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[svn] Improve documentation of mktime_from_utc.

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Rearrange http_atotm.
Published in <sxsoftjlyku.fsf@florida.arsdigita.de>.
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hniksic 2001-04-26 22:11:38 -07:00
parent 07abfad1c2
commit 26ddb28a7c
2 changed files with 87 additions and 47 deletions
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src/ChangeLog
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@ -1,3 +1,8 @@
2001-04-27 Hrvoje Niksic <hniksic@arsdigita.com>
* http.c (mktime_from_utc): Improve documentation.
(http_atotm): Put format strings into a separate array.
2001-04-27 Hrvoje Niksic <hniksic@arsdigita.com>
* safe-ctype.h: Instead of throwing #error when isalpha is

129
src/http.c
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@ -1828,7 +1828,38 @@ The sizes do not match (local %ld) -- retrieving.\n"), local_size);
}
/* Converts struct tm to time_t, assuming the data in tm is UTC rather
than local timezone (mktime assumes the latter).
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.
@ -1870,8 +1901,8 @@ mktime_from_utc (struct tm *t)
`+X', or at the end of the string.
In extended regexp parlance, the function returns 1 if P matches
"^ *(GMT|[+-][0-9]|$)", 0 otherwise. P being NULL (a valid result of
strptime()) is considered a failure and 0 is returned. */
"^ *(GMT|[+-][0-9]|$)", 0 otherwise. P being NULL (which strptime
can return) is considered a failure and 0 is returned. */
static int
check_end (const char *p)
{
@ -1887,28 +1918,50 @@ check_end (const char *p)
return 0;
}
/* Convert TIME_STRING time to time_t. TIME_STRING can be in any of
the three formats RFC2068 allows the HTTP servers to emit --
RFC1123-date, RFC850-date or asctime-date. Timezones are ignored,
and should be GMT.
/* Convert the textual specification of time in TIME_STRING to the
number of seconds since the Epoch.
We use strptime() to recognize various dates, which makes it a
little bit slacker than the RFC1123/RFC850/asctime (e.g. it always
allows shortened dates and months, one-digit days, etc.). It also
allows more than one space anywhere where the specs require one SP.
The routine should probably be even more forgiving (as recommended
by RFC2068), but I do not have the time to write one.
TIME_STRING can be in any of the three formats RFC2068 allows the
HTTP servers to emit -- RFC1123-date, RFC850-date or asctime-date.
Timezones are ignored, and should be GMT.
Return the computed time_t representation, or -1 if all the
schemes fail.
Return the computed time_t representation, or -1 if the conversion
fails.
This function uses strptime with various string formats for parsing
TIME_STRING. This results in a parser that is not as lenient in
interpreting TIME_STRING as I would like it to be. Being based on
strptime, it always allows shortened months, one-digit days, etc.,
but due to the multitude of formats in which time can be
represented, an ideal HTTP time parser would be even more
forgiving. It should completely ignore things like week days and
concentrate only on the various forms of representing years,
months, days, hours, minutes, and seconds. For example, it would
be nice if it accepted ISO 8601 out of the box.
I've investigated free and PD code for this purpose, but none was
usable. getdate was big and unwieldy, and had potential copyright
issues, or so I was informed. Dr. Marcus Hennecke's atotm(),
distributed with phttpd, is excellent, but we cannot use it because
it is not assigned to the FSF. So I stuck it with strptime. */
Needless to say, what we *really* need here is something like
Marcus Hennecke's atotm(), which is forgiving, fast, to-the-point,
and does not use strptime(). atotm() is to be found in the sources
of `phttpd', a little-known HTTP server written by Peter Erikson. */
time_t
http_atotm (char *time_string)
{
/* NOTE: Solaris strptime man page claims that %n and %t match white
space, but that's not universally available. Instead, we simply
use ` ' to mean "skip all WS", which works under all strptime
implementations I've tested. */
static const char *time_formats[] = {
"%a, %d %b %Y %T", /* RFC1123: Thu, 29 Jan 1998 22:12:57 */
"%A, %d-%b-%y %T", /* RFC850: Thursday, 29-Jan-98 22:12:57 */
"%a, %d-%b-%Y %T", /* pseudo-RFC850: Thu, 29-Jan-1998 22:12:57
(google.com uses this for their cookies.) */
"%a %b %d %T %Y" /* asctime: Thu Jan 29 22:12:57 1998 */
};
int i;
struct tm t;
/* According to Roger Beeman, we need to initialize tm_isdst, since
@ -1916,41 +1969,23 @@ http_atotm (char *time_string)
t.tm_isdst = 0;
/* Note that under foreign locales Solaris strptime() fails to
recognize English dates, which renders this function useless. I
assume that other non-GNU strptime's are plagued by the same
disease. We solve this by setting only LC_MESSAGES in
i18n_initialize(), instead of LC_ALL.
recognize English dates, which renders this function useless. We
solve this by being careful not to affect LC_TIME when
initializing locale.
Another solution could be to temporarily set locale to C, invoke
Another solution would be to temporarily set locale to C, invoke
strptime(), and restore it back. This is slow and dirty,
however, and locale support other than LC_MESSAGES can mess other
things, so I rather chose to stick with just setting LC_MESSAGES.
Also note that none of this is necessary under GNU strptime(),
because it recognizes both international and local dates. */
GNU strptime does not have this problem because it recognizes
both international and local dates. */
/* NOTE: We don't use `%n' for white space, as OSF's strptime uses
it to eat all white space up to (and including) a newline, and
the function fails if there is no newline (!).
for (i = 0; i < ARRAY_SIZE (time_formats); i++)
if (check_end (strptime (time_string, time_formats[i], &t)))
return mktime_from_utc (&t);
Let's hope all strptime() implementations use ` ' to skip *all*
whitespace instead of just one (it works that way on all the
systems I've tested it on). */
/* RFC1123: Thu, 29 Jan 1998 22:12:57 */
if (check_end (strptime (time_string, "%a, %d %b %Y %T", &t)))
return mktime_from_utc (&t);
/* RFC850: Thursday, 29-Jan-98 22:12:57 */
if (check_end (strptime (time_string, "%A, %d-%b-%y %T", &t)))
return mktime_from_utc (&t);
/* pseudo-RFC850: Thu, 29-Jan-1998 22:12:57
(google.com uses this for their cookies.)*/
if (check_end (strptime (time_string, "%a, %d-%b-%Y %T", &t)))
return mktime_from_utc (&t);
/* asctime: Thu Jan 29 22:12:57 1998 */
if (check_end (strptime (time_string, "%a %b %d %T %Y", &t)))
return mktime_from_utc (&t);
/* Failure. */
/* All formats have failed. */
return -1;
}