time: read 64-bit data if available

Also store 64-bit data in lib/time/zoneinfo.zip.

The comments argue that we don't need the 64-bit data until 2037 or
2106, but that turns out not to be the case. We also need them for
dates before December 13, 1901, which is time.Unix(-0x80000000, 0).

Fixes #30099

Change-Id: Ib8c9efb29b7b3c08531ae69912c588209d6320e9
Reviewed-on: https://go-review.googlesource.com/c/161202
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

4 files changed, 105 insertions, 25 deletions

diff --git a/lib/time/update.bash b/lib/time/update.bash
index 8d6785b9af..5dc74f9f0b 100755
--- a/lib/time/update.bash
+++ b/lib/time/update.bash
@@ -21,21 +21,8 @@ curl -L -O https://www.iana.org/time-zones/repository/releases/tzdata$DATA.tar.g
 tar xzf tzcode$CODE.tar.gz
 tar xzf tzdata$DATA.tar.gz
 
-# Turn off 64-bit output in time zone files.
-# We don't need those until 2037.
-perl -p -i -e 's/pass <= 2/pass <= 1/' zic.c
-
 make CFLAGS=-DSTD_INSPIRED AWK=awk TZDIR=zoneinfo posix_only
 
-# America/Los_Angeles should not be bigger than 1100 bytes.
-# If it is, we probably failed to disable the 64-bit output, which
-# triples the size of the files.
-size=$(ls -l zoneinfo/America/Los_Angeles | awk '{print $5}')
-if [ $size -gt 1200 ]; then
-	echo 'zone file too large; 64-bit edit failed?' >&2
-	exit 2
-fi
-
 cd zoneinfo
 rm -f ../../zoneinfo.zip
 zip -0 -r ../../zoneinfo.zip *
diff --git a/lib/time/zoneinfo.zip b/lib/time/zoneinfo.zip
index bacb724322..a79e5d98fd 100644
--- a/lib/time/zoneinfo.zip
+++ b/lib/time/zoneinfo.zip
diff --git a/src/time/zoneinfo_read.go b/src/time/zoneinfo_read.go
index d8d4070d5b..d54632fb49 100644
--- a/src/time/zoneinfo_read.go
+++ b/src/time/zoneinfo_read.go
@@ -59,6 +59,16 @@ func (d *dataIO) big4() (n uint32, ok bool) {
 	return uint32(p[3]) | uint32(p[2])<<8 | uint32(p[1])<<16 | uint32(p[0])<<24, true
 }
 
+func (d *dataIO) big8() (n uint64, ok bool) {
+	n1, ok1 := d.big4()
+	n2, ok2 := d.big4()
+	if !ok1 || !ok2 {
+		d.error = true
+		return 0, false
+	}
+	return (uint64(n1) << 32) | uint64(n2), true
+}
+
 func (d *dataIO) byte() (n byte, ok bool) {
 	p := d.read(1)
 	if len(p) < 1 {
@@ -93,9 +103,21 @@ func LoadLocationFromTZData(name string, data []byte) (*Location, error) {
 	}
 
 	// 1-byte version, then 15 bytes of padding
+	var version int
 	var p []byte
-	if p = d.read(16); len(p) != 16 || p[0] != 0 && p[0] != '2' && p[0] != '3' {
+	if p = d.read(16); len(p) != 16 {
 		return nil, badData
+	} else {
+		switch p[0] {
+		case 0:
+			version = 1
+		case '2':
+			version = 2
+		case '3':
+			version = 3
+		default:
+			return nil, badData
+		}
 	}
 
 	// six big-endian 32-bit integers:
@@ -119,11 +141,53 @@ func LoadLocationFromTZData(name string, data []byte) (*Location, error) {
 		if !ok {
 			return nil, badData
 		}
+		if uint32(int(nn)) != nn {
+			return nil, badData
+		}
 		n[i] = int(nn)
 	}
 
+	// If we have version 2 or 3, then the data is first written out
+	// in a 32-bit format, then written out again in a 64-bit format.
+	// Skip the 32-bit format and read the 64-bit one, as it can
+	// describe a broader range of dates.
+
+	is64 := false
+	if version > 1 {
+		// Skip the 32-bit data.
+		skip := n[NTime]*4 +
+			n[NTime] +
+			n[NZone]*6 +
+			n[NChar] +
+			n[NLeap]*8 +
+			n[NStdWall] +
+			n[NUTCLocal]
+		// Skip the version 2 header that we just read.
+		skip += 4 + 16
+		d.read(skip)
+
+		is64 = true
+
+		// Read the counts again, they can differ.
+		for i := 0; i < 6; i++ {
+			nn, ok := d.big4()
+			if !ok {
+				return nil, badData
+			}
+			if uint32(int(nn)) != nn {
+				return nil, badData
+			}
+			n[i] = int(nn)
+		}
+	}
+
+	size := 4
+	if is64 {
+		size = 8
+	}
+
 	// Transition times.
-	txtimes := dataIO{d.read(n[NTime] * 4), false}
+	txtimes := dataIO{d.read(n[NTime] * size), false}
 
 	// Time zone indices for transition times.
 	txzones := d.read(n[NTime])
@@ -135,7 +199,7 @@ func LoadLocationFromTZData(name string, data []byte) (*Location, error) {
 	abbrev := d.read(n[NChar])
 
 	// Leap-second time pairs
-	d.read(n[NLeap] * 8)
+	d.read(n[NLeap] * (size + 4))
 
 	// Whether tx times associated with local time types
 	// are specified as standard time or wall time.
@@ -149,10 +213,6 @@ func LoadLocationFromTZData(name string, data []byte) (*Location, error) {
 		return nil, badData
 	}
 
-	// If version == 2 or 3, 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]
@@ -163,6 +223,9 @@ func LoadLocationFromTZData(name string, data []byte) (*Location, error) {
 		if n, ok = zonedata.big4(); !ok {
 			return nil, badData
 		}
+		if uint32(int(n)) != n {
+			return nil, badData
+		}
 		zone[i].offset = int(int32(n))
 		var b byte
 		if b, ok = zonedata.byte(); !ok {
@@ -186,12 +249,21 @@ func LoadLocationFromTZData(name string, data []byte) (*Location, error) {
 	// Now the transition time info.
 	tx := make([]zoneTrans, n[NTime])
 	for i := range tx {
-		var ok bool
-		var n uint32
-		if n, ok = txtimes.big4(); !ok {
-			return nil, badData
+		var n int64
+		if !is64 {
+			if n4, ok := txtimes.big4(); !ok {
+				return nil, badData
+			} else {
+				n = int64(int32(n4))
+			}
+		} else {
+			if n8, ok := txtimes.big8(); !ok {
+				return nil, badData
+			} else {
+				n = int64(n8)
+			}
 		}
-		tx[i].when = int64(int32(n))
+		tx[i].when = n
 		if int(txzones[i]) >= len(zone) {
 			return nil, badData
 		}
diff --git a/src/time/zoneinfo_test.go b/src/time/zoneinfo_test.go
index 4458ba8e26..cd0731768e 100644
--- a/src/time/zoneinfo_test.go
+++ b/src/time/zoneinfo_test.go
@@ -152,3 +152,24 @@ func TestLoadLocationFromTZData(t *testing.T) {
 		t.Errorf("return values of LoadLocationFromTZData and LoadLocation don't match")
 	}
 }
+
+// Issue 30099.
+func TestEarlyLocation(t *testing.T) {
+	time.ForceZipFileForTesting(true)
+	defer time.ForceZipFileForTesting(false)
+
+	const locName = "America/New_York"
+	loc, err := time.LoadLocation(locName)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	d := time.Date(1900, time.January, 1, 0, 0, 0, 0, loc)
+	tzName, tzOffset := d.Zone()
+	if want := "EST"; tzName != want {
+		t.Errorf("Zone name == %s, want %s", tzName, want)
+	}
+	if want := -18000; tzOffset != want {
+		t.Errorf("Zone offset == %d, want %d", tzOffset, want)
+	}
+}