golang dial 代码
文件路径：/src/net/dial.go
/ 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
testHookDialTCP func(ctx context.Context, net string, laddr, raddr *TCPAddr) (*TCPConn, error)
}
/ 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)
}