From: hniksic Date: Fri, 27 Apr 2001 05:11:38 +0000 (-0700) Subject: [svn] Improve documentation of mktime_from_utc. X-Git-Tag: v1.13~2168 X-Git-Url: http://sjero.net/git/?p=wget;a=commitdiff_plain;h=26ddb28a7c98ee2c6aa4f107d40b3adac5d6cec3 [svn] Improve documentation of mktime_from_utc. Rearrange http_atotm. Published in . --- diff --git a/src/ChangeLog b/src/ChangeLog index 752155a0..cadb7bb1 100644 --- a/src/ChangeLog +++ b/src/ChangeLog @@ -1,3 +1,8 @@ +2001-04-27 Hrvoje Niksic + + * http.c (mktime_from_utc): Improve documentation. + (http_atotm): Put format strings into a separate array. + 2001-04-27 Hrvoje Niksic * safe-ctype.h: Instead of throwing #error when isalpha is diff --git a/src/http.c b/src/http.c index 64744288..34f97ce7 100644 --- a/src/http.c +++ b/src/http.c @@ -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 , with the help of Mark Baushke 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. - - 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. - - Return the computed time_t representation, or -1 if all the - schemes fail. - - 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. */ +/* Convert the textual specification of time in TIME_STRING to the + number of seconds since the Epoch. + + 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 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. */ + 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. */ - - /* 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 (!). - - 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. */ + GNU strptime does not have this problem because it recognizes + both international and local dates. */ + + for (i = 0; i < ARRAY_SIZE (time_formats); i++) + if (check_end (strptime (time_string, time_formats[i], &t))) + return mktime_from_utc (&t); + + /* All formats have failed. */ return -1; }