Source file src/time/zoneinfo.go

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package time
     6  
     7  import (
     8  	"errors"
     9  	"sync"
    10  	"syscall"
    11  )
    12  
    13  //go:generate env ZONEINFO=$GOROOT/lib/time/zoneinfo.zip go run genzabbrs.go -output zoneinfo_abbrs_windows.go
    14  
    15  // A Location maps time instants to the zone in use at that time.
    16  // Typically, the Location represents the collection of time offsets
    17  // in use in a geographical area. For many Locations the time offset varies
    18  // depending on whether daylight savings time is in use at the time instant.
    19  type Location struct {
    20  	name string
    21  	zone []zone
    22  	tx   []zoneTrans
    23  
    24  	// The tzdata information can be followed by a string that describes
    25  	// how to handle DST transitions not recorded in zoneTrans.
    26  	// The format is the TZ environment variable without a colon; see
    27  	// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html.
    28  	// Example string, for America/Los_Angeles: PST8PDT,M3.2.0,M11.1.0
    29  	extend string
    30  
    31  	// Most lookups will be for the current time.
    32  	// To avoid the binary search through tx, keep a
    33  	// static one-element cache that gives the correct
    34  	// zone for the time when the Location was created.
    35  	// if cacheStart <= t < cacheEnd,
    36  	// lookup can return cacheZone.
    37  	// The units for cacheStart and cacheEnd are seconds
    38  	// since January 1, 1970 UTC, to match the argument
    39  	// to lookup.
    40  	cacheStart int64
    41  	cacheEnd   int64
    42  	cacheZone  *zone
    43  }
    44  
    45  // A zone represents a single time zone such as CET.
    46  type zone struct {
    47  	name   string // abbreviated name, "CET"
    48  	offset int    // seconds east of UTC
    49  	isDST  bool   // is this zone Daylight Savings Time?
    50  }
    51  
    52  // A zoneTrans represents a single time zone transition.
    53  type zoneTrans struct {
    54  	when         int64 // transition time, in seconds since 1970 GMT
    55  	index        uint8 // the index of the zone that goes into effect at that time
    56  	isstd, isutc bool  // ignored - no idea what these mean
    57  }
    58  
    59  // alpha and omega are the beginning and end of time for zone
    60  // transitions.
    61  const (
    62  	alpha = -1 << 63  // math.MinInt64
    63  	omega = 1<<63 - 1 // math.MaxInt64
    64  )
    65  
    66  // UTC represents Universal Coordinated Time (UTC).
    67  var UTC *Location = &utcLoc
    68  
    69  // utcLoc is separate so that get can refer to &utcLoc
    70  // and ensure that it never returns a nil *Location,
    71  // even if a badly behaved client has changed UTC.
    72  var utcLoc = Location{name: "UTC"}
    73  
    74  // Local represents the system's local time zone.
    75  // On Unix systems, Local consults the TZ environment
    76  // variable to find the time zone to use. No TZ means
    77  // use the system default /etc/localtime.
    78  // TZ="" means use UTC.
    79  // TZ="foo" means use file foo in the system timezone directory.
    80  var Local *Location = &localLoc
    81  
    82  // localLoc is separate so that initLocal can initialize
    83  // it even if a client has changed Local.
    84  var localLoc Location
    85  var localOnce sync.Once
    86  
    87  func (l *Location) get() *Location {
    88  	if l == nil {
    89  		return &utcLoc
    90  	}
    91  	if l == &localLoc {
    92  		localOnce.Do(initLocal)
    93  	}
    94  	return l
    95  }
    96  
    97  // String returns a descriptive name for the time zone information,
    98  // corresponding to the name argument to LoadLocation or FixedZone.
    99  func (l *Location) String() string {
   100  	return l.get().name
   101  }
   102  
   103  // FixedZone returns a Location that always uses
   104  // the given zone name and offset (seconds east of UTC).
   105  func FixedZone(name string, offset int) *Location {
   106  	l := &Location{
   107  		name:       name,
   108  		zone:       []zone{{name, offset, false}},
   109  		tx:         []zoneTrans{{alpha, 0, false, false}},
   110  		cacheStart: alpha,
   111  		cacheEnd:   omega,
   112  	}
   113  	l.cacheZone = &l.zone[0]
   114  	return l
   115  }
   116  
   117  // lookup returns information about the time zone in use at an
   118  // instant in time expressed as seconds since January 1, 1970 00:00:00 UTC.
   119  //
   120  // The returned information gives the name of the zone (such as "CET"),
   121  // the start and end times bracketing sec when that zone is in effect,
   122  // the offset in seconds east of UTC (such as -5*60*60), and whether
   123  // the daylight savings is being observed at that time.
   124  func (l *Location) lookup(sec int64) (name string, offset int, start, end int64, isDST bool) {
   125  	l = l.get()
   126  
   127  	if len(l.zone) == 0 {
   128  		name = "UTC"
   129  		offset = 0
   130  		start = alpha
   131  		end = omega
   132  		isDST = false
   133  		return
   134  	}
   135  
   136  	if zone := l.cacheZone; zone != nil && l.cacheStart <= sec && sec < l.cacheEnd {
   137  		name = zone.name
   138  		offset = zone.offset
   139  		start = l.cacheStart
   140  		end = l.cacheEnd
   141  		isDST = zone.isDST
   142  		return
   143  	}
   144  
   145  	if len(l.tx) == 0 || sec < l.tx[0].when {
   146  		zone := &l.zone[l.lookupFirstZone()]
   147  		name = zone.name
   148  		offset = zone.offset
   149  		start = alpha
   150  		if len(l.tx) > 0 {
   151  			end = l.tx[0].when
   152  		} else {
   153  			end = omega
   154  		}
   155  		isDST = zone.isDST
   156  		return
   157  	}
   158  
   159  	// Binary search for entry with largest time <= sec.
   160  	// Not using sort.Search to avoid dependencies.
   161  	tx := l.tx
   162  	end = omega
   163  	lo := 0
   164  	hi := len(tx)
   165  	for hi-lo > 1 {
   166  		m := lo + (hi-lo)/2
   167  		lim := tx[m].when
   168  		if sec < lim {
   169  			end = lim
   170  			hi = m
   171  		} else {
   172  			lo = m
   173  		}
   174  	}
   175  	zone := &l.zone[tx[lo].index]
   176  	name = zone.name
   177  	offset = zone.offset
   178  	start = tx[lo].when
   179  	// end = maintained during the search
   180  	isDST = zone.isDST
   181  
   182  	// If we're at the end of the known zone transitions,
   183  	// try the extend string.
   184  	if lo == len(tx)-1 && l.extend != "" {
   185  		if ename, eoffset, estart, eend, eisDST, ok := tzset(l.extend, end, sec); ok {
   186  			return ename, eoffset, estart, eend, eisDST
   187  		}
   188  	}
   189  
   190  	return
   191  }
   192  
   193  // lookupFirstZone returns the index of the time zone to use for times
   194  // before the first transition time, or when there are no transition
   195  // times.
   196  //
   197  // The reference implementation in localtime.c from
   198  // https://www.iana.org/time-zones/repository/releases/tzcode2013g.tar.gz
   199  // implements the following algorithm for these cases:
   200  //  1. If the first zone is unused by the transitions, use it.
   201  //  2. Otherwise, if there are transition times, and the first
   202  //     transition is to a zone in daylight time, find the first
   203  //     non-daylight-time zone before and closest to the first transition
   204  //     zone.
   205  //  3. Otherwise, use the first zone that is not daylight time, if
   206  //     there is one.
   207  //  4. Otherwise, use the first zone.
   208  func (l *Location) lookupFirstZone() int {
   209  	// Case 1.
   210  	if !l.firstZoneUsed() {
   211  		return 0
   212  	}
   213  
   214  	// Case 2.
   215  	if len(l.tx) > 0 && l.zone[l.tx[0].index].isDST {
   216  		for zi := int(l.tx[0].index) - 1; zi >= 0; zi-- {
   217  			if !l.zone[zi].isDST {
   218  				return zi
   219  			}
   220  		}
   221  	}
   222  
   223  	// Case 3.
   224  	for zi := range l.zone {
   225  		if !l.zone[zi].isDST {
   226  			return zi
   227  		}
   228  	}
   229  
   230  	// Case 4.
   231  	return 0
   232  }
   233  
   234  // firstZoneUsed reports whether the first zone is used by some
   235  // transition.
   236  func (l *Location) firstZoneUsed() bool {
   237  	for _, tx := range l.tx {
   238  		if tx.index == 0 {
   239  			return true
   240  		}
   241  	}
   242  	return false
   243  }
   244  
   245  // tzset takes a timezone string like the one found in the TZ environment
   246  // variable, the end of the last time zone transition expressed as seconds
   247  // since January 1, 1970 00:00:00 UTC, and a time expressed the same way.
   248  // We call this a tzset string since in C the function tzset reads TZ.
   249  // The return values are as for lookup, plus ok which reports whether the
   250  // parse succeeded.
   251  func tzset(s string, initEnd, sec int64) (name string, offset int, start, end int64, isDST, ok bool) {
   252  	var (
   253  		stdName, dstName     string
   254  		stdOffset, dstOffset int
   255  	)
   256  
   257  	stdName, s, ok = tzsetName(s)
   258  	if ok {
   259  		stdOffset, s, ok = tzsetOffset(s)
   260  	}
   261  	if !ok {
   262  		return "", 0, 0, 0, false, false
   263  	}
   264  
   265  	// The numbers in the tzset string are added to local time to get UTC,
   266  	// but our offsets are added to UTC to get local time,
   267  	// so we negate the number we see here.
   268  	stdOffset = -stdOffset
   269  
   270  	if len(s) == 0 || s[0] == ',' {
   271  		// No daylight savings time.
   272  		return stdName, stdOffset, initEnd, omega, false, true
   273  	}
   274  
   275  	dstName, s, ok = tzsetName(s)
   276  	if ok {
   277  		if len(s) == 0 || s[0] == ',' {
   278  			dstOffset = stdOffset + secondsPerHour
   279  		} else {
   280  			dstOffset, s, ok = tzsetOffset(s)
   281  			dstOffset = -dstOffset // as with stdOffset, above
   282  		}
   283  	}
   284  	if !ok {
   285  		return "", 0, 0, 0, false, false
   286  	}
   287  
   288  	if len(s) == 0 {
   289  		// Default DST rules per tzcode.
   290  		s = ",M3.2.0,M11.1.0"
   291  	}
   292  	// The TZ definition does not mention ';' here but tzcode accepts it.
   293  	if s[0] != ',' && s[0] != ';' {
   294  		return "", 0, 0, 0, false, false
   295  	}
   296  	s = s[1:]
   297  
   298  	var startRule, endRule rule
   299  	startRule, s, ok = tzsetRule(s)
   300  	if !ok || len(s) == 0 || s[0] != ',' {
   301  		return "", 0, 0, 0, false, false
   302  	}
   303  	s = s[1:]
   304  	endRule, s, ok = tzsetRule(s)
   305  	if !ok || len(s) > 0 {
   306  		return "", 0, 0, 0, false, false
   307  	}
   308  
   309  	year, _, _, yday := absDate(uint64(sec+unixToInternal+internalToAbsolute), false)
   310  
   311  	ysec := int64(yday*secondsPerDay) + sec%secondsPerDay
   312  
   313  	// Compute start of year in seconds since Unix epoch.
   314  	d := daysSinceEpoch(year)
   315  	abs := int64(d * secondsPerDay)
   316  	abs += absoluteToInternal + internalToUnix
   317  
   318  	startSec := int64(tzruleTime(year, startRule, stdOffset))
   319  	endSec := int64(tzruleTime(year, endRule, dstOffset))
   320  	dstIsDST, stdIsDST := true, false
   321  	// Note: this is a flipping of "DST" and "STD" while retaining the labels
   322  	// This happens in southern hemispheres. The labelling here thus is a little
   323  	// inconsistent with the goal.
   324  	if endSec < startSec {
   325  		startSec, endSec = endSec, startSec
   326  		stdName, dstName = dstName, stdName
   327  		stdOffset, dstOffset = dstOffset, stdOffset
   328  		stdIsDST, dstIsDST = dstIsDST, stdIsDST
   329  	}
   330  
   331  	// The start and end values that we return are accurate
   332  	// close to a daylight savings transition, but are otherwise
   333  	// just the start and end of the year. That suffices for
   334  	// the only caller that cares, which is Date.
   335  	if ysec < startSec {
   336  		return stdName, stdOffset, abs, startSec + abs, stdIsDST, true
   337  	} else if ysec >= endSec {
   338  		return stdName, stdOffset, endSec + abs, abs + 365*secondsPerDay, stdIsDST, true
   339  	} else {
   340  		return dstName, dstOffset, startSec + abs, endSec + abs, dstIsDST, true
   341  	}
   342  }
   343  
   344  // tzsetName returns the timezone name at the start of the tzset string s,
   345  // and the remainder of s, and reports whether the parsing is OK.
   346  func tzsetName(s string) (string, string, bool) {
   347  	if len(s) == 0 {
   348  		return "", "", false
   349  	}
   350  	if s[0] != '<' {
   351  		for i, r := range s {
   352  			switch r {
   353  			case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ',', '-', '+':
   354  				if i < 3 {
   355  					return "", "", false
   356  				}
   357  				return s[:i], s[i:], true
   358  			}
   359  		}
   360  		if len(s) < 3 {
   361  			return "", "", false
   362  		}
   363  		return s, "", true
   364  	} else {
   365  		for i, r := range s {
   366  			if r == '>' {
   367  				return s[1:i], s[i+1:], true
   368  			}
   369  		}
   370  		return "", "", false
   371  	}
   372  }
   373  
   374  // tzsetOffset returns the timezone offset at the start of the tzset string s,
   375  // and the remainder of s, and reports whether the parsing is OK.
   376  // The timezone offset is returned as a number of seconds.
   377  func tzsetOffset(s string) (offset int, rest string, ok bool) {
   378  	if len(s) == 0 {
   379  		return 0, "", false
   380  	}
   381  	neg := false
   382  	if s[0] == '+' {
   383  		s = s[1:]
   384  	} else if s[0] == '-' {
   385  		s = s[1:]
   386  		neg = true
   387  	}
   388  
   389  	// The tzdata code permits values up to 24 * 7 here,
   390  	// although POSIX does not.
   391  	var hours int
   392  	hours, s, ok = tzsetNum(s, 0, 24*7)
   393  	if !ok {
   394  		return 0, "", false
   395  	}
   396  	off := hours * secondsPerHour
   397  	if len(s) == 0 || s[0] != ':' {
   398  		if neg {
   399  			off = -off
   400  		}
   401  		return off, s, true
   402  	}
   403  
   404  	var mins int
   405  	mins, s, ok = tzsetNum(s[1:], 0, 59)
   406  	if !ok {
   407  		return 0, "", false
   408  	}
   409  	off += mins * secondsPerMinute
   410  	if len(s) == 0 || s[0] != ':' {
   411  		if neg {
   412  			off = -off
   413  		}
   414  		return off, s, true
   415  	}
   416  
   417  	var secs int
   418  	secs, s, ok = tzsetNum(s[1:], 0, 59)
   419  	if !ok {
   420  		return 0, "", false
   421  	}
   422  	off += secs
   423  
   424  	if neg {
   425  		off = -off
   426  	}
   427  	return off, s, true
   428  }
   429  
   430  // ruleKind is the kinds of rules that can be seen in a tzset string.
   431  type ruleKind int
   432  
   433  const (
   434  	ruleJulian ruleKind = iota
   435  	ruleDOY
   436  	ruleMonthWeekDay
   437  )
   438  
   439  // rule is a rule read from a tzset string.
   440  type rule struct {
   441  	kind ruleKind
   442  	day  int
   443  	week int
   444  	mon  int
   445  	time int // transition time
   446  }
   447  
   448  // tzsetRule parses a rule from a tzset string.
   449  // It returns the rule, and the remainder of the string, and reports success.
   450  func tzsetRule(s string) (rule, string, bool) {
   451  	var r rule
   452  	if len(s) == 0 {
   453  		return rule{}, "", false
   454  	}
   455  	ok := false
   456  	if s[0] == 'J' {
   457  		var jday int
   458  		jday, s, ok = tzsetNum(s[1:], 1, 365)
   459  		if !ok {
   460  			return rule{}, "", false
   461  		}
   462  		r.kind = ruleJulian
   463  		r.day = jday
   464  	} else if s[0] == 'M' {
   465  		var mon int
   466  		mon, s, ok = tzsetNum(s[1:], 1, 12)
   467  		if !ok || len(s) == 0 || s[0] != '.' {
   468  			return rule{}, "", false
   469  
   470  		}
   471  		var week int
   472  		week, s, ok = tzsetNum(s[1:], 1, 5)
   473  		if !ok || len(s) == 0 || s[0] != '.' {
   474  			return rule{}, "", false
   475  		}
   476  		var day int
   477  		day, s, ok = tzsetNum(s[1:], 0, 6)
   478  		if !ok {
   479  			return rule{}, "", false
   480  		}
   481  		r.kind = ruleMonthWeekDay
   482  		r.day = day
   483  		r.week = week
   484  		r.mon = mon
   485  	} else {
   486  		var day int
   487  		day, s, ok = tzsetNum(s, 0, 365)
   488  		if !ok {
   489  			return rule{}, "", false
   490  		}
   491  		r.kind = ruleDOY
   492  		r.day = day
   493  	}
   494  
   495  	if len(s) == 0 || s[0] != '/' {
   496  		r.time = 2 * secondsPerHour // 2am is the default
   497  		return r, s, true
   498  	}
   499  
   500  	offset, s, ok := tzsetOffset(s[1:])
   501  	if !ok {
   502  		return rule{}, "", false
   503  	}
   504  	r.time = offset
   505  
   506  	return r, s, true
   507  }
   508  
   509  // tzsetNum parses a number from a tzset string.
   510  // It returns the number, and the remainder of the string, and reports success.
   511  // The number must be between min and max.
   512  func tzsetNum(s string, min, max int) (num int, rest string, ok bool) {
   513  	if len(s) == 0 {
   514  		return 0, "", false
   515  	}
   516  	num = 0
   517  	for i, r := range s {
   518  		if r < '0' || r > '9' {
   519  			if i == 0 || num < min {
   520  				return 0, "", false
   521  			}
   522  			return num, s[i:], true
   523  		}
   524  		num *= 10
   525  		num += int(r) - '0'
   526  		if num > max {
   527  			return 0, "", false
   528  		}
   529  	}
   530  	if num < min {
   531  		return 0, "", false
   532  	}
   533  	return num, "", true
   534  }
   535  
   536  // tzruleTime takes a year, a rule, and a timezone offset,
   537  // and returns the number of seconds since the start of the year
   538  // that the rule takes effect.
   539  func tzruleTime(year int, r rule, off int) int {
   540  	var s int
   541  	switch r.kind {
   542  	case ruleJulian:
   543  		s = (r.day - 1) * secondsPerDay
   544  		if isLeap(year) && r.day >= 60 {
   545  			s += secondsPerDay
   546  		}
   547  	case ruleDOY:
   548  		s = r.day * secondsPerDay
   549  	case ruleMonthWeekDay:
   550  		// Zeller's Congruence.
   551  		m1 := (r.mon+9)%12 + 1
   552  		yy0 := year
   553  		if r.mon <= 2 {
   554  			yy0--
   555  		}
   556  		yy1 := yy0 / 100
   557  		yy2 := yy0 % 100
   558  		dow := ((26*m1-2)/10 + 1 + yy2 + yy2/4 + yy1/4 - 2*yy1) % 7
   559  		if dow < 0 {
   560  			dow += 7
   561  		}
   562  		// Now dow is the day-of-week of the first day of r.mon.
   563  		// Get the day-of-month of the first "dow" day.
   564  		d := r.day - dow
   565  		if d < 0 {
   566  			d += 7
   567  		}
   568  		for i := 1; i < r.week; i++ {
   569  			if d+7 >= daysIn(Month(r.mon), year) {
   570  				break
   571  			}
   572  			d += 7
   573  		}
   574  		d += int(daysBefore[r.mon-1])
   575  		if isLeap(year) && r.mon > 2 {
   576  			d++
   577  		}
   578  		s = d * secondsPerDay
   579  	}
   580  
   581  	return s + r.time - off
   582  }
   583  
   584  // lookupName returns information about the time zone with
   585  // the given name (such as "EST") at the given pseudo-Unix time
   586  // (what the given time of day would be in UTC).
   587  func (l *Location) lookupName(name string, unix int64) (offset int, ok bool) {
   588  	l = l.get()
   589  
   590  	// First try for a zone with the right name that was actually
   591  	// in effect at the given time. (In Sydney, Australia, both standard
   592  	// and daylight-savings time are abbreviated "EST". Using the
   593  	// offset helps us pick the right one for the given time.
   594  	// It's not perfect: during the backward transition we might pick
   595  	// either one.)
   596  	for i := range l.zone {
   597  		zone := &l.zone[i]
   598  		if zone.name == name {
   599  			nam, offset, _, _, _ := l.lookup(unix - int64(zone.offset))
   600  			if nam == zone.name {
   601  				return offset, true
   602  			}
   603  		}
   604  	}
   605  
   606  	// Otherwise fall back to an ordinary name match.
   607  	for i := range l.zone {
   608  		zone := &l.zone[i]
   609  		if zone.name == name {
   610  			return zone.offset, true
   611  		}
   612  	}
   613  
   614  	// Otherwise, give up.
   615  	return
   616  }
   617  
   618  // NOTE(rsc): Eventually we will need to accept the POSIX TZ environment
   619  // syntax too, but I don't feel like implementing it today.
   620  
   621  var errLocation = errors.New("time: invalid location name")
   622  
   623  var zoneinfo *string
   624  var zoneinfoOnce sync.Once
   625  
   626  // LoadLocation returns the Location with the given name.
   627  //
   628  // If the name is "" or "UTC", LoadLocation returns UTC.
   629  // If the name is "Local", LoadLocation returns Local.
   630  //
   631  // Otherwise, the name is taken to be a location name corresponding to a file
   632  // in the IANA Time Zone database, such as "America/New_York".
   633  //
   634  // LoadLocation looks for the IANA Time Zone database in the following
   635  // locations in order:
   636  //
   637  // - the directory or uncompressed zip file named by the ZONEINFO environment variable
   638  // - on a Unix system, the system standard installation location
   639  // - $GOROOT/lib/time/zoneinfo.zip
   640  // - the time/tzdata package, if it was imported
   641  func LoadLocation(name string) (*Location, error) {
   642  	if name == "" || name == "UTC" {
   643  		return UTC, nil
   644  	}
   645  	if name == "Local" {
   646  		return Local, nil
   647  	}
   648  	if containsDotDot(name) || name[0] == '/' || name[0] == '\\' {
   649  		// No valid IANA Time Zone name contains a single dot,
   650  		// much less dot dot. Likewise, none begin with a slash.
   651  		return nil, errLocation
   652  	}
   653  	zoneinfoOnce.Do(func() {
   654  		env, _ := syscall.Getenv("ZONEINFO")
   655  		zoneinfo = &env
   656  	})
   657  	var firstErr error
   658  	if *zoneinfo != "" {
   659  		if zoneData, err := loadTzinfoFromDirOrZip(*zoneinfo, name); err == nil {
   660  			if z, err := LoadLocationFromTZData(name, zoneData); err == nil {
   661  				return z, nil
   662  			}
   663  			firstErr = err
   664  		} else if err != syscall.ENOENT {
   665  			firstErr = err
   666  		}
   667  	}
   668  	if z, err := loadLocation(name, platformZoneSources); err == nil {
   669  		return z, nil
   670  	} else if firstErr == nil {
   671  		firstErr = err
   672  	}
   673  	return nil, firstErr
   674  }
   675  
   676  // containsDotDot reports whether s contains "..".
   677  func containsDotDot(s string) bool {
   678  	if len(s) < 2 {
   679  		return false
   680  	}
   681  	for i := 0; i < len(s)-1; i++ {
   682  		if s[i] == '.' && s[i+1] == '.' {
   683  			return true
   684  		}
   685  	}
   686  	return false
   687  }
   688  

View as plain text