网络授时服务是一些网络上的时间服务器提供的时间，一般用于本地时钟同步。 授时服务有很多种，一般我们选择RFC-868。这个协议的工作流程是：(S代表Server，C代表Client)
S: 检测端口37
U: 连接到端口37
S: 以32位二进制数发送时间
U: 接收时间
U: 关闭连接
S: 关闭连接
协议非常简单，用TCP连接上后，服务器直接把时间发送回来。发送的是从1900年1月1日午夜到现在的秒数。
使用luasocket
实现的方案有很多种，Lua不一定是最简单的，选择只是出于个人兴趣。直接上代码吧
—————————————————————————–
— 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
代码原理不细说，非常简单。唯一值得一提的是socket库包含。最开始用的这句 require “socket”
在解释器中表现很好，但在用C中调用会找不到相应的module。错误提示
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’.
网上也有好多类似的提问，大抵是没仔细看作者的Guide。显著的有这么一句
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默认安装位于“\socket\core.dll”。
C宿主调用
#include
#include
#include
#include
#include
#include
#include
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;
}