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ladybird/Userland/Libraries/LibCore/DateTime.cpp
Timothy Flynn a4a7efaf5f LibC+LibCore: Use tm_isdst to handle time zone offsets in DST 
Previously, we were incorrectly assuming that the daylight global
variable indicated whether the current time zone is in DST. In reality,
the daylight variable only indicates whether a time zone *can* be in
DST.

Instead, the tm structure has a tm_isdst member that should be used for
this purpose. Ensure our LibC handles tm_isdst, and avoid errant usage
of the daylight variable in Core::DateTime.
2022-08-02 21:10:44 +01:00

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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/CharacterTypes.h>
#include <AK/DateConstants.h>
#include <AK/StringBuilder.h>
#include <AK/Time.h>
#include <LibCore/DateTime.h>
#include <errno.h>
#include <time.h>
namespace Core {
DateTime DateTime::now()
{
return from_timestamp(time(nullptr));
}
DateTime DateTime::create(int year, int month, int day, int hour, int minute, int second)
{
DateTime dt;
dt.set_time(year, month, day, hour, minute, second);
return dt;
}
DateTime DateTime::from_timestamp(time_t timestamp)
{
struct tm tm;
localtime_r(&timestamp, &tm);
DateTime dt;
dt.m_year = tm.tm_year + 1900;
dt.m_month = tm.tm_mon + 1;
dt.m_day = tm.tm_mday;
dt.m_hour = tm.tm_hour;
dt.m_minute = tm.tm_min;
dt.m_second = tm.tm_sec;
dt.m_timestamp = timestamp;
return dt;
}
unsigned DateTime::weekday() const
{
return ::day_of_week(m_year, m_month, m_day);
}
unsigned DateTime::days_in_month() const
{
return ::days_in_month(m_year, m_month);
}
unsigned DateTime::day_of_year() const
{
return ::day_of_year(m_year, m_month, m_day);
}
bool DateTime::is_leap_year() const
{
return ::is_leap_year(m_year);
}
void DateTime::set_time(int year, int month, int day, int hour, int minute, int second)
{
struct tm tm = {};
tm.tm_sec = second;
tm.tm_min = minute;
tm.tm_hour = hour;
tm.tm_mday = day;
tm.tm_mon = month - 1;
tm.tm_year = year - 1900;
tm.tm_isdst = -1;
// mktime() doesn't read tm.tm_wday and tm.tm_yday, no need to fill them in.
m_timestamp = mktime(&tm);
// mktime() normalizes the components to the right ranges (Jan 32 -> Feb 1 etc), so read fields back out from tm.
m_year = tm.tm_year + 1900;
m_month = tm.tm_mon + 1;
m_day = tm.tm_mday;
m_hour = tm.tm_hour;
m_minute = tm.tm_min;
m_second = tm.tm_sec;
}
String DateTime::to_string(StringView format) const
{
struct tm tm;
localtime_r(&m_timestamp, &tm);
StringBuilder builder;
int const format_len = format.length();
auto format_time_zone_offset = [&](bool with_separator) {
struct tm gmt_tm;
gmtime_r(&m_timestamp, &gmt_tm);
gmt_tm.tm_isdst = -1;
auto gmt_timestamp = mktime(&gmt_tm);
auto offset_seconds = static_cast<time_t>(difftime(m_timestamp, gmt_timestamp));
StringView offset_sign;
if (offset_seconds >= 0) {
offset_sign = "+"sv;
} else {
offset_sign = "-"sv;
offset_seconds *= -1;
}
auto offset_hours = offset_seconds / 3600;
auto offset_minutes = (offset_seconds % 3600) / 60;
auto separator = with_separator ? ":"sv : ""sv;
builder.appendff("{}{:02}{}{:02}", offset_sign, offset_hours, separator, offset_minutes);
};
for (int i = 0; i < format_len; ++i) {
if (format[i] != '%') {
builder.append(format[i]);
} else {
if (++i == format_len)
return String();
switch (format[i]) {
case 'a':
builder.append(short_day_names[tm.tm_wday]);
break;
case 'A':
builder.append(long_day_names[tm.tm_wday]);
break;
case 'b':
builder.append(short_month_names[tm.tm_mon]);
break;
case 'B':
builder.append(long_month_names[tm.tm_mon]);
break;
case 'C':
builder.appendff("{:02}", (tm.tm_year + 1900) / 100);
break;
case 'd':
builder.appendff("{:02}", tm.tm_mday);
break;
case 'D':
builder.appendff("{:02}/{:02}/{:02}", tm.tm_mon + 1, tm.tm_mday, (tm.tm_year + 1900) % 100);
break;
case 'e':
builder.appendff("{:2}", tm.tm_mday);
break;
case 'h':
builder.append(short_month_names[tm.tm_mon]);
break;
case 'H':
builder.appendff("{:02}", tm.tm_hour);
break;
case 'I': {
int display_hour = tm.tm_hour % 12;
if (display_hour == 0)
display_hour = 12;
builder.appendff("{:02}", display_hour);
break;
}
case 'j':
builder.appendff("{:03}", tm.tm_yday + 1);
break;
case 'm':
builder.appendff("{:02}", tm.tm_mon + 1);
break;
case 'M':
builder.appendff("{:02}", tm.tm_min);
break;
case 'n':
builder.append('\n');
break;
case 'p':
builder.append(tm.tm_hour < 12 ? "AM"sv : "PM"sv);
break;
case 'r': {
int display_hour = tm.tm_hour % 12;
if (display_hour == 0)
display_hour = 12;
builder.appendff("{:02}:{:02}:{:02} {}", display_hour, tm.tm_min, tm.tm_sec, tm.tm_hour < 12 ? "AM" : "PM");
break;
}
case 'R':
builder.appendff("{:02}:{:02}", tm.tm_hour, tm.tm_min);
break;
case 'S':
builder.appendff("{:02}", tm.tm_sec);
break;
case 't':
builder.append('\t');
break;
case 'T':
builder.appendff("{:02}:{:02}:{:02}", tm.tm_hour, tm.tm_min, tm.tm_sec);
break;
case 'u':
builder.appendff("{}", tm.tm_wday ? tm.tm_wday : 7);
break;
case 'U': {
int const wday_of_year_beginning = (tm.tm_wday + 6 * tm.tm_yday) % 7;
int const week_number = (tm.tm_yday + wday_of_year_beginning) / 7;
builder.appendff("{:02}", week_number);
break;
}
case 'V': {
int const wday_of_year_beginning = (tm.tm_wday + 6 + 6 * tm.tm_yday) % 7;
int week_number = (tm.tm_yday + wday_of_year_beginning) / 7 + 1;
if (wday_of_year_beginning > 3) {
if (tm.tm_yday >= 7 - wday_of_year_beginning)
--week_number;
else {
int const days_of_last_year = days_in_year(tm.tm_year + 1900 - 1);
int const wday_of_last_year_beginning = (wday_of_year_beginning + 6 * days_of_last_year) % 7;
week_number = (days_of_last_year + wday_of_last_year_beginning) / 7 + 1;
if (wday_of_last_year_beginning > 3)
--week_number;
}
}
builder.appendff("{:02}", week_number);
break;
}
case 'w':
builder.appendff("{}", tm.tm_wday);
break;
case 'W': {
int const wday_of_year_beginning = (tm.tm_wday + 6 + 6 * tm.tm_yday) % 7;
int const week_number = (tm.tm_yday + wday_of_year_beginning) / 7;
builder.appendff("{:02}", week_number);
break;
}
case 'y':
builder.appendff("{:02}", (tm.tm_year + 1900) % 100);
break;
case 'Y':
builder.appendff("{}", tm.tm_year + 1900);
break;
case 'z':
format_time_zone_offset(false);
break;
case ':':
if (++i == format_len) {
builder.append("%:"sv);
break;
}
if (format[i] != 'z') {
builder.append("%:"sv);
builder.append(format[i]);
break;
}
format_time_zone_offset(true);
break;
case 'Z': {
auto const* timezone_name = tzname[tm.tm_isdst == 0 ? 0 : 1];
builder.append({ timezone_name, strlen(timezone_name) });
break;
}
case '%':
builder.append('%');
break;
default:
builder.append('%');
builder.append(format[i]);
break;
}
}
}
return builder.build();
}
Optional<DateTime> DateTime::parse(StringView format, String const& string)
{
unsigned format_pos = 0;
unsigned string_pos = 0;
struct tm tm = {};
auto parsing_failed = false;
auto parse_number = [&] {
if (string_pos >= string.length()) {
parsing_failed = true;
return 0;
}
char* end_ptr = nullptr;
errno = 0;
int number = strtol(string.characters() + string_pos, &end_ptr, 10);
auto chars_parsed = end_ptr - (string.characters() + string_pos);
if (chars_parsed == 0 || errno != 0)
parsing_failed = true;
else
string_pos += chars_parsed;
return number;
};
auto consume = [&](char x) {
if (string_pos >= string.length()) {
parsing_failed = true;
return;
}
if (string[string_pos] != x)
parsing_failed = true;
else
string_pos++;
};
while (format_pos < format.length() && string_pos < string.length()) {
if (format[format_pos] != '%') {
if (format[format_pos] != string[string_pos]) {
return {};
}
format_pos++;
string_pos++;
continue;
}
format_pos++;
if (format_pos == format.length()) {
return {};
}
switch (format[format_pos]) {
case 'a': {
auto wday = 0;
for (auto name : short_day_names) {
if (string.substring_view(string_pos).starts_with(name, AK::CaseSensitivity::CaseInsensitive)) {
string_pos += name.length();
tm.tm_wday = wday;
break;
}
++wday;
}
if (wday == 7)
return {};
break;
}
case 'A': {
auto wday = 0;
for (auto name : long_day_names) {
if (string.substring_view(string_pos).starts_with(name, AK::CaseSensitivity::CaseInsensitive)) {
string_pos += name.length();
tm.tm_wday = wday;
break;
}
++wday;
}
if (wday == 7)
return {};
break;
}
case 'h':
case 'b': {
auto mon = 0;
for (auto name : short_month_names) {
if (string.substring_view(string_pos).starts_with(name, AK::CaseSensitivity::CaseInsensitive)) {
string_pos += name.length();
tm.tm_mon = mon;
break;
}
++mon;
}
if (mon == 12)
return {};
break;
}
case 'B': {
auto mon = 0;
for (auto name : long_month_names) {
if (string.substring_view(string_pos).starts_with(name, AK::CaseSensitivity::CaseInsensitive)) {
string_pos += name.length();
tm.tm_mon = mon;
break;
}
++mon;
}
if (mon == 12)
return {};
break;
}
case 'C': {
int num = parse_number();
tm.tm_year = (num - 19) * 100;
break;
}
case 'd': {
tm.tm_mday = parse_number();
break;
}
case 'D': {
int mon = parse_number();
consume('/');
int day = parse_number();
consume('/');
int year = parse_number();
tm.tm_mon = mon + 1;
tm.tm_mday = day;
tm.tm_year = (year + 1900) % 100;
break;
}
case 'e': {
tm.tm_mday = parse_number();
break;
}
case 'H': {
tm.tm_hour = parse_number();
break;
}
case 'I': {
int num = parse_number();
tm.tm_hour = num % 12;
break;
}
case 'j': {
// a little trickery here... we can get mktime() to figure out mon and mday using out of range values.
// yday is not used so setting it is pointless.
tm.tm_mday = parse_number();
tm.tm_mon = 0;
mktime(&tm);
break;
}
case 'm': {
int num = parse_number();
tm.tm_mon = num - 1;
break;
}
case 'M': {
tm.tm_min = parse_number();
break;
}
case 'n':
case 't':
while (is_ascii_blank(string[string_pos])) {
string_pos++;
}
break;
case 'p': {
auto ampm = string.substring_view(string_pos, 2);
if (ampm == "PM" && tm.tm_hour < 12) {
tm.tm_hour += 12;
}
string_pos += 2;
break;
}
case 'r': {
auto ampm = string.substring_view(string_pos, 2);
if (ampm == "PM" && tm.tm_hour < 12) {
tm.tm_hour += 12;
}
string_pos += 2;
break;
}
case 'R': {
tm.tm_hour = parse_number();
consume(':');
tm.tm_min = parse_number();
break;
}
case 'S':
tm.tm_sec = parse_number();
break;
case 'T':
tm.tm_hour = parse_number();
consume(':');
tm.tm_min = parse_number();
consume(':');
tm.tm_sec = parse_number();
break;
case 'w':
tm.tm_wday = parse_number();
break;
case 'y': {
int year = parse_number();
tm.tm_year = year <= 99 && year > 69 ? 1900 + year : 2000 + year;
break;
}
case 'Y': {
int year = parse_number();
tm.tm_year = year - 1900;
break;
}
case 'z': {
if (string[string_pos] == 'Z') {
// UTC time
string_pos++;
break;
}
int sign;
if (string[string_pos] == '+')
sign = -1;
else if (string[string_pos] == '-')
sign = +1;
else
return {};
string_pos++;
auto hours = parse_number();
int minutes;
if (string_pos < string.length() && string[string_pos] == ':') {
string_pos++;
minutes = parse_number();
} else {
minutes = hours % 100;
hours = hours / 100;
}
tm.tm_hour += sign * hours;
tm.tm_min += sign * minutes;
break;
}
case '%':
if (string[string_pos] != '%') {
return {};
}
string_pos += 1;
break;
default:
parsing_failed = true;
break;
}
if (parsing_failed) {
return {};
}
format_pos++;
}
if (string_pos != string.length() || format_pos != format.length()) {
return {};
}
return DateTime::from_timestamp(mktime(&tm));
}
}
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