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LibCore+LibTimeZone: Support time zone names in Core::DateTime::parse

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LibCore currently cannot depend on LibTimeZone directly. All build-time
code generators depend on LibCore, so there'd be a circular dependency:
LibCore -> LibTimeZone -> GenerateTZData -> LibCore.

So to support parsing time zone names and applying their offsets, add a
couple of weakly-defined helper functions. These work similar to the way
AK::String declares some methods that LibUnicode defines. Any user who
wants to parse time zone names (from outside of LibCore itself) can link
against LibTimeZone to receive full support.
This commit is contained in:
Timothy Flynn 2023-11-06 20:50:11 -05:00 • committed by Andreas Kling
parent fd0075083a
commit 350fdf1e43
7 changed files with 169 additions and 4 deletions
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26
Userland/Libraries/LibCore/DateTime.cpp
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@ -11,11 +11,15 @@
#include <AK/StringBuilder.h>
#include <AK/Time.h>
#include <LibCore/DateTime.h>
#include <LibTimeZone/DateTime.h>
#include <errno.h>
#include <time.h>
namespace Core {
Optional<StringView> __attribute__((weak)) parse_time_zone_name(GenericLexer&) { return {}; }
void __attribute__((weak)) apply_time_zone_offset(StringView, UnixDateTime&) { }
DateTime DateTime::now()
{
return from_timestamp(time(nullptr));
@ -293,6 +297,7 @@ Optional<DateTime> DateTime::parse(StringView format, StringView string)
auto parsing_failed = false;
auto tm_represents_utc_time = false;
Optional<StringView> parsed_time_zone;
GenericLexer string_lexer(string);
@ -500,6 +505,13 @@ Optional<DateTime> DateTime::parse(StringView format, StringView string)
tm.tm_min += sign * minutes;
break;
}
case 'Z':
parsed_time_zone = parse_time_zone_name(string_lexer);
if (!parsed_time_zone.has_value())
return {};
tm_represents_utc_time = true;
break;
case '%':
consume('%');
break;
@ -517,11 +529,17 @@ Optional<DateTime> DateTime::parse(StringView format, StringView string)
if (!string_lexer.is_eof() || format_pos != format.length())
return {};
// If an explicit timezone was present, the time in tm was shifted to UTC.
// Convert it to local time, since that is what `mktime` expects.
// If an explicit time zone offset was present, the time in tm was shifted to UTC. If a time zone name was present,
// the time in tm needs to be shifted to UTC. In both cases, convert the result to local time, as that is what is
// expected by `mktime`.
if (tm_represents_utc_time) {
auto utc_time = timegm(&tm);
localtime_r(&utc_time, &tm);
auto utc_time = UnixDateTime::from_seconds_since_epoch(timegm(&tm));
if (parsed_time_zone.has_value())
apply_time_zone_offset(*parsed_time_zone, utc_time);
time_t utc_time_t = utc_time.seconds_since_epoch();
localtime_r(&utc_time_t, &tm);
}
return DateTime::from_timestamp(mktime(&tm));