1// Copyright 2009 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
5package net
6
7import (
8	"internal/bytealg"
9	"sync"
10	"time"
11)
12
13const cacheMaxAge = 5 * time.Second
14
15func parseLiteralIP(addr string) string {
16	var ip IP
17	var zone string
18	ip = parseIPv4(addr)
19	if ip == nil {
20		ip, zone = parseIPv6Zone(addr)
21	}
22	if ip == nil {
23		return ""
24	}
25	if zone == "" {
26		return ip.String()
27	}
28	return ip.String() + "%" + zone
29}
30
31// hosts contains known host entries.
32var hosts struct {
33	sync.Mutex
34
35	// Key for the list of literal IP addresses must be a host
36	// name. It would be part of DNS labels, a FQDN or an absolute
37	// FQDN.
38	// For now the key is converted to lower case for convenience.
39	byName map[string][]string
40
41	// Key for the list of host names must be a literal IP address
42	// including IPv6 address with zone identifier.
43	// We don't support old-classful IP address notation.
44	byAddr map[string][]string
45
46	expire time.Time
47	path   string
48	mtime  time.Time
49	size   int64
50}
51
52func readHosts() {
53	now := time.Now()
54	hp := testHookHostsPath
55
56	if now.Before(hosts.expire) && hosts.path == hp && len(hosts.byName) > 0 {
57		return
58	}
59	mtime, size, err := stat(hp)
60	if err == nil && hosts.path == hp && hosts.mtime.Equal(mtime) && hosts.size == size {
61		hosts.expire = now.Add(cacheMaxAge)
62		return
63	}
64
65	hs := make(map[string][]string)
66	is := make(map[string][]string)
67	var file *file
68	if file, _ = open(hp); file == nil {
69		return
70	}
71	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
72		if i := bytealg.IndexByteString(line, '#'); i >= 0 {
73			// Discard comments.
74			line = line[0:i]
75		}
76		f := getFields(line)
77		if len(f) < 2 {
78			continue
79		}
80		addr := parseLiteralIP(f[0])
81		if addr == "" {
82			continue
83		}
84		for i := 1; i < len(f); i++ {
85			name := absDomainName([]byte(f[i]))
86			h := []byte(f[i])
87			lowerASCIIBytes(h)
88			key := absDomainName(h)
89			hs[key] = append(hs[key], addr)
90			is[addr] = append(is[addr], name)
91		}
92	}
93	// Update the data cache.
94	hosts.expire = now.Add(cacheMaxAge)
95	hosts.path = hp
96	hosts.byName = hs
97	hosts.byAddr = is
98	hosts.mtime = mtime
99	hosts.size = size
100	file.close()
101}
102
103// lookupStaticHost looks up the addresses for the given host from /etc/hosts.
104func lookupStaticHost(host string) []string {
105	hosts.Lock()
106	defer hosts.Unlock()
107	readHosts()
108	if len(hosts.byName) != 0 {
109		// TODO(jbd,bradfitz): avoid this alloc if host is already all lowercase?
110		// or linear scan the byName map if it's small enough?
111		lowerHost := []byte(host)
112		lowerASCIIBytes(lowerHost)
113		if ips, ok := hosts.byName[absDomainName(lowerHost)]; ok {
114			ipsCp := make([]string, len(ips))
115			copy(ipsCp, ips)
116			return ipsCp
117		}
118	}
119	return nil
120}
121
122// lookupStaticAddr looks up the hosts for the given address from /etc/hosts.
123func lookupStaticAddr(addr string) []string {
124	hosts.Lock()
125	defer hosts.Unlock()
126	readHosts()
127	addr = parseLiteralIP(addr)
128	if addr == "" {
129		return nil
130	}
131	if len(hosts.byAddr) != 0 {
132		if hosts, ok := hosts.byAddr[addr]; ok {
133			hostsCp := make([]string, len(hosts))
134			copy(hostsCp, hosts)
135			return hostsCp
136		}
137	}
138	return nil
139}
140