/usr/share/go-1.6/src/net/hosts.go is in golang-1.6-src 1.6.1-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 | // Copyright 2009 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 net
import (
"sync"
"time"
)
const cacheMaxAge = 5 * time.Second
func parseLiteralIP(addr string) string {
var ip IP
var zone string
ip = parseIPv4(addr)
if ip == nil {
ip, zone = parseIPv6(addr, true)
}
if ip == nil {
return ""
}
if zone == "" {
return ip.String()
}
return ip.String() + "%" + zone
}
// hosts contains known host entries.
var hosts struct {
sync.Mutex
// Key for the list of literal IP addresses must be a host
// name. It would be part of DNS labels, a FQDN or an absolute
// FQDN.
// For now the key is converted to lower case for convenience.
byName map[string][]string
// Key for the list of host names must be a literal IP address
// including IPv6 address with zone identifier.
// We don't support old-classful IP address notation.
byAddr map[string][]string
expire time.Time
path string
mtime time.Time
size int64
}
func readHosts() {
now := time.Now()
hp := testHookHostsPath
if now.Before(hosts.expire) && hosts.path == hp && len(hosts.byName) > 0 {
return
}
mtime, size, err := stat(hp)
if err == nil && hosts.path == hp && hosts.mtime.Equal(mtime) && hosts.size == size {
hosts.expire = now.Add(cacheMaxAge)
return
}
hs := make(map[string][]string)
is := make(map[string][]string)
var file *file
if file, _ = open(hp); file == nil {
return
}
for line, ok := file.readLine(); ok; line, ok = file.readLine() {
if i := byteIndex(line, '#'); i >= 0 {
// Discard comments.
line = line[0:i]
}
f := getFields(line)
if len(f) < 2 {
continue
}
addr := parseLiteralIP(f[0])
if addr == "" {
continue
}
for i := 1; i < len(f); i++ {
name := absDomainName([]byte(f[i]))
h := []byte(f[i])
lowerASCIIBytes(h)
key := absDomainName(h)
hs[key] = append(hs[key], addr)
is[addr] = append(is[addr], name)
}
}
// Update the data cache.
hosts.expire = now.Add(cacheMaxAge)
hosts.path = hp
hosts.byName = hs
hosts.byAddr = is
hosts.mtime = mtime
hosts.size = size
file.close()
}
// lookupStaticHost looks up the addresses for the given host from /etc/hosts.
func lookupStaticHost(host string) []string {
hosts.Lock()
defer hosts.Unlock()
readHosts()
if len(hosts.byName) != 0 {
// TODO(jbd,bradfitz): avoid this alloc if host is already all lowercase?
// or linear scan the byName map if it's small enough?
lowerHost := []byte(host)
lowerASCIIBytes(lowerHost)
if ips, ok := hosts.byName[absDomainName(lowerHost)]; ok {
return ips
}
}
return nil
}
// lookupStaticAddr looks up the hosts for the given address from /etc/hosts.
func lookupStaticAddr(addr string) []string {
hosts.Lock()
defer hosts.Unlock()
readHosts()
addr = parseLiteralIP(addr)
if addr == "" {
return nil
}
if len(hosts.byAddr) != 0 {
if hosts, ok := hosts.byAddr[addr]; ok {
return hosts
}
}
return nil
}
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