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// 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"
"time"
)
// 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.
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 dialing a 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 enables RFC 6555-compliant "Happy Eyeballs" dialing
// when the network is "tcp" and the destination is a host name
// with both IPv4 and IPv6 addresses. This allows a client to
// tolerate networks where one address family is silently broken.
DualStack bool
// FallbackDelay specifies the length of time to wait before
// spawning a fallback connection, when DualStack is enabled.
// If zero, a default delay of 300ms is used.
FallbackDelay time.Duration
// KeepAlive specifies the keep-alive period for an active
// network connection.
// If zero, keep-alives are not enabled. Network protocols
// that do not support keep-alives ignore this field.
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
// cancelation.
//
// Deprecated: Use DialContext instead.
Cancel <-chan struct{}
}
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, net string) (afnet string, proto int, err error) {
i := last(net, ':')
if i < 0 { // no colon
switch net {
case "tcp", "tcp4", "tcp6":
case "udp", "udp4", "udp6":
case "ip", "ip4", "ip6":
case "unix", "unixgram", "unixpacket":
default:
return "", 0, UnknownNetworkError(net)
}
return net, 0, nil
}
afnet = net[:i]
switch afnet {
case "ip", "ip4", "ip6":
protostr := net[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(net)
}
// 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)
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, addresses have the form host:port.
// If host is a literal IPv6 address it must be enclosed
// in square brackets as in "[::1]:80" or "[ipv6-host%zone]:80".
// The functions JoinHostPort and SplitHostPort manipulate addresses
// in this form.
// If the host is empty, as in ":80", the local system is assumed.
//
// Examples:
// Dial("tcp", "192.0.2.1:80")
// Dial("tcp", "golang.org:http")
// Dial("tcp", "[2001:db8::1]:http")
// Dial("tcp", "[fe80::1%lo0]:80")
// Dial("tcp", ":80")
//
// For IP networks, the network must be "ip", "ip4" or "ip6" followed
// by a colon and a protocol number or name and the addr must be a
// literal IP address.
//
// Examples:
// Dial("ip4:1", "192.0.2.1")
// Dial("ip6:ipv6-icmp", "2001:db8::1")
//
// For Unix networks, the address must be a file system path.
//
// If the host is resolved to multiple addresses,
// Dial will try each address in order until one succeeds.
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.
func DialTimeout(network, address string, timeout time.Duration) (Conn, error) {
d := Dialer{Timeout: timeout}
return d.Dial(network, address)
}
// dialParam contains a Dial's parameters and configuration.
type dialParam 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.
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}
}
dp := &dialParam{
Dialer: *d,
network: network,
address: address,
}
var primaries, fallbacks addrList
if d.DualStack && network == "tcp" {
primaries, fallbacks = addrs.partition(isIPv4)
} else {
primaries = addrs
}
var c Conn
if len(fallbacks) > 0 {
c, err = dialParallel(ctx, dp, primaries, fallbacks)
} else {
c, err = dialSerial(ctx, dp, primaries)
}
if err != nil {
return nil, err
}
if tc, ok := c.(*TCPConn); ok && d.KeepAlive > 0 {
setKeepAlive(tc.fd, true)
setKeepAlivePeriod(tc.fd, d.KeepAlive)
testHookSetKeepAlive()
}
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 dialParallel(ctx context.Context, dp *dialParam, primaries, fallbacks addrList) (Conn, error) {
if len(fallbacks) == 0 {
return dialSerial(ctx, dp, 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 := dialSerial(ctx, dp, 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(dp.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 dialSerial(ctx context.Context, dp *dialParam, 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: dp.network, Source: dp.LocalAddr, Addr: ra, Err: mapErr(ctx.Err())}
default:
}
deadline, _ := ctx.Deadline()
partialDeadline, err := partialDeadline(time.Now(), deadline, len(ras)-i)
if err != nil {
// Ran out of time.
if firstErr == nil {
firstErr = &OpError{Op: "dial", Net: dp.network, Source: dp.LocalAddr, Addr: ra, Err: err}
}
break
}
dialCtx := ctx
if partialDeadline.Before(deadline) {
var cancel context.CancelFunc
dialCtx, cancel = context.WithDeadline(ctx, partialDeadline)
defer cancel()
}
c, err := dialSingle(dialCtx, dp, ra)
if err == nil {
return c, nil
}
if firstErr == nil {
firstErr = err
}
}
if firstErr == nil {
firstErr = &OpError{Op: "dial", Net: dp.network, Source: nil, Addr: nil, Err: errMissingAddress}
}
return nil, firstErr
}
// dialSingle attempts to establish and returns a single connection to
// the destination address.
func dialSingle(ctx context.Context, dp *dialParam, 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(dp.network, raStr)
}
if trace.ConnectDone != nil {
defer func() { trace.ConnectDone(dp.network, raStr, err) }()
}
}
la := dp.LocalAddr
switch ra := ra.(type) {
case *TCPAddr:
la, _ := la.(*TCPAddr)
c, err = dialTCP(ctx, dp.network, la, ra)
case *UDPAddr:
la, _ := la.(*UDPAddr)
c, err = dialUDP(ctx, dp.network, la, ra)
case *IPAddr:
la, _ := la.(*IPAddr)
c, err = dialIP(ctx, dp.network, la, ra)
case *UnixAddr:
la, _ := la.(*UnixAddr)
c, err = dialUnix(ctx, dp.network, la, ra)
default:
return nil, &OpError{Op: "dial", Net: dp.network, Source: la, Addr: ra, Err: &AddrError{Err: "unexpected address type", Addr: dp.address}}
}
if err != nil {
return nil, &OpError{Op: "dial", Net: dp.network, Source: la, Addr: ra, Err: err} // c is non-nil interface containing nil pointer
}
return c, nil
}
// Listen announces on the local network address laddr.
// The network net must be a stream-oriented network: "tcp", "tcp4",
// "tcp6", "unix" or "unixpacket".
// For TCP and UDP, the syntax of laddr is "host:port", like "127.0.0.1:8080".
// If host is omitted, as in ":8080", Listen listens on all available interfaces
// instead of just the interface with the given host address.
// See Dial for more details about address syntax.
//
// Listening on a hostname is not recommended because this creates a socket
// for at most one of its IP addresses.
func Listen(net, laddr string) (Listener, error) {
addrs, err := DefaultResolver.resolveAddrList(context.Background(), "listen", net, laddr, nil)
if err != nil {
return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: nil, Err: err}
}
var l Listener
switch la := addrs.first(isIPv4).(type) {
case *TCPAddr:
l, err = ListenTCP(net, la)
case *UnixAddr:
l, err = ListenUnix(net, la)
default:
return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: la, Err: &AddrError{Err: "unexpected address type", Addr: laddr}}
}
if err != nil {
return nil, err // l is non-nil interface containing nil pointer
}
return l, nil
}
// ListenPacket announces on the local network address laddr.
// The network net must be a packet-oriented network: "udp", "udp4",
// "udp6", "ip", "ip4", "ip6" or "unixgram".
// For TCP and UDP, the syntax of laddr is "host:port", like "127.0.0.1:8080".
// If host is omitted, as in ":8080", ListenPacket listens on all available interfaces
// instead of just the interface with the given host address.
// See Dial for the syntax of laddr.
//
// Listening on a hostname is not recommended because this creates a socket
// for at most one of its IP addresses.
func ListenPacket(net, laddr string) (PacketConn, error) {
addrs, err := DefaultResolver.resolveAddrList(context.Background(), "listen", net, laddr, nil)
if err != nil {
return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: nil, Err: err}
}
var l PacketConn
switch la := addrs.first(isIPv4).(type) {
case *UDPAddr:
l, err = ListenUDP(net, la)
case *IPAddr:
l, err = ListenIP(net, la)
case *UnixAddr:
l, err = ListenUnixgram(net, la)
default:
return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: la, Err: &AddrError{Err: "unexpected address type", Addr: laddr}}
}
if err != nil {
return nil, err // l is non-nil interface containing nil pointer
}
return l, nil
}