網絡授時服務是一些網絡上的時間服務器提供的時間，一般用于本地時鐘同步。 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）
S: 檢測端口37
U: 連接到端口37
S: 以32位二進制數發送時間
U: 接收時間
U: 關閉連接
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，選擇只是出于個人興趣。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 nend-- get time from a ip address, use tcp protoclfunction 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 nilendfunction nettime() for _, ip in pairs(server_ip) do time = gettime(ip) if time then return time end endend
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
至于"socket.core"，windows默認安裝位于“/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;}
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