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// 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.
// Read static host/IP entries from /etc/hosts.
package net
import (
"sync"
"time"
)
const cacheMaxAge = 5 * time.Minute
// hostsPath points to the file with static IP/address entries.
var hostsPath = "/etc/hosts"
// Simple cache.
var hosts struct {
sync.Mutex
byName map[string][]string
byAddr map[string][]string
expire time.Time
path string
}
func readHosts() {
now := time.Now()
hp := hostsPath
if len(hosts.byName) == 0 || now.After(hosts.expire) || hosts.path != hp {
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 || ParseIP(f[0]) == nil {
continue
}
for i := 1; i < len(f); i++ {
h := f[i]
hs[h] = append(hs[h], f[0])
is[f[0]] = append(is[f[0]], h)
}
}
// Update the data cache.
hosts.expire = now.Add(cacheMaxAge)
hosts.path = hp
hosts.byName = hs
hosts.byAddr = is
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 {
if ips, ok := hosts.byName[host]; 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()
if len(hosts.byAddr) != 0 {
if hosts, ok := hosts.byAddr[addr]; ok {
return hosts
}
}
return nil
}
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