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// Copyright 2020 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 tzdata provides an embedded copy of the timezone database.
// If this package is imported anywhere in the program, then if
// the time package cannot find tzdata files on the system,
// it will use this embedded information.
//
// Importing this package will increase the size of a program by about
// 450 KB.
//
// This package should normally be imported by a program's main package,
// not by a library. Libraries normally shouldn't decide whether to
// include the timezone database in a program.
//
// This package will be automatically imported if you build with
// -tags timetzdata.
package tzdata
// The test for this package is time/tzdata_test.go.
import (
"errors"
"syscall"
_ "unsafe" // for go:linkname
)
// registerLoadFromEmbeddedTZData is defined in package time.
//
//go:linkname registerLoadFromEmbeddedTZData time.registerLoadFromEmbeddedTZData
func registerLoadFromEmbeddedTZData(func(string) (string, error))
func init() {
registerLoadFromEmbeddedTZData(loadFromEmbeddedTZData)
}
// get4s returns the little-endian 32-bit value at the start of s.
func get4s(s string) int {
if len(s) < 4 {
return 0
}
return int(s[0]) | int(s[1])<<8 | int(s[2])<<16 | int(s[3])<<24
}
// get2s returns the little-endian 16-bit value at the start of s.
func get2s(s string) int {
if len(s) < 2 {
return 0
}
return int(s[0]) | int(s[1])<<8
}
// loadFromEmbeddedTZData returns the contents of the file with the given
// name in an uncompressed zip file, where the contents of the file can
// be found in embeddedTzdata.
// This is similar to time.loadTzinfoFromZip.
func loadFromEmbeddedTZData(name string) (string, error) {
const (
zecheader = 0x06054b50
zcheader = 0x02014b50
ztailsize = 22
zheadersize = 30
zheader = 0x04034b50
)
// zipdata is provided by zzipdata.go,
// which is generated by cmd/dist during make.bash.
z := zipdata
idx := len(z) - ztailsize
n := get2s(z[idx+10:])
idx = get4s(z[idx+16:])
for i := 0; i < n; i++ {
// See time.loadTzinfoFromZip for zip entry layout.
if get4s(z[idx:]) != zcheader {
break
}
meth := get2s(z[idx+10:])
size := get4s(z[idx+24:])
namelen := get2s(z[idx+28:])
xlen := get2s(z[idx+30:])
fclen := get2s(z[idx+32:])
off := get4s(z[idx+42:])
zname := z[idx+46 : idx+46+namelen]
idx += 46 + namelen + xlen + fclen
if zname != name {
continue
}
if meth != 0 {
return "", errors.New("unsupported compression for " + name + " in embedded tzdata")
}
// See time.loadTzinfoFromZip for zip per-file header layout.
idx = off
if get4s(z[idx:]) != zheader ||
get2s(z[idx+8:]) != meth ||
get2s(z[idx+26:]) != namelen ||
z[idx+30:idx+30+namelen] != name {
return "", errors.New("corrupt embedded tzdata")
}
xlen = get2s(z[idx+28:])
idx += 30 + namelen + xlen
return z[idx : idx+size], nil
}
return "", syscall.ENOENT
}
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