端口37
3. S: 以32位二進制數發送時間
4. U: 接收時間
5. U: 關閉連接
6. S: 關閉連接

協議非常簡單，用TCP連接上后，服務器直接把時間發送回來。發送的是從1900年1月1日午夜到現在的秒數。

使用luasocket

實現的方案有很多種，Lua不一定是最簡單的，選擇只是出於個人興趣。直接上代碼吧

-----------------------------------------------------------------------------
-- Network Time Protocal
-- Author: ani_di
-----------------------------------------------------------------------------
package.cpath = package.cpath .. ';D:\\tools\\Lua\\5.1\\clibs\\?.dll;?.dll'
local socket = require "socket.core"

server_ip = {
        -- "129.6.15.29",
        "132.163.4.101",
        "132.163.4.102",
        "132.163.4.103",
        "128.138.140.44",
        "192.43.244.18",
        "131.107.1.10",
        "66.243.43.21",
        "216.200.93.8",
        "208.184.49.9",
        "207.126.98.204",
        "207.200.81.113",
        "205.188.185.33"}

function nstol(str)
    assert(str and #str == 4)
    local t = {str:byte(1,-1)}
    local n = 0
    for k = 1, #t do
        n= n*256 + t[k]
    end
    return n
end

-- get time from a ip address, use tcp protocl
function gettime(ip)
    print('connect ', ip)
    local tcp = socket.tcp()
    tcp:settimeout(10)
    tcp:connect(ip, 37)
    success, time = pcall(nstol, tcp:receive(4))
    tcp:close()
    return success and time or nil
end

function nettime()
    for _, ip in pairs(server_ip) do
        time = gettime(ip)
        if time then 
            return time
        end
    end
end

代碼原理不細說，非常簡單。唯一值得一提的是socket庫包含。最開始用的這句 require "socket"

在解釋器中表現很好，但在用C中調用會找不到相應的module。錯誤提示

    no field package.preload['socket']
    no file '.\socket.lua'
    no file 'F:\Projects\Lua\nettime\lua\socket.lua'
    no file 'F:\Projects\Lua\nettime\lua\socket\init.lua'
    no file 'F:\Projects\Lua\nettime\socket.lua'
    no file 'F:\Projects\Lua\nettime\socket\init.lua'
    no file 'D:\tools\Lua\5.1\lua\socket.luac'
    no file '.\socket.dll'
    no file '.\socket51.dll'
    no file 'F:\Projects\Lua\nettime\socket.dll'
    no file 'F:\Projects\Lua\nettime\socket51.dll'
    no file 'F:\Projects\Lua\nettime\clibs\socket.dll'
    no file 'F:\Projects\Lua\nettime\clibs\socket51.dll'
    no file 'F:\Projects\Lua\nettime\loadall.dll'
    no file 'F:\Projects\Lua\nettime\clibs\loadall.dll'.

網上也有好多類似的提問，大抵是沒仔細看作者的Guide。顯著的有這么一句

The other two environment variables instruct the compatibility module to look for dynamic libraries and extension modules in the appropriate directories and with the appropriate filename extensions.>

LUAPATH=/?.lua;?.lua LUACPATH=/?.dll;?.dll

至於"socket.core"，windows默認安裝位於“\socket\core.dll”。

C宿主調用

#include <stdio.h>
#include <string.h>
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>
#include <time.h>
#include <Windows.h>

int load(lua_State* L, const char* func, unsigned int* utc) {
   lua_getglobal(L, func);
   if (lua_pcall(L, 0, 1, 0)) {
        printf("Error Msg pcall %s.\n", lua_tostring(L, -1));
        return -1;
   }

   if (!lua_isnumber(L,-1)) {
       printf("time should be a number\n" );
       return -2;
   }

   *utc = lua_tonumber(L,-1);
   lua_pop(L, -1);
   return 0;
}

void TimetToFileTime( time_t t, LPFILETIME pft )
{
    LONGLONG ll = Int32x32To64(t, 10000000) + 116444736000000000;
    pft->dwLowDateTime = (DWORD) ll;
    pft->dwHighDateTime = ll >>32;
}

int main()
{
   lua_State* L = luaL_newstate();
   unsigned int utc = 0;
   luaL_openlibs(L);
  if (luaL_loadfile(L, "nettime.lua") || lua_pcall(L, 0, 0, 0)) {
       printf("Error Msg load %s.\n", lua_tostring(L, -1));
       return -1;
   }
   do {
    if(load(L,"nettime", &utc) == 0) {
        time_t tt = utc - 2208988800L;
        SYSTEMTIME st;
        FILETIME ft;
        TimetToFileTime(tt, &ft);
        if (FileTimeToSystemTime(&ft, &st))
        {
            printf("Today is: %d-%d-%d\n", st.wYear, st.wMonth, st.wDay);
            SetSystemTime(&st);
        }
        break;
    } else {
        puts("No network!");
        Sleep(10000);
    }
   } while (1);
   lua_close(L);
   return 0;
}