1// Copyright 2011 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//go:build unix || js || wasip1
6
7package net
8
9import (
10	"context"
11	"internal/bytealg"
12	"sync"
13)
14
15var onceReadProtocols sync.Once
16
17// readProtocols loads contents of /etc/protocols into protocols map
18// for quick access.
19func readProtocols() {
20	file, err := open("/etc/protocols")
21	if err != nil {
22		return
23	}
24	defer file.close()
25
26	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
27		// tcp    6   TCP    # transmission control protocol
28		if i := bytealg.IndexByteString(line, '#'); i >= 0 {
29			line = line[0:i]
30		}
31		f := getFields(line)
32		if len(f) < 2 {
33			continue
34		}
35		if proto, _, ok := dtoi(f[1]); ok {
36			if _, ok := protocols[f[0]]; !ok {
37				protocols[f[0]] = proto
38			}
39			for _, alias := range f[2:] {
40				if _, ok := protocols[alias]; !ok {
41					protocols[alias] = proto
42				}
43			}
44		}
45	}
46}
47
48// lookupProtocol looks up IP protocol name in /etc/protocols and
49// returns correspondent protocol number.
50func lookupProtocol(_ context.Context, name string) (int, error) {
51	onceReadProtocols.Do(readProtocols)
52	return lookupProtocolMap(name)
53}
54
55func (r *Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
56	order, conf := systemConf().hostLookupOrder(r, host)
57	if order == hostLookupCgo {
58		return cgoLookupHost(ctx, host)
59	}
60	return r.goLookupHostOrder(ctx, host, order, conf)
61}
62
63func (r *Resolver) lookupIP(ctx context.Context, network, host string) (addrs []IPAddr, err error) {
64	order, conf := systemConf().hostLookupOrder(r, host)
65	if order == hostLookupCgo {
66		return cgoLookupIP(ctx, network, host)
67	}
68	ips, _, err := r.goLookupIPCNAMEOrder(ctx, network, host, order, conf)
69	return ips, err
70}
71
72func (r *Resolver) lookupPort(ctx context.Context, network, service string) (int, error) {
73	// Port lookup is not a DNS operation.
74	// Prefer the cgo resolver if possible.
75	if !systemConf().mustUseGoResolver(r) {
76		port, err := cgoLookupPort(ctx, network, service)
77		if err != nil {
78			// Issue 18213: if cgo fails, first check to see whether we
79			// have the answer baked-in to the net package.
80			if port, err := goLookupPort(network, service); err == nil {
81				return port, nil
82			}
83		}
84		return port, err
85	}
86	return goLookupPort(network, service)
87}
88
89func (r *Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
90	order, conf := systemConf().hostLookupOrder(r, name)
91	if order == hostLookupCgo {
92		if cname, err, ok := cgoLookupCNAME(ctx, name); ok {
93			return cname, err
94		}
95	}
96	return r.goLookupCNAME(ctx, name, order, conf)
97}
98
99func (r *Resolver) lookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
100	return r.goLookupSRV(ctx, service, proto, name)
101}
102
103func (r *Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
104	return r.goLookupMX(ctx, name)
105}
106
107func (r *Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) {
108	return r.goLookupNS(ctx, name)
109}
110
111func (r *Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
112	return r.goLookupTXT(ctx, name)
113}
114
115func (r *Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error) {
116	order, conf := systemConf().addrLookupOrder(r, addr)
117	if order == hostLookupCgo {
118		return cgoLookupPTR(ctx, addr)
119	}
120	return r.goLookupPTR(ctx, addr, order, conf)
121}
122