src/net/tcpsock_posix.go - go - Git at Google

 // Copyright 2009 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.

 // +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows

 package net

 import (
 	"io"
 	"os"
 	"syscall"
 	"time"
 )

 func sockaddrToTCP(sa syscall.Sockaddr) Addr {
 	switch sa := sa.(type) {
 	case *syscall.SockaddrInet4:
 		return &TCPAddr{IP: sa.Addr[0:], Port: sa.Port}
 	case *syscall.SockaddrInet6:
 		return &TCPAddr{IP: sa.Addr[0:], Port: sa.Port, Zone: zoneToString(int(sa.ZoneId))}
 	}
 	return nil
 }

 func (a *TCPAddr) family() int {
 	if a == nil || len(a.IP) <= IPv4len {
 		return syscall.AF_INET
 	}
 	if a.IP.To4() != nil {
 		return syscall.AF_INET
 	}
 	return syscall.AF_INET6
 }

 func (a *TCPAddr) sockaddr(family int) (syscall.Sockaddr, error) {
 	if a == nil {
 		return nil, nil
 	}
 	return ipToSockaddr(family, a.IP, a.Port, a.Zone)
 }

 // TCPConn is an implementation of the Conn interface for TCP network
 // connections.
 type TCPConn struct {
 	conn
 }

 func newTCPConn(fd *netFD) *TCPConn {
 	c := &TCPConn{conn{fd}}
 	setNoDelay(c.fd, true)
 	return c
 }

 // ReadFrom implements the io.ReaderFrom ReadFrom method.
 func (c *TCPConn) ReadFrom(r io.Reader) (int64, error) {
 	if n, err, handled := sendFile(c.fd, r); handled {
 		if err != nil && err != io.EOF {
 			err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 		}
 		return n, err
 	}
 	n, err := genericReadFrom(c, r)
 	if err != nil && err != io.EOF {
 		err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return n, err
 }

 // CloseRead shuts down the reading side of the TCP connection.
 // Most callers should just use Close.
 func (c *TCPConn) CloseRead() error {
 	if !c.ok() {
 		return syscall.EINVAL
 	}
 	err := c.fd.closeRead()
 	if err != nil {
 		err = &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return err
 }

 // CloseWrite shuts down the writing side of the TCP connection.
 // Most callers should just use Close.
 func (c *TCPConn) CloseWrite() error {
 	if !c.ok() {
 		return syscall.EINVAL
 	}
 	err := c.fd.closeWrite()
 	if err != nil {
 		err = &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return err
 }

 // SetLinger sets the behavior of Close on a connection which still
 // has data waiting to be sent or to be acknowledged.
 //
 // If sec < 0 (the default), the operating system finishes sending the
 // data in the background.
 //
 // If sec == 0, the operating system discards any unsent or
 // unacknowledged data.
 //
 // If sec > 0, the data is sent in the background as with sec < 0. On
 // some operating systems after sec seconds have elapsed any remaining
 // unsent data may be discarded.
 func (c *TCPConn) SetLinger(sec int) error {
 	if !c.ok() {
 		return syscall.EINVAL
 	}
 	if err := setLinger(c.fd, sec); err != nil {
 		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }

 // SetKeepAlive sets whether the operating system should send
 // keepalive messages on the connection.
 func (c *TCPConn) SetKeepAlive(keepalive bool) error {
 	if !c.ok() {
 		return syscall.EINVAL
 	}
 	if err := setKeepAlive(c.fd, keepalive); err != nil {
 		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }

 // SetKeepAlivePeriod sets period between keep alives.
 func (c *TCPConn) SetKeepAlivePeriod(d time.Duration) error {
 	if !c.ok() {
 		return syscall.EINVAL
 	}
 	if err := setKeepAlivePeriod(c.fd, d); err != nil {
 		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }

 // SetNoDelay controls whether the operating system should delay
 // packet transmission in hopes of sending fewer packets (Nagle's
 // algorithm).  The default is true (no delay), meaning that data is
 // sent as soon as possible after a Write.
 func (c *TCPConn) SetNoDelay(noDelay bool) error {
 	if !c.ok() {
 		return syscall.EINVAL
 	}
 	if err := setNoDelay(c.fd, noDelay); err != nil {
 		return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }

 // DialTCP connects to the remote address raddr on the network net,
 // which must be "tcp", "tcp4", or "tcp6".  If laddr is not nil, it is
 // used as the local address for the connection.
 func DialTCP(net string, laddr, raddr *TCPAddr) (*TCPConn, error) {
 	switch net {
 	case "tcp", "tcp4", "tcp6":
 	default:
 		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(net)}
 	}
 	if raddr == nil {
 		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
 	}
 	return dialTCP(net, laddr, raddr, noDeadline)
 }

 func dialTCP(net string, laddr, raddr *TCPAddr, deadline time.Time) (*TCPConn, error) {
 	fd, err := internetSocket(net, laddr, raddr, deadline, syscall.SOCK_STREAM, 0, "dial")

 	// TCP has a rarely used mechanism called a 'simultaneous connection' in
 	// which Dial("tcp", addr1, addr2) run on the machine at addr1 can
 	// connect to a simultaneous Dial("tcp", addr2, addr1) run on the machine
 	// at addr2, without either machine executing Listen.  If laddr == nil,
 	// it means we want the kernel to pick an appropriate originating local
 	// address.  Some Linux kernels cycle blindly through a fixed range of
 	// local ports, regardless of destination port.  If a kernel happens to
 	// pick local port 50001 as the source for a Dial("tcp", "", "localhost:50001"),
 	// then the Dial will succeed, having simultaneously connected to itself.
 	// This can only happen when we are letting the kernel pick a port (laddr == nil)
 	// and when there is no listener for the destination address.
 	// It's hard to argue this is anything other than a kernel bug.  If we
 	// see this happen, rather than expose the buggy effect to users, we
 	// close the fd and try again.  If it happens twice more, we relent and
 	// use the result.  See also:
 	//	https://golang.org/issue/2690
 	//	http://stackoverflow.com/questions/4949858/
 	//
 	// The opposite can also happen: if we ask the kernel to pick an appropriate
 	// originating local address, sometimes it picks one that is already in use.
 	// So if the error is EADDRNOTAVAIL, we have to try again too, just for
 	// a different reason.
 	//
 	// The kernel socket code is no doubt enjoying watching us squirm.
 	for i := 0; i < 2 && (laddr == nil || laddr.Port == 0) && (selfConnect(fd, err) || spuriousENOTAVAIL(err)); i++ {
 		if err == nil {
 			fd.Close()
 		}
 		fd, err = internetSocket(net, laddr, raddr, deadline, syscall.SOCK_STREAM, 0, "dial")
 	}

 	if err != nil {
 		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
 	}
 	return newTCPConn(fd), nil
 }

 func selfConnect(fd *netFD, err error) bool {
 	// If the connect failed, we clearly didn't connect to ourselves.
 	if err != nil {
 		return false
 	}

 	// The socket constructor can return an fd with raddr nil under certain
 	// unknown conditions. The errors in the calls there to Getpeername
 	// are discarded, but we can't catch the problem there because those
 	// calls are sometimes legally erroneous with a "socket not connected".
 	// Since this code (selfConnect) is already trying to work around
 	// a problem, we make sure if this happens we recognize trouble and
 	// ask the DialTCP routine to try again.
 	// TODO: try to understand what's really going on.
 	if fd.laddr == nil || fd.raddr == nil {
 		return true
 	}
 	l := fd.laddr.(*TCPAddr)
 	r := fd.raddr.(*TCPAddr)
 	return l.Port == r.Port && l.IP.Equal(r.IP)
 }

 func spuriousENOTAVAIL(err error) bool {
 	if op, ok := err.(*OpError); ok {
 		err = op.Err
 	}
 	if sys, ok := err.(*os.SyscallError); ok {
 		err = sys.Err
 	}
 	return err == syscall.EADDRNOTAVAIL
 }

 // TCPListener is a TCP network listener.  Clients should typically
 // use variables of type Listener instead of assuming TCP.
 type TCPListener struct {
 	fd *netFD
 }

 // AcceptTCP accepts the next incoming call and returns the new
 // connection.
 func (l *TCPListener) AcceptTCP() (*TCPConn, error) {
 	if l == nil || l.fd == nil {
 		return nil, syscall.EINVAL
 	}
 	fd, err := l.fd.accept()
 	if err != nil {
 		return nil, &OpError{Op: "accept", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return newTCPConn(fd), nil
 }

 // Accept implements the Accept method in the Listener interface; it
 // waits for the next call and returns a generic Conn.
 func (l *TCPListener) Accept() (Conn, error) {
 	c, err := l.AcceptTCP()
 	if err != nil {
 		return nil, err
 	}
 	return c, nil
 }

 // Close stops listening on the TCP address.
 // Already Accepted connections are not closed.
 func (l *TCPListener) Close() error {
 	if l == nil || l.fd == nil {
 		return syscall.EINVAL
 	}
 	err := l.fd.Close()
 	if err != nil {
 		err = &OpError{Op: "close", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return err
 }

 // Addr returns the listener's network address, a *TCPAddr.
 // The Addr returned is shared by all invocations of Addr, so
 // do not modify it.
 func (l *TCPListener) Addr() Addr { return l.fd.laddr }

 // SetDeadline sets the deadline associated with the listener.
 // A zero time value disables the deadline.
 func (l *TCPListener) SetDeadline(t time.Time) error {
 	if l == nil || l.fd == nil {
 		return syscall.EINVAL
 	}
 	if err := l.fd.setDeadline(t); err != nil {
 		return &OpError{Op: "set", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return nil
 }

 // File returns a copy of the underlying os.File, set to blocking
 // mode.  It is the caller's responsibility to close f when finished.
 // Closing l does not affect f, and closing f does not affect l.
 //
 // The returned os.File's file descriptor is different from the
 // connection's.  Attempting to change properties of the original
 // using this duplicate may or may not have the desired effect.
 func (l *TCPListener) File() (f *os.File, err error) {
 	f, err = l.fd.dup()
 	if err != nil {
 		err = &OpError{Op: "file", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return
 }

 // ListenTCP announces on the TCP address laddr and returns a TCP
 // listener.  Net must be "tcp", "tcp4", or "tcp6".  If laddr has a
 // port of 0, ListenTCP will choose an available port.  The caller can
 // use the Addr method of TCPListener to retrieve the chosen address.
 func ListenTCP(net string, laddr *TCPAddr) (*TCPListener, error) {
 	switch net {
 	case "tcp", "tcp4", "tcp6":
 	default:
 		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr.opAddr(), Err: UnknownNetworkError(net)}
 	}
 	if laddr == nil {
 		laddr = &TCPAddr{}
 	}
 	fd, err := internetSocket(net, laddr, nil, noDeadline, syscall.SOCK_STREAM, 0, "listen")
 	if err != nil {
 		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
 	}
 	return &TCPListener{fd}, nil
 }
	// Copyright 2009 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.

	// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows

	package net

	import (
	"io"
	"os"
	"syscall"
	"time"
	)

	func sockaddrToTCP(sa syscall.Sockaddr) Addr {
	switch sa := sa.(type) {
	case *syscall.SockaddrInet4:
	return &TCPAddr{IP: sa.Addr[0:], Port: sa.Port}
	case *syscall.SockaddrInet6:
	return &TCPAddr{IP: sa.Addr[0:], Port: sa.Port, Zone: zoneToString(int(sa.ZoneId))}
	}
	return nil
	}

	func (a *TCPAddr) family() int {
	if a == nil \|\| len(a.IP) <= IPv4len {
	return syscall.AF_INET
	}
	if a.IP.To4() != nil {
	return syscall.AF_INET
	}
	return syscall.AF_INET6
	}

	func (a *TCPAddr) sockaddr(family int) (syscall.Sockaddr, error) {
	if a == nil {
	return nil, nil
	}
	return ipToSockaddr(family, a.IP, a.Port, a.Zone)
	}

	// TCPConn is an implementation of the Conn interface for TCP network
	// connections.
	type TCPConn struct {
	conn
	}

	func newTCPConn(fd netFD) TCPConn {
	c := &TCPConn{conn{fd}}
	setNoDelay(c.fd, true)
	return c
	}

	// ReadFrom implements the io.ReaderFrom ReadFrom method.
	func (c *TCPConn) ReadFrom(r io.Reader) (int64, error) {
	if n, err, handled := sendFile(c.fd, r); handled {
	if err != nil && err != io.EOF {
	err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return n, err
	}
	n, err := genericReadFrom(c, r)
	if err != nil && err != io.EOF {
	err = &OpError{Op: "read", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return n, err
	}

	// CloseRead shuts down the reading side of the TCP connection.
	// Most callers should just use Close.
	func (c *TCPConn) CloseRead() error {
	if !c.ok() {
	return syscall.EINVAL
	}
	err := c.fd.closeRead()
	if err != nil {
	err = &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return err
	}

	// CloseWrite shuts down the writing side of the TCP connection.
	// Most callers should just use Close.
	func (c *TCPConn) CloseWrite() error {
	if !c.ok() {
	return syscall.EINVAL
	}
	err := c.fd.closeWrite()
	if err != nil {
	err = &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return err
	}

	// SetLinger sets the behavior of Close on a connection which still
	// has data waiting to be sent or to be acknowledged.
	//
	// If sec < 0 (the default), the operating system finishes sending the
	// data in the background.
	//
	// If sec == 0, the operating system discards any unsent or
	// unacknowledged data.
	//
	// If sec > 0, the data is sent in the background as with sec < 0. On
	// some operating systems after sec seconds have elapsed any remaining
	// unsent data may be discarded.
	func (c *TCPConn) SetLinger(sec int) error {
	if !c.ok() {
	return syscall.EINVAL
	}
	if err := setLinger(c.fd, sec); err != nil {
	return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return nil
	}

	// SetKeepAlive sets whether the operating system should send
	// keepalive messages on the connection.
	func (c *TCPConn) SetKeepAlive(keepalive bool) error {
	if !c.ok() {
	return syscall.EINVAL
	}
	if err := setKeepAlive(c.fd, keepalive); err != nil {
	return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return nil
	}

	// SetKeepAlivePeriod sets period between keep alives.
	func (c *TCPConn) SetKeepAlivePeriod(d time.Duration) error {
	if !c.ok() {
	return syscall.EINVAL
	}
	if err := setKeepAlivePeriod(c.fd, d); err != nil {
	return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return nil
	}

	// SetNoDelay controls whether the operating system should delay
	// packet transmission in hopes of sending fewer packets (Nagle's
	// algorithm). The default is true (no delay), meaning that data is
	// sent as soon as possible after a Write.
	func (c *TCPConn) SetNoDelay(noDelay bool) error {
	if !c.ok() {
	return syscall.EINVAL
	}
	if err := setNoDelay(c.fd, noDelay); err != nil {
	return &OpError{Op: "set", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return nil
	}

	// DialTCP connects to the remote address raddr on the network net,
	// which must be "tcp", "tcp4", or "tcp6". If laddr is not nil, it is
	// used as the local address for the connection.
	func DialTCP(net string, laddr, raddr TCPAddr) (TCPConn, error) {
	switch net {
	case "tcp", "tcp4", "tcp6":
	default:
	return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(net)}
	}
	if raddr == nil {
	return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
	}
	return dialTCP(net, laddr, raddr, noDeadline)
	}

	func dialTCP(net string, laddr, raddr TCPAddr, deadline time.Time) (TCPConn, error) {
	fd, err := internetSocket(net, laddr, raddr, deadline, syscall.SOCK_STREAM, 0, "dial")

	// TCP has a rarely used mechanism called a 'simultaneous connection' in
	// which Dial("tcp", addr1, addr2) run on the machine at addr1 can
	// connect to a simultaneous Dial("tcp", addr2, addr1) run on the machine
	// at addr2, without either machine executing Listen. If laddr == nil,
	// it means we want the kernel to pick an appropriate originating local
	// address. Some Linux kernels cycle blindly through a fixed range of
	// local ports, regardless of destination port. If a kernel happens to
	// pick local port 50001 as the source for a Dial("tcp", "", "localhost:50001"),
	// then the Dial will succeed, having simultaneously connected to itself.
	// This can only happen when we are letting the kernel pick a port (laddr == nil)
	// and when there is no listener for the destination address.
	// It's hard to argue this is anything other than a kernel bug. If we
	// see this happen, rather than expose the buggy effect to users, we
	// close the fd and try again. If it happens twice more, we relent and
	// use the result. See also:
	// https://golang.org/issue/2690
	// http://stackoverflow.com/questions/4949858/
	//
	// The opposite can also happen: if we ask the kernel to pick an appropriate
	// originating local address, sometimes it picks one that is already in use.
	// So if the error is EADDRNOTAVAIL, we have to try again too, just for
	// a different reason.
	//
	// The kernel socket code is no doubt enjoying watching us squirm.
	for i := 0; i < 2 && (laddr == nil \|\| laddr.Port == 0) && (selfConnect(fd, err) \|\| spuriousENOTAVAIL(err)); i++ {
	if err == nil {
	fd.Close()
	}
	fd, err = internetSocket(net, laddr, raddr, deadline, syscall.SOCK_STREAM, 0, "dial")
	}

	if err != nil {
	return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
	}
	return newTCPConn(fd), nil
	}

	func selfConnect(fd *netFD, err error) bool {
	// If the connect failed, we clearly didn't connect to ourselves.
	if err != nil {
	return false
	}

	// The socket constructor can return an fd with raddr nil under certain
	// unknown conditions. The errors in the calls there to Getpeername
	// are discarded, but we can't catch the problem there because those
	// calls are sometimes legally erroneous with a "socket not connected".
	// Since this code (selfConnect) is already trying to work around
	// a problem, we make sure if this happens we recognize trouble and
	// ask the DialTCP routine to try again.
	// TODO: try to understand what's really going on.
	if fd.laddr == nil \|\| fd.raddr == nil {
	return true
	}
	l := fd.laddr.(*TCPAddr)
	r := fd.raddr.(*TCPAddr)
	return l.Port == r.Port && l.IP.Equal(r.IP)
	}

	func spuriousENOTAVAIL(err error) bool {
	if op, ok := err.(*OpError); ok {
	err = op.Err
	}
	if sys, ok := err.(*os.SyscallError); ok {
	err = sys.Err
	}
	return err == syscall.EADDRNOTAVAIL
	}

	// TCPListener is a TCP network listener. Clients should typically
	// use variables of type Listener instead of assuming TCP.
	type TCPListener struct {
	fd *netFD
	}

	// AcceptTCP accepts the next incoming call and returns the new
	// connection.
	func (l TCPListener) AcceptTCP() (TCPConn, error) {
	if l == nil \|\| l.fd == nil {
	return nil, syscall.EINVAL
	}
	fd, err := l.fd.accept()
	if err != nil {
	return nil, &OpError{Op: "accept", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
	}
	return newTCPConn(fd), nil
	}

	// Accept implements the Accept method in the Listener interface; it
	// waits for the next call and returns a generic Conn.
	func (l *TCPListener) Accept() (Conn, error) {
	c, err := l.AcceptTCP()
	if err != nil {
	return nil, err
	}
	return c, nil
	}

	// Close stops listening on the TCP address.
	// Already Accepted connections are not closed.
	func (l *TCPListener) Close() error {
	if l == nil \|\| l.fd == nil {
	return syscall.EINVAL
	}
	err := l.fd.Close()
	if err != nil {
	err = &OpError{Op: "close", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
	}
	return err
	}

	// Addr returns the listener's network address, a *TCPAddr.
	// The Addr returned is shared by all invocations of Addr, so
	// do not modify it.
	func (l *TCPListener) Addr() Addr { return l.fd.laddr }

	// SetDeadline sets the deadline associated with the listener.
	// A zero time value disables the deadline.
	func (l *TCPListener) SetDeadline(t time.Time) error {
	if l == nil \|\| l.fd == nil {
	return syscall.EINVAL
	}
	if err := l.fd.setDeadline(t); err != nil {
	return &OpError{Op: "set", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
	}
	return nil
	}

	// File returns a copy of the underlying os.File, set to blocking
	// mode. It is the caller's responsibility to close f when finished.
	// Closing l does not affect f, and closing f does not affect l.
	//
	// The returned os.File's file descriptor is different from the
	// connection's. Attempting to change properties of the original
	// using this duplicate may or may not have the desired effect.
	func (l TCPListener) File() (f os.File, err error) {
	f, err = l.fd.dup()
	if err != nil {
	err = &OpError{Op: "file", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
	}
	return
	}

	// ListenTCP announces on the TCP address laddr and returns a TCP
	// listener. Net must be "tcp", "tcp4", or "tcp6". If laddr has a
	// port of 0, ListenTCP will choose an available port. The caller can
	// use the Addr method of TCPListener to retrieve the chosen address.
	func ListenTCP(net string, laddr TCPAddr) (TCPListener, error) {
	switch net {
	case "tcp", "tcp4", "tcp6":
	default:
	return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr.opAddr(), Err: UnknownNetworkError(net)}
	}
	if laddr == nil {
	laddr = &TCPAddr{}
	}
	fd, err := internetSocket(net, laddr, nil, noDeadline, syscall.SOCK_STREAM, 0, "listen")
	if err != nil {
	return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
	}
	return &TCPListener{fd}, nil
	}