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TimeZoneInfo.Unix.cs
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TimeZoneInfo.Unix.cs
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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Buffers;
using System.Buffers.Binary;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.IO;
using System.Text;
using System.Threading;
using System.Security;
using Internal.IO;
namespace System
{
public sealed partial class TimeZoneInfo
{
private const string DefaultTimeZoneDirectory = "/usr/share/zoneinfo/";
private const string ZoneTabFileName = "zone.tab";
private const string TimeZoneEnvironmentVariable = "TZ";
private const string TimeZoneDirectoryEnvironmentVariable = "TZDIR";
private const string FallbackCultureName = "en-US";
private TimeZoneInfo(byte[] data, string id, bool dstDisabled)
{
TZifHead t;
DateTime[] dts;
byte[] typeOfLocalTime;
TZifType[] transitionType;
string zoneAbbreviations;
bool[] StandardTime;
bool[] GmtTime;
string? futureTransitionsPosixFormat;
// parse the raw TZif bytes; this method can throw ArgumentException when the data is malformed.
TZif_ParseRaw(data, out t, out dts, out typeOfLocalTime, out transitionType, out zoneAbbreviations, out StandardTime, out GmtTime, out futureTransitionsPosixFormat);
_id = id;
_displayName = LocalId;
_baseUtcOffset = TimeSpan.Zero;
// find the best matching baseUtcOffset and display strings based on the current utcNow value.
// NOTE: read the display strings from the tzfile now in case they can't be loaded later
// from the globalization data.
DateTime utcNow = DateTime.UtcNow;
for (int i = 0; i < dts.Length && dts[i] <= utcNow; i++)
{
int type = typeOfLocalTime[i];
if (!transitionType[type].IsDst)
{
_baseUtcOffset = transitionType[type].UtcOffset;
_standardDisplayName = TZif_GetZoneAbbreviation(zoneAbbreviations, transitionType[type].AbbreviationIndex);
}
else
{
_daylightDisplayName = TZif_GetZoneAbbreviation(zoneAbbreviations, transitionType[type].AbbreviationIndex);
}
}
if (dts.Length == 0)
{
// time zones like Africa/Bujumbura and Etc/GMT* have no transition times but still contain
// TZifType entries that may contain a baseUtcOffset and display strings
for (int i = 0; i < transitionType.Length; i++)
{
if (!transitionType[i].IsDst)
{
_baseUtcOffset = transitionType[i].UtcOffset;
_standardDisplayName = TZif_GetZoneAbbreviation(zoneAbbreviations, transitionType[i].AbbreviationIndex);
}
else
{
_daylightDisplayName = TZif_GetZoneAbbreviation(zoneAbbreviations, transitionType[i].AbbreviationIndex);
}
}
}
_displayName = _standardDisplayName;
string uiCulture = CultureInfo.CurrentUICulture.Name.Length == 0 ? FallbackCultureName : CultureInfo.CurrentUICulture.Name; // ICU doesn't work nicely with Invariant
GetDisplayName(Interop.Globalization.TimeZoneDisplayNameType.Generic, uiCulture, ref _displayName);
GetDisplayName(Interop.Globalization.TimeZoneDisplayNameType.Standard, uiCulture, ref _standardDisplayName);
GetDisplayName(Interop.Globalization.TimeZoneDisplayNameType.DaylightSavings, uiCulture, ref _daylightDisplayName);
if (_standardDisplayName == _displayName)
{
if (_baseUtcOffset >= TimeSpan.Zero)
_displayName = $"(UTC+{_baseUtcOffset:hh\\:mm}) {_standardDisplayName}";
else
_displayName = $"(UTC-{_baseUtcOffset:hh\\:mm}) {_standardDisplayName}";
}
// TZif supports seconds-level granularity with offsets but TimeZoneInfo only supports minutes since it aligns
// with DateTimeOffset, SQL Server, and the W3C XML Specification
if (_baseUtcOffset.Ticks % TimeSpan.TicksPerMinute != 0)
{
_baseUtcOffset = new TimeSpan(_baseUtcOffset.Hours, _baseUtcOffset.Minutes, 0);
}
if (!dstDisabled)
{
// only create the adjustment rule if DST is enabled
TZif_GenerateAdjustmentRules(out _adjustmentRules, _baseUtcOffset, dts, typeOfLocalTime, transitionType, StandardTime, GmtTime, futureTransitionsPosixFormat);
}
ValidateTimeZoneInfo(_id, _baseUtcOffset, _adjustmentRules, out _supportsDaylightSavingTime);
}
/// <summary>
/// Returns a cloned array of AdjustmentRule objects
/// </summary>
public AdjustmentRule[] GetAdjustmentRules()
{
if (_adjustmentRules == null)
{
return Array.Empty<AdjustmentRule>();
}
// The rules we use in Unix care mostly about the start and end dates but don't fill the transition start and end info.
// as the rules now is public, we should fill it properly so the caller doesn't have to know how we use it internally
// and can use it as it is used in Windows
AdjustmentRule[] rules = new AdjustmentRule[_adjustmentRules.Length];
for (int i = 0; i < _adjustmentRules.Length; i++)
{
AdjustmentRule? rule = _adjustmentRules[i];
DateTime start = rule.DateStart.Kind == DateTimeKind.Utc ?
// At the daylight start we didn't start the daylight saving yet then we convert to Local time
// by adding the _baseUtcOffset to the UTC time
new DateTime(rule.DateStart.Ticks + _baseUtcOffset.Ticks, DateTimeKind.Unspecified) :
rule.DateStart;
DateTime end = rule.DateEnd.Kind == DateTimeKind.Utc ?
// At the daylight saving end, the UTC time is mapped to local time which is already shifted by the daylight delta
// we calculate the local time by adding _baseUtcOffset + DaylightDelta to the UTC time
new DateTime(rule.DateEnd.Ticks + _baseUtcOffset.Ticks + rule.DaylightDelta.Ticks, DateTimeKind.Unspecified) :
rule.DateEnd;
TransitionTime startTransition = TimeZoneInfo.TransitionTime.CreateFixedDateRule(new DateTime(1, 1, 1, start.Hour, start.Minute, start.Second), start.Month, start.Day);
TransitionTime endTransition = TimeZoneInfo.TransitionTime.CreateFixedDateRule(new DateTime(1, 1, 1, end.Hour, end.Minute, end.Second), end.Month, end.Day);
rules[i] = TimeZoneInfo.AdjustmentRule.CreateAdjustmentRule(start.Date, end.Date, rule.DaylightDelta, startTransition, endTransition);
}
return rules;
}
private static void PopulateAllSystemTimeZones(CachedData cachedData)
{
Debug.Assert(Monitor.IsEntered(cachedData));
string timeZoneDirectory = GetTimeZoneDirectory();
foreach (string timeZoneId in GetTimeZoneIds(timeZoneDirectory))
{
TryGetTimeZone(timeZoneId, false, out _, out _, cachedData, alwaysFallbackToLocalMachine: true); // populate the cache
}
}
/// <summary>
/// Helper function for retrieving the local system time zone.
/// May throw COMException, TimeZoneNotFoundException, InvalidTimeZoneException.
/// Assumes cachedData lock is taken.
/// </summary>
/// <returns>A new TimeZoneInfo instance.</returns>
private static TimeZoneInfo GetLocalTimeZone(CachedData cachedData)
{
Debug.Assert(Monitor.IsEntered(cachedData));
// Without Registry support, create the TimeZoneInfo from a TZ file
return GetLocalTimeZoneFromTzFile();
}
private static TimeZoneInfoResult TryGetTimeZoneFromLocalMachine(string id, out TimeZoneInfo? value, out Exception? e)
{
value = null;
e = null;
string timeZoneDirectory = GetTimeZoneDirectory();
string timeZoneFilePath = Path.Combine(timeZoneDirectory, id);
byte[] rawData;
try
{
rawData = File.ReadAllBytes(timeZoneFilePath);
}
catch (UnauthorizedAccessException ex)
{
e = ex;
return TimeZoneInfoResult.SecurityException;
}
catch (FileNotFoundException ex)
{
e = ex;
return TimeZoneInfoResult.TimeZoneNotFoundException;
}
catch (DirectoryNotFoundException ex)
{
e = ex;
return TimeZoneInfoResult.TimeZoneNotFoundException;
}
catch (IOException ex)
{
e = new InvalidTimeZoneException(SR.Format(SR.InvalidTimeZone_InvalidFileData, id, timeZoneFilePath), ex);
return TimeZoneInfoResult.InvalidTimeZoneException;
}
value = GetTimeZoneFromTzData(rawData, id);
if (value == null)
{
e = new InvalidTimeZoneException(SR.Format(SR.InvalidTimeZone_InvalidFileData, id, timeZoneFilePath));
return TimeZoneInfoResult.InvalidTimeZoneException;
}
return TimeZoneInfoResult.Success;
}
/// <summary>
/// Returns a collection of TimeZone Id values from the zone.tab file in the timeZoneDirectory.
/// </summary>
/// <remarks>
/// Lines that start with # are comments and are skipped.
/// </remarks>
private static List<string> GetTimeZoneIds(string timeZoneDirectory)
{
List<string> timeZoneIds = new List<string>();
try
{
using (StreamReader sr = new StreamReader(Path.Combine(timeZoneDirectory, ZoneTabFileName), Encoding.UTF8))
{
string? zoneTabFileLine;
while ((zoneTabFileLine = sr.ReadLine()) != null)
{
if (!string.IsNullOrEmpty(zoneTabFileLine) && zoneTabFileLine[0] != '#')
{
// the format of the line is "country-code \t coordinates \t TimeZone Id \t comments"
int firstTabIndex = zoneTabFileLine.IndexOf('\t');
if (firstTabIndex != -1)
{
int secondTabIndex = zoneTabFileLine.IndexOf('\t', firstTabIndex + 1);
if (secondTabIndex != -1)
{
string timeZoneId;
int startIndex = secondTabIndex + 1;
int thirdTabIndex = zoneTabFileLine.IndexOf('\t', startIndex);
if (thirdTabIndex != -1)
{
int length = thirdTabIndex - startIndex;
timeZoneId = zoneTabFileLine.Substring(startIndex, length);
}
else
{
timeZoneId = zoneTabFileLine.Substring(startIndex);
}
if (!string.IsNullOrEmpty(timeZoneId))
{
timeZoneIds.Add(timeZoneId);
}
}
}
}
}
}
}
catch (IOException) { }
catch (UnauthorizedAccessException) { }
return timeZoneIds;
}
/// <summary>
/// Gets the tzfile raw data for the current 'local' time zone using the following rules.
/// 1. Read the TZ environment variable. If it is set, use it.
/// 2. Look for the data in /etc/localtime.
/// 3. Look for the data in GetTimeZoneDirectory()/localtime.
/// 4. Use UTC if all else fails.
/// </summary>
private static bool TryGetLocalTzFile([NotNullWhen(true)] out byte[]? rawData, [NotNullWhen(true)] out string? id)
{
rawData = null;
id = null;
string? tzVariable = GetTzEnvironmentVariable();
// If the env var is null, use the localtime file
if (tzVariable == null)
{
return
TryLoadTzFile("/etc/localtime", ref rawData, ref id) ||
TryLoadTzFile(Path.Combine(GetTimeZoneDirectory(), "localtime"), ref rawData, ref id);
}
// If it's empty, use UTC (TryGetLocalTzFile() should return false).
if (tzVariable.Length == 0)
{
return false;
}
// Otherwise, use the path from the env var. If it's not absolute, make it relative
// to the system timezone directory
string tzFilePath;
if (tzVariable[0] != '/')
{
id = tzVariable;
tzFilePath = Path.Combine(GetTimeZoneDirectory(), tzVariable);
}
else
{
tzFilePath = tzVariable;
}
return TryLoadTzFile(tzFilePath, ref rawData, ref id);
}
private static string? GetTzEnvironmentVariable()
{
string? result = Environment.GetEnvironmentVariable(TimeZoneEnvironmentVariable);
if (!string.IsNullOrEmpty(result))
{
if (result[0] == ':')
{
// strip off the ':' prefix
result = result.Substring(1);
}
}
return result;
}
private static bool TryLoadTzFile(string tzFilePath, [NotNullWhen(true)] ref byte[]? rawData, [NotNullWhen(true)] ref string? id)
{
if (File.Exists(tzFilePath))
{
try
{
rawData = File.ReadAllBytes(tzFilePath);
if (string.IsNullOrEmpty(id))
{
id = FindTimeZoneIdUsingReadLink(tzFilePath);
if (string.IsNullOrEmpty(id))
{
id = FindTimeZoneId(rawData);
}
}
return true;
}
catch (IOException) { }
catch (SecurityException) { }
catch (UnauthorizedAccessException) { }
}
return false;
}
/// <summary>
/// Finds the time zone id by using 'readlink' on the path to see if tzFilePath is
/// a symlink to a file.
/// </summary>
private static string? FindTimeZoneIdUsingReadLink(string tzFilePath)
{
string? id = null;
string? symlinkPath = Interop.Sys.ReadLink(tzFilePath);
if (symlinkPath != null)
{
// symlinkPath can be relative path, use Path to get the full absolute path.
symlinkPath = Path.GetFullPath(symlinkPath, Path.GetDirectoryName(tzFilePath)!);
string timeZoneDirectory = GetTimeZoneDirectory();
if (symlinkPath.StartsWith(timeZoneDirectory, StringComparison.Ordinal))
{
id = symlinkPath.Substring(timeZoneDirectory.Length);
}
}
return id;
}
private static string? GetDirectoryEntryFullPath(ref Interop.Sys.DirectoryEntry dirent, string currentPath)
{
ReadOnlySpan<char> direntName = dirent.GetName(stackalloc char[Interop.Sys.DirectoryEntry.NameBufferSize]);
if ((direntName.Length == 1 && direntName[0] == '.') ||
(direntName.Length == 2 && direntName[0] == '.' && direntName[1] == '.'))
return null;
return Path.Join(currentPath.AsSpan(), direntName);
}
/// <summary>
/// Enumerate files
/// </summary>
private static unsafe void EnumerateFilesRecursively(string path, Predicate<string> condition)
{
List<string>? toExplore = null; // List used as a stack
int bufferSize = Interop.Sys.GetReadDirRBufferSize();
byte[]? dirBuffer = null;
try
{
dirBuffer = ArrayPool<byte>.Shared.Rent(bufferSize);
string currentPath = path;
fixed (byte* dirBufferPtr = dirBuffer)
{
while (true)
{
IntPtr dirHandle = Interop.Sys.OpenDir(currentPath);
if (dirHandle == IntPtr.Zero)
{
throw Interop.GetExceptionForIoErrno(Interop.Sys.GetLastErrorInfo(), currentPath, isDirectory: true);
}
try
{
// Read each entry from the enumerator
Interop.Sys.DirectoryEntry dirent;
while (Interop.Sys.ReadDirR(dirHandle, dirBufferPtr, bufferSize, out dirent) == 0)
{
string? fullPath = GetDirectoryEntryFullPath(ref dirent, currentPath);
if (fullPath == null)
continue;
// Get from the dir entry whether the entry is a file or directory.
// We classify everything as a file unless we know it to be a directory.
bool isDir;
if (dirent.InodeType == Interop.Sys.NodeType.DT_DIR)
{
// We know it's a directory.
isDir = true;
}
else if (dirent.InodeType == Interop.Sys.NodeType.DT_LNK || dirent.InodeType == Interop.Sys.NodeType.DT_UNKNOWN)
{
// It's a symlink or unknown: stat to it to see if we can resolve it to a directory.
// If we can't (e.g. symlink to a file, broken symlink, etc.), we'll just treat it as a file.
Interop.Sys.FileStatus fileinfo;
if (Interop.Sys.Stat(fullPath, out fileinfo) >= 0)
{
isDir = (fileinfo.Mode & Interop.Sys.FileTypes.S_IFMT) == Interop.Sys.FileTypes.S_IFDIR;
}
else
{
isDir = false;
}
}
else
{
// Otherwise, treat it as a file. This includes regular files, FIFOs, etc.
isDir = false;
}
// Yield the result if the user has asked for it. In the case of directories,
// always explore it by pushing it onto the stack, regardless of whether
// we're returning directories.
if (isDir)
{
toExplore ??= new List<string>();
toExplore.Add(fullPath);
}
else if (condition(fullPath))
{
return;
}
}
}
finally
{
if (dirHandle != IntPtr.Zero)
Interop.Sys.CloseDir(dirHandle);
}
if (toExplore == null || toExplore.Count == 0)
break;
currentPath = toExplore[toExplore.Count - 1];
toExplore.RemoveAt(toExplore.Count - 1);
}
}
}
finally
{
if (dirBuffer != null)
ArrayPool<byte>.Shared.Return(dirBuffer);
}
}
/// <summary>
/// Find the time zone id by searching all the tzfiles for the one that matches rawData
/// and return its file name.
/// </summary>
private static string FindTimeZoneId(byte[] rawData)
{
// default to "Local" if we can't find the right tzfile
string id = LocalId;
string timeZoneDirectory = GetTimeZoneDirectory();
string localtimeFilePath = Path.Combine(timeZoneDirectory, "localtime");
string posixrulesFilePath = Path.Combine(timeZoneDirectory, "posixrules");
byte[] buffer = new byte[rawData.Length];
try
{
EnumerateFilesRecursively(timeZoneDirectory, (string filePath) =>
{
// skip the localtime and posixrules file, since they won't give us the correct id
if (!string.Equals(filePath, localtimeFilePath, StringComparison.OrdinalIgnoreCase)
&& !string.Equals(filePath, posixrulesFilePath, StringComparison.OrdinalIgnoreCase))
{
if (CompareTimeZoneFile(filePath, buffer, rawData))
{
// if all bytes are the same, this must be the right tz file
id = filePath;
// strip off the root time zone directory
if (id.StartsWith(timeZoneDirectory, StringComparison.Ordinal))
{
id = id.Substring(timeZoneDirectory.Length);
}
return true;
}
}
return false;
});
}
catch (IOException) { }
catch (SecurityException) { }
catch (UnauthorizedAccessException) { }
return id;
}
private static bool CompareTimeZoneFile(string filePath, byte[] buffer, byte[] rawData)
{
try
{
// bufferSize == 1 used to avoid unnecessary buffer in FileStream
using (FileStream stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize: 1))
{
if (stream.Length == rawData.Length)
{
int index = 0;
int count = rawData.Length;
while (count > 0)
{
int n = stream.Read(buffer, index, count);
if (n == 0)
throw Error.GetEndOfFile();
int end = index + n;
for (; index < end; index++)
{
if (buffer[index] != rawData[index])
{
return false;
}
}
count -= n;
}
return true;
}
}
}
catch (IOException) { }
catch (SecurityException) { }
catch (UnauthorizedAccessException) { }
return false;
}
/// <summary>
/// Helper function used by 'GetLocalTimeZone()' - this function wraps the call
/// for loading time zone data from computers without Registry support.
///
/// The TryGetLocalTzFile() call returns a Byte[] containing the compiled tzfile.
/// </summary>
private static TimeZoneInfo GetLocalTimeZoneFromTzFile()
{
byte[]? rawData;
string? id;
if (TryGetLocalTzFile(out rawData, out id))
{
TimeZoneInfo? result = GetTimeZoneFromTzData(rawData, id);
if (result != null)
{
return result;
}
}
// if we can't find a local time zone, return UTC
return Utc;
}
private static TimeZoneInfo? GetTimeZoneFromTzData(byte[]? rawData, string id)
{
if (rawData != null)
{
try
{
return new TimeZoneInfo(rawData, id, dstDisabled: false); // create a TimeZoneInfo instance from the TZif data w/ DST support
}
catch (ArgumentException) { }
catch (InvalidTimeZoneException) { }
try
{
return new TimeZoneInfo(rawData, id, dstDisabled: true); // create a TimeZoneInfo instance from the TZif data w/o DST support
}
catch (ArgumentException) { }
catch (InvalidTimeZoneException) { }
}
return null;
}
private static string GetTimeZoneDirectory()
{
string? tzDirectory = Environment.GetEnvironmentVariable(TimeZoneDirectoryEnvironmentVariable);
if (tzDirectory == null)
{
tzDirectory = DefaultTimeZoneDirectory;
}
else if (!tzDirectory.EndsWith(Path.DirectorySeparatorChar))
{
tzDirectory += PathInternal.DirectorySeparatorCharAsString;
}
return tzDirectory;
}
/// <summary>
/// Helper function for retrieving a TimeZoneInfo object by time_zone_name.
/// This function wraps the logic necessary to keep the private
/// SystemTimeZones cache in working order
///
/// This function will either return a valid TimeZoneInfo instance or
/// it will throw 'InvalidTimeZoneException' / 'TimeZoneNotFoundException'.
/// </summary>
public static TimeZoneInfo FindSystemTimeZoneById(string id)
{
// Special case for Utc as it will not exist in the dictionary with the rest
// of the system time zones. There is no need to do this check for Local.Id
// since Local is a real time zone that exists in the dictionary cache
if (string.Equals(id, UtcId, StringComparison.OrdinalIgnoreCase))
{
return Utc;
}
if (id == null)
{
throw new ArgumentNullException(nameof(id));
}
else if (id.Length == 0 || id.Contains('\0'))
{
throw new TimeZoneNotFoundException(SR.Format(SR.TimeZoneNotFound_MissingData, id));
}
TimeZoneInfo? value;
Exception? e;
TimeZoneInfoResult result;
CachedData cachedData = s_cachedData;
lock (cachedData)
{
result = TryGetTimeZone(id, false, out value, out e, cachedData, alwaysFallbackToLocalMachine: true);
}
if (result == TimeZoneInfoResult.Success)
{
return value!;
}
else if (result == TimeZoneInfoResult.InvalidTimeZoneException)
{
Debug.Assert(e is InvalidTimeZoneException,
"TryGetTimeZone must create an InvalidTimeZoneException when it returns TimeZoneInfoResult.InvalidTimeZoneException");
throw e;
}
else if (result == TimeZoneInfoResult.SecurityException)
{
throw new SecurityException(SR.Format(SR.Security_CannotReadFileData, id), e);
}
else
{
throw new TimeZoneNotFoundException(SR.Format(SR.TimeZoneNotFound_MissingData, id), e);
}
}
// DateTime.Now fast path that avoids allocating an historically accurate TimeZoneInfo.Local and just creates a 1-year (current year) accurate time zone
internal static TimeSpan GetDateTimeNowUtcOffsetFromUtc(DateTime time, out bool isAmbiguousLocalDst)
{
bool isDaylightSavings;
// Use the standard code path for Unix since there isn't a faster way of handling current-year-only time zones
return GetUtcOffsetFromUtc(time, Local, out isDaylightSavings, out isAmbiguousLocalDst);
}
// TZFILE(5) BSD File Formats Manual TZFILE(5)
//
// NAME
// tzfile -- timezone information
//
// SYNOPSIS
// #include "/usr/src/lib/libc/stdtime/tzfile.h"
//
// DESCRIPTION
// The time zone information files used by tzset(3) begin with the magic
// characters ``TZif'' to identify them as time zone information files, fol-
// lowed by sixteen bytes reserved for future use, followed by four four-
// byte values written in a ``standard'' byte order (the high-order byte of
// the value is written first). These values are, in order:
//
// tzh_ttisgmtcnt The number of UTC/local indicators stored in the file.
// tzh_ttisstdcnt The number of standard/wall indicators stored in the
// file.
// tzh_leapcnt The number of leap seconds for which data is stored in
// the file.
// tzh_timecnt The number of ``transition times'' for which data is
// stored in the file.
// tzh_typecnt The number of ``local time types'' for which data is
// stored in the file (must not be zero).
// tzh_charcnt The number of characters of ``time zone abbreviation
// strings'' stored in the file.
//
// The above header is followed by tzh_timecnt four-byte values of type
// long, sorted in ascending order. These values are written in ``stan-
// dard'' byte order. Each is used as a transition time (as returned by
// time(3)) at which the rules for computing local time change. Next come
// tzh_timecnt one-byte values of type unsigned char; each one tells which
// of the different types of ``local time'' types described in the file is
// associated with the same-indexed transition time. These values serve as
// indices into an array of ttinfo structures that appears next in the file;
// these structures are defined as follows:
//
// struct ttinfo {
// long tt_gmtoff;
// int tt_isdst;
// unsigned int tt_abbrind;
// };
//
// Each structure is written as a four-byte value for tt_gmtoff of type
// long, in a standard byte order, followed by a one-byte value for tt_isdst
// and a one-byte value for tt_abbrind. In each structure, tt_gmtoff gives
// the number of seconds to be added to UTC, tt_isdst tells whether tm_isdst
// should be set by localtime(3) and tt_abbrind serves as an index into the
// array of time zone abbreviation characters that follow the ttinfo struc-
// ture(s) in the file.
//
// Then there are tzh_leapcnt pairs of four-byte values, written in standard
// byte order; the first value of each pair gives the time (as returned by
// time(3)) at which a leap second occurs; the second gives the total number
// of leap seconds to be applied after the given time. The pairs of values
// are sorted in ascending order by time.b
//
// Then there are tzh_ttisstdcnt standard/wall indicators, each stored as a
// one-byte value; they tell whether the transition times associated with
// local time types were specified as standard time or wall clock time, and
// are used when a time zone file is used in handling POSIX-style time zone
// environment variables.
//
// Finally there are tzh_ttisgmtcnt UTC/local indicators, each stored as a
// one-byte value; they tell whether the transition times associated with
// local time types were specified as UTC or local time, and are used when a
// time zone file is used in handling POSIX-style time zone environment
// variables.
//
// localtime uses the first standard-time ttinfo structure in the file (or
// simply the first ttinfo structure in the absence of a standard-time
// structure) if either tzh_timecnt is zero or the time argument is less
// than the first transition time recorded in the file.
//
// SEE ALSO
// ctime(3), time2posix(3), zic(8)
//
// BSD September 13, 1994 BSD
//
//
//
// TIME(3) BSD Library Functions Manual TIME(3)
//
// NAME
// time -- get time of day
//
// LIBRARY
// Standard C Library (libc, -lc)
//
// SYNOPSIS
// #include <time.h>
//
// time_t
// time(time_t *tloc);
//
// DESCRIPTION
// The time() function returns the value of time in seconds since 0 hours, 0
// minutes, 0 seconds, January 1, 1970, Coordinated Universal Time, without
// including leap seconds. If an error occurs, time() returns the value
// (time_t)-1.
//
// The return value is also stored in *tloc, provided that tloc is non-null.
//
// ERRORS
// The time() function may fail for any of the reasons described in
// gettimeofday(2).
//
// SEE ALSO
// gettimeofday(2), ctime(3)
//
// STANDARDS
// The time function conforms to IEEE Std 1003.1-2001 (``POSIX.1'').
//
// BUGS
// Neither ISO/IEC 9899:1999 (``ISO C99'') nor IEEE Std 1003.1-2001
// (``POSIX.1'') requires time() to set errno on failure; thus, it is impos-
// sible for an application to distinguish the valid time value -1 (repre-
// senting the last UTC second of 1969) from the error return value.
//
// Systems conforming to earlier versions of the C and POSIX standards
// (including older versions of FreeBSD) did not set *tloc in the error
// case.
//
// HISTORY
// A time() function appeared in Version 6 AT&T UNIX.
//
// BSD July 18, 2003 BSD
//
//
private static void TZif_GenerateAdjustmentRules(out AdjustmentRule[]? rules, TimeSpan baseUtcOffset, DateTime[] dts, byte[] typeOfLocalTime,
TZifType[] transitionType, bool[] StandardTime, bool[] GmtTime, string? futureTransitionsPosixFormat)
{
rules = null;
if (dts.Length > 0)
{
int index = 0;
List<AdjustmentRule> rulesList = new List<AdjustmentRule>();
while (index <= dts.Length)
{
TZif_GenerateAdjustmentRule(ref index, baseUtcOffset, rulesList, dts, typeOfLocalTime, transitionType, StandardTime, GmtTime, futureTransitionsPosixFormat);
}
rules = rulesList.ToArray();
if (rules != null && rules.Length == 0)
{
rules = null;
}
}
}
private static void TZif_GenerateAdjustmentRule(ref int index, TimeSpan timeZoneBaseUtcOffset, List<AdjustmentRule> rulesList, DateTime[] dts,
byte[] typeOfLocalTime, TZifType[] transitionTypes, bool[] StandardTime, bool[] GmtTime, string? futureTransitionsPosixFormat)
{
// To generate AdjustmentRules, use the following approach:
// The first AdjustmentRule will go from DateTime.MinValue to the first transition time greater than DateTime.MinValue.
// Each middle AdjustmentRule wil go from dts[index-1] to dts[index].
// The last AdjustmentRule will go from dts[dts.Length-1] to Datetime.MaxValue.
// 0. Skip any DateTime.MinValue transition times. In newer versions of the tzfile, there
// is a "big bang" transition time, which is before the year 0001. Since any times before year 0001
// cannot be represented by DateTime, there is no reason to make AdjustmentRules for these unrepresentable time periods.
// 1. If there are no DateTime.MinValue times, the first AdjustmentRule goes from DateTime.MinValue
// to the first transition and uses the first standard transitionType (or the first transitionType if none of them are standard)
// 2. Create an AdjustmentRule for each transition, i.e. from dts[index - 1] to dts[index].
// This rule uses the transitionType[index - 1] and the whole AdjustmentRule only describes a single offset - either
// all daylight savings, or all standard time.
// 3. After all the transitions are filled out, the last AdjustmentRule is created from either:
// a. a POSIX-style timezone description ("futureTransitionsPosixFormat"), if there is one or
// b. continue the last transition offset until DateTime.Max
while (index < dts.Length && dts[index] == DateTime.MinValue)
{
index++;
}
if (rulesList.Count == 0 && index < dts.Length)
{
TZifType transitionType = TZif_GetEarlyDateTransitionType(transitionTypes);
DateTime endTransitionDate = dts[index];
TimeSpan transitionOffset = TZif_CalculateTransitionOffsetFromBase(transitionType.UtcOffset, timeZoneBaseUtcOffset);
TimeSpan daylightDelta = transitionType.IsDst ? transitionOffset : TimeSpan.Zero;
TimeSpan baseUtcDelta = transitionType.IsDst ? TimeSpan.Zero : transitionOffset;
AdjustmentRule r = AdjustmentRule.CreateAdjustmentRule(
DateTime.MinValue,
endTransitionDate.AddTicks(-1),
daylightDelta,
default,
default,
baseUtcDelta,
noDaylightTransitions: true);
if (!IsValidAdjustmentRuleOffest(timeZoneBaseUtcOffset, r))
{
NormalizeAdjustmentRuleOffset(timeZoneBaseUtcOffset, ref r);
}
rulesList.Add(r);
}
else if (index < dts.Length)
{
DateTime startTransitionDate = dts[index - 1];
TZifType startTransitionType = transitionTypes[typeOfLocalTime[index - 1]];
DateTime endTransitionDate = dts[index];
TimeSpan transitionOffset = TZif_CalculateTransitionOffsetFromBase(startTransitionType.UtcOffset, timeZoneBaseUtcOffset);
TimeSpan daylightDelta = startTransitionType.IsDst ? transitionOffset : TimeSpan.Zero;
TimeSpan baseUtcDelta = startTransitionType.IsDst ? TimeSpan.Zero : transitionOffset;
TransitionTime dstStart;
if (startTransitionType.IsDst)
{
// the TransitionTime fields are not used when AdjustmentRule.NoDaylightTransitions == true.
// However, there are some cases in the past where DST = true, and the daylight savings offset
// now equals what the current BaseUtcOffset is. In that case, the AdjustmentRule.DaylightOffset
// is going to be TimeSpan.Zero. But we still need to return 'true' from AdjustmentRule.HasDaylightSaving.
// To ensure we always return true from HasDaylightSaving, make a "special" dstStart that will make the logic
// in HasDaylightSaving return true.
dstStart = TransitionTime.CreateFixedDateRule(DateTime.MinValue.AddMilliseconds(2), 1, 1);
}
else
{
dstStart = default;
}
AdjustmentRule r = AdjustmentRule.CreateAdjustmentRule(
startTransitionDate,
endTransitionDate.AddTicks(-1),
daylightDelta,
dstStart,
default,
baseUtcDelta,
noDaylightTransitions: true);
if (!IsValidAdjustmentRuleOffest(timeZoneBaseUtcOffset, r))
{
NormalizeAdjustmentRuleOffset(timeZoneBaseUtcOffset, ref r);
}
rulesList.Add(r);
}
else
{
// create the AdjustmentRule that will be used for all DateTimes after the last transition
// NOTE: index == dts.Length
DateTime startTransitionDate = dts[index - 1];
AdjustmentRule? r = !string.IsNullOrEmpty(futureTransitionsPosixFormat) ?
TZif_CreateAdjustmentRuleForPosixFormat(futureTransitionsPosixFormat, startTransitionDate, timeZoneBaseUtcOffset) :
null;
if (r == null)
{
// just use the last transition as the rule which will be used until the end of time
TZifType transitionType = transitionTypes[typeOfLocalTime[index - 1]];
TimeSpan transitionOffset = TZif_CalculateTransitionOffsetFromBase(transitionType.UtcOffset, timeZoneBaseUtcOffset);
TimeSpan daylightDelta = transitionType.IsDst ? transitionOffset : TimeSpan.Zero;
TimeSpan baseUtcDelta = transitionType.IsDst ? TimeSpan.Zero : transitionOffset;
r = AdjustmentRule.CreateAdjustmentRule(
startTransitionDate,
DateTime.MaxValue,
daylightDelta,
default,
default,
baseUtcDelta,
noDaylightTransitions: true);
}
if (!IsValidAdjustmentRuleOffest(timeZoneBaseUtcOffset, r))
{
NormalizeAdjustmentRuleOffset(timeZoneBaseUtcOffset, ref r);
}
rulesList.Add(r);
}
index++;
}
private static TimeSpan TZif_CalculateTransitionOffsetFromBase(TimeSpan transitionOffset, TimeSpan timeZoneBaseUtcOffset)
{
TimeSpan result = transitionOffset - timeZoneBaseUtcOffset;
// TZif supports seconds-level granularity with offsets but TimeZoneInfo only supports minutes since it aligns
// with DateTimeOffset, SQL Server, and the W3C XML Specification
if (result.Ticks % TimeSpan.TicksPerMinute != 0)
{
result = new TimeSpan(result.Hours, result.Minutes, 0);
}
return result;
}