Frank's synctime.c example and an updated list in README

docs/examples/Makefile.am

@@ -11,7 +11,7 @@ EXTRA_DIST = README curlgtk.c sepheaders.c simple.c postit2.c		\
  multi-post.c fopen.c simplepost.c makefile.dj curlx.c https.c		\
  multi-debugcallback.c fileupload.c getinfo.c ftp3rdparty.c debug.c	\
  anyauthput.c htmltitle.cc htmltidy.c opensslthreadlock.c		\
- cookie_interface.c cacertinmem.c
+ cookie_interface.c cacertinmem.c synctime.c
 
 all:
 	@echo "done"

docs/examples/README

@@ -33,6 +33,8 @@ we expect you to actually torture our web site with your tests! Thanks.
 EXAMPLES
 
 anyauthput.c   - HTTP PUT using "any" authentication method
+cacertinmem.c  - Use a built-in PEM certificate to retrieve a https page
+cookie_interface.c - shows usage of simple cookie interface
 curlgtk.c      - download using a GTK progress bar
 curlx.c        - getting file info from the remote cert data
 debug.c        - showing how to use the debug callback
@@ -55,6 +57,7 @@ multi-double.c - a multi-interface app doing two simultaneous transfers
 multi-post.c   - a multi-interface app doing a multipart formpost
 multi-single.c - a multi-interface app getting a single file
 multithread.c  - an example using multi-treading transfering multiple files
+opensslthreadlock.c - show how to do locking when using OpenSSL multi-threaded
 persistant.c   - request two URLs with a persistant connection
 post-callback.c - send a HTTP POST using a callback
 postit2.c      - send a HTTP multipart formpost
@@ -62,3 +65,4 @@ sepheaders.c   - download headers to a separate file
 simple.c       - the most simple download a URL source
 simplepost.c   - HTTP POST
 simplessl.c    - HTTPS example with certificates many options set
+synctime.c     - Sync local time by extracing date from remote HTTP servers

docs/examples/synctime.c

+/*****************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * $Id$
+ *
+ * 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 synchronisation but it does not work very 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 very 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 will set 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.
+ *
+ * References:
+ * http://tf.nist.gov/timefreq/service/its.htm
+ * http://tf.nist.gov/timefreq/service/firewall.htm
+ *
+ * Usage:
+ * This software will synchronise 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 <windows.h>
+#include <curl/curl.h>
+
+
+#define MAX_STRING              256
+#define MAX_STRING1             MAX_STRING+1
+
+typedef struct
+{
+  char http_proxy[MAX_STRING1];
+  char proxy_user[MAX_STRING1];
+  char timeserver[MAX_STRING1];
+} conf_t;
+
+char DefaultTimeServer[4][MAX_STRING1] =
+{
+  "http://nist.time.gov/timezone.cgi?UTC/s/0",
+  "http://www.google.com/",
+  "http://www.worldtimeserver.com/current_time_in_UTC.aspx",
+  "http://www.worldtime.com/cgi-bin/wt.cgi"
+};
+
+char *DayStr[] = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
+char *MthStr[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
+                  "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
+
+int  ShowAllHeader;
+int  AutoSyncTime;
+SYSTEMTIME SYSTime;
+SYSTEMTIME LOCALTime;
+
+#define HTTP_COMMAND_HEAD       0
+#define HTTP_COMMAND_GET        1
+
+
+size_t SyncTime_CURL_WriteOutput(void *ptr, size_t size, size_t nmemb,
+                                 void *stream)
+{
+  fwrite(ptr, size, nmemb, stream);
+  return(nmemb*size);
+}
+
+size_t SyncTime_CURL_WriteHeader(void *ptr, size_t size, size_t nmemb,
+                                 void *stream)
+{
+  int   i, RetVal;
+  char  TmpStr1[26], TmpStr2[26];
+
+  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 {
+        RetVal = sscanf ((char *)(ptr), "Date: %s %d %s %d %d:%d:%d",
+                         TmpStr1, &SYSTime.wDay, TmpStr2, &SYSTime.wYear,
+                         &SYSTime.wHour, &SYSTime.wMinute, &SYSTime.wSecond);
+
+        if (RetVal == 7) {
+
+          SYSTime.wMilliseconds = 500;    /* adjust to midpoint, 0.5 sec */
+          for (i=0; i<12; i++) {
+            if (strcmp(MthStr[i], TmpStr2) == 0) {
+              SYSTime.wMonth = i+1;
+              break;
+            }
+          }
+          AutoSyncTime = 3;       /* Computer clock will be 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);
+}
+
+void SyncTime_CURL_Init(CURL *curl, char *proxy_port,
+                        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);
+
+  /* Trick Webserver by claiming that you are using Microsoft WinXP SP2, IE6 */
+  curl_easy_setopt(curl, CURLOPT_USERAGENT,
+                   "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
+  curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, *SyncTime_CURL_WriteOutput);
+  curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, *SyncTime_CURL_WriteHeader);
+}
+
+int SyncTime_CURL_Fetch(CURL *curl, char *URL_Str, char *OutFileName,
+                        int HttpGetBody)
+{
+  FILE *outfile;
+  CURLcode res;
+
+  outfile = NULL;
+  if (HttpGetBody == HTTP_COMMAND_HEAD)
+    curl_easy_setopt(curl, CURLOPT_NOBODY, 1);
+  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 != NULL)
+    fclose(outfile);
+  return res;  /* (CURLE_OK) */
+}
+
+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;
+}
+
+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     OptionIndex;
+  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];
+  int     RetValue;
+
+  OptionIndex     = 0;
+  ShowAllHeader   = 0;    /* Do not show HTTP Header */
+  AutoSyncTime    = 0;    /* Do not synchronise computer clock */
+  RetValue        = 0;    /* Successful Exit */
+  conf_init(conf);
+
+  if (argc > 1) {
+    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) {
+    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, 15, "%+03d'00'", tzonediffWord);
+    else
+      snprintf(tzoneBuf, 15, "%+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, "\nBefore HTTP. Date: %s%s\n\n", timeBuf, tzoneBuf);
+
+    /* HTTP HEAD command to the Webserver */
+    fprintf(stderr, "Fetch: %s\n", conf->timeserver);
+    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;
+}