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Source file src/net/dial.go

Documentation: net

  // 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"
  	"internal/poll"
  	"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 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 enables RFC 6555-compliant "Happy Eyeballs"
  	// dialing when the network is "tcp" and the host in the
  	// address parameter resolves to 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{}, poll.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)
  }
  
  // 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.
  //
  // 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.
  func Listen(network, address string) (Listener, error) {
  	addrs, err := DefaultResolver.resolveAddrList(context.Background(), "listen", network, address, nil)
  	if err != nil {
  		return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: nil, Err: err}
  	}
  	var l Listener
  	switch la := addrs.first(isIPv4).(type) {
  	case *TCPAddr:
  		l, err = ListenTCP(network, la)
  	case *UnixAddr:
  		l, err = ListenUnix(network, la)
  	default:
  		return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: la, Err: &AddrError{Err: "unexpected address type", Addr: address}}
  	}
  	if err != nil {
  		return nil, err // l is non-nil interface containing nil pointer
  	}
  	return l, nil
  }
  
  // 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.
  func ListenPacket(network, address string) (PacketConn, error) {
  	addrs, err := DefaultResolver.resolveAddrList(context.Background(), "listen", network, address, nil)
  	if err != nil {
  		return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: nil, Err: err}
  	}
  	var l PacketConn
  	switch la := addrs.first(isIPv4).(type) {
  	case *UDPAddr:
  		l, err = ListenUDP(network, la)
  	case *IPAddr:
  		l, err = ListenIP(network, la)
  	case *UnixAddr:
  		l, err = ListenUnixgram(network, la)
  	default:
  		return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: la, Err: &AddrError{Err: "unexpected address type", Addr: address}}
  	}
  	if err != nil {
  		return nil, err // l is non-nil interface containing nil pointer
  	}
  	return l, nil
  }
  

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