src/pkg/time/zoneinfo_unix.go

// 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.

// +build darwin freebsd linux netbsd openbsd

// 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 (
	"errors"
	"runtime"
	"syscall"
)

func initTestingZone() {
	z, err := loadZoneFile(runtime.GOROOT()+"/lib/time/zoneinfo.zip", "America/Los_Angeles")
	if err != nil {
		panic("cannot load America/Los_Angeles for testing: " + err.Error())
	}
	z.name = "Local"
	localLoc = *z
}

// Many systems use /usr/share/zoneinfo, Solaris 2 has
// /usr/share/lib/zoneinfo, IRIX 6 has /usr/lib/locale/TZ.
var zoneDirs = []string{
	"/usr/share/zoneinfo/",
	"/usr/share/lib/zoneinfo/",
	"/usr/lib/locale/TZ/",
	runtime.GOROOT() + "/lib/time/zoneinfo/",
}

func initLocal() {
	// 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, ok := syscall.Getenv("TZ")
	switch {
	case !ok:
		z, err := loadZoneFile("", "/etc/localtime")
		if err == nil {
			localLoc = *z
			localLoc.name = "Local"
			return
		}
	case tz != "" && tz != "UTC":
		if z, err := loadLocation(tz); err == nil {
			localLoc = *z
			return
		}
	}

	// Fall back to UTC.
	localLoc.name = "UTC"
}

func loadLocation(name string) (*Location, error) {
	for _, zoneDir := range zoneDirs {
		if z, err := loadZoneFile(zoneDir, name); err == nil {
			z.name = name
			return z, nil
		}
	}
	return nil, errors.New("unknown time zone " + name)
}