// 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 (
	
	
	
	
)

// 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 ( *Dialer) () bool { return .FallbackDelay >= 0 }

func minNonzeroTime(,  time.Time) time.Time {
	if .IsZero() {
		return 
	}
	if .IsZero() || .Before() {
		return 
	}
	return 
}

// 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 ( *Dialer) ( context.Context,  time.Time) ( time.Time) {
	if .Timeout != 0 { // including negative, for historical reasons
		 = .Add(.Timeout)
	}
	if ,  := .Deadline();  {
		 = minNonzeroTime(, )
	}
	return minNonzeroTime(, .Deadline)
}

func ( *Dialer) () *Resolver {
	if .Resolver != nil {
		return .Resolver
	}
	return DefaultResolver
}

// partialDeadline returns the deadline to use for a single address,
// when multiple addresses are pending.
func partialDeadline(,  time.Time,  int) (time.Time, error) {
	if .IsZero() {
		return , nil
	}
	 := .Sub()
	if  <= 0 {
		return time.Time{}, errTimeout
	}
	// Tentatively allocate equal time to each remaining address.
	 :=  / time.Duration()
	// If the time per address is too short, steal from the end of the list.
	const  = 2 * time.Second
	if  <  {
		if  <  {
			 = 
		} else {
			 = 
		}
	}
	return .Add(), nil
}

func ( *Dialer) () time.Duration {
	if .FallbackDelay > 0 {
		return .FallbackDelay
	} else {
		return 300 * time.Millisecond
	}
}

func parseNetwork( context.Context,  string,  bool) ( string,  int,  error) {
	 := last(, ':')
	if  < 0 { // no colon
		switch  {
		case "tcp", "tcp4", "tcp6":
		case "udp", "udp4", "udp6":
		case "ip", "ip4", "ip6":
			if  {
				return "", 0, UnknownNetworkError()
			}
		case "unix", "unixgram", "unixpacket":
		default:
			return "", 0, UnknownNetworkError()
		}
		return , 0, nil
	}
	 = [:]
	switch  {
	case "ip", "ip4", "ip6":
		 := [+1:]
		, ,  := dtoi()
		if ! ||  != len() {
			,  = lookupProtocol(, )
			if  != nil {
				return "", 0, 
			}
		}
		return , , nil
	}
	return "", 0, UnknownNetworkError()
}

// resolveAddrList resolves addr using hint and returns a list of
// addresses. The result contains at least one address when error is
// nil.
func ( *Resolver) ( context.Context, , ,  string,  Addr) (addrList, error) {
	, ,  := parseNetwork(, , true)
	if  != nil {
		return nil, 
	}
	if  == "dial" &&  == "" {
		return nil, errMissingAddress
	}
	switch  {
	case "unix", "unixgram", "unixpacket":
		,  := ResolveUnixAddr(, )
		if  != nil {
			return nil, 
		}
		if  == "dial" &&  != nil && .Network() != .Network() {
			return nil, &AddrError{Err: "mismatched local address type", Addr: .String()}
		}
		return addrList{}, nil
	}
	,  := .internetAddrList(, , )
	if  != nil ||  != "dial" ||  == nil {
		return , 
	}
	var (
		      *TCPAddr
		      *UDPAddr
		       *IPAddr
		 bool
	)
	switch hint := .(type) {
	case *TCPAddr:
		 = 
		 = .isWildcard()
	case *UDPAddr:
		 = 
		 = .isWildcard()
	case *IPAddr:
		 = 
		 = .isWildcard()
	}
	 := [:0]
	for ,  := range  {
		if .Network() != .Network() {
			return nil, &AddrError{Err: "mismatched local address type", Addr: .String()}
		}
		switch addr := .(type) {
		case *TCPAddr:
			if ! && !.isWildcard() && !.IP.matchAddrFamily(.IP) {
				continue
			}
			 = append(, )
		case *UDPAddr:
			if ! && !.isWildcard() && !.IP.matchAddrFamily(.IP) {
				continue
			}
			 = append(, )
		case *IPAddr:
			if ! && !.isWildcard() && !.IP.matchAddrFamily(.IP) {
				continue
			}
			 = append(, )
		}
	}
	if len() == 0 {
		return nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: .String()}
	}
	return , 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 (,  string) (Conn, error) {
	var  Dialer
	return .Dial(, )
}

// 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 (,  string,  time.Duration) (Conn, error) {
	 := Dialer{Timeout: }
	return .Dial(, )
}

// 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 ( *Dialer) (,  string) (Conn, error) {
	return .DialContext(context.Background(), , )
}

// 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 ( *Dialer) ( context.Context, ,  string) (Conn, error) {
	if  == nil {
		panic("nil context")
	}
	 := .deadline(, time.Now())
	if !.IsZero() {
		if ,  := .Deadline(); ! || .Before() {
			,  := context.WithDeadline(, )
			defer ()
			 = 
		}
	}
	if  := .Cancel;  != nil {
		,  := context.WithCancel()
		defer ()
		go func() {
			select {
			case <-:
				()
			case <-.Done():
			}
		}()
		 = 
	}

	// Shadow the nettrace (if any) during resolve so Connect events don't fire for DNS lookups.
	 := 
	if ,  := .Value(nettrace.TraceKey{}).(*nettrace.Trace);  != nil {
		 := *
		.ConnectStart = nil
		.ConnectDone = nil
		 = context.WithValue(, nettrace.TraceKey{}, &)
	}

	,  := .resolver().resolveAddrList(, "dial", , , .LocalAddr)
	if  != nil {
		return nil, &OpError{Op: "dial", Net: , Source: nil, Addr: nil, Err: }
	}

	 := &sysDialer{
		Dialer:  *,
		network: ,
		address: ,
	}

	var ,  addrList
	if .dualStack() &&  == "tcp" {
		,  = .partition(isIPv4)
	} else {
		 = 
	}

	var  Conn
	if len() > 0 {
		,  = .dialParallel(, , )
	} else {
		,  = .dialSerial(, )
	}
	if  != nil {
		return nil, 
	}

	if ,  := .(*TCPConn);  && .KeepAlive >= 0 {
		setKeepAlive(.fd, true)
		 := .KeepAlive
		if .KeepAlive == 0 {
			 = defaultTCPKeepAlive
		}
		setKeepAlivePeriod(.fd, )
		testHookSetKeepAlive()
	}
	return , 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 ( *sysDialer) ( context.Context, ,  addrList) (Conn, error) {
	if len() == 0 {
		return .dialSerial(, )
	}

	 := make(chan struct{})
	defer close()

	type  struct {
		Conn
		error
		 bool
		    bool
	}
	 := make(chan ) // unbuffered

	 := func( context.Context,  bool) {
		 := 
		if ! {
			 = 
		}
		,  := .dialSerial(, )
		select {
		case  <- {: , : , : , : true}:
		case <-:
			if  != nil {
				.Close()
			}
		}
	}

	var ,  

	// Start the main racer.
	,  := context.WithCancel()
	defer ()
	go (, true)

	// Start the timer for the fallback racer.
	 := time.NewTimer(.fallbackDelay())
	defer .Stop()

	for {
		select {
		case <-.C:
			,  := context.WithCancel()
			defer ()
			go (, false)

		case  := <-:
			if . == nil {
				return ., nil
			}
			if . {
				 = 
			} else {
				 = 
			}
			if . && . {
				return nil, .
			}
			if . && .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).
				.Reset(0)
			}
		}
	}
}

// dialSerial connects to a list of addresses in sequence, returning
// either the first successful connection, or the first error.
func ( *sysDialer) ( context.Context,  addrList) (Conn, error) {
	var  error // The error from the first address is most relevant.

	for ,  := range  {
		select {
		case <-.Done():
			return nil, &OpError{Op: "dial", Net: .network, Source: .LocalAddr, Addr: , Err: mapErr(.Err())}
		default:
		}

		 := 
		if ,  := .Deadline();  {
			,  := partialDeadline(time.Now(), , len()-)
			if  != nil {
				// Ran out of time.
				if  == nil {
					 = &OpError{Op: "dial", Net: .network, Source: .LocalAddr, Addr: , Err: }
				}
				break
			}
			if .Before() {
				var  context.CancelFunc
				,  = context.WithDeadline(, )
				defer ()
			}
		}

		,  := .dialSingle(, )
		if  == nil {
			return , nil
		}
		if  == nil {
			 = 
		}
	}

	if  == nil {
		 = &OpError{Op: "dial", Net: .network, Source: nil, Addr: nil, Err: errMissingAddress}
	}
	return nil, 
}

// dialSingle attempts to establish and returns a single connection to
// the destination address.
func ( *sysDialer) ( context.Context,  Addr) ( Conn,  error) {
	,  := .Value(nettrace.TraceKey{}).(*nettrace.Trace)
	if  != nil {
		 := .String()
		if .ConnectStart != nil {
			.ConnectStart(.network, )
		}
		if .ConnectDone != nil {
			defer func() { .ConnectDone(.network, , ) }()
		}
	}
	 := .LocalAddr
	switch ra := .(type) {
	case *TCPAddr:
		,  := .(*TCPAddr)
		,  = .dialTCP(, , )
	case *UDPAddr:
		,  := .(*UDPAddr)
		,  = .dialUDP(, , )
	case *IPAddr:
		,  := .(*IPAddr)
		,  = .dialIP(, , )
	case *UnixAddr:
		,  := .(*UnixAddr)
		,  = .dialUnix(, , )
	default:
		return nil, &OpError{Op: "dial", Net: .network, Source: , Addr: , Err: &AddrError{Err: "unexpected address type", Addr: .address}}
	}
	if  != nil {
		return nil, &OpError{Op: "dial", Net: .network, Source: , Addr: , Err: } // c is non-nil interface containing nil pointer
	}
	return , 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 ( *ListenConfig) ( context.Context, ,  string) (Listener, error) {
	,  := DefaultResolver.resolveAddrList(, "listen", , , nil)
	if  != nil {
		return nil, &OpError{Op: "listen", Net: , Source: nil, Addr: nil, Err: }
	}
	 := &sysListener{
		ListenConfig: *,
		network:      ,
		address:      ,
	}
	var  Listener
	 := .first(isIPv4)
	switch la := .(type) {
	case *TCPAddr:
		,  = .listenTCP(, )
	case *UnixAddr:
		,  = .listenUnix(, )
	default:
		return nil, &OpError{Op: "listen", Net: .network, Source: nil, Addr: , Err: &AddrError{Err: "unexpected address type", Addr: }}
	}
	if  != nil {
		return nil, &OpError{Op: "listen", Net: .network, Source: nil, Addr: , Err: } // l is non-nil interface containing nil pointer
	}
	return , nil
}

// ListenPacket announces on the local network address.
//
// See func ListenPacket for a description of the network and address
// parameters.
func ( *ListenConfig) ( context.Context, ,  string) (PacketConn, error) {
	,  := DefaultResolver.resolveAddrList(, "listen", , , nil)
	if  != nil {
		return nil, &OpError{Op: "listen", Net: , Source: nil, Addr: nil, Err: }
	}
	 := &sysListener{
		ListenConfig: *,
		network:      ,
		address:      ,
	}
	var  PacketConn
	 := .first(isIPv4)
	switch la := .(type) {
	case *UDPAddr:
		,  = .listenUDP(, )
	case *IPAddr:
		,  = .listenIP(, )
	case *UnixAddr:
		,  = .listenUnixgram(, )
	default:
		return nil, &OpError{Op: "listen", Net: .network, Source: nil, Addr: , Err: &AddrError{Err: "unexpected address type", Addr: }}
	}
	if  != nil {
		return nil, &OpError{Op: "listen", Net: .network, Source: nil, Addr: , Err: } // c is non-nil interface containing nil pointer
	}
	return , 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 (,  string) (Listener, error) {
	var  ListenConfig
	return .Listen(context.Background(), , )
}

// 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 (,  string) (PacketConn, error) {
	var  ListenConfig
	return .ListenPacket(context.Background(), , )
}