// 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 name argument to LoadLocation or FixedZone.
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, start, end int64) {
l = l.get()
if len(l.zone) == 0 {
name = "UTC"
offset = 0
start = alpha
end = omega
return
}
if zone := l.cacheZone; zone != nil && l.cacheStart <= sec && sec < l.cacheEnd {
name = zone.name
offset = zone.offset
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
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
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
// https://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 reports 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, 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, _, _ := l.lookup(unix - int64(zone.offset))
if nam == zone.name {
return offset, 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, 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
})
var firstErr error
if *zoneinfo != "" {
if zoneData, err := loadTzinfoFromDirOrZip(*zoneinfo, name); err == nil {
if z, err := LoadLocationFromTZData(name, zoneData); err == nil {
return z, nil
}
firstErr = err
} else if err != syscall.ENOENT {
firstErr = err
}
}
if z, err := loadLocation(name, zoneSources); err == nil {
return z, nil
} else if firstErr == nil {
firstErr = err
}
return nil, firstErr
}
// 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
}