time: load time zones from the system tzdata file on Android

Android timezones are in a packed format, different from the separate
files of a regular Unix system. This CL contain the necessary code to
parse the packed tzdata file and extract time zones from it. It also
adds a basic test to ensure the new parser works.

Fixes #13581

Change-Id: Idebe73726c3d4c2de89dd6ae1d7d19f975207500
Reviewed-on: https://go-review.googlesource.com/24494Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/time/export_android_test.go

+// Copyright 2016 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
+
+func ForceAndroidTzdataForTest(tzdata bool) {
+	tzdataPaths = origTzdataPaths
+	if tzdata {
+		tzdataPaths = tzdataPaths[:1]
+	}
+}

src/time/zoneinfo_android.go

+// Copyright 2016 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 the "tzdata" packed timezone file used on Android.
+// The format is lifted from ZoneInfoDB.java and ZoneInfo.java in
+// java/libcore/util in the AOSP.
+
+package time
+
+import (
+	"errors"
+	"runtime"
+)
+
+var tzdataPaths = []string{
+	"/system/usr/share/zoneinfo/tzdata",
+	"/data/misc/zoneinfo/current/tzdata",
+	runtime.GOROOT() + "/lib/time/zoneinfo.zip",
+}
+
+var origTzdataPaths = tzdataPaths
+
+func forceZipFileForTesting(zipOnly bool) {
+	tzdataPaths = make([]string, len(origTzdataPaths))
+	copy(tzdataPaths, origTzdataPaths)
+	if zipOnly {
+		for i := 0; i < len(tzdataPaths)-1; i++ {
+			tzdataPaths[i] = "/XXXNOEXIST"
+		}
+	}
+}
+
+func initTestingZone() {
+	z, err := loadLocation("America/Los_Angeles")
+	if err != nil {
+		panic("cannot load America/Los_Angeles for testing: " + err.Error())
+	}
+	z.name = "Local"
+	localLoc = *z
+}
+
+func initLocal() {
+	// TODO(elias.naur): getprop persist.sys.timezone
+	localLoc = *UTC
+}
+
+func loadLocation(name string) (*Location, error) {
+	var firstErr error
+	for _, path := range tzdataPaths {
+		var z *Location
+		var err error
+		if len(path) > 4 && path[len(path)-4:] == ".zip" {
+			z, err = loadZoneZip(path, name)
+		} else {
+			z, err = loadTzdataFile(path, name)
+		}
+		if err == nil {
+			z.name = name
+			return z, nil
+		} else if firstErr == nil && !isNotExist(err) {
+			firstErr = err
+		}
+	}
+	if firstErr != nil {
+		return nil, firstErr
+	}
+	return nil, errors.New("unknown time zone " + name)
+}
+
+func loadTzdataFile(file, name string) (*Location, error) {
+	const (
+		headersize = 12 + 3*4
+		namesize   = 40
+		entrysize  = namesize + 3*4
+	)
+	if len(name) > namesize {
+		return nil, errors.New(name + " is longer than the maximum zone name length (40 bytes)")
+	}
+	fd, err := open(file)
+	if err != nil {
+		return nil, err
+	}
+	defer closefd(fd)
+
+	buf := make([]byte, headersize)
+	if err := preadn(fd, buf, 0); err != nil {
+		return nil, errors.New("corrupt tzdata file " + file)
+	}
+	d := data{buf, false}
+	if magic := d.read(6); string(magic) != "tzdata" {
+		return nil, errors.New("corrupt tzdata file " + file)
+	}
+	d = data{buf[12:], false}
+	indexOff, _ := d.big4()
+	dataOff, _ := d.big4()
+	indexSize := dataOff - indexOff
+	entrycount := indexSize / entrysize
+	buf = make([]byte, indexSize)
+	if err := preadn(fd, buf, int(indexOff)); err != nil {
+		return nil, errors.New("corrupt tzdata file " + file)
+	}
+	for i := 0; i < int(entrycount); i++ {
+		entry := buf[i*entrysize : (i+1)*entrysize]
+		// len(name) <= namesize is checked at function entry
+		if string(entry[:len(name)]) != name {
+			continue
+		}
+		d := data{entry[namesize:], false}
+		off, _ := d.big4()
+		size, _ := d.big4()
+		buf := make([]byte, size)
+		if err := preadn(fd, buf, int(off+dataOff)); err != nil {
+			return nil, errors.New("corrupt tzdata file " + file)
+		}
+		return loadZoneData(buf)
+	}
+	return nil, errors.New("cannot find " + name + " in tzdata file " + file)
+}

src/time/zoneinfo_android_test.go

+// Copyright 2016 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_test
+
+import (
+	"testing"
+	. "time"
+)
+
+func TestAndroidTzdata(t *testing.T) {
+	ForceAndroidTzdataForTest(true)
+	defer ForceAndroidTzdataForTest(false)
+	if _, err := LoadLocation("America/Los_Angeles"); err != nil {
+		t.Error(err)
+	}
+}

src/time/zoneinfo_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin,386 darwin,amd64 dragonfly freebsd linux nacl netbsd openbsd solaris
+// +build darwin,386 darwin,amd64 dragonfly freebsd linux,!android nacl netbsd openbsd solaris
 
 // Parse "zoneinfo" time zone file.
 // This is a fairly standard file format used on OS X, Linux, BSD, Sun, and others.