src/time/zoneinfo.go - go - Git at Google

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package time

 import (
 	"errors"
 	"sync"
 	"syscall"
 )

 //go:generate env ZONEINFO=$GOROOT/lib/time/zoneinfo.zip go run genzabbrs.go -output zoneinfo_abbrs_windows.go

 // A Location maps time instants to the zone in use at that time.
 // Typically, the Location represents the collection of time offsets
 // in use in a geographical area, such as CEST and CET for central Europe.
 type Location struct {
 	name string
 	zone []zone
 	tx   []zoneTrans

 	// Most lookups will be for the current time.
 	// To avoid the binary search through tx, keep a
 	// static one-element cache that gives the correct
 	// zone for the time when the Location was created.
 	// if cacheStart <= t < cacheEnd,
 	// lookup can return cacheZone.
 	// The units for cacheStart and cacheEnd are seconds
 	// since January 1, 1970 UTC, to match the argument
 	// to lookup.
 	cacheStart int64
 	cacheEnd   int64
 	cacheZone  *zone
 }

 // A zone represents a single time zone such as CEST or CET.
 type zone struct {
 	name   string // abbreviated name, "CET"
 	offset int    // seconds east of UTC
 	isDST  bool   // is this zone Daylight Savings Time?
 }

 // A zoneTrans represents a single time zone transition.
 type zoneTrans struct {
 	when         int64 // transition time, in seconds since 1970 GMT
 	index        uint8 // the index of the zone that goes into effect at that time
 	isstd, isutc bool  // ignored - no idea what these mean
 }

 // alpha and omega are the beginning and end of time for zone
 // transitions.
 const (
 	alpha = -1 << 63  // math.MinInt64
 	omega = 1<<63 - 1 // math.MaxInt64
 )

 // UTC represents Universal Coordinated Time (UTC).
 var UTC *Location = &utcLoc

 // utcLoc is separate so that get can refer to &utcLoc
 // and ensure that it never returns a nil *Location,
 // even if a badly behaved client has changed UTC.
 var utcLoc = Location{name: "UTC"}

 // Local represents the system's local time zone.
 var Local *Location = &localLoc

 // localLoc is separate so that initLocal can initialize
 // it even if a client has changed Local.
 var localLoc Location
 var localOnce sync.Once

 func (l *Location) get() *Location {
 	if l == nil {
 		return &utcLoc
 	}
 	if l == &localLoc {
 		localOnce.Do(initLocal)
 	}
 	return l
 }

 // String returns a descriptive name for the time zone information,
 // corresponding to the argument to LoadLocation.
 func (l *Location) String() string {
 	return l.get().name
 }

 // FixedZone returns a Location that always uses
 // the given zone name and offset (seconds east of UTC).
 func FixedZone(name string, offset int) *Location {
 	l := &Location{
 		name:       name,
 		zone:       []zone{{name, offset, false}},
 		tx:         []zoneTrans{{alpha, 0, false, false}},
 		cacheStart: alpha,
 		cacheEnd:   omega,
 	}
 	l.cacheZone = &l.zone[0]
 	return l
 }

 // lookup returns information about the time zone in use at an
 // instant in time expressed as seconds since January 1, 1970 00:00:00 UTC.
 //
 // The returned information gives the name of the zone (such as "CET"),
 // the start and end times bracketing sec when that zone is in effect,
 // the offset in seconds east of UTC (such as -5*60*60), and whether
 // the daylight savings is being observed at that time.
 func (l *Location) lookup(sec int64) (name string, offset int, isDST bool, start, end int64) {
 	l = l.get()

 	if len(l.zone) == 0 {
 		name = "UTC"
 		offset = 0
 		isDST = false
 		start = alpha
 		end = omega
 		return
 	}

 	if zone := l.cacheZone; zone != nil && l.cacheStart <= sec && sec < l.cacheEnd {
 		name = zone.name
 		offset = zone.offset
 		isDST = zone.isDST
 		start = l.cacheStart
 		end = l.cacheEnd
 		return
 	}

 	if len(l.tx) == 0 || sec < l.tx[0].when {
 		zone := &l.zone[l.lookupFirstZone()]
 		name = zone.name
 		offset = zone.offset
 		isDST = zone.isDST
 		start = alpha
 		if len(l.tx) > 0 {
 			end = l.tx[0].when
 		} else {
 			end = omega
 		}
 		return
 	}

 	// Binary search for entry with largest time <= sec.
 	// Not using sort.Search to avoid dependencies.
 	tx := l.tx
 	end = omega
 	lo := 0
 	hi := len(tx)
 	for hi-lo > 1 {
 		m := lo + (hi-lo)/2
 		lim := tx[m].when
 		if sec < lim {
 			end = lim
 			hi = m
 		} else {
 			lo = m
 		}
 	}
 	zone := &l.zone[tx[lo].index]
 	name = zone.name
 	offset = zone.offset
 	isDST = zone.isDST
 	start = tx[lo].when
 	// end = maintained during the search
 	return
 }

 // lookupFirstZone returns the index of the time zone to use for times
 // before the first transition time, or when there are no transition
 // times.
 //
 // The reference implementation in localtime.c from
 // http://www.iana.org/time-zones/repository/releases/tzcode2013g.tar.gz
 // implements the following algorithm for these cases:
 // 1) If the first zone is unused by the transitions, use it.
 // 2) Otherwise, if there are transition times, and the first
 //    transition is to a zone in daylight time, find the first
 //    non-daylight-time zone before and closest to the first transition
 //    zone.
 // 3) Otherwise, use the first zone that is not daylight time, if
 //    there is one.
 // 4) Otherwise, use the first zone.
 func (l *Location) lookupFirstZone() int {
 	// Case 1.
 	if !l.firstZoneUsed() {
 		return 0
 	}

 	// Case 2.
 	if len(l.tx) > 0 && l.zone[l.tx[0].index].isDST {
 		for zi := int(l.tx[0].index) - 1; zi >= 0; zi-- {
 			if !l.zone[zi].isDST {
 				return zi
 			}
 		}
 	}

 	// Case 3.
 	for zi := range l.zone {
 		if !l.zone[zi].isDST {
 			return zi
 		}
 	}

 	// Case 4.
 	return 0
 }

 // firstZoneUsed returns whether the first zone is used by some
 // transition.
 func (l *Location) firstZoneUsed() bool {
 	for _, tx := range l.tx {
 		if tx.index == 0 {
 			return true
 		}
 	}
 	return false
 }

 // lookupName returns information about the time zone with
 // the given name (such as "EST") at the given pseudo-Unix time
 // (what the given time of day would be in UTC).
 func (l *Location) lookupName(name string, unix int64) (offset int, isDST bool, ok bool) {
 	l = l.get()

 	// First try for a zone with the right name that was actually
 	// in effect at the given time. (In Sydney, Australia, both standard
 	// and daylight-savings time are abbreviated "EST". Using the
 	// offset helps us pick the right one for the given time.
 	// It's not perfect: during the backward transition we might pick
 	// either one.)
 	for i := range l.zone {
 		zone := &l.zone[i]
 		if zone.name == name {
 			nam, offset, isDST, _, _ := l.lookup(unix - int64(zone.offset))
 			if nam == zone.name {
 				return offset, isDST, true
 			}
 		}
 	}

 	// Otherwise fall back to an ordinary name match.
 	for i := range l.zone {
 		zone := &l.zone[i]
 		if zone.name == name {
 			return zone.offset, zone.isDST, true
 		}
 	}

 	// Otherwise, give up.
 	return
 }

 // NOTE(rsc): Eventually we will need to accept the POSIX TZ environment
 // syntax too, but I don't feel like implementing it today.

 var errLocation = errors.New("time: invalid location name")

 var zoneinfo *string
 var zoneinfoOnce sync.Once

 // LoadLocation returns the Location with the given name.
 //
 // If the name is "" or "UTC", LoadLocation returns UTC.
 // If the name is "Local", LoadLocation returns Local.
 //
 // Otherwise, the name is taken to be a location name corresponding to a file
 // in the IANA Time Zone database, such as "America/New_York".
 //
 // The time zone database needed by LoadLocation may not be
 // present on all systems, especially non-Unix systems.
 // LoadLocation looks in the directory or uncompressed zip file
 // named by the ZONEINFO environment variable, if any, then looks in
 // known installation locations on Unix systems,
 // and finally looks in $GOROOT/lib/time/zoneinfo.zip.
 func LoadLocation(name string) (*Location, error) {
 	if name == "" || name == "UTC" {
 		return UTC, nil
 	}
 	if name == "Local" {
 		return Local, nil
 	}
 	if containsDotDot(name) || name[0] == '/' || name[0] == '\\' {
 		// No valid IANA Time Zone name contains a single dot,
 		// much less dot dot. Likewise, none begin with a slash.
 		return nil, errLocation
 	}
 	zoneinfoOnce.Do(func() {
 		env, _ := syscall.Getenv("ZONEINFO")
 		zoneinfo = &env
 	})
 	if zoneinfo != nil && *zoneinfo != "" {
 		if z, err := loadZoneFile(*zoneinfo, name); err == nil {
 			z.name = name
 			return z, nil
 		}
 	}
 	return loadLocation(name)
 }

 // containsDotDot reports whether s contains "..".
 func containsDotDot(s string) bool {
 	if len(s) < 2 {
 		return false
 	}
 	for i := 0; i < len(s)-1; i++ {
 		if s[i] == '.' && s[i+1] == '.' {
 			return true
 		}
 	}
 	return false
 }
	// Copyright 2011 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package time

	import (
	"errors"
	"sync"
	"syscall"
	)

	//go:generate env ZONEINFO=$GOROOT/lib/time/zoneinfo.zip go run genzabbrs.go -output zoneinfo_abbrs_windows.go

	// A Location maps time instants to the zone in use at that time.
	// Typically, the Location represents the collection of time offsets
	// in use in a geographical area, such as CEST and CET for central Europe.
	type Location struct {
	name string
	zone []zone
	tx []zoneTrans

	// Most lookups will be for the current time.
	// To avoid the binary search through tx, keep a
	// static one-element cache that gives the correct
	// zone for the time when the Location was created.
	// if cacheStart <= t < cacheEnd,
	// lookup can return cacheZone.
	// The units for cacheStart and cacheEnd are seconds
	// since January 1, 1970 UTC, to match the argument
	// to lookup.
	cacheStart int64
	cacheEnd int64
	cacheZone *zone
	}

	// A zone represents a single time zone such as CEST or CET.
	type zone struct {
	name string // abbreviated name, "CET"
	offset int // seconds east of UTC
	isDST bool // is this zone Daylight Savings Time?
	}

	// A zoneTrans represents a single time zone transition.
	type zoneTrans struct {
	when int64 // transition time, in seconds since 1970 GMT
	index uint8 // the index of the zone that goes into effect at that time
	isstd, isutc bool // ignored - no idea what these mean
	}

	// alpha and omega are the beginning and end of time for zone
	// transitions.
	const (
	alpha = -1 << 63 // math.MinInt64
	omega = 1<<63 - 1 // math.MaxInt64
	)

	// UTC represents Universal Coordinated Time (UTC).
	var UTC *Location = &utcLoc

	// utcLoc is separate so that get can refer to &utcLoc
	// and ensure that it never returns a nil *Location,
	// even if a badly behaved client has changed UTC.
	var utcLoc = Location{name: "UTC"}

	// Local represents the system's local time zone.
	var Local *Location = &localLoc

	// localLoc is separate so that initLocal can initialize
	// it even if a client has changed Local.
	var localLoc Location
	var localOnce sync.Once

	func (l Location) get() Location {
	if l == nil {
	return &utcLoc
	}
	if l == &localLoc {
	localOnce.Do(initLocal)
	}
	return l
	}

	// String returns a descriptive name for the time zone information,
	// corresponding to the argument to LoadLocation.
	func (l *Location) String() string {
	return l.get().name
	}

	// FixedZone returns a Location that always uses
	// the given zone name and offset (seconds east of UTC).
	func FixedZone(name string, offset int) *Location {
	l := &Location{
	name: name,
	zone: []zone{{name, offset, false}},
	tx: []zoneTrans{{alpha, 0, false, false}},
	cacheStart: alpha,
	cacheEnd: omega,
	}
	l.cacheZone = &l.zone[0]
	return l
	}

	// lookup returns information about the time zone in use at an
	// instant in time expressed as seconds since January 1, 1970 00:00:00 UTC.
	//
	// The returned information gives the name of the zone (such as "CET"),
	// the start and end times bracketing sec when that zone is in effect,
	// the offset in seconds east of UTC (such as -56060), and whether
	// the daylight savings is being observed at that time.
	func (l *Location) lookup(sec int64) (name string, offset int, isDST bool, start, end int64) {
	l = l.get()

	if len(l.zone) == 0 {
	name = "UTC"
	offset = 0
	isDST = false
	start = alpha
	end = omega
	return
	}

	if zone := l.cacheZone; zone != nil && l.cacheStart <= sec && sec < l.cacheEnd {
	name = zone.name
	offset = zone.offset
	isDST = zone.isDST
	start = l.cacheStart
	end = l.cacheEnd
	return
	}

	if len(l.tx) == 0 \|\| sec < l.tx[0].when {
	zone := &l.zone[l.lookupFirstZone()]
	name = zone.name
	offset = zone.offset
	isDST = zone.isDST
	start = alpha
	if len(l.tx) > 0 {
	end = l.tx[0].when
	} else {
	end = omega
	}
	return
	}

	// Binary search for entry with largest time <= sec.
	// Not using sort.Search to avoid dependencies.
	tx := l.tx
	end = omega
	lo := 0
	hi := len(tx)
	for hi-lo > 1 {
	m := lo + (hi-lo)/2
	lim := tx[m].when
	if sec < lim {
	end = lim
	hi = m
	} else {
	lo = m
	}
	}
	zone := &l.zone[tx[lo].index]
	name = zone.name
	offset = zone.offset
	isDST = zone.isDST
	start = tx[lo].when
	// end = maintained during the search
	return
	}

	// lookupFirstZone returns the index of the time zone to use for times
	// before the first transition time, or when there are no transition
	// times.
	//
	// The reference implementation in localtime.c from
	// http://www.iana.org/time-zones/repository/releases/tzcode2013g.tar.gz
	// implements the following algorithm for these cases:
	// 1) If the first zone is unused by the transitions, use it.
	// 2) Otherwise, if there are transition times, and the first
	// transition is to a zone in daylight time, find the first
	// non-daylight-time zone before and closest to the first transition
	// zone.
	// 3) Otherwise, use the first zone that is not daylight time, if
	// there is one.
	// 4) Otherwise, use the first zone.
	func (l *Location) lookupFirstZone() int {
	// Case 1.
	if !l.firstZoneUsed() {
	return 0
	}

	// Case 2.
	if len(l.tx) > 0 && l.zone[l.tx[0].index].isDST {
	for zi := int(l.tx[0].index) - 1; zi >= 0; zi-- {
	if !l.zone[zi].isDST {
	return zi
	}
	}
	}

	// Case 3.
	for zi := range l.zone {
	if !l.zone[zi].isDST {
	return zi
	}
	}

	// Case 4.
	return 0
	}

	// firstZoneUsed returns whether the first zone is used by some
	// transition.
	func (l *Location) firstZoneUsed() bool {
	for _, tx := range l.tx {
	if tx.index == 0 {
	return true
	}
	}
	return false
	}

	// lookupName returns information about the time zone with
	// the given name (such as "EST") at the given pseudo-Unix time
	// (what the given time of day would be in UTC).
	func (l *Location) lookupName(name string, unix int64) (offset int, isDST bool, ok bool) {
	l = l.get()

	// First try for a zone with the right name that was actually
	// in effect at the given time. (In Sydney, Australia, both standard
	// and daylight-savings time are abbreviated "EST". Using the
	// offset helps us pick the right one for the given time.
	// It's not perfect: during the backward transition we might pick
	// either one.)
	for i := range l.zone {
	zone := &l.zone[i]
	if zone.name == name {
	nam, offset, isDST, _, _ := l.lookup(unix - int64(zone.offset))
	if nam == zone.name {
	return offset, isDST, true
	}
	}
	}

	// Otherwise fall back to an ordinary name match.
	for i := range l.zone {
	zone := &l.zone[i]
	if zone.name == name {
	return zone.offset, zone.isDST, true
	}
	}

	// Otherwise, give up.
	return
	}

	// NOTE(rsc): Eventually we will need to accept the POSIX TZ environment
	// syntax too, but I don't feel like implementing it today.

	var errLocation = errors.New("time: invalid location name")

	var zoneinfo *string
	var zoneinfoOnce sync.Once

	// LoadLocation returns the Location with the given name.
	//
	// If the name is "" or "UTC", LoadLocation returns UTC.
	// If the name is "Local", LoadLocation returns Local.
	//
	// Otherwise, the name is taken to be a location name corresponding to a file
	// in the IANA Time Zone database, such as "America/New_York".
	//
	// The time zone database needed by LoadLocation may not be
	// present on all systems, especially non-Unix systems.
	// LoadLocation looks in the directory or uncompressed zip file
	// named by the ZONEINFO environment variable, if any, then looks in
	// known installation locations on Unix systems,
	// and finally looks in $GOROOT/lib/time/zoneinfo.zip.
	func LoadLocation(name string) (*Location, error) {
	if name == "" \|\| name == "UTC" {
	return UTC, nil
	}
	if name == "Local" {
	return Local, nil
	}
	if containsDotDot(name) \|\| name[0] == '/' \|\| name[0] == '\\' {
	// No valid IANA Time Zone name contains a single dot,
	// much less dot dot. Likewise, none begin with a slash.
	return nil, errLocation
	}
	zoneinfoOnce.Do(func() {
	env, _ := syscall.Getenv("ZONEINFO")
	zoneinfo = &env
	})
	if zoneinfo != nil && *zoneinfo != "" {
	if z, err := loadZoneFile(*zoneinfo, name); err == nil {
	z.name = name
	return z, nil
	}
	}
	return loadLocation(name)
	}

	// containsDotDot reports whether s contains "..".
	func containsDotDot(s string) bool {
	if len(s) < 2 {
	return false
	}
	for i := 0; i < len(s)-1; i++ {
	if s[i] == '.' && s[i+1] == '.' {
	return true
	}
	}
	return false
	}