Add SNTP client implementation for time synchronization

This file implements an SNTP client for Windows NT 3.51 that retrieves time from an NTP server and optionally sets the system time.

w32time/w32time.cpp

@@ -0,0 +1,137 @@
+// w32time.cpp
+// SNTP client for Windows NT 3.51
+// Build as Win32 Console Application with VC++ 4.0/4.2
+
+#include <windows.h>
+#include <winsock.h>
+#include <stdio.h>
+
+#pragma comment(lib,"wsock32.lib")
+
+#define NTP_PORT 123
+#define NTP_PACKET_SIZE 48
+
+const unsigned __int64 FILETIME_TICKS_PER_SEC = 10000000i64;
+const unsigned __int64 FILETIME_UNIX_EPOCH    = 11644473600i64;
+const unsigned __int64 NTP_EPOCH_UNIX         = 2208988800i64;
+
+typedef struct _NTP_PACKET {
+    unsigned char li_vn_mode;
+    unsigned char stratum;
+    unsigned char poll;
+    signed char  precision;
+    unsigned long rootDelay;
+    unsigned long rootDispersion;
+    unsigned long refId;
+    unsigned long refTS_sec;
+    unsigned long refTS_frac;
+    unsigned long origTS_sec;
+    unsigned long origTS_frac;
+    unsigned long rxTS_sec;
+    unsigned long rxTS_frac;
+    unsigned long txTS_sec;
+    unsigned long txTS_frac;
+} NTP_PACKET;
+
+static unsigned long be32_read(const unsigned long be) {
+    const unsigned char *p = (const unsigned char *)&be;
+    return ((unsigned long)p[0] << 24) | ((unsigned long)p[1] << 16) |
+    ((unsigned long)p[2] << 8) | (unsigned long)p[3];
+}
+
+static BOOL EnableSetTimePrivilege(void) {
+    HANDLE hToken;
+    TOKEN_PRIVILEGES tp;
+    LUID luid;
+    if(!OpenProcessToken(GetCurrentProcess(),TOKEN_ADJUST_PRIVILEGES|TOKEN_QUERY,&hToken))
+        return FALSE;
+    if(!LookupPrivilegeValueA(NULL,"SeSystemtimePrivilege",&luid)) {
+        CloseHandle(hToken);
+        return FALSE;
+    }
+    tp.PrivilegeCount=1;
+    tp.Privileges[0].Luid=luid;
+    tp.Privileges[0].Attributes=SE_PRIVILEGE_ENABLED;
+    AdjustTokenPrivileges(hToken,FALSE,&tp,sizeof(tp),NULL,NULL);
+    CloseHandle(hToken);
+    return (GetLastError()==ERROR_SUCCESS);
+}
+
+/* Convert NTP timestamp to SYSTEMTIME (UTC) */
+static BOOL NtpToSystemTime(unsigned long sec_be, unsigned long frac_be, SYSTEMTIME *outSt) {
+    unsigned long sec  = be32_read(sec_be);
+    unsigned long frac = be32_read(frac_be);
+
+    // Convert NTP seconds (since 1900) -> Unix (1970) -> FileTime (1601)
+    unsigned __int64 unix_seconds = (unsigned __int64)sec - NTP_EPOCH_UNIX;
+    unsigned __int64 file_seconds = unix_seconds + FILETIME_UNIX_EPOCH;
+    unsigned __int64 file_ticks   = file_seconds * FILETIME_TICKS_PER_SEC;
+    unsigned __int64 frac_ticks   = ((unsigned __int64)frac * FILETIME_TICKS_PER_SEC) / 4294967296ui64;
+
+    ULARGE_INTEGER uli;
+    uli.QuadPart = file_ticks + frac_ticks;
+
+    FILETIME ft;
+    ft.dwLowDateTime  = uli.LowPart;
+    ft.dwHighDateTime = uli.HighPart;
+
+    return FileTimeToSystemTime(&ft,outSt);
+}
+
+int main(int argc,char**argv) {
+    if(argc<2) {
+        printf("Usage: %s <server> [-set]\n",argv[0]);
+        return 1;
+    }
+    const char* server=argv[1];
+    BOOL doSet=(argc>2 && !_stricmp(argv[2],"-set"));
+
+    WSADATA wsa;
+    if(WSAStartup(MAKEWORD(1,1),&wsa)!=0) { printf("WSAStartup failed\n"); return 1; }
+    SOCKET s=socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);
+    if(s==INVALID_SOCKET) { printf("socket failed\n"); return 1; }
+    struct hostent *he=gethostbyname(server);
+    if(!he) { printf("DNS failed\n"); return 1; }
+    struct sockaddr_in addr;
+    ZeroMemory(&addr,sizeof(addr));
+    addr.sin_family=AF_INET;
+    addr.sin_port=htons(NTP_PORT);
+    memcpy(&addr.sin_addr,he->h_addr,sizeof(struct in_addr));
+
+    NTP_PACKET req;
+    ZeroMemory(&req,sizeof(req));
+    req.li_vn_mode=0x1B; // LI=0, VN=3, Mode=3 (client)
+
+    sendto(s,(const char*)&req,sizeof(req),0,(struct sockaddr*)&addr,sizeof(addr));
+
+    struct sockaddr_in from; int fromlen=sizeof(from);
+    NTP_PACKET resp;
+    int recvd=recvfrom(s,(char*)&resp,sizeof(resp),0,(struct sockaddr*)&from,&fromlen);
+    closesocket(s);
+    WSACleanup();
+
+    if(recvd<(int)NTP_PACKET_SIZE) { printf("short response\n"); return 1; }
+
+    SYSTEMTIME stSrv;
+    if(!NtpToSystemTime(resp.txTS_sec,resp.txTS_frac,&stSrv)) {
+        printf("Conversion failed\n");
+        return 1;
+    }
+
+    printf("Server %s UTC time: %04u-%02u-%02u %02u:%02u:%02u\n",
+           server,stSrv.wYear,stSrv.wMonth,stSrv.wDay,
+           stSrv.wHour,stSrv.wMinute,stSrv.wSecond);
+
+    if(doSet) {
+        if(!EnableSetTimePrivilege()) {
+            printf("Privilege not enabled (%lu)\n",GetLastError());
+            return 1;
+        }
+        if(!SetSystemTime(&stSrv)) {
+            printf("SetSystemTime failed (%lu)\n",GetLastError());
+            return 1;
+        }
+        printf("System time updated.\n");
+    }
+    return 0;
+}