From 2951f909eae0afc4bea4067c98fef1a4f760006c Mon Sep 17 00:00:00 2001
From: Florian Uekermann <florian@uekermann.me>
Date: Fri, 6 Oct 2017 17:16:43 +0200
Subject: [PATCH] time: enable Location loading from user provided timezone
 data

The return values of the LoadLocation are inherently dependent
on the runtime environment. Add LoadLocationFromTZData, whose
results depend only on the timezone data provided as arguments.

Fixes #20629

Change-Id: I43b181f4c05c219be3ec57327540263b7cb3b2aa
Reviewed-on: https://go-review.googlesource.com/68890
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
---
 src/time/export_test.go   |  1 +
 src/time/internal_test.go |  6 +++---
 src/time/zoneinfo.go      |  2 +-
 src/time/zoneinfo_read.go | 13 +++++++------
 src/time/zoneinfo_test.go | 25 +++++++++++++++++++++++++
 5 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/src/time/export_test.go b/src/time/export_test.go
index 4c08ab13af..ae24ceb99a 100644
--- a/src/time/export_test.go
+++ b/src/time/export_test.go
@@ -34,4 +34,5 @@ var (
 	GetMono                = (*Time).mono
 	ErrLocation            = errLocation
 	ReadFile               = readFile
+	LoadTzinfo             = loadTzinfo
 )
diff --git a/src/time/internal_test.go b/src/time/internal_test.go
index 07ebe5e03d..76d5524124 100644
--- a/src/time/internal_test.go
+++ b/src/time/internal_test.go
@@ -18,11 +18,11 @@ func initTestingZone() {
 	localLoc = *z
 }
 
-var origZoneSources = zoneSources
+var OrigZoneSources = zoneSources
 
 func forceZipFileForTesting(zipOnly bool) {
-	zoneSources = make([]string, len(origZoneSources))
-	copy(zoneSources, origZoneSources)
+	zoneSources = make([]string, len(OrigZoneSources))
+	copy(zoneSources, OrigZoneSources)
 	if zipOnly {
 		zoneSources = zoneSources[len(zoneSources)-1:]
 	}
diff --git a/src/time/zoneinfo.go b/src/time/zoneinfo.go
index 4424b44106..96ff8d3970 100644
--- a/src/time/zoneinfo.go
+++ b/src/time/zoneinfo.go
@@ -294,7 +294,7 @@ func LoadLocation(name string) (*Location, error) {
 	})
 	if *zoneinfo != "" {
 		if zoneData, err := loadTzinfoFromDirOrZip(*zoneinfo, name); err == nil {
-			if z, err := newLocationFromTzinfo(name, zoneData); err == nil {
+			if z, err := LoadLocationFromTZData(name, zoneData); err == nil {
 				return z, nil
 			}
 		}
diff --git a/src/time/zoneinfo_read.go b/src/time/zoneinfo_read.go
index 6fdcc1a2a8..839b37aac4 100644
--- a/src/time/zoneinfo_read.go
+++ b/src/time/zoneinfo_read.go
@@ -79,11 +79,12 @@ func byteString(p []byte) string {
 
 var badData = errors.New("malformed time zone information")
 
-// newLocationFromTzinfo returns the Location described by Tzinfo with the given name.
-// The expected format for Tzinfo is that of a timezone file as they are found in the
-// the IANA Time Zone database.
-func newLocationFromTzinfo(name string, Tzinfo []byte) (*Location, error) {
-	d := dataIO{Tzinfo, false}
+// LoadLocationFromTZData returns a Location with the given name
+// initialized from the IANA Time Zone database-formatted data.
+// The data should be in the format of a standard IANA time zone file
+// (for example, the content of /etc/localtime on Unix systems).
+func LoadLocationFromTZData(name string, data []byte) (*Location, error) {
+	d := dataIO{data, false}
 
 	// 4-byte magic "TZif"
 	if magic := d.read(4); string(magic) != "TZif" {
@@ -390,7 +391,7 @@ func loadLocation(name string, sources []string) (z *Location, firstErr error) {
 	for _, source := range sources {
 		var zoneData, err = loadTzinfo(name, source)
 		if err == nil {
-			if z, err = newLocationFromTzinfo(name, zoneData); err == nil {
+			if z, err = LoadLocationFromTZData(name, zoneData); err == nil {
 				return z, nil
 			}
 		}
diff --git a/src/time/zoneinfo_test.go b/src/time/zoneinfo_test.go
index 452262f2ca..b9455db025 100644
--- a/src/time/zoneinfo_test.go
+++ b/src/time/zoneinfo_test.go
@@ -7,6 +7,7 @@ package time_test
 import (
 	"fmt"
 	"os"
+	"reflect"
 	"testing"
 	"time"
 )
@@ -116,3 +117,27 @@ func TestLocationNames(t *testing.T) {
 		t.Errorf(`invalid UTC location name: got %q want "UTC"`, time.UTC)
 	}
 }
+
+func TestLoadLocationFromTzinfo(t *testing.T) {
+	time.ForceZipFileForTesting(true)
+	defer time.ForceZipFileForTesting(false)
+
+	const locationName = "Asia/Jerusalem"
+	reference, err := time.LoadLocation(locationName)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tzinfo, err := time.LoadTzinfo(locationName, time.OrigZoneSources[len(time.OrigZoneSources)-1])
+	if err != nil {
+		t.Fatal(err)
+	}
+	sample, err := time.LoadLocationFromTZData(locationName, tzinfo)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !reflect.DeepEqual(reference, sample) {
+		t.Errorf("return values of LoadLocationFromTZData and LoadLocation don't match")
+	}
+}
-- 
2.50.0