--- a/ChangeLog	Sun Nov 10 18:49:41 2002 +0000
+++ b/ChangeLog	Sun Nov 17 15:18:19 2002 +0000
@@ -1,3 +1,19 @@
+Sun Nov 17 2002 Jim Hague <jim.hague@acm.org>
+
+* src/util.c: localTimeDiff() cached its value and recalculated it every
+  hour of clock time, regardless of the time the calculated was based on.
+  This is potentially dangerous at daylight saving changes. So instead
+  use the cached last result only when the new request is to be based on
+  a time in the same hour as the cached result.
+* src/util.c: Replace the alternate Utl_mktimeGMT() implementation used when
+  timegm() is not available. The previous version, as suggested by the
+  glibc timegm() man page, used setenv() and unsetenv() for changing the
+  environment. These aren't POSIX function, and the POSIX putenv()
+  (a) is tricky to manage if the same var is being constantly update and
+  memory isn't to leak, and (b) provides no way to remove an environment
+  entry. So change to an implementation Wget uses. This should compile on
+  not glibc systems - the previous version failed to build on Solaris.
+	
 Sun Nov 10 2002 Jim Hague <jim.hague@acm.org>
 
 * src/client.c,src/fetch.c,src/lock.c.src/protocol.c,src/util.h,src/util.c:

--- a/src/util.c	Sun Nov 10 18:49:41 2002 +0000
+++ b/src/util.c	Sun Nov 17 15:18:19 2002 +0000
@@ -1,7 +1,7 @@
 /*
   util.c
 
-  $Id: util.c 403 2002-11-10 11:32:17Z bears $
+  $Id: util.c 411 2002-11-17 15:18:19Z bears $
 */
 
 #if HAVE_CONFIG_H
@@ -300,18 +300,22 @@
  * is < 24hrs. Sounds reasonable to me. It also assumes it can ignore seconds.
  * Returns localtime - GMT seconds. It will also trash the localtime/
  * gmtime/etc. static buffer.
+ *
+ * Do some basic caching by returning the previous result if the new request
+ * is in the same hour as the previous one.
  */
 static int
 localTimeDiff( time_t t )
 {
-    time_t now;
     struct tm local, gmt, *tm;
-    static time_t nextCalc = 0;
+    static time_t resHourStart = 0;
     static int res = 0;
 
-    now = time( NULL );
-    if ( now < nextCalc )
+    if ( labs( t - resHourStart ) < 60 )
 	return res;
+
+    /* Calculating for new hour */
+    resHourStart = ( t / 60 ) * 60;
     
     tm = localtime( &t );
     if ( tm == NULL )
@@ -334,9 +338,6 @@
     res += local.tm_min - gmt.tm_min;
     res *= 60;
 
-    /* Need to recalc at start of next hour */
-    nextCalc = now + ( 60 - local.tm_sec ) + 60 * ( 59 - local.tm_min );
-    
     return res;
 }
 
@@ -345,24 +346,73 @@
 {
 #if HAVE_TIMEGM
     return timegm( t );
-#else    
-    /*
-     * Based on the portable implementation suggested in the glibc man page
-     * for timegm.
+#else
+    /* This comment and implmentation is taken from Wget's mktime_from_utc().
+     * We could 
+     *
+     * Converts struct tm to time_t, assuming the data in tm is UTC rather
+     * than local timezone.
+     *
+     * mktime is similar but assumes struct tm, also known as the
+     * "broken-down" form of time, is in local time zone.  mktime_from_utc
+     * uses mktime to make the conversion understanding that an offset
+     * will be introduced by the local time assumption.
+     *
+     * mktime_from_utc then measures the introduced offset by applying
+     * gmtime to the initial result and applying mktime to the resulting
+     * "broken-down" form.  The difference between the two mktime results
+     * is the measured offset which is then subtracted from the initial
+     * mktime result to yield a calendar time which is the value returned.
+     *
+     * tm_isdst in struct tm is set to 0 to force mktime to introduce a
+     * consistent offset (the non DST offset) since tm and tm+o might be
+     * on opposite sides of a DST change.
+     * 
+     * Some implementations of mktime return -1 for the nonexistent
+     * localtime hour at the beginning of DST.  In this event, use
+     * mktime(tm - 1hr) + 3600.
+     * 
+     * Schematically
+     * mktime(tm)   --> t+o
+     * gmtime(t+o)  --> tm+o
+     * mktime(tm+o) --> t+2o
+     * t+o - (t+2o - t+o) = t
+     *
+     * Note that glibc contains a function of the same purpose named
+     * `timegm' (reverse of gmtime).  But obviously, it is not universally
+     * available, and unfortunately it is not straightforwardly
+     * extractable for use here.  Perhaps configure should detect timegm
+     * and use it where available.
+     * 
+     * Contributed by Roger Beeman <beeman@cisco.com>, with the help of
+     * Mark Baushke <mdb@cisco.com> and the rest of the Gurus at CISCO.
+     * Further improved by Roger with assistance from Edward J. Sabol
+     * based on input by Jamie Zawinski.
      */
-    time_t ret;
-    char *tz;
+    time_t tl, tb;
+    struct tm *tg;
 
-    tz = getenv("TZ");
-    setenv("TZ", "", 1);
-    tzset();
-    ret = mktime(t);
-    if (tz)
-	setenv("TZ", tz, 1);
-    else
-	unsetenv("TZ");
-    tzset();
-    return ret;
+    tl = mktime (t);
+    if (tl == -1)
+    {
+	t->tm_hour--;
+	tl = mktime (t);
+	if (tl == -1)
+	    return -1; /* can't deal with output from strptime */
+	tl += 3600;
+    }
+    tg = gmtime (&tl);
+    tg->tm_isdst = 0;
+    tb = mktime (tg);
+    if (tb == -1)
+    {
+	tg->tm_hour--;
+	tb = mktime (tg);
+	if (tb == -1)
+	    return -1; /* can't deal with output from gmtime */
+	tb += 3600;
+    }
+    return (tl - (tb - tl));    
 #endif    
 }