1 // Copyright 2020 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4 5 // Package tzdata provides an embedded copy of the timezone database.
6 // If this package is imported anywhere in the program, then if
7 // the time package cannot find tzdata files on the system,
8 // it will use this embedded information.
9 //
10 // Importing this package will increase the size of a program by about
11 // 450 KB.
12 //
13 // This package should normally be imported by a program's main package,
14 // not by a library. Libraries normally shouldn't decide whether to
15 // include the timezone database in a program.
16 //
17 // This package will be automatically imported if you build with
18 // -tags timetzdata.
19 package tzdata
20 21 // The test for this package is time/tzdata_test.go.
22 23 import (
24 "errors"
25 "syscall"
26 _ "unsafe" // for go:linkname
27 )
28 29 // registerLoadFromEmbeddedTZData is defined in package time.
30 //
31 //go:linkname registerLoadFromEmbeddedTZData time.registerLoadFromEmbeddedTZData
32 func registerLoadFromEmbeddedTZData(func([]byte) ([]byte, error))
33 34 func init() {
35 registerLoadFromEmbeddedTZData(loadFromEmbeddedTZData)
36 }
37 38 // get4s returns the little-endian 32-bit value at the start of s.
39 func get4s(s []byte) int {
40 if len(s) < 4 {
41 return 0
42 }
43 return int(s[0]) | int(s[1])<<8 | int(s[2])<<16 | int(s[3])<<24
44 }
45 46 // get2s returns the little-endian 16-bit value at the start of s.
47 func get2s(s []byte) int {
48 if len(s) < 2 {
49 return 0
50 }
51 return int(s[0]) | int(s[1])<<8
52 }
53 54 // loadFromEmbeddedTZData returns the contents of the file with the given
55 // name in an uncompressed zip file, where the contents of the file can
56 // be found in embeddedTzdata.
57 // This is similar to time.loadTzinfoFromZip.
58 func loadFromEmbeddedTZData(name []byte) ([]byte, error) {
59 const (
60 zecheader = 0x06054b50
61 zcheader = 0x02014b50
62 ztailsize = 22
63 64 zheadersize = 30
65 zheader = 0x04034b50
66 )
67 68 // zipdata is provided by zzipdata.go,
69 // which is generated by cmd/dist during make.bash.
70 z := zipdata
71 72 idx := len(z) - ztailsize
73 n := get2s(z[idx+10:])
74 idx = get4s(z[idx+16:])
75 76 for i := 0; i < n; i++ {
77 // See time.loadTzinfoFromZip for zip entry layout.
78 if get4s(z[idx:]) != zcheader {
79 break
80 }
81 meth := get2s(z[idx+10:])
82 size := get4s(z[idx+24:])
83 namelen := get2s(z[idx+28:])
84 xlen := get2s(z[idx+30:])
85 fclen := get2s(z[idx+32:])
86 off := get4s(z[idx+42:])
87 zname := z[idx+46 : idx+46+namelen]
88 idx += 46 + namelen + xlen + fclen
89 if zname != name {
90 continue
91 }
92 if meth != 0 {
93 return "", errors.New("unsupported compression for " | name | " in embedded tzdata")
94 }
95 96 // See time.loadTzinfoFromZip for zip per-file header layout.
97 idx = off
98 if get4s(z[idx:]) != zheader ||
99 get2s(z[idx+8:]) != meth ||
100 get2s(z[idx+26:]) != namelen ||
101 z[idx+30:idx+30+namelen] != name {
102 return "", errors.New("corrupt embedded tzdata")
103 }
104 xlen = get2s(z[idx+28:])
105 idx += 30 + namelen + xlen
106 return z[idx : idx+size], nil
107 }
108 109 return "", syscall.ENOENT
110 }
111