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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 (
"errors"
"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
// Cancel is an optional channel whose closure indicates that
// the dial should be canceled. Not all types of dials support
// cancelation.
Cancel <-chan struct{}
}
// Return either now+Timeout or Deadline, whichever comes first.
// Or zero, if neither is set.
func (d *Dialer) deadline(now time.Time) time.Time {
if d.Timeout == 0 {
return d.Deadline
}
timeoutDeadline := now.Add(d.Timeout)
if d.Deadline.IsZero() || timeoutDeadline.Before(d.Deadline) {
return timeoutDeadline
} else {
return d.Deadline
}
}
// 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(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, 0)
if !ok || i != len(protostr) {
proto, err = lookupProtocol(protostr)
if err != nil {
return "", 0, err
}
}
return afnet, proto, nil
}
return "", 0, UnknownNetworkError(net)
}
func resolveAddrList(op, net, addr string, deadline time.Time) (addrList, error) {
afnet, _, err := parseNetwork(net)
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
}
return addrList{addr}, nil
}
return internetAddrList(afnet, addr, deadline)
}
// 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.
//
// Examples:
// Dial("tcp", "12.34.56.78:80")
// Dial("tcp", "google.com:http")
// Dial("tcp", "[2001:db8::1]:http")
// Dial("tcp", "[fe80::1%lo0]: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", "127.0.0.1")
// Dial("ip6:ospf", "::1")
//
// 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.
func DialTimeout(network, address string, timeout time.Duration) (Conn, error) {
d := Dialer{Timeout: timeout}
return d.Dial(network, address)
}
// dialContext holds common state for all dial operations.
type dialContext struct {
Dialer
network, address string
finalDeadline time.Time
}
// 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) {
finalDeadline := d.deadline(time.Now())
addrs, err := resolveAddrList("dial", network, address, finalDeadline)
if err != nil {
return nil, &OpError{Op: "dial", Net: network, Source: nil, Addr: nil, Err: err}
}
ctx := &dialContext{
Dialer: *d,
network: network,
address: address,
finalDeadline: finalDeadline,
}
var primaries, fallbacks addrList
if d.DualStack && network == "tcp" {
primaries, fallbacks = addrs.partition(isIPv4)
} else {
primaries = addrs
}
var c Conn
if len(fallbacks) == 0 {
// dialParallel can accept an empty fallbacks list,
// but this shortcut avoids the goroutine/channel overhead.
c, err = dialSerial(ctx, primaries, nil)
} else {
c, err = dialParallel(ctx, primaries, fallbacks)
}
if d.KeepAlive > 0 && err == nil {
if tc, ok := c.(*TCPConn); ok {
setKeepAlive(tc.fd, true)
setKeepAlivePeriod(tc.fd, d.KeepAlive)
testHookSetKeepAlive()
}
}
return c, err
}
// 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 *dialContext, primaries, fallbacks addrList) (Conn, error) {
results := make(chan dialResult) // unbuffered, so dialSerialAsync can detect race loss & cleanup
cancel := make(chan struct{})
defer close(cancel)
// Spawn the primary racer.
go dialSerialAsync(ctx, primaries, nil, cancel, results)
// Spawn the fallback racer.
fallbackTimer := time.NewTimer(ctx.fallbackDelay())
go dialSerialAsync(ctx, fallbacks, fallbackTimer, cancel, results)
var primaryErr error
for nracers := 2; nracers > 0; nracers-- {
res := <-results
// If we're still waiting for a connection, then hasten the delay.
// Otherwise, disable the Timer and let cancel take over.
if fallbackTimer.Stop() && res.error != nil {
fallbackTimer.Reset(0)
}
if res.error == nil {
return res.Conn, nil
}
if res.primary {
primaryErr = res.error
}
}
return nil, primaryErr
}
type dialResult struct {
Conn
error
primary bool
}
// dialSerialAsync runs dialSerial after some delay, and returns the
// resulting connection through a channel. When racing two connections,
// the primary goroutine uses a nil timer to omit the delay.
func dialSerialAsync(ctx *dialContext, ras addrList, timer *time.Timer, cancel <-chan struct{}, results chan<- dialResult) {
if timer != nil {
// We're in the fallback goroutine; sleep before connecting.
select {
case <-timer.C:
case <-cancel:
return
}
}
c, err := dialSerial(ctx, ras, cancel)
select {
case results <- dialResult{c, err, timer == nil}:
// We won the race.
case <-cancel:
// The other goroutine won the race.
if c != nil {
c.Close()
}
}
}
// dialSerial connects to a list of addresses in sequence, returning
// either the first successful connection, or the first error.
func dialSerial(ctx *dialContext, ras addrList, cancel <-chan struct{}) (Conn, error) {
var firstErr error // The error from the first address is most relevant.
for i, ra := range ras {
select {
case <-cancel:
return nil, &OpError{Op: "dial", Net: ctx.network, Source: ctx.LocalAddr, Addr: ra, Err: errCanceled}
default:
}
partialDeadline, err := partialDeadline(time.Now(), ctx.finalDeadline, len(ras)-i)
if err != nil {
// Ran out of time.
if firstErr == nil {
firstErr = &OpError{Op: "dial", Net: ctx.network, Source: ctx.LocalAddr, Addr: ra, Err: err}
}
break
}
// dialTCP does not support cancelation (see golang.org/issue/11225),
// so if cancel fires, we'll continue trying to connect until the next
// timeout, or return a spurious connection for the caller to close.
dialer := func(d time.Time) (Conn, error) {
return dialSingle(ctx, ra, d)
}
c, err := dial(ctx.network, ra, dialer, partialDeadline)
if err == nil {
return c, nil
}
if firstErr == nil {
firstErr = err
}
}
if firstErr == nil {
firstErr = &OpError{Op: "dial", Net: ctx.network, Source: nil, Addr: nil, Err: errMissingAddress}
}
return nil, firstErr
}
// dialSingle attempts to establish and returns a single connection to
// the destination address. This must be called through the OS-specific
// dial function, because some OSes don't implement the deadline feature.
func dialSingle(ctx *dialContext, ra Addr, deadline time.Time) (c Conn, err error) {
la := ctx.LocalAddr
if la != nil && la.Network() != ra.Network() {
return nil, &OpError{Op: "dial", Net: ctx.network, Source: la, Addr: ra, Err: errors.New("mismatched local address type " + la.Network())}
}
switch ra := ra.(type) {
case *TCPAddr:
la, _ := la.(*TCPAddr)
c, err = testHookDialTCP(ctx.network, la, ra, deadline, ctx.Cancel)
case *UDPAddr:
la, _ := la.(*UDPAddr)
c, err = dialUDP(ctx.network, la, ra, deadline)
case *IPAddr:
la, _ := la.(*IPAddr)
c, err = dialIP(ctx.network, la, ra, deadline)
case *UnixAddr:
la, _ := la.(*UnixAddr)
c, err = dialUnix(ctx.network, la, ra, deadline)
default:
return nil, &OpError{Op: "dial", Net: ctx.network, Source: la, Addr: ra, Err: &AddrError{Err: "unexpected address type", Addr: ctx.address}}
}
if err != nil {
return nil, 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".
// See Dial for the syntax of laddr.
func Listen(net, laddr string) (Listener, error) {
addrs, err := resolveAddrList("listen", net, laddr, noDeadline)
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".
// See Dial for the syntax of laddr.
func ListenPacket(net, laddr string) (PacketConn, error) {
addrs, err := resolveAddrList("listen", net, laddr, noDeadline)
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
}