src/net/tcpsock.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.

 package net

 import (
 	"context"
 	"internal/itoa"
 	"io"
 	"net/netip"
 	"os"
 	"syscall"
 	"time"
 )

 // BUG(mikio): On JS and Windows, the File method of TCPConn and
 // TCPListener is not implemented.

 // TCPAddr represents the address of a TCP end point.
 type TCPAddr struct {
 	IP   IP
 	Port int
 	Zone string // IPv6 scoped addressing zone
 }

 // AddrPort returns the TCPAddr a as a netip.AddrPort.
 //
 // If a.Port does not fit in a uint16, it's silently truncated.
 //
 // If a is nil, a zero value is returned.
 func (a *TCPAddr) AddrPort() netip.AddrPort {
 	if a == nil {
 		return netip.AddrPort{}
 	}
 	na, _ := netip.AddrFromSlice(a.IP)
 	na = na.WithZone(a.Zone)
 	return netip.AddrPortFrom(na, uint16(a.Port))
 }

 // Network returns the address's network name, "tcp".
 func (a *TCPAddr) Network() string { return "tcp" }

 func (a *TCPAddr) String() string {
 	if a == nil {
 		return "<nil>"
 	}
 	ip := ipEmptyString(a.IP)
 	if a.Zone != "" {
 		return JoinHostPort(ip+"%"+a.Zone, itoa.Itoa(a.Port))
 	}
 	return JoinHostPort(ip, itoa.Itoa(a.Port))
 }

 func (a *TCPAddr) isWildcard() bool {
 	if a == nil || a.IP == nil {
 		return true
 	}
 	return a.IP.IsUnspecified()
 }

 func (a *TCPAddr) opAddr() Addr {
 	if a == nil {
 		return nil
 	}
 	return a
 }

 // ResolveTCPAddr returns an address of TCP end point.
 //
 // The network must be a TCP network name.
 //
 // If the host in the address parameter is not a literal IP address or
 // the port is not a literal port number, ResolveTCPAddr resolves the
 // address to an address of TCP end point.
 // Otherwise, it parses the address as a pair of literal IP address
 // and port number.
 // The address parameter can use a host name, but this is not
 // recommended, because it will return at most one of the host name's
 // IP addresses.
 //
 // See func Dial for a description of the network and address
 // parameters.
 func ResolveTCPAddr(network, address string) (*TCPAddr, error) {
 	switch network {
 	case "tcp", "tcp4", "tcp6":
 	case "": // a hint wildcard for Go 1.0 undocumented behavior
 		network = "tcp"
 	default:
 		return nil, UnknownNetworkError(network)
 	}
 	addrs, err := DefaultResolver.internetAddrList(context.Background(), network, address)
 	if err != nil {
 		return nil, err
 	}
 	return addrs.forResolve(network, address).(*TCPAddr), nil
 }

 // TCPAddrFromAddrPort returns addr as a TCPAddr. If addr.IsValid() is false,
 // then the returned TCPAddr will contain a nil IP field, indicating an
 // address family-agnostic unspecified address.
 func TCPAddrFromAddrPort(addr netip.AddrPort) *TCPAddr {
 	return &TCPAddr{
 		IP:   addr.Addr().AsSlice(),
 		Zone: addr.Addr().Zone(),
 		Port: int(addr.Port()),
 	}
 }

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

 // SyscallConn returns a raw network connection.
 // This implements the syscall.Conn interface.
 func (c *TCPConn) SyscallConn() (syscall.RawConn, error) {
 	if !c.ok() {
 		return nil, syscall.EINVAL
 	}
 	return newRawConn(c.fd)
 }

 // ReadFrom implements the io.ReaderFrom ReadFrom method.
 func (c *TCPConn) ReadFrom(r io.Reader) (int64, error) {
 	if !c.ok() {
 		return 0, syscall.EINVAL
 	}
 	n, err := c.readFrom(r)
 	if err != nil && err != io.EOF {
 		err = &OpError{Op: "readfrom", 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
 	}
 	if err := c.fd.closeRead(); err != nil {
 		return &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }

 // 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
 	}
 	if err := c.fd.closeWrite(); err != nil {
 		return &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
 	}
 	return nil
 }

 // 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
 // keep-alive 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
 }

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

 // DialTCP acts like Dial for TCP networks.
 //
 // The network must be a TCP network name; see func Dial for details.
 //
 // If laddr is nil, a local address is automatically chosen.
 // If the IP field of raddr is nil or an unspecified IP address, the
 // local system is assumed.
 func DialTCP(network string, laddr, raddr *TCPAddr) (*TCPConn, error) {
 	switch network {
 	case "tcp", "tcp4", "tcp6":
 	default:
 		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(network)}
 	}
 	if raddr == nil {
 		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
 	}
 	sd := &sysDialer{network: network, address: raddr.String()}
 	c, err := sd.dialTCP(context.Background(), laddr, raddr)
 	if err != nil {
 		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
 	}
 	return c, nil
 }

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

 // SyscallConn returns a raw network connection.
 // This implements the syscall.Conn interface.
 //
 // The returned RawConn only supports calling Control. Read and
 // Write return an error.
 func (l *TCPListener) SyscallConn() (syscall.RawConn, error) {
 	if !l.ok() {
 		return nil, syscall.EINVAL
 	}
 	return newRawListener(l.fd)
 }

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

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

 // 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.ok() {
 		return syscall.EINVAL
 	}
 	if err := l.fd.pfd.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.
 // 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) {
 	if !l.ok() {
 		return nil, syscall.EINVAL
 	}
 	f, err = l.file()
 	if err != nil {
 		return nil, &OpError{Op: "file", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
 	}
 	return
 }

 // ListenTCP acts like Listen for TCP networks.
 //
 // The network must be a TCP network name; see func Dial for details.
 //
 // If the IP field of laddr is nil or an unspecified IP address,
 // ListenTCP listens on all available unicast and anycast IP addresses
 // of the local system.
 // If the Port field of laddr is 0, a port number is automatically
 // chosen.
 func ListenTCP(network string, laddr *TCPAddr) (*TCPListener, error) {
 	switch network {
 	case "tcp", "tcp4", "tcp6":
 	default:
 		return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: laddr.opAddr(), Err: UnknownNetworkError(network)}
 	}
 	if laddr == nil {
 		laddr = &TCPAddr{}
 	}
 	sl := &sysListener{network: network, address: laddr.String()}
 	ln, err := sl.listenTCP(context.Background(), laddr)
 	if err != nil {
 		return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: laddr.opAddr(), Err: err}
 	}
 	return ln, nil
 }

 // roundDurationUp rounds d to the next multiple of to.
 func roundDurationUp(d time.Duration, to time.Duration) time.Duration {
 	return (d + to - 1) / to
 }
	// 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.

	package net

	import (
	"context"
	"internal/itoa"
	"io"
	"net/netip"
	"os"
	"syscall"
	"time"
	)

	// BUG(mikio): On JS and Windows, the File method of TCPConn and
	// TCPListener is not implemented.

	// TCPAddr represents the address of a TCP end point.
	type TCPAddr struct {
	IP IP
	Port int
	Zone string // IPv6 scoped addressing zone
	}

	// AddrPort returns the TCPAddr a as a netip.AddrPort.
	//
	// If a.Port does not fit in a uint16, it's silently truncated.
	//
	// If a is nil, a zero value is returned.
	func (a *TCPAddr) AddrPort() netip.AddrPort {
	if a == nil {
	return netip.AddrPort{}
	}
	na, _ := netip.AddrFromSlice(a.IP)
	na = na.WithZone(a.Zone)
	return netip.AddrPortFrom(na, uint16(a.Port))
	}

	// Network returns the address's network name, "tcp".
	func (a *TCPAddr) Network() string { return "tcp" }

	func (a *TCPAddr) String() string {
	if a == nil {
	return "<nil>"
	}
	ip := ipEmptyString(a.IP)
	if a.Zone != "" {
	return JoinHostPort(ip+"%"+a.Zone, itoa.Itoa(a.Port))
	}
	return JoinHostPort(ip, itoa.Itoa(a.Port))
	}

	func (a *TCPAddr) isWildcard() bool {
	if a == nil \|\| a.IP == nil {
	return true
	}
	return a.IP.IsUnspecified()
	}

	func (a *TCPAddr) opAddr() Addr {
	if a == nil {
	return nil
	}
	return a
	}

	// ResolveTCPAddr returns an address of TCP end point.
	//
	// The network must be a TCP network name.
	//
	// If the host in the address parameter is not a literal IP address or
	// the port is not a literal port number, ResolveTCPAddr resolves the
	// address to an address of TCP end point.
	// Otherwise, it parses the address as a pair of literal IP address
	// and port number.
	// The address parameter can use a host name, but this is not
	// recommended, because it will return at most one of the host name's
	// IP addresses.
	//
	// See func Dial for a description of the network and address
	// parameters.
	func ResolveTCPAddr(network, address string) (*TCPAddr, error) {
	switch network {
	case "tcp", "tcp4", "tcp6":
	case "": // a hint wildcard for Go 1.0 undocumented behavior
	network = "tcp"
	default:
	return nil, UnknownNetworkError(network)
	}
	addrs, err := DefaultResolver.internetAddrList(context.Background(), network, address)
	if err != nil {
	return nil, err
	}
	return addrs.forResolve(network, address).(*TCPAddr), nil
	}

	// TCPAddrFromAddrPort returns addr as a TCPAddr. If addr.IsValid() is false,
	// then the returned TCPAddr will contain a nil IP field, indicating an
	// address family-agnostic unspecified address.
	func TCPAddrFromAddrPort(addr netip.AddrPort) *TCPAddr {
	return &TCPAddr{
	IP: addr.Addr().AsSlice(),
	Zone: addr.Addr().Zone(),
	Port: int(addr.Port()),
	}
	}

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

	// SyscallConn returns a raw network connection.
	// This implements the syscall.Conn interface.
	func (c *TCPConn) SyscallConn() (syscall.RawConn, error) {
	if !c.ok() {
	return nil, syscall.EINVAL
	}
	return newRawConn(c.fd)
	}

	// ReadFrom implements the io.ReaderFrom ReadFrom method.
	func (c *TCPConn) ReadFrom(r io.Reader) (int64, error) {
	if !c.ok() {
	return 0, syscall.EINVAL
	}
	n, err := c.readFrom(r)
	if err != nil && err != io.EOF {
	err = &OpError{Op: "readfrom", 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
	}
	if err := c.fd.closeRead(); err != nil {
	return &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return nil
	}

	// 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
	}
	if err := c.fd.closeWrite(); err != nil {
	return &OpError{Op: "close", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
	}
	return nil
	}

	// 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
	// keep-alive 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
	}

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

	// DialTCP acts like Dial for TCP networks.
	//
	// The network must be a TCP network name; see func Dial for details.
	//
	// If laddr is nil, a local address is automatically chosen.
	// If the IP field of raddr is nil or an unspecified IP address, the
	// local system is assumed.
	func DialTCP(network string, laddr, raddr TCPAddr) (TCPConn, error) {
	switch network {
	case "tcp", "tcp4", "tcp6":
	default:
	return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(network)}
	}
	if raddr == nil {
	return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
	}
	sd := &sysDialer{network: network, address: raddr.String()}
	c, err := sd.dialTCP(context.Background(), laddr, raddr)
	if err != nil {
	return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
	}
	return c, nil
	}

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

	// SyscallConn returns a raw network connection.
	// This implements the syscall.Conn interface.
	//
	// The returned RawConn only supports calling Control. Read and
	// Write return an error.
	func (l *TCPListener) SyscallConn() (syscall.RawConn, error) {
	if !l.ok() {
	return nil, syscall.EINVAL
	}
	return newRawListener(l.fd)
	}

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

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

	// 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.ok() {
	return syscall.EINVAL
	}
	if err := l.fd.pfd.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.
	// 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) {
	if !l.ok() {
	return nil, syscall.EINVAL
	}
	f, err = l.file()
	if err != nil {
	return nil, &OpError{Op: "file", Net: l.fd.net, Source: nil, Addr: l.fd.laddr, Err: err}
	}
	return
	}

	// ListenTCP acts like Listen for TCP networks.
	//
	// The network must be a TCP network name; see func Dial for details.
	//
	// If the IP field of laddr is nil or an unspecified IP address,
	// ListenTCP listens on all available unicast and anycast IP addresses
	// of the local system.
	// If the Port field of laddr is 0, a port number is automatically
	// chosen.
	func ListenTCP(network string, laddr TCPAddr) (TCPListener, error) {
	switch network {
	case "tcp", "tcp4", "tcp6":
	default:
	return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: laddr.opAddr(), Err: UnknownNetworkError(network)}
	}
	if laddr == nil {
	laddr = &TCPAddr{}
	}
	sl := &sysListener{network: network, address: laddr.String()}
	ln, err := sl.listenTCP(context.Background(), laddr)
	if err != nil {
	return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: laddr.opAddr(), Err: err}
	}
	return ln, nil
	}

	// roundDurationUp rounds d to the next multiple of to.
	func roundDurationUp(d time.Duration, to time.Duration) time.Duration {
	return (d + to - 1) / to
	}