net: add Dialer.Cancel to cancel pending dials

Dialer.Cancel is a new optional <-chan struct{} channel whose closure
indicates that the dial should be canceled. It is compatible with the
x/net/context and http.Request.Cancel types.

Tested by hand with:

package main

    import (
            "log"
            "net"
            "time"
    )

    func main() {
            log.Printf("start.")
            var d net.Dialer
            cancel := make(chan struct{})
            time.AfterFunc(2*time.Second, func() {
                    log.Printf("timeout firing")
                    close(cancel)
            })
            d.Cancel = cancel
            c, err := d.Dial("tcp", "192.168.0.1:22")
            if err != nil {
                    log.Print(err)
                    return
            }
            log.Fatalf("unexpected connect: %v", c)
    }

Which says:

    2015/12/14 22:24:58 start.
    2015/12/14 22:25:00 timeout firing
    2015/12/14 22:25:00 dial tcp 192.168.0.1:22: operation was canceled

Fixes #11225

Change-Id: I2ef39e3a540e29fe6bfec03ab7a629a6b187fcb3
Reviewed-on: https://go-review.googlesource.com/17821Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/dial.go

@@ -57,6 +57,11 @@ type Dialer struct {
 	// 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.
@@ -361,7 +366,7 @@ func dialSingle(ctx *dialContext, ra Addr, deadline time.Time) (c Conn, err erro
 	switch ra := ra.(type) {
 	case *TCPAddr:
 		la, _ := la.(*TCPAddr)
-		c, err = testHookDialTCP(ctx.network, la, ra, deadline)
+		c, err = testHookDialTCP(ctx.network, la, ra, deadline, ctx.Cancel)
 	case *UDPAddr:
 		la, _ := la.(*UDPAddr)
 		c, err = dialUDP(ctx.network, la, ra, deadline)

src/net/dial_test.go

@@ -5,6 +5,7 @@
 package net
 
 import (
+	"internal/testenv"
 	"io"
 	"net/internal/socktest"
 	"runtime"
@@ -236,8 +237,8 @@ const (
 // In some environments, the slow IPs may be explicitly unreachable, and fail
 // more quickly than expected. This test hook prevents dialTCP from returning
 // before the deadline.
-func slowDialTCP(net string, laddr, raddr *TCPAddr, deadline time.Time) (*TCPConn, error) {
-	c, err := dialTCP(net, laddr, raddr, deadline)
+func slowDialTCP(net string, laddr, raddr *TCPAddr, deadline time.Time, cancel <-chan struct{}) (*TCPConn, error) {
+	c, err := dialTCP(net, laddr, raddr, deadline, cancel)
 	if ParseIP(slowDst4).Equal(raddr.IP) || ParseIP(slowDst6).Equal(raddr.IP) {
 		time.Sleep(deadline.Sub(time.Now()))
 	}
@@ -716,3 +717,64 @@ func TestDialerKeepAlive(t *testing.T) {
 		}
 	}
 }
+
+func TestDialCancel(t *testing.T) {
+	if runtime.GOOS == "plan9" || runtime.GOOS == "nacl" {
+		// plan9 is not implemented and nacl doesn't have
+		// external network access.
+		t.Skip("skipping on %s", runtime.GOOS)
+	}
+	onGoBuildFarm := testenv.Builder() != ""
+	if testing.Short() && !onGoBuildFarm {
+		t.Skip("skipping in short mode")
+	}
+
+	blackholeIPPort := JoinHostPort(slowDst4, "1234")
+	if !supportsIPv4 {
+		blackholeIPPort = JoinHostPort(slowDst6, "1234")
+	}
+
+	ticker := time.NewTicker(10 * time.Millisecond)
+	defer ticker.Stop()
+
+	const cancelTick = 5 // the timer tick we cancel the dial at
+	const timeoutTick = 100
+
+	var d Dialer
+	cancel := make(chan struct{})
+	d.Cancel = cancel
+	errc := make(chan error, 1)
+	connc := make(chan Conn, 1)
+	go func() {
+		if c, err := d.Dial("tcp", blackholeIPPort); err != nil {
+			errc <- err
+		} else {
+			connc <- c
+		}
+	}()
+	ticks := 0
+	for {
+		select {
+		case <-ticker.C:
+			ticks++
+			if ticks == cancelTick {
+				close(cancel)
+			}
+			if ticks == timeoutTick {
+				t.Fatal("timeout waiting for dial to fail")
+			}
+		case c := <-connc:
+			c.Close()
+			t.Fatal("unexpected successful connection")
+		case err := <-errc:
+			if ticks < cancelTick {
+				t.Fatalf("dial error after %d ticks (%d before cancel sent): %v",
+					ticks, cancelTick-ticks, err)
+			}
+			if oe, ok := err.(*OpError); !ok || oe.Err != errCanceled {
+				t.Fatalf("dial error = %v (%T); want OpError with Err == errCanceled", err, err)
+			}
+			return // success.
+		}
+	}
+}

src/net/fd_unix.go

@@ -68,7 +68,7 @@ func (fd *netFD) name() string {
 	return fd.net + ":" + ls + "->" + rs
 }
 
-func (fd *netFD) connect(la, ra syscall.Sockaddr, deadline time.Time) error {
+func (fd *netFD) connect(la, ra syscall.Sockaddr, deadline time.Time, cancel <-chan struct{}) error {
 	// Do not need to call fd.writeLock here,
 	// because fd is not yet accessible to user,
 	// so no concurrent operations are possible.
@@ -102,6 +102,19 @@ func (fd *netFD) connect(la, ra syscall.Sockaddr, deadline time.Time) error {
 		fd.setWriteDeadline(deadline)
 		defer fd.setWriteDeadline(noDeadline)
 	}
+	if cancel != nil {
+		done := make(chan bool)
+		defer close(done)
+		go func() {
+			select {
+			case <-cancel:
+				// Force the runtime's poller to immediately give
+				// up waiting for writability.
+				fd.setWriteDeadline(aLongTimeAgo)
+			case <-done:
+			}
+		}()
+	}
 	for {
 		// Performing multiple connect system calls on a
 		// non-blocking socket under Unix variants does not
@@ -112,6 +125,11 @@ func (fd *netFD) connect(la, ra syscall.Sockaddr, deadline time.Time) error {
 		// succeeded or failed. See issue 7474 for further
 		// details.
 		if err := fd.pd.WaitWrite(); err != nil {
+			select {
+			case <-cancel:
+				return errCanceled
+			default:
+			}
 			return err
 		}
 		nerr, err := getsockoptIntFunc(fd.sysfd, syscall.SOL_SOCKET, syscall.SO_ERROR)

src/net/fd_windows.go

@@ -320,7 +320,7 @@ func (fd *netFD) setAddr(laddr, raddr Addr) {
 	runtime.SetFinalizer(fd, (*netFD).Close)
 }
 
-func (fd *netFD) connect(la, ra syscall.Sockaddr, deadline time.Time) error {
+func (fd *netFD) connect(la, ra syscall.Sockaddr, deadline time.Time, cancel <-chan struct{}) error {
 	// Do not need to call fd.writeLock here,
 	// because fd is not yet accessible to user,
 	// so no concurrent operations are possible.
@@ -351,14 +351,38 @@ func (fd *netFD) connect(la, ra syscall.Sockaddr, deadline time.Time) error {
 	// Call ConnectEx API.
 	o := &fd.wop
 	o.sa = ra
+	if cancel != nil {
+		done := make(chan struct{})
+		defer close(done)
+		go func() {
+			select {
+			case <-cancel:
+				// TODO(bradfitz,brainman): cancel the dial operation
+				// somehow. Brad doesn't know Windows but is going to
+				// try this:
+				if canCancelIO {
+					syscall.CancelIoEx(o.fd.sysfd, &o.o)
+				} else {
+					wsrv.req <- ioSrvReq{o, nil}
+					<-o.errc
+				}
+			case <-done:
+			}
+		}()
+	}
 	_, err := wsrv.ExecIO(o, "ConnectEx", func(o *operation) error {
 		return connectExFunc(o.fd.sysfd, o.sa, nil, 0, nil, &o.o)
 	})
 	if err != nil {
-		if _, ok := err.(syscall.Errno); ok {
-			err = os.NewSyscallError("connectex", err)
+		select {
+		case <-cancel:
+			return errCanceled
+		default:
+			if _, ok := err.(syscall.Errno); ok {
+				err = os.NewSyscallError("connectex", err)
+			}
+			return err
 		}
-		return err
 	}
 	// Refresh socket properties.
 	return os.NewSyscallError("setsockopt", syscall.Setsockopt(fd.sysfd, syscall.SOL_SOCKET, syscall.SO_UPDATE_CONNECT_CONTEXT, (*byte)(unsafe.Pointer(&fd.sysfd)), int32(unsafe.Sizeof(fd.sysfd))))

src/net/iprawsock_posix.go

@@ -220,7 +220,7 @@ func dialIP(netProto string, laddr, raddr *IPAddr, deadline time.Time) (*IPConn,
 	if raddr == nil {
 		return nil, &OpError{Op: "dial", Net: netProto, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
 	}
-	fd, err := internetSocket(net, laddr, raddr, deadline, syscall.SOCK_RAW, proto, "dial")
+	fd, err := internetSocket(net, laddr, raddr, deadline, syscall.SOCK_RAW, proto, "dial", noCancel)
 	if err != nil {
 		return nil, &OpError{Op: "dial", Net: netProto, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
 	}
@@ -241,7 +241,7 @@ func ListenIP(netProto string, laddr *IPAddr) (*IPConn, error) {
 	default:
 		return nil, &OpError{Op: "listen", Net: netProto, Source: nil, Addr: laddr.opAddr(), Err: UnknownNetworkError(netProto)}
 	}
-	fd, err := internetSocket(net, laddr, nil, noDeadline, syscall.SOCK_RAW, proto, "listen")
+	fd, err := internetSocket(net, laddr, nil, noDeadline, syscall.SOCK_RAW, proto, "listen", noCancel)
 	if err != nil {
 		return nil, &OpError{Op: "listen", Net: netProto, Source: nil, Addr: laddr.opAddr(), Err: err}
 	}

src/net/ipsock_posix.go

@@ -156,9 +156,9 @@ func favoriteAddrFamily(net string, laddr, raddr sockaddr, mode string) (family
 
 // Internet sockets (TCP, UDP, IP)
 
-func internetSocket(net string, laddr, raddr sockaddr, deadline time.Time, sotype, proto int, mode string) (fd *netFD, err error) {
+func internetSocket(net string, laddr, raddr sockaddr, deadline time.Time, sotype, proto int, mode string, cancel <-chan struct{}) (fd *netFD, err error) {
 	family, ipv6only := favoriteAddrFamily(net, laddr, raddr, mode)
-	return socket(net, family, sotype, proto, ipv6only, laddr, raddr, deadline)
+	return socket(net, family, sotype, proto, ipv6only, laddr, raddr, deadline, cancel)
 }
 
 func ipToSockaddr(family int, ip IP, port int, zone string) (syscall.Sockaddr, error) {

src/net/net.go

@@ -426,7 +426,16 @@ func (e *OpError) Error() string {
 	return s
 }
 
-var noDeadline = time.Time{}
+var (
+	// aLongTimeAgo is a non-zero time, far in the past, used for
+	// immediate cancelation of dials.
+	aLongTimeAgo = time.Unix(233431200, 0)
+
+	// nonDeadline and noCancel are just zero values for
+	// readability with functions taking too many parameters.
+	noDeadline = time.Time{}
+	noCancel   = (chan struct{})(nil)
+)
 
 type timeout interface {
 	Timeout() bool

src/net/sock_posix.go

@@ -34,7 +34,7 @@ type sockaddr interface {
 
 // socket returns a network file descriptor that is ready for
 // asynchronous I/O using the network poller.
-func socket(net string, family, sotype, proto int, ipv6only bool, laddr, raddr sockaddr, deadline time.Time) (fd *netFD, err error) {
+func socket(net string, family, sotype, proto int, ipv6only bool, laddr, raddr sockaddr, deadline time.Time, cancel <-chan struct{}) (fd *netFD, err error) {
 	s, err := sysSocket(family, sotype, proto)
 	if err != nil {
 		return nil, err
@@ -86,7 +86,7 @@ func socket(net string, family, sotype, proto int, ipv6only bool, laddr, raddr s
 			return fd, nil
 		}
 	}
-	if err := fd.dial(laddr, raddr, deadline); err != nil {
+	if err := fd.dial(laddr, raddr, deadline, cancel); err != nil {
 		fd.Close()
 		return nil, err
 	}
@@ -117,7 +117,7 @@ func (fd *netFD) addrFunc() func(syscall.Sockaddr) Addr {
 	return func(syscall.Sockaddr) Addr { return nil }
 }
 
-func (fd *netFD) dial(laddr, raddr sockaddr, deadline time.Time) error {
+func (fd *netFD) dial(laddr, raddr sockaddr, deadline time.Time, cancel <-chan struct{}) error {
 	var err error
 	var lsa syscall.Sockaddr
 	if laddr != nil {
@@ -134,7 +134,7 @@ func (fd *netFD) dial(laddr, raddr sockaddr, deadline time.Time) error {
 		if rsa, err = raddr.sockaddr(fd.family); err != nil {
 			return err
 		}
-		if err := fd.connect(lsa, rsa, deadline); err != nil {
+		if err := fd.connect(lsa, rsa, deadline, cancel); err != nil {
 			return err
 		}
 		fd.isConnected = true

src/net/tcpsock_plan9.go

@@ -107,13 +107,14 @@ func (c *TCPConn) SetNoDelay(noDelay bool) error {
 // 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) {
-	return dialTCP(net, laddr, raddr, noDeadline)
+	return dialTCP(net, laddr, raddr, noDeadline, noCancel)
 }
 
-func dialTCP(net string, laddr, raddr *TCPAddr, deadline time.Time) (*TCPConn, error) {
+func dialTCP(net string, laddr, raddr *TCPAddr, deadline time.Time, cancel <-chan struct{}) (*TCPConn, error) {
 	if !deadline.IsZero() {
 		panic("net.dialTCP: deadline not implemented on Plan 9")
 	}
+	// TODO(bradfitz,0intro): also use the cancel channel.
 	switch net {
 	case "tcp", "tcp4", "tcp6":
 	default:

src/net/tcpsock_posix.go

@@ -164,11 +164,11 @@ func DialTCP(net string, laddr, raddr *TCPAddr) (*TCPConn, error) {
 	if raddr == nil {
 		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
 	}
-	return dialTCP(net, laddr, raddr, noDeadline)
+	return dialTCP(net, laddr, raddr, noDeadline, noCancel)
 }
 
-func dialTCP(net string, laddr, raddr *TCPAddr, deadline time.Time) (*TCPConn, error) {
-	fd, err := internetSocket(net, laddr, raddr, deadline, syscall.SOCK_STREAM, 0, "dial")
+func dialTCP(net string, laddr, raddr *TCPAddr, deadline time.Time, cancel <-chan struct{}) (*TCPConn, error) {
+	fd, err := internetSocket(net, laddr, raddr, deadline, syscall.SOCK_STREAM, 0, "dial", cancel)
 
 	// TCP has a rarely used mechanism called a 'simultaneous connection' in
 	// which Dial("tcp", addr1, addr2) run on the machine at addr1 can
@@ -198,7 +198,7 @@ func dialTCP(net string, laddr, raddr *TCPAddr, deadline time.Time) (*TCPConn, e
 		if err == nil {
 			fd.Close()
 		}
-		fd, err = internetSocket(net, laddr, raddr, deadline, syscall.SOCK_STREAM, 0, "dial")
+		fd, err = internetSocket(net, laddr, raddr, deadline, syscall.SOCK_STREAM, 0, "dial", cancel)
 	}
 
 	if err != nil {
@@ -326,7 +326,7 @@ func ListenTCP(net string, laddr *TCPAddr) (*TCPListener, error) {
 	if laddr == nil {
 		laddr = &TCPAddr{}
 	}
-	fd, err := internetSocket(net, laddr, nil, noDeadline, syscall.SOCK_STREAM, 0, "listen")
+	fd, err := internetSocket(net, laddr, nil, noDeadline, syscall.SOCK_STREAM, 0, "listen", noCancel)
 	if err != nil {
 		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
 	}

src/net/udpsock_posix.go

@@ -189,7 +189,7 @@ func DialUDP(net string, laddr, raddr *UDPAddr) (*UDPConn, error) {
 }
 
 func dialUDP(net string, laddr, raddr *UDPAddr, deadline time.Time) (*UDPConn, error) {
-	fd, err := internetSocket(net, laddr, raddr, deadline, syscall.SOCK_DGRAM, 0, "dial")
+	fd, err := internetSocket(net, laddr, raddr, deadline, syscall.SOCK_DGRAM, 0, "dial", noCancel)
 	if err != nil {
 		return nil, &OpError{Op: "dial", Net: net, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
 	}
@@ -212,7 +212,7 @@ func ListenUDP(net string, laddr *UDPAddr) (*UDPConn, error) {
 	if laddr == nil {
 		laddr = &UDPAddr{}
 	}
-	fd, err := internetSocket(net, laddr, nil, noDeadline, syscall.SOCK_DGRAM, 0, "listen")
+	fd, err := internetSocket(net, laddr, nil, noDeadline, syscall.SOCK_DGRAM, 0, "listen", noCancel)
 	if err != nil {
 		return nil, &OpError{Op: "listen", Net: net, Source: nil, Addr: laddr, Err: err}
 	}
@@ -239,7 +239,7 @@ func ListenMulticastUDP(network string, ifi *Interface, gaddr *UDPAddr) (*UDPCon
 	if gaddr == nil || gaddr.IP == nil {
 		return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: gaddr.opAddr(), Err: errMissingAddress}
 	}
-	fd, err := internetSocket(network, gaddr, nil, noDeadline, syscall.SOCK_DGRAM, 0, "listen")
+	fd, err := internetSocket(network, gaddr, nil, noDeadline, syscall.SOCK_DGRAM, 0, "listen", noCancel)
 	if err != nil {
 		return nil, &OpError{Op: "listen", Net: network, Source: nil, Addr: gaddr, Err: err}
 	}

src/net/unixsock_posix.go

@@ -42,7 +42,7 @@ func unixSocket(net string, laddr, raddr sockaddr, mode string, deadline time.Ti
 		return nil, errors.New("unknown mode: " + mode)
 	}
 
-	fd, err := socket(net, syscall.AF_UNIX, sotype, 0, false, laddr, raddr, deadline)
+	fd, err := socket(net, syscall.AF_UNIX, sotype, 0, false, laddr, raddr, deadline, noCancel)
 	if err != nil {
 		return nil, err
 	}