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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef vm_DateTime_h
+#define vm_DateTime_h
+
+#include "mozilla/UniquePtr.h"
+
+#include <stdint.h>
+
+#include "js/Utility.h"
+#include "threading/ExclusiveData.h"
+
+#if JS_HAS_INTL_API
+# include "mozilla/intl/ICU4CGlue.h"
+# include "mozilla/intl/TimeZone.h"
+#endif
+
+namespace JS {
+class Realm;
+}
+
+namespace js {
+
+/* Constants defined by ES5 15.9.1.10. */
+constexpr double HoursPerDay = 24;
+constexpr double MinutesPerHour = 60;
+constexpr double SecondsPerMinute = 60;
+constexpr double msPerSecond = 1000;
+constexpr double msPerMinute = msPerSecond * SecondsPerMinute;
+constexpr double msPerHour = msPerMinute * MinutesPerHour;
+
+/* ES5 15.9.1.2. */
+constexpr double msPerDay = msPerHour * HoursPerDay;
+
+/*
+ * Additional quantities not mentioned in the spec. Be careful using these!
+ * They aren't doubles and aren't defined in terms of all the other constants.
+ * If you need constants that trigger floating point semantics, you'll have to
+ * manually cast to get it.
+ */
+constexpr unsigned SecondsPerHour = 60 * 60;
+constexpr unsigned SecondsPerDay = SecondsPerHour * 24;
+
+constexpr double StartOfTime = -8.64e15;
+constexpr double EndOfTime = 8.64e15;
+
+extern bool InitDateTimeState();
+
+extern void FinishDateTimeState();
+
+enum class ResetTimeZoneMode : bool {
+ DontResetIfOffsetUnchanged,
+ ResetEvenIfOffsetUnchanged,
+};
+
+/**
+ * Engine-internal variant of JS::ResetTimeZone with an additional flag to
+ * control whether to forcibly reset all time zone data (this is the default
+ * behavior when calling JS::ResetTimeZone) or to try to reuse the previous
+ * time zone data.
+ */
+extern void ResetTimeZoneInternal(ResetTimeZoneMode mode);
+
+/**
+ * Stores date/time information, particularly concerning the current local
+ * time zone, and implements a small cache for daylight saving time offset
+ * computation.
+ *
+ * The basic idea is premised upon this fact: the DST offset never changes more
+ * than once in any thirty-day period. If we know the offset at t_0 is o_0,
+ * the offset at [t_1, t_2] is also o_0, where t_1 + 3_0 days == t_2,
+ * t_1 <= t_0, and t0 <= t2. (In other words, t_0 is always somewhere within a
+ * thirty-day range where the DST offset is constant: DST changes never occur
+ * more than once in any thirty-day period.) Therefore, if we intelligently
+ * retain knowledge of the offset for a range of dates (which may vary over
+ * time), and if requests are usually for dates within that range, we can often
+ * provide a response without repeated offset calculation.
+ *
+ * Our caching strategy is as follows: on the first request at date t_0 compute
+ * the requested offset o_0. Save { start: t_0, end: t_0, offset: o_0 } as the
+ * cache's state. Subsequent requests within that range are straightforwardly
+ * handled. If a request for t_i is far outside the range (more than thirty
+ * days), compute o_i = dstOffset(t_i) and save { start: t_i, end: t_i,
+ * offset: t_i }. Otherwise attempt to *overextend* the range to either
+ * [start - 30d, end] or [start, end + 30d] as appropriate to encompass
+ * t_i. If the offset o_i30 is the same as the cached offset, extend the
+ * range. Otherwise the over-guess crossed a DST change -- compute
+ * o_i = dstOffset(t_i) and either extend the original range (if o_i == offset)
+ * or start a new one beneath/above the current one with o_i30 as the offset.
+ *
+ * This cache strategy results in 0 to 2 DST offset computations. The naive
+ * always-compute strategy is 1 computation, and since cache maintenance is a
+ * handful of integer arithmetic instructions the speed difference between
+ * always-1 and 1-with-cache is negligible. Caching loses if two computations
+ * happen: when the date is within 30 days of the cached range and when that
+ * 30-day range crosses a DST change. This is relatively uncommon. Further,
+ * instances of such are often dominated by in-range hits, so caching is an
+ * overall slight win.
+ *
+ * Why 30 days? For correctness the duration must be smaller than any possible
+ * duration between DST changes. Past that, note that 1) a large duration
+ * increases the likelihood of crossing a DST change while reducing the number
+ * of cache misses, and 2) a small duration decreases the size of the cached
+ * range while producing more misses. Using a month as the interval change is
+ * a balance between these two that tries to optimize for the calendar month at
+ * a time that a site might display. (One could imagine an adaptive duration
+ * that accommodates near-DST-change dates better; we don't believe the
+ * potential win from better caching offsets the loss from extra complexity.)
+ */
+class DateTimeInfo {
+ public:
+ // For realms that force the UTC time zone (for fingerprinting protection) a
+ // separate DateTimeInfo instance is used that is always in the UTC time zone.
+ enum class ForceUTC { No, Yes };
+
+ private:
+ static ExclusiveData<DateTimeInfo>* instance;
+ static ExclusiveData<DateTimeInfo>* instanceUTC;
+
+ friend class ExclusiveData<DateTimeInfo>;
+
+ friend bool InitDateTimeState();
+ friend void FinishDateTimeState();
+
+ explicit DateTimeInfo(bool forceUTC);
+ ~DateTimeInfo();
+
+ static auto acquireLockWithValidTimeZone(ForceUTC forceUTC) {
+ auto guard =
+ forceUTC == ForceUTC::Yes ? instanceUTC->lock() : instance->lock();
+ if (guard->timeZoneStatus_ != TimeZoneStatus::Valid) {
+ guard->updateTimeZone();
+ }
+ return guard;
+ }
+
+ public:
+ static ForceUTC forceUTC(JS::Realm* realm);
+
+ // The spec implicitly assumes DST and time zone adjustment information
+ // never change in the course of a function -- sometimes even across
+ // reentrancy. So make critical sections as narrow as possible.
+
+ /**
+ * Get the DST offset in milliseconds at a UTC time. This is usually
+ * either 0 or |msPerSecond * SecondsPerHour|, but at least one exotic time
+ * zone (Lord Howe Island, Australia) has a fractional-hour offset, just to
+ * keep things interesting.
+ */
+ static int32_t getDSTOffsetMilliseconds(ForceUTC forceUTC,
+ int64_t utcMilliseconds) {
+ auto guard = acquireLockWithValidTimeZone(forceUTC);
+ return guard->internalGetDSTOffsetMilliseconds(utcMilliseconds);
+ }
+
+ /**
+ * The offset in seconds from the current UTC time to the current local
+ * standard time (i.e. not including any offset due to DST) as computed by the
+ * operating system.
+ */
+ static int32_t utcToLocalStandardOffsetSeconds(ForceUTC forceUTC) {
+ auto guard = acquireLockWithValidTimeZone(forceUTC);
+ return guard->utcToLocalStandardOffsetSeconds_;
+ }
+
+#if JS_HAS_INTL_API
+ enum class TimeZoneOffset { UTC, Local };
+
+ /**
+ * Return the time zone offset, including DST, in milliseconds at the
+ * given time. The input time can be either at UTC or at local time.
+ */
+ static int32_t getOffsetMilliseconds(ForceUTC forceUTC, int64_t milliseconds,
+ TimeZoneOffset offset) {
+ auto guard = acquireLockWithValidTimeZone(forceUTC);
+ return guard->internalGetOffsetMilliseconds(milliseconds, offset);
+ }
+
+ /**
+ * Copy the display name for the current time zone at the given time,
+ * localized for the specified locale, into the supplied buffer. If the
+ * buffer is too small, an empty string is stored. The stored display name
+ * is null-terminated in any case.
+ */
+ static bool timeZoneDisplayName(ForceUTC forceUTC, char16_t* buf,
+ size_t buflen, int64_t utcMilliseconds,
+ const char* locale) {
+ auto guard = acquireLockWithValidTimeZone(forceUTC);
+ return guard->internalTimeZoneDisplayName(buf, buflen, utcMilliseconds,
+ locale);
+ }
+
+ /**
+ * Copy the identifier for the current time zone to the provided resizable
+ * buffer.
+ */
+ template <typename B>
+ static mozilla::intl::ICUResult timeZoneId(ForceUTC forceUTC, B& buffer) {
+ auto guard = acquireLockWithValidTimeZone(forceUTC);
+ return guard->timeZone()->GetId(buffer);
+ }
+
+ /**
+ * A number indicating the raw offset from GMT in milliseconds.
+ */
+ static mozilla::Result<int32_t, mozilla::intl::ICUError> getRawOffsetMs(
+ ForceUTC forceUTC) {
+ auto guard = acquireLockWithValidTimeZone(forceUTC);
+ return guard->timeZone()->GetRawOffsetMs();
+ }
+#else
+ /**
+ * Return the local time zone adjustment (ES2019 20.3.1.7) as computed by
+ * the operating system.
+ */
+ static int32_t localTZA(ForceUTC forceUTC) {
+ return utcToLocalStandardOffsetSeconds(forceUTC) * msPerSecond;
+ }
+#endif /* JS_HAS_INTL_API */
+
+ private:
+ // The method below should only be called via js::ResetTimeZoneInternal().
+ friend void js::ResetTimeZoneInternal(ResetTimeZoneMode);
+
+ static void resetTimeZone(ResetTimeZoneMode mode) {
+ {
+ auto guard = instance->lock();
+ guard->internalResetTimeZone(mode);
+ }
+ {
+ // Only needed to initialize the default state and any later call will
+ // perform an unnecessary reset.
+ auto guard = instanceUTC->lock();
+ guard->internalResetTimeZone(mode);
+ }
+ }
+
+ struct RangeCache {
+ // Start and end offsets in seconds describing the current and the
+ // last cached range.
+ int64_t startSeconds, endSeconds;
+ int64_t oldStartSeconds, oldEndSeconds;
+
+ // The current and the last cached offset in milliseconds.
+ int32_t offsetMilliseconds;
+ int32_t oldOffsetMilliseconds;
+
+ void reset();
+
+ void sanityCheck();
+ };
+
+ bool forceUTC_;
+
+ enum class TimeZoneStatus : uint8_t { Valid, NeedsUpdate, UpdateIfChanged };
+
+ TimeZoneStatus timeZoneStatus_;
+
+ /**
+ * The offset in seconds from the current UTC time to the current local
+ * standard time (i.e. not including any offset due to DST) as computed by the
+ * operating system.
+ *
+ * Cached because retrieving this dynamically is Slow, and a certain venerable
+ * benchmark which shall not be named depends on it being fast.
+ *
+ * SpiderMonkey occasionally and arbitrarily updates this value from the
+ * system time zone to attempt to keep this reasonably up-to-date. If
+ * temporary inaccuracy can't be tolerated, JSAPI clients may call
+ * JS::ResetTimeZone to forcibly sync this with the system time zone.
+ *
+ * In most cases this value is consistent with the raw time zone offset as
+ * returned by the ICU default time zone (`icu::TimeZone::getRawOffset()`),
+ * but it is possible to create cases where the operating system default time
+ * zone differs from the ICU default time zone. For example ICU doesn't
+ * support the full range of TZ environment variable settings, which can
+ * result in <ctime> returning a different time zone than what's returned by
+ * ICU. One example is "TZ=WGT3WGST,M3.5.0/-2,M10.5.0/-1", where <ctime>
+ * returns -3 hours as the local offset, but ICU flat out rejects the TZ value
+ * and instead infers the default time zone via "/etc/localtime" (on Unix).
+ * This offset can also differ from ICU when the operating system and ICU use
+ * different tzdata versions and the time zone rules of the current system
+ * time zone have changed. Or, on Windows, when the Windows default time zone
+ * can't be mapped to a IANA time zone, see for example
+ * <https://unicode-org.atlassian.net/browse/ICU-13845>.
+ *
+ * When ICU is exclusively used for time zone computations, that means when
+ * |JS_HAS_INTL_API| is true, this field is only used to detect system default
+ * time zone changes. It must not be used to convert between local and UTC
+ * time, because, as outlined above, this could lead to different results when
+ * compared to ICU.
+ */
+ int32_t utcToLocalStandardOffsetSeconds_;
+
+ RangeCache dstRange_; // UTC-based ranges
+
+#if JS_HAS_INTL_API
+ // Use the full date-time range when we can use mozilla::intl::TimeZone.
+ static constexpr int64_t MinTimeT =
+ static_cast<int64_t>(StartOfTime / msPerSecond);
+ static constexpr int64_t MaxTimeT =
+ static_cast<int64_t>(EndOfTime / msPerSecond);
+
+ RangeCache utcRange_; // localtime-based ranges
+ RangeCache localRange_; // UTC-based ranges
+
+ /**
+ * The current time zone. Lazily constructed to avoid potential I/O access
+ * when initializing this class.
+ */
+ mozilla::UniquePtr<mozilla::intl::TimeZone> timeZone_;
+
+ /**
+ * Cached names of the standard and daylight savings display names of the
+ * current time zone for the default locale.
+ */
+ JS::UniqueChars locale_;
+ JS::UniqueTwoByteChars standardName_;
+ JS::UniqueTwoByteChars daylightSavingsName_;
+#else
+ // Restrict the data-time range to the minimum required time_t range as
+ // specified in POSIX. Most operating systems support 64-bit time_t
+ // values, but we currently still have some configurations which use
+ // 32-bit time_t, e.g. the ARM simulator on 32-bit Linux (bug 1406993).
+ // Bug 1406992 explores to use 64-bit time_t when supported by the
+ // underlying operating system.
+ static constexpr int64_t MinTimeT = 0; /* time_t 01/01/1970 */
+ static constexpr int64_t MaxTimeT = 2145830400; /* time_t 12/31/2037 */
+#endif /* JS_HAS_INTL_API */
+
+ static constexpr int64_t RangeExpansionAmount = 30 * SecondsPerDay;
+
+ void internalResetTimeZone(ResetTimeZoneMode mode);
+
+ void updateTimeZone();
+
+ void internalResyncICUDefaultTimeZone();
+
+ int64_t toClampedSeconds(int64_t milliseconds);
+
+ using ComputeFn = int32_t (DateTimeInfo::*)(int64_t);
+
+ /**
+ * Get or compute an offset value for the requested seconds value.
+ */
+ int32_t getOrComputeValue(RangeCache& range, int64_t seconds,
+ ComputeFn compute);
+
+ /**
+ * Compute the DST offset at the given UTC time in seconds from the epoch.
+ * (getDSTOffsetMilliseconds attempts to return a cached value from the
+ * dstRange_ member, but in case of a cache miss it calls this method.)
+ */
+ int32_t computeDSTOffsetMilliseconds(int64_t utcSeconds);
+
+ int32_t internalGetDSTOffsetMilliseconds(int64_t utcMilliseconds);
+
+#if JS_HAS_INTL_API
+ /**
+ * Compute the UTC offset in milliseconds for the given local time. Called
+ * by internalGetOffsetMilliseconds on a cache miss.
+ */
+ int32_t computeUTCOffsetMilliseconds(int64_t localSeconds);
+
+ /**
+ * Compute the local time offset in milliseconds for the given UTC time.
+ * Called by internalGetOffsetMilliseconds on a cache miss.
+ */
+ int32_t computeLocalOffsetMilliseconds(int64_t utcSeconds);
+
+ int32_t internalGetOffsetMilliseconds(int64_t milliseconds,
+ TimeZoneOffset offset);
+
+ bool internalTimeZoneDisplayName(char16_t* buf, size_t buflen,
+ int64_t utcMilliseconds, const char* locale);
+
+ mozilla::intl::TimeZone* timeZone();
+#endif /* JS_HAS_INTL_API */
+};
+
+} /* namespace js */
+
+#endif /* vm_DateTime_h */