forked from golang/go
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathdial.go
More file actions
741 lines (688 loc) · 22.6 KB
/
dial.go
File metadata and controls
741 lines (688 loc) · 22.6 KB
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
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
// Copyright 2010 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 (
"context"
"internal/nettrace"
"syscall"
"time"
)
// defaultTCPKeepAlive is a default constant value for TCPKeepAlive times
// See golang.org/issue/31510
const (
defaultTCPKeepAlive = 15 * time.Second
)
// A Dialer contains options for connecting to an address.
//
// The zero value for each field is equivalent to dialing
// without that option. Dialing with the zero value of Dialer
// is therefore equivalent to just calling the Dial function.
//
// It is safe to call Dialer's methods concurrently.
type Dialer struct {
// Timeout is the maximum amount of time a dial will wait for
// a connect to complete. If Deadline is also set, it may fail
// earlier.
//
// The default is no timeout.
//
// When using TCP and dialing a host name with multiple IP
// addresses, the timeout may be divided between them.
//
// With or without a timeout, the operating system may impose
// its own earlier timeout. For instance, TCP timeouts are
// often around 3 minutes.
Timeout time.Duration
// Deadline is the absolute point in time after which dials
// will fail. If Timeout is set, it may fail earlier.
// Zero means no deadline, or dependent on the operating system
// as with the Timeout option.
Deadline time.Time
// LocalAddr is the local address to use when dialing an
// address. The address must be of a compatible type for the
// network being dialed.
// If nil, a local address is automatically chosen.
LocalAddr Addr
// DualStack previously enabled RFC 6555 Fast Fallback
// support, also known as "Happy Eyeballs", in which IPv4 is
// tried soon if IPv6 appears to be misconfigured and
// hanging.
//
// Deprecated: Fast Fallback is enabled by default. To
// disable, set FallbackDelay to a negative value.
DualStack bool
// FallbackDelay specifies the length of time to wait before
// spawning a RFC 6555 Fast Fallback connection. That is, this
// is the amount of time to wait for IPv6 to succeed before
// assuming that IPv6 is misconfigured and falling back to
// IPv4.
//
// If zero, a default delay of 300ms is used.
// A negative value disables Fast Fallback support.
FallbackDelay time.Duration
// KeepAlive specifies the interval between keep-alive
// probes for an active network connection.
// If zero, keep-alive probes are sent with a default value
// (currently 15 seconds), if supported by the protocol and operating
// system. Network protocols or operating systems that do
// not support keep-alives ignore this field.
// If negative, keep-alive probes are disabled.
KeepAlive time.Duration
// Resolver optionally specifies an alternate resolver to use.
Resolver *Resolver
// Cancel is an optional channel whose closure indicates that
// the dial should be canceled. Not all types of dials support
// cancellation.
//
// Deprecated: Use DialContext instead.
Cancel <-chan struct{}
// If Control is not nil, it is called after creating the network
// connection but before actually dialing.
//
// Network and address parameters passed to Control method are not
// necessarily the ones passed to Dial. For example, passing "tcp" to Dial
// will cause the Control function to be called with "tcp4" or "tcp6".
Control func(network, address string, c syscall.RawConn) error
}
func (d *Dialer) dualStack() bool { return d.FallbackDelay >= 0 }
func minNonzeroTime(a, b time.Time) time.Time {
if a.IsZero() {
return b
}
if b.IsZero() || a.Before(b) {
return a
}
return b
}
// deadline returns the earliest of:
// - now+Timeout
// - d.Deadline
// - the context's deadline
//
// Or zero, if none of Timeout, Deadline, or context's deadline is set.
func (d *Dialer) deadline(ctx context.Context, now time.Time) (earliest time.Time) {
if d.Timeout != 0 { // including negative, for historical reasons
earliest = now.Add(d.Timeout)
}
if d, ok := ctx.Deadline(); ok {
earliest = minNonzeroTime(earliest, d)
}
return minNonzeroTime(earliest, d.Deadline)
}
func (d *Dialer) resolver() *Resolver {
if d.Resolver != nil {
return d.Resolver
}
return DefaultResolver
}
// partialDeadline returns the deadline to use for a single address,
// when multiple addresses are pending.
func partialDeadline(now, deadline time.Time, addrsRemaining int) (time.Time, error) {
if deadline.IsZero() {
return deadline, nil
}
timeRemaining := deadline.Sub(now)
if timeRemaining <= 0 {
return time.Time{}, errTimeout
}
// Tentatively allocate equal time to each remaining address.
timeout := timeRemaining / time.Duration(addrsRemaining)
// If the time per address is too short, steal from the end of the list.
const saneMinimum = 2 * time.Second
if timeout < saneMinimum {
if timeRemaining < saneMinimum {
timeout = timeRemaining
} else {
timeout = saneMinimum
}
}
return now.Add(timeout), nil
}
func (d *Dialer) fallbackDelay() time.Duration {
if d.FallbackDelay > 0 {
return d.FallbackDelay
} else {
return 300 * time.Millisecond
}
}
func parseNetwork(ctx context.Context, network string, needsProto bool) (afnet string, proto int, err error) {
i := last(network, ':')
if i < 0 { // no colon
switch network {
case "tcp", "tcp4", "tcp6":
case "udp", "udp4", "udp6":
case "ip", "ip4", "ip6":
if needsProto {
return "", 0, UnknownNetworkError(network)
}
case "unix", "unixgram", "unixpacket":
default:
return "", 0, UnknownNetworkError(network)
}
return network, 0, nil
}
afnet = network[:i]
switch afnet {
case "ip", "ip4", "ip6":
protostr := network[i+1:]
proto, i, ok := dtoi(protostr)
if !ok || i != len(protostr) {
proto, err = lookupProtocol(ctx, protostr)
if err != nil {
return "", 0, err
}
}
return afnet, proto, nil
}
return "", 0, UnknownNetworkError(network)
}
// resolveAddrList resolves addr using hint and returns a list of
// addresses. The result contains at least one address when error is
// nil.
func (r *Resolver) resolveAddrList(ctx context.Context, op, network, addr string, hint Addr) (addrList, error) {
afnet, _, err := parseNetwork(ctx, network, true)
if err != nil {
return nil, err
}
if op == "dial" && addr == "" {
return nil, errMissingAddress
}
switch afnet {
case "unix", "unixgram", "unixpacket":
addr, err := ResolveUnixAddr(afnet, addr)
if err != nil {
return nil, err
}
if op == "dial" && hint != nil && addr.Network() != hint.Network() {
return nil, &AddrError{Err: "mismatched local address type", Addr: hint.String()}
}
return addrList{addr}, nil
}
addrs, err := r.internetAddrList(ctx, afnet, addr)
if err != nil || op != "dial" || hint == nil {
return addrs, err
}
var (
tcp *TCPAddr
udp *UDPAddr
ip *IPAddr
wildcard bool
)
switch hint := hint.(type) {
case *TCPAddr:
tcp = hint
wildcard = tcp.isWildcard()
case *UDPAddr:
udp = hint
wildcard = udp.isWildcard()
case *IPAddr:
ip = hint
wildcard = ip.isWildcard()
}
naddrs := addrs[:0]
for _, addr := range addrs {
if addr.Network() != hint.Network() {
return nil, &AddrError{Err: "mismatched local address type", Addr: hint.String()}
}
switch addr := addr.(type) {
case *TCPAddr:
if !wildcard && !addr.isWildcard() && !addr.IP.matchAddrFamily(tcp.IP) {
continue
}
naddrs = append(naddrs, addr)
case *UDPAddr:
if !wildcard && !addr.isWildcard() && !addr.IP.matchAddrFamily(udp.IP) {
continue
}
naddrs = append(naddrs, addr)
case *IPAddr:
if !wildcard && !addr.isWildcard() && !addr.IP.matchAddrFamily(ip.IP) {
continue
}
naddrs = append(naddrs, addr)
}
}
if len(naddrs) == 0 {
return nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: hint.String()}
}
return naddrs, nil
}
// Dial connects to the address on the named network.
//
// Known networks are "tcp", "tcp4" (IPv4-only), "tcp6" (IPv6-only),
// "udp", "udp4" (IPv4-only), "udp6" (IPv6-only), "ip", "ip4"
// (IPv4-only), "ip6" (IPv6-only), "unix", "unixgram" and
// "unixpacket".
//
// For TCP and UDP networks, the address has the form "host:port".
// The host must be a literal IP address, or a host name that can be
// resolved to IP addresses.
// The port must be a literal port number or a service name.
// If the host is a literal IPv6 address it must be enclosed in square
// brackets, as in "[2001:db8::1]:80" or "[fe80::1%zone]:80".
// The zone specifies the scope of the literal IPv6 address as defined
// in RFC 4007.
// The functions JoinHostPort and SplitHostPort manipulate a pair of
// host and port in this form.
// When using TCP, and the host resolves to multiple IP addresses,
// Dial will try each IP address in order until one succeeds.
//
// Examples:
//
// Dial("tcp", "golang.org:http")
// Dial("tcp", "192.0.2.1:http")
// Dial("tcp", "198.51.100.1:80")
// Dial("udp", "[2001:db8::1]:domain")
// Dial("udp", "[fe80::1%lo0]:53")
// Dial("tcp", ":80")
//
// For IP networks, the network must be "ip", "ip4" or "ip6" followed
// by a colon and a literal protocol number or a protocol name, and
// the address has the form "host". The host must be a literal IP
// address or a literal IPv6 address with zone.
// It depends on each operating system how the operating system
// behaves with a non-well known protocol number such as "0" or "255".
//
// Examples:
//
// Dial("ip4:1", "192.0.2.1")
// Dial("ip6:ipv6-icmp", "2001:db8::1")
// Dial("ip6:58", "fe80::1%lo0")
//
// For TCP, UDP and IP networks, if the host is empty or a literal
// unspecified IP address, as in ":80", "0.0.0.0:80" or "[::]:80" for
// TCP and UDP, "", "0.0.0.0" or "::" for IP, the local system is
// assumed.
//
// For Unix networks, the address must be a file system path.
func Dial(network, address string) (Conn, error) {
var d Dialer
return d.Dial(network, address)
}
// DialTimeout acts like Dial but takes a timeout.
//
// The timeout includes name resolution, if required.
// When using TCP, and the host in the address parameter resolves to
// multiple IP addresses, the timeout is spread over each consecutive
// dial, such that each is given an appropriate fraction of the time
// to connect.
//
// See func Dial for a description of the network and address
// parameters.
func DialTimeout(network, address string, timeout time.Duration) (Conn, error) {
d := Dialer{Timeout: timeout}
return d.Dial(network, address)
}
// sysDialer contains a Dial's parameters and configuration.
type sysDialer struct {
Dialer
network, address string
}
// Dial connects to the address on the named network.
//
// See func Dial for a description of the network and address
// parameters.
//
// Dial uses context.Background internally; to specify the context, use
// DialContext.
func (d *Dialer) Dial(network, address string) (Conn, error) {
return d.DialContext(context.Background(), network, address)
}
// DialContext connects to the address on the named network using
// the provided context.
//
// The provided Context must be non-nil. If the context expires before
// the connection is complete, an error is returned. Once successfully
// connected, any expiration of the context will not affect the
// connection.
//
// When using TCP, and the host in the address parameter resolves to multiple
// network addresses, any dial timeout (from d.Timeout or ctx) is spread
// over each consecutive dial, such that each is given an appropriate
// fraction of the time to connect.
// For example, if a host has 4 IP addresses and the timeout is 1 minute,
// the connect to each single address will be given 15 seconds to complete
// before trying the next one.
//
// See func Dial for a description of the network and address
// parameters.
func (d *Dialer) DialContext(ctx context.Context, network, address string) (Conn, error) {
if ctx == nil {
panic("nil context")
}
deadline := d.deadline(ctx, time.Now())
if !deadline.IsZero() {
if d, ok := ctx.Deadline(); !ok || deadline.Before(d) {
subCtx, cancel := context.WithDeadline(ctx, deadline)
defer cancel()
ctx = subCtx
}
}
if oldCancel := d.Cancel; oldCancel != nil {
subCtx, cancel := context.WithCancel(ctx)
defer cancel()
go func() {
select {
case <-oldCancel:
cancel()
case <-subCtx.Done():
}
}()
ctx = subCtx
}
// Shadow the nettrace (if any) during resolve so Connect events don't fire for DNS lookups.
resolveCtx := ctx
if trace, _ := ctx.Value(nettrace.TraceKey{}).(*nettrace.Trace); trace != nil {
shadow := *trace
shadow.ConnectStart = nil
shadow.ConnectDone = nil
resolveCtx = context.WithValue(resolveCtx, nettrace.TraceKey{}, &shadow)
}
addrs, err := d.resolver().resolveAddrList(resolveCtx, "dial", network, address, d.LocalAddr)
if err != nil {
return nil, &OpError{Op: "dial", Net: network, Source: nil, Addr: nil, Err: err}
}
sd := &sysDialer{
Dialer: *d,
network: network,
address: address,
}
var primaries, fallbacks addrList
if d.dualStack() && network == "tcp" {
primaries, fallbacks = addrs.partition(isIPv4)
} else {
primaries = addrs
}
c, err := sd.dialParallel(ctx, primaries, fallbacks)
if err != nil {
return nil, err
}
if tc, ok := c.(*TCPConn); ok && d.KeepAlive >= 0 {
setKeepAlive(tc.fd, true)
ka := d.KeepAlive
if d.KeepAlive == 0 {
ka = defaultTCPKeepAlive
}
setKeepAlivePeriod(tc.fd, ka)
testHookSetKeepAlive(ka)
}
return c, nil
}
// dialParallel races two copies of dialSerial, giving the first a
// head start. It returns the first established connection and
// closes the others. Otherwise it returns an error from the first
// primary address.
func (sd *sysDialer) dialParallel(ctx context.Context, primaries, fallbacks addrList) (Conn, error) {
if len(fallbacks) == 0 {
return sd.dialSerial(ctx, primaries)
}
returned := make(chan struct{})
defer close(returned)
type dialResult struct {
Conn
error
primary bool
done bool
}
results := make(chan dialResult) // unbuffered
startRacer := func(ctx context.Context, primary bool) {
ras := primaries
if !primary {
ras = fallbacks
}
c, err := sd.dialSerial(ctx, ras)
select {
case results <- dialResult{Conn: c, error: err, primary: primary, done: true}:
case <-returned:
if c != nil {
c.Close()
}
}
}
var primary, fallback dialResult
// Start the main racer.
primaryCtx, primaryCancel := context.WithCancel(ctx)
defer primaryCancel()
go startRacer(primaryCtx, true)
// Start the timer for the fallback racer.
fallbackTimer := time.NewTimer(sd.fallbackDelay())
defer fallbackTimer.Stop()
for {
select {
case <-fallbackTimer.C:
fallbackCtx, fallbackCancel := context.WithCancel(ctx)
defer fallbackCancel()
go startRacer(fallbackCtx, false)
case res := <-results:
if res.error == nil {
return res.Conn, nil
}
if res.primary {
primary = res
} else {
fallback = res
}
if primary.done && fallback.done {
return nil, primary.error
}
if res.primary && fallbackTimer.Stop() {
// If we were able to stop the timer, that means it
// was running (hadn't yet started the fallback), but
// we just got an error on the primary path, so start
// the fallback immediately (in 0 nanoseconds).
fallbackTimer.Reset(0)
}
}
}
}
// dialSerial connects to a list of addresses in sequence, returning
// either the first successful connection, or the first error.
func (sd *sysDialer) dialSerial(ctx context.Context, ras addrList) (Conn, error) {
var firstErr error // The error from the first address is most relevant.
for i, ra := range ras {
select {
case <-ctx.Done():
return nil, &OpError{Op: "dial", Net: sd.network, Source: sd.LocalAddr, Addr: ra, Err: mapErr(ctx.Err())}
default:
}
dialCtx := ctx
if deadline, hasDeadline := ctx.Deadline(); hasDeadline {
partialDeadline, err := partialDeadline(time.Now(), deadline, len(ras)-i)
if err != nil {
// Ran out of time.
if firstErr == nil {
firstErr = &OpError{Op: "dial", Net: sd.network, Source: sd.LocalAddr, Addr: ra, Err: err}
}
break
}
if partialDeadline.Before(deadline) {
var cancel context.CancelFunc
dialCtx, cancel = context.WithDeadline(ctx, partialDeadline)
defer cancel()
}
}
c, err := sd.dialSingle(dialCtx, ra)
if err == nil {
return c, nil
}
if firstErr == nil {
firstErr = err
}
}
if firstErr == nil {
firstErr = &OpError{Op: "dial", Net: sd.network, Source: nil, Addr: nil, Err: errMissingAddress}
}
return nil, firstErr
}
// dialSingle attempts to establish and returns a single connection to
// the destination address.
func (sd *sysDialer) dialSingle(ctx context.Context, ra Addr) (c Conn, err error) {
trace, _ := ctx.Value(nettrace.TraceKey{}).(*nettrace.Trace)
if trace != nil {
raStr := ra.String()
if trace.ConnectStart != nil {
trace.ConnectStart(sd.network, raStr)
}
if trace.ConnectDone != nil {
defer func() { trace.ConnectDone(sd.network, raStr, err) }()
}
}
la := sd.LocalAddr
switch ra := ra.(type) {
case *TCPAddr:
la, _ := la.(*TCPAddr)
c, err = sd.dialTCP(ctx, la, ra)
case *UDPAddr:
la, _ := la.(*UDPAddr)
c, err = sd.dialUDP(ctx, la, ra)
case *IPAddr:
la, _ := la.(*IPAddr)
c, err = sd.dialIP(ctx, la, ra)
case *UnixAddr:
la, _ := la.(*UnixAddr)
c, err = sd.dialUnix(ctx, la, ra)
default:
return nil, &OpError{Op: "dial", Net: sd.network, Source: la, Addr: ra, Err: &AddrError{Err: "unexpected address type", Addr: sd.address}}
}
if err != nil {
return nil, &OpError{Op: "dial", Net: sd.network, Source: la, Addr: ra, Err: err} // c is non-nil interface containing nil pointer
}
return c, nil
}
// ListenConfig contains options for listening to an address.
type ListenConfig struct {
// If Control is not nil, it is called after creating the network
// connection but before binding it to the operating system.
//
// Network and address parameters passed to Control method are not
// necessarily the ones passed to Listen. For example, passing "tcp" to
// Listen will cause the Control function to be called with "tcp4" or "tcp6".
Control func(network, address string, c syscall.RawConn) error
// KeepAlive specifies the keep-alive period for network
// connections accepted by this listener.
// If zero, keep-alives are enabled if supported by the protocol
// and operating system. Network protocols or operating systems
// that do not support keep-alives ignore this field.
// If negative, keep-alives are disabled.
KeepAlive time.Duration
}
// Listen announces on the local network address.
//
// See func Listen for a description of the network and address
// parameters.
func (lc *ListenConfig) Listen(ctx context.Context, network, address string) (Listener, error) {
addrs, err := DefaultResolver.resolveAddrList(ctx, "listen", network, address, nil)
if err != nil {
return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: nil, Err: err}
}
sl := &sysListener{
ListenConfig: *lc,
network: network,
address: address,
}
var l Listener
la := addrs.first(isIPv4)
switch la := la.(type) {
case *TCPAddr:
l, err = sl.listenTCP(ctx, la)
case *UnixAddr:
l, err = sl.listenUnix(ctx, la)
default:
return nil, &OpError{Op: "listen", Net: sl.network, Source: nil, Addr: la, Err: &AddrError{Err: "unexpected address type", Addr: address}}
}
if err != nil {
return nil, &OpError{Op: "listen", Net: sl.network, Source: nil, Addr: la, Err: err} // l is non-nil interface containing nil pointer
}
return l, nil
}
// ListenPacket announces on the local network address.
//
// See func ListenPacket for a description of the network and address
// parameters.
func (lc *ListenConfig) ListenPacket(ctx context.Context, network, address string) (PacketConn, error) {
addrs, err := DefaultResolver.resolveAddrList(ctx, "listen", network, address, nil)
if err != nil {
return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: nil, Err: err}
}
sl := &sysListener{
ListenConfig: *lc,
network: network,
address: address,
}
var c PacketConn
la := addrs.first(isIPv4)
switch la := la.(type) {
case *UDPAddr:
c, err = sl.listenUDP(ctx, la)
case *IPAddr:
c, err = sl.listenIP(ctx, la)
case *UnixAddr:
c, err = sl.listenUnixgram(ctx, la)
default:
return nil, &OpError{Op: "listen", Net: sl.network, Source: nil, Addr: la, Err: &AddrError{Err: "unexpected address type", Addr: address}}
}
if err != nil {
return nil, &OpError{Op: "listen", Net: sl.network, Source: nil, Addr: la, Err: err} // c is non-nil interface containing nil pointer
}
return c, nil
}
// sysListener contains a Listen's parameters and configuration.
type sysListener struct {
ListenConfig
network, address string
}
// Listen announces on the local network address.
//
// The network must be "tcp", "tcp4", "tcp6", "unix" or "unixpacket".
//
// For TCP networks, if the host in the address parameter is empty or
// a literal unspecified IP address, Listen listens on all available
// unicast and anycast IP addresses of the local system.
// To only use IPv4, use network "tcp4".
// The address can use a host name, but this is not recommended,
// because it will create a listener for at most one of the host's IP
// addresses.
// If the port in the address parameter is empty or "0", as in
// "127.0.0.1:" or "[::1]:0", a port number is automatically chosen.
// The Addr method of Listener can be used to discover the chosen
// port.
//
// See func Dial for a description of the network and address
// parameters.
//
// Listen uses context.Background internally; to specify the context, use
// ListenConfig.Listen.
func Listen(network, address string) (Listener, error) {
var lc ListenConfig
return lc.Listen(context.Background(), network, address)
}
// ListenPacket announces on the local network address.
//
// The network must be "udp", "udp4", "udp6", "unixgram", or an IP
// transport. The IP transports are "ip", "ip4", or "ip6" followed by
// a colon and a literal protocol number or a protocol name, as in
// "ip:1" or "ip:icmp".
//
// For UDP and IP networks, if the host in the address parameter is
// empty or a literal unspecified IP address, ListenPacket listens on
// all available IP addresses of the local system except multicast IP
// addresses.
// To only use IPv4, use network "udp4" or "ip4:proto".
// The address can use a host name, but this is not recommended,
// because it will create a listener for at most one of the host's IP
// addresses.
// If the port in the address parameter is empty or "0", as in
// "127.0.0.1:" or "[::1]:0", a port number is automatically chosen.
// The LocalAddr method of PacketConn can be used to discover the
// chosen port.
//
// See func Dial for a description of the network and address
// parameters.
//
// ListenPacket uses context.Background internally; to specify the context, use
// ListenConfig.ListenPacket.
func ListenPacket(network, address string) (PacketConn, error) {
var lc ListenConfig
return lc.ListenPacket(context.Background(), network, address)
}