synctime.c
/*************************************************************************** * _ _ ____ _ * Project ___| | | | _ \| | * / __| | | | |_) | | * | (__| |_| | _ <| |___ * \___|\___/|_| \_\_____| * * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. * * This software is licensed as described in the file COPYING, which * you should have received as part of this distribution. The terms * are also available at https://curl.se/docs/copyright.html. * * You may opt to use, copy, modify, merge, publish, distribute and/or sell * copies of the Software, and permit persons to whom the Software is * furnished to do so, under the terms of the COPYING file. * * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY * KIND, either express or implied. * * SPDX-License-Identifier: curl * ***************************************************************************/ /* <DESC> * Set your system time from a remote HTTP server's Date: header. * </DESC> */ /* This example code only builds as-is on Windows. * * Synchronising your computer clock via Internet time server usually relies * on DAYTIME, TIME, or NTP protocols. These protocols provide good accurate * time synchronization but it does not work well through a firewall/proxy. * Some adjustment has to be made to the firewall/proxy for these protocols to * work properly. * * There is an indirect method. Since most webserver provide server time in * their HTTP header, therefore you could synchronise your computer clock * using HTTP protocol which has no problem with firewall/proxy. * * For this software to work, you should take note of these items. * 1. Your firewall/proxy must allow your computer to surf Internet. * 2. Webserver system time must in sync with the NTP time server, * or at least provide an accurate time keeping. * 3. Webserver HTTP header does not provide the milliseconds units, * so there is no way to get an accurate time. * 4. This software could only provide an accuracy of +- a few seconds, * as Round-Trip delay time is not taken into consideration. * Compensation of network, firewall/proxy delay cannot be simply divide * the Round-Trip delay time by half. * 5. Win32 SetSystemTime() API sets your computer clock according to * GMT/UTC time. Therefore your computer timezone must be properly set. * 6. Webserver data should not be cached by the proxy server. Some * webserver provide Cache-Control to prevent caching. * * Usage: * This software synchronises your computer clock only when you issue * it with --synctime. By default, it only display the webserver's clock. * * Written by: Frank (contributed to libcurl) * * THE SOFTWARE IS PROVIDED "AS-IS" AND WITHOUT WARRANTY OF ANY KIND, * EXPRESS, IMPLIED OR OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY * WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. * * IN NO EVENT SHALL THE AUTHOR OF THIS SOFTWARE BE LIABLE FOR * ANY SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND, * OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, * WHETHER OR NOT ADVISED OF THE POSSIBILITY OF DAMAGE, AND ON ANY THEORY OF * LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE * OF THIS SOFTWARE. * */ #include <stdio.h> #include <time.h> #include <curl/curl.h> #ifdef _WIN32 #include <windows.h> #else #error "This example requires Windows." #endif #define MAX_STRING 256 #define MAX_STRING1 MAX_STRING + 1 #define SYNCTIME_UA "synctime/1.0" typedef struct { char http_proxy[MAX_STRING1]; char proxy_user[MAX_STRING1]; char timeserver[MAX_STRING1]; } conf_t; static const char DefaultTimeServer[3][MAX_STRING1] = { "https://nist.time.gov/", "https://www.google.com/" }; static const char *DayStr[] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"}; static const char *MthStr[] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"}; static int ShowAllHeader; static int AutoSyncTime; static SYSTEMTIME SYSTime; static SYSTEMTIME LOCALTime; #define HTTP_COMMAND_HEAD 0 #define HTTP_COMMAND_GET 1 static size_t SyncTime_CURL_WriteOutput(void *ptr, size_t size, size_t nmemb, void *stream) { fwrite(ptr, size, nmemb, stream); return (nmemb*size); } static size_t SyncTime_CURL_WriteHeader(void *ptr, size_t size, size_t nmemb, void *stream) { char TmpStr1[26], TmpStr2[26]; (void)stream; if(ShowAllHeader == 1) fprintf(stderr, "%s", (char *)(ptr)); if(strncmp((char *)(ptr), "Date:", 5) == 0) { if(ShowAllHeader == 0) fprintf(stderr, "HTTP Server. %s", (char *)(ptr)); if(AutoSyncTime == 1) { *TmpStr1 = 0; *TmpStr2 = 0; if(strlen((char *)(ptr)) > 50) /* Can prevent buffer overflow to TmpStr1 & 2? */ AutoSyncTime = 0; else { int RetVal = sscanf((char *)(ptr), "Date: %25s %hu %s %hu %hu:%hu:%hu", TmpStr1, &SYSTime.wDay, TmpStr2, &SYSTime.wYear, &SYSTime.wHour, &SYSTime.wMinute, &SYSTime.wSecond); if(RetVal == 7) { int i; SYSTime.wMilliseconds = 500; /* adjust to midpoint, 0.5 sec */ for(i = 0; i < 12; i++) { if(strcmp(MthStr[i], TmpStr2) == 0) { SYSTime.wMonth = (WORD)(i + 1); break; } } AutoSyncTime = 3; /* Computer clock is adjusted */ } else { AutoSyncTime = 0; /* Error in sscanf() fields conversion */ } } } } if(strncmp((char *)(ptr), "X-Cache: HIT", 12) == 0) { fprintf(stderr, "ERROR: HTTP Server data is cached." " Server Date is no longer valid.\n"); AutoSyncTime = 0; } return (nmemb*size); } static void SyncTime_CURL_Init(CURL *curl, const char *proxy_port, const char *proxy_user_password) { if(strlen(proxy_port) > 0) curl_easy_setopt(curl, CURLOPT_PROXY, proxy_port); if(strlen(proxy_user_password) > 0) curl_easy_setopt(curl, CURLOPT_PROXYUSERPWD, proxy_user_password); curl_easy_setopt(curl, CURLOPT_USERAGENT, SYNCTIME_UA); curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, SyncTime_CURL_WriteOutput); curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, SyncTime_CURL_WriteHeader); } static CURLcode SyncTime_CURL_Fetch(CURL *curl, const char *URL_Str, const char *OutFileName, int HttpGetBody) { FILE *outfile; CURLcode res; outfile = NULL; if(HttpGetBody == HTTP_COMMAND_HEAD) curl_easy_setopt(curl, CURLOPT_NOBODY, 1L); else { outfile = fopen(OutFileName, "wb"); curl_easy_setopt(curl, CURLOPT_WRITEDATA, outfile); } curl_easy_setopt(curl, CURLOPT_URL, URL_Str); res = curl_easy_perform(curl); if(outfile) fclose(outfile); return res; /* (CURLE_OK) */ } static void showUsage(void) { fprintf(stderr, "synctime: Synchronising computer clock with time server" " using HTTP protocol.\n"); fprintf(stderr, "Usage : synctime [Option]\n"); fprintf(stderr, "Options :\n"); fprintf(stderr, " --server=WEBSERVER Use this time server instead" " of default.\n"); fprintf(stderr, " --showall Show all HTTP header.\n"); fprintf(stderr, " --synctime Synchronising computer clock" " with time server.\n"); fprintf(stderr, " --proxy-user=USER[:PASS] Set proxy username and" " password.\n"); fprintf(stderr, " --proxy=HOST[:PORT] Use HTTP proxy on given" " port.\n"); fprintf(stderr, " --help Print this help.\n"); fprintf(stderr, "\n"); return; } static int conf_init(conf_t *conf) { int i; *conf->http_proxy = 0; for(i = 0; i < MAX_STRING1; i++) conf->proxy_user[i] = 0; /* Clean up password from memory */ *conf->timeserver = 0; return 1; } int main(int argc, char *argv[]) { CURL *curl; conf_t conf[1]; int RetValue; ShowAllHeader = 0; /* Do not show HTTP Header */ AutoSyncTime = 0; /* Do not synchronise computer clock */ RetValue = 0; /* Successful Exit */ conf_init(conf); if(argc > 1) { int OptionIndex = 0; while(OptionIndex < argc) { if(strncmp(argv[OptionIndex], "--server=", 9) == 0) snprintf(conf->timeserver, MAX_STRING, "%s", &argv[OptionIndex][9]); if(strcmp(argv[OptionIndex], "--showall") == 0) ShowAllHeader = 1; if(strcmp(argv[OptionIndex], "--synctime") == 0) AutoSyncTime = 1; if(strncmp(argv[OptionIndex], "--proxy-user=", 13) == 0) snprintf(conf->proxy_user, MAX_STRING, "%s", &argv[OptionIndex][13]); if(strncmp(argv[OptionIndex], "--proxy=", 8) == 0) snprintf(conf->http_proxy, MAX_STRING, "%s", &argv[OptionIndex][8]); if((strcmp(argv[OptionIndex], "--help") == 0) || (strcmp(argv[OptionIndex], "/?") == 0)) { showUsage(); return 0; } OptionIndex++; } } if(*conf->timeserver == 0) /* Use default server for time information */ snprintf(conf->timeserver, MAX_STRING, "%s", DefaultTimeServer[0]); /* Init CURL before usage */ curl_global_init(CURL_GLOBAL_ALL); curl = curl_easy_init(); if(curl) { struct tm *lt; struct tm *gmt; time_t tt; time_t tt_local; time_t tt_gmt; double tzonediffFloat; int tzonediffWord; char timeBuf[61]; char tzoneBuf[16]; SyncTime_CURL_Init(curl, conf->http_proxy, conf->proxy_user); /* Calculating time diff between GMT and localtime */ tt = time(0); lt = localtime(&tt); tt_local = mktime(lt); gmt = gmtime(&tt); tt_gmt = mktime(gmt); tzonediffFloat = difftime(tt_local, tt_gmt); tzonediffWord = (int)(tzonediffFloat/3600.0); if((double)(tzonediffWord * 3600) == tzonediffFloat) snprintf(tzoneBuf, sizeof(tzoneBuf), "%+03d'00'", tzonediffWord); else snprintf(tzoneBuf, sizeof(tzoneBuf), "%+03d'30'", tzonediffWord); /* Get current system time and local time */ GetSystemTime(&SYSTime); GetLocalTime(&LOCALTime); snprintf(timeBuf, 60, "%s, %02d %s %04d %02d:%02d:%02d.%03d, ", DayStr[LOCALTime.wDayOfWeek], LOCALTime.wDay, MthStr[LOCALTime.wMonth-1], LOCALTime.wYear, LOCALTime.wHour, LOCALTime.wMinute, LOCALTime.wSecond, LOCALTime.wMilliseconds); fprintf(stderr, "Fetch: %s\n\n", conf->timeserver); fprintf(stderr, "Before HTTP. Date: %s%s\n\n", timeBuf, tzoneBuf); /* HTTP HEAD command to the Webserver */ SyncTime_CURL_Fetch(curl, conf->timeserver, "index.htm", HTTP_COMMAND_HEAD); GetLocalTime(&LOCALTime); snprintf(timeBuf, 60, "%s, %02d %s %04d %02d:%02d:%02d.%03d, ", DayStr[LOCALTime.wDayOfWeek], LOCALTime.wDay, MthStr[LOCALTime.wMonth-1], LOCALTime.wYear, LOCALTime.wHour, LOCALTime.wMinute, LOCALTime.wSecond, LOCALTime.wMilliseconds); fprintf(stderr, "\nAfter HTTP. Date: %s%s\n", timeBuf, tzoneBuf); if(AutoSyncTime == 3) { /* Synchronising computer clock */ if(!SetSystemTime(&SYSTime)) { /* Set system time */ fprintf(stderr, "ERROR: Unable to set system time.\n"); RetValue = 1; } else { /* Successfully re-adjusted computer clock */ GetLocalTime(&LOCALTime); snprintf(timeBuf, 60, "%s, %02d %s %04d %02d:%02d:%02d.%03d, ", DayStr[LOCALTime.wDayOfWeek], LOCALTime.wDay, MthStr[LOCALTime.wMonth-1], LOCALTime.wYear, LOCALTime.wHour, LOCALTime.wMinute, LOCALTime.wSecond, LOCALTime.wMilliseconds); fprintf(stderr, "\nNew System's Date: %s%s\n", timeBuf, tzoneBuf); } } /* Cleanup before exit */ conf_init(conf); curl_easy_cleanup(curl); } return RetValue; }
Notice
This source code example is simplified and ignores return
codes and error checks to a large extent. We do this to highlight the libcurl
function calls and related options and reduce unrelated code.
A real-world application will of course properly check every return value and exit correctly at the first serious error.