time: implement timezones for windows

Fixes issue 761.

R=PeterGo, adg, rsc
CC=golang-dev
http://codereview.appspot.com/1121042

Committer: Russ Cox <rsc@golang.org>

4 files changed, 472 insertions, 9 deletions

diff --git a/src/pkg/time/Makefile b/src/pkg/time/Makefile
index 1dbdb22d5..6732d6a79 100644
--- a/src/pkg/time/Makefile
+++ b/src/pkg/time/Makefile
@@ -10,6 +10,22 @@ GOFILES=\
 	sleep.go\
 	tick.go\
 	time.go\
-	zoneinfo.go\
+
+GOFILES_freebsd=\
+	zoneinfo_unix.go\
+
+GOFILES_darwin=\
+	zoneinfo_unix.go\
+
+GOFILES_linux=\
+	zoneinfo_unix.go\
+
+GOFILES_nacl=\
+	zoneinfo_unix.go\
+
+GOFILES_windows=\
+	zoneinfo_windows.go\
+
+GOFILES+=$(GOFILES_$(GOOS))
 
 include ../../Make.pkg
diff --git a/src/pkg/time/format.go b/src/pkg/time/format.go
index 226826aca..c04325126 100644
--- a/src/pkg/time/format.go
+++ b/src/pkg/time/format.go
@@ -2,7 +2,6 @@ package time
 
 import (
 	"bytes"
-	"once"
 	"os"
 	"strconv"
 )
@@ -581,13 +580,9 @@ func Parse(alayout, avalue string) (*Time, os.Error) {
 			}
 			// It's a valid format.
 			t.Zone = p
-			// Can we find it in the table?
-			once.Do(setupZone)
-			for _, z := range zones {
-				if p == z.zone.name {
-					t.ZoneOffset = z.zone.utcoff
-					break
-				}
+			// Can we find its offset?
+			if offset, found := lookupByName(p); found {
+				t.ZoneOffset = offset
 			}
 		}
 		if rangeErrString != "" {
diff --git a/src/pkg/time/zoneinfo_unix.go b/src/pkg/time/zoneinfo_unix.go
new file mode 100644
index 000000000..5a8c94aaf
--- /dev/null
+++ b/src/pkg/time/zoneinfo_unix.go
@@ -0,0 +1,261 @@
+// Copyright 2009 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.
+
+// Parse "zoneinfo" time zone file.
+// This is a fairly standard file format used on OS X, Linux, BSD, Sun, and others.
+// See tzfile(5), http://en.wikipedia.org/wiki/Zoneinfo,
+// and ftp://munnari.oz.au/pub/oldtz/
+
+package time
+
+import (
+	"io/ioutil"
+	"once"
+	"os"
+)
+
+const (
+	headerSize = 4 + 16 + 4*7
+	zoneDir    = "/usr/share/zoneinfo/"
+)
+
+// Simple I/O interface to binary blob of data.
+type data struct {
+	p     []byte
+	error bool
+}
+
+
+func (d *data) read(n int) []byte {
+	if len(d.p) < n {
+		d.p = nil
+		d.error = true
+		return nil
+	}
+	p := d.p[0:n]
+	d.p = d.p[n:]
+	return p
+}
+
+func (d *data) big4() (n uint32, ok bool) {
+	p := d.read(4)
+	if len(p) < 4 {
+		d.error = true
+		return 0, false
+	}
+	return uint32(p[0])<<24 | uint32(p[1])<<16 | uint32(p[2])<<8 | uint32(p[3]), true
+}
+
+func (d *data) byte() (n byte, ok bool) {
+	p := d.read(1)
+	if len(p) < 1 {
+		d.error = true
+		return 0, false
+	}
+	return p[0], true
+}
+
+
+// Make a string by stopping at the first NUL
+func byteString(p []byte) string {
+	for i := 0; i < len(p); i++ {
+		if p[i] == 0 {
+			return string(p[0:i])
+		}
+	}
+	return string(p)
+}
+
+// Parsed representation
+type zone struct {
+	utcoff int
+	isdst  bool
+	name   string
+}
+
+type zonetime struct {
+	time         int32 // transition time, in seconds since 1970 GMT
+	zone         *zone // the zone that goes into effect at that time
+	isstd, isutc bool  // ignored - no idea what these mean
+}
+
+func parseinfo(bytes []byte) (zt []zonetime, ok bool) {
+	d := data{bytes, false}
+
+	// 4-byte magic "TZif"
+	if magic := d.read(4); string(magic) != "TZif" {
+		return nil, false
+	}
+
+	// 1-byte version, then 15 bytes of padding
+	var p []byte
+	if p = d.read(16); len(p) != 16 || p[0] != 0 && p[0] != '2' {
+		return nil, false
+	}
+
+	// six big-endian 32-bit integers:
+	//	number of UTC/local indicators
+	//	number of standard/wall indicators
+	//	number of leap seconds
+	//	number of transition times
+	//	number of local time zones
+	//	number of characters of time zone abbrev strings
+	const (
+		NUTCLocal = iota
+		NStdWall
+		NLeap
+		NTime
+		NZone
+		NChar
+	)
+	var n [6]int
+	for i := 0; i < 6; i++ {
+		nn, ok := d.big4()
+		if !ok {
+			return nil, false
+		}
+		n[i] = int(nn)
+	}
+
+	// Transition times.
+	txtimes := data{d.read(n[NTime] * 4), false}
+
+	// Time zone indices for transition times.
+	txzones := d.read(n[NTime])
+
+	// Zone info structures
+	zonedata := data{d.read(n[NZone] * 6), false}
+
+	// Time zone abbreviations.
+	abbrev := d.read(n[NChar])
+
+	// Leap-second time pairs
+	d.read(n[NLeap] * 8)
+
+	// Whether tx times associated with local time types
+	// are specified as standard time or wall time.
+	isstd := d.read(n[NStdWall])
+
+	// Whether tx times associated with local time types
+	// are specified as UTC or local time.
+	isutc := d.read(n[NUTCLocal])
+
+	if d.error { // ran out of data
+		return nil, false
+	}
+
+	// If version == 2, the entire file repeats, this time using
+	// 8-byte ints for txtimes and leap seconds.
+	// We won't need those until 2106.
+
+	// Now we can build up a useful data structure.
+	// First the zone information.
+	//	utcoff[4] isdst[1] nameindex[1]
+	z := make([]zone, n[NZone])
+	for i := 0; i < len(z); i++ {
+		var ok bool
+		var n uint32
+		if n, ok = zonedata.big4(); !ok {
+			return nil, false
+		}
+		z[i].utcoff = int(n)
+		var b byte
+		if b, ok = zonedata.byte(); !ok {
+			return nil, false
+		}
+		z[i].isdst = b != 0
+		if b, ok = zonedata.byte(); !ok || int(b) >= len(abbrev) {
+			return nil, false
+		}
+		z[i].name = byteString(abbrev[b:])
+	}
+
+	// Now the transition time info.
+	zt = make([]zonetime, n[NTime])
+	for i := 0; i < len(zt); i++ {
+		var ok bool
+		var n uint32
+		if n, ok = txtimes.big4(); !ok {
+			return nil, false
+		}
+		zt[i].time = int32(n)
+		if int(txzones[i]) >= len(z) {
+			return nil, false
+		}
+		zt[i].zone = &z[txzones[i]]
+		if i < len(isstd) {
+			zt[i].isstd = isstd[i] != 0
+		}
+		if i < len(isutc) {
+			zt[i].isutc = isutc[i] != 0
+		}
+	}
+	return zt, true
+}
+
+func readinfofile(name string) ([]zonetime, bool) {
+	buf, err := ioutil.ReadFile(name)
+	if err != nil {
+		return nil, false
+	}
+	return parseinfo(buf)
+}
+
+var zones []zonetime
+
+func setupZone() {
+	// consult $TZ to find the time zone to use.
+	// no $TZ means use the system default /etc/localtime.
+	// $TZ="" means use UTC.
+	// $TZ="foo" means use /usr/share/zoneinfo/foo.
+
+	tz, err := os.Getenverror("TZ")
+	switch {
+	case err == os.ENOENV:
+		zones, _ = readinfofile("/etc/localtime")
+	case len(tz) > 0:
+		zones, _ = readinfofile(zoneDir + tz)
+	case len(tz) == 0:
+		// do nothing: use UTC
+	}
+}
+
+// Look up the correct time zone (daylight savings or not) for the given unix time, in the current location.
+func lookupTimezone(sec int64) (zone string, offset int) {
+	once.Do(setupZone)
+	if len(zones) == 0 {
+		return "UTC", 0
+	}
+
+	// Binary search for entry with largest time <= sec
+	tz := zones
+	for len(tz) > 1 {
+		m := len(tz) / 2
+		if sec < int64(tz[m].time) {
+			tz = tz[0:m]
+		} else {
+			tz = tz[m:]
+		}
+	}
+	z := tz[0].zone
+	return z.name, z.utcoff
+}
+
+// lookupByName returns the time offset for the
+// time zone with the given abbreviation. It only considers
+// time zones that apply to the current system.
+// For example, for a system configured as being in New York,
+// it only recognizes "EST" and "EDT".
+// For a system in San Francisco, "PST" and "PDT".
+// For a system in Sydney, "EST" and "EDT", though they have
+// different meanings than they do in New York.
+func lookupByName(name string) (off int, found bool) {
+	once.Do(setupZone)
+	for _, z := range zones {
+		if name == z.zone.name {
+			return z.zone.utcoff, true
+		}
+	}
+	return 0, false
+}
diff --git a/src/pkg/time/zoneinfo_windows.go b/src/pkg/time/zoneinfo_windows.go
new file mode 100644
index 000000000..d249165c1
--- /dev/null
+++ b/src/pkg/time/zoneinfo_windows.go
@@ -0,0 +1,191 @@
+// Copyright 2009 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 (
+	"syscall"
+	"os"
+	"once"
+)
+
+// BUG(brainman): The Windows implementation assumes that
+// this year's rules for daylight savings time apply to all previous
+// and future years as well.
+
+// TODO(brainman): use GetDynamicTimeZoneInformation, whenever posible (Vista and up),
+// to improve on situation described in the bug above.
+
+type zone struct {
+	name                  string
+	offset                int
+	year                  int64
+	month, day, dayofweek int
+	hour, minute, second  int
+	abssec                int64
+	prev                  *zone
+}
+
+// Populate zone struct with Windows supplied information. Returns true, if data is valid.
+func (z *zone) populate(bias, biasdelta int32, d *syscall.Systemtime, name []uint16) (dateisgood bool) {
+	z.name = syscall.UTF16ToString(name)
+	z.offset = int(bias)
+	z.year = int64(d.Year)
+	z.month = int(d.Month)
+	z.day = int(d.Day)
+	z.dayofweek = int(d.DayOfWeek)
+	z.hour = int(d.Hour)
+	z.minute = int(d.Minute)
+	z.second = int(d.Second)
+	dateisgood = d.Month != 0
+	if dateisgood {
+		z.offset += int(biasdelta)
+	}
+	z.offset = -z.offset * 60
+	return
+}
+
+// Pre-calculte cutoff time in seconds since the Unix epoch, if data is supplied in "absolute" format.
+func (z *zone) preCalculateAbsSec() {
+	if z.year != 0 {
+		z.abssec = (&Time{z.year, int(z.month), int(z.day), int(z.hour), int(z.minute), int(z.second), 0, 0, ""}).Seconds()
+		// Time given is in "local" time. Adjust it for "utc".
+		z.abssec -= int64(z.prev.offset)
+	}
+}
+
+// Convert zone cutoff time to sec in number of seconds since the Unix epoch, given particualar year.
+func (z *zone) cutoffSeconds(year int64) int64 {
+	// Windows specifies daylight savings information in "day in month" format:
+	// z.month is month number (1-12)
+	// z.dayofweek is appropriate weekday (Sunday=0 to Saturday=6)
+	// z.day is week within the month (1 to 5, where 5 is last week of the month)
+	// z.hour, z.minute and z.second are absolute time
+	t := &Time{year, int(z.month), 1, int(z.hour), int(z.minute), int(z.second), 0, 0, ""}
+	t = SecondsToUTC(t.Seconds())
+	i := int(z.dayofweek) - t.Weekday
+	if i < 0 {
+		i += 7
+	}
+	t.Day += i
+	if week := int(z.day) - 1; week < 4 {
+		t.Day += week * 7
+	} else {
+		// "Last" instance of the day.
+		t.Day += 4 * 7
+		if t.Day > months(year)[t.Month] {
+			t.Day -= 7
+		}
+	}
+	// Result is in "local" time. Adjust it for "utc".
+	return t.Seconds() - int64(z.prev.offset)
+}
+
+// Is t before the cutoff for switching to z?
+func (z *zone) isBeforeCutoff(t *Time) bool {
+	var coff int64
+	if z.year == 0 {
+		// "day in month" format used
+		coff = z.cutoffSeconds(t.Year)
+	} else {
+		// "absolute" format used
+		coff = z.abssec
+	}
+	return t.Seconds() < coff
+}
+
+type zoneinfo struct {
+	disabled         bool // daylight saving time is not used localy
+	offsetIfDisabled int
+	januaryIsStd     bool // is january 1 standard time?
+	std, dst         zone
+}
+
+// Pick zone (std or dst) t time belongs to.
+func (zi *zoneinfo) pickZone(t *Time) *zone {
+	z := &zi.std
+	if tz.januaryIsStd {
+		if !zi.dst.isBeforeCutoff(t) && zi.std.isBeforeCutoff(t) {
+			// after switch to daylight time and before the switch back to standard
+			z = &zi.dst
+		}
+	} else {
+		if zi.std.isBeforeCutoff(t) || !zi.dst.isBeforeCutoff(t) {
+			// before switch to standard time or after the switch back to daylight
+			z = &zi.dst
+		}
+	}
+	return z
+}
+
+var tz zoneinfo
+var initError os.Error
+
+func setupZone() {
+	var i syscall.Timezoneinformation
+	if _, e := syscall.GetTimeZoneInformation(&i); e != 0 {
+		initError = os.NewSyscallError("GetTimeZoneInformation", e)
+		return
+	}
+	if !tz.std.populate(i.Bias, i.StandardBias, &i.StandardDate, i.StandardName[0:]) {
+		tz.disabled = true
+		tz.offsetIfDisabled = tz.std.offset
+		return
+	}
+	tz.std.prev = &tz.dst
+	tz.dst.populate(i.Bias, i.DaylightBias, &i.DaylightDate, i.DaylightName[0:])
+	tz.dst.prev = &tz.std
+	tz.std.preCalculateAbsSec()
+	tz.dst.preCalculateAbsSec()
+	// Is january 1 standard time this year?
+	t := UTC()
+	tz.januaryIsStd = tz.dst.cutoffSeconds(t.Year) < tz.std.cutoffSeconds(t.Year)
+}
+
+// Look up the correct time zone (daylight savings or not) for the given unix time, in the current location.
+func lookupTimezone(sec int64) (zone string, offset int) {
+	once.Do(setupZone)
+	if initError != nil {
+		return "", 0
+	}
+	if tz.disabled {
+		return "", tz.offsetIfDisabled
+	}
+	t := SecondsToUTC(sec)
+	z := &tz.std
+	if tz.std.year == 0 {
+		// "day in month" format used
+		z = tz.pickZone(t)
+	} else {
+		// "absolute" format used
+		if tz.std.year == t.Year {
+			// we have rule for the year in question
+			z = tz.pickZone(t)
+		} else {
+			// we do not have any information for that year,
+			// will assume standard offset all year around
+		}
+	}
+	return z.name, z.offset
+}
+
+// lookupByName returns the time offset for the
+// time zone with the given abbreviation. It only considers
+// time zones that apply to the current system.
+func lookupByName(name string) (off int, found bool) {
+	once.Do(setupZone)
+	if initError != nil {
+		return 0, false
+	}
+	if tz.disabled {
+		return tz.offsetIfDisabled, false
+	}
+	switch name {
+	case tz.std.name:
+		return tz.std.offset, true
+	case tz.dst.name:
+		return tz.dst.offset, true
+	}
+	return 0, false
+}