net: add KeepAlive with default to ListenConfig

This commit adds a KeepAlive field to ListenConfig and uses it
analogously to Dialer.KeepAlive to set TCP KeepAlives per default on
Accept()

src/net/dial.go

@@ -596,6 +596,14 @@ type ListenConfig struct {
 	// 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.

src/net/file_plan9.go

@@ -127,7 +127,7 @@ func fileListener(f *os.File) (Listener, error) {
 		return nil, errors.New("file does not represent a listener")
 	}
 
-	return &TCPListener{fd}, nil
+	return &TCPListener{fd: fd}, nil
 }
 
 func filePacketConn(f *os.File) (PacketConn, error) {

src/net/file_unix.go

@@ -93,7 +93,7 @@ func fileListener(f *os.File) (Listener, error) {
 	}
 	switch laddr := fd.laddr.(type) {
 	case *TCPAddr:
-		return &TCPListener{fd}, nil
+		return &TCPListener{fd: fd}, nil
 	case *UnixAddr:
 		return &UnixListener{fd: fd, path: laddr.Name, unlink: false}, nil
 	}

src/net/http/server.go

@@ -2792,7 +2792,7 @@ func (srv *Server) ListenAndServe() error {
 	if err != nil {
 		return err
 	}
-	return srv.Serve(tcpKeepAliveListener{ln.(*net.TCPListener)})
+	return srv.Serve(ln)
 }
 
 var testHookServerServe func(*Server, net.Listener) // used if non-nil
@@ -3076,7 +3076,7 @@ func (srv *Server) ListenAndServeTLS(certFile, keyFile string) error {
 
 	defer ln.Close()
 
-	return srv.ServeTLS(tcpKeepAliveListener{ln.(*net.TCPListener)}, certFile, keyFile)
+	return srv.ServeTLS(ln, certFile, keyFile)
 }
 
 // setupHTTP2_ServeTLS conditionally configures HTTP/2 on
@@ -3269,24 +3269,6 @@ func (tw *timeoutWriter) writeHeader(code int) {
 	tw.code = code
 }
 
-// tcpKeepAliveListener sets TCP keep-alive timeouts on accepted
-// connections. It's used by ListenAndServe and ListenAndServeTLS so
-// dead TCP connections (e.g. closing laptop mid-download) eventually
-// go away.
-type tcpKeepAliveListener struct {
-	*net.TCPListener
-}
-
-func (ln tcpKeepAliveListener) Accept() (net.Conn, error) {
-	tc, err := ln.AcceptTCP()
-	if err != nil {
-		return nil, err
-	}
-	tc.SetKeepAlive(true)
-	tc.SetKeepAlivePeriod(3 * time.Minute)
-	return tc, nil
-}
-
 // onceCloseListener wraps a net.Listener, protecting it from
 // multiple Close calls.
 type onceCloseListener struct {

src/net/tcpsock.go

@@ -224,6 +224,7 @@ func DialTCP(network string, laddr, raddr *TCPAddr) (*TCPConn, error) {
 // use variables of type Listener instead of assuming TCP.
 type TCPListener struct {
 	fd *netFD
+	lc ListenConfig
 }
 
 // SyscallConn returns a raw network connection.

src/net/tcpsock_plan9.go

@@ -8,6 +8,7 @@ import (
 	"context"
 	"io"
 	"os"
+	"time"
 )
 
 func (c *TCPConn) readFrom(r io.Reader) (int64, error) {
@@ -44,7 +45,16 @@ func (ln *TCPListener) accept() (*TCPConn, error) {
 	if err != nil {
 		return nil, err
 	}
-	return newTCPConn(fd), nil
+	tc := newTCPConn(fd)
+	if ln.lc.KeepAlive >= 0 {
+		setKeepAlive(fd, true)
+		ka := ln.lc.KeepAlive
+		if ln.lc.KeepAlive == 0 {
+			ka = 3 * time.Minute
+		}
+		setKeepAlivePeriod(fd, ka)
+	}
+	return tc, nil
 }
 
 func (ln *TCPListener) close() error {
@@ -74,5 +84,5 @@ func (sl *sysListener) listenTCP(ctx context.Context, laddr *TCPAddr) (*TCPListe
 	if err != nil {
 		return nil, err
 	}
-	return &TCPListener{fd}, nil
+	return &TCPListener{fd: fd, lc: sl.ListenConfig}, nil
 }

src/net/tcpsock_posix.go

@@ -11,6 +11,7 @@ import (
 	"io"
 	"os"
 	"syscall"
+	"time"
 )
 
 func sockaddrToTCP(sa syscall.Sockaddr) Addr {
@@ -140,7 +141,16 @@ func (ln *TCPListener) accept() (*TCPConn, error) {
 	if err != nil {
 		return nil, err
 	}
-	return newTCPConn(fd), nil
+	tc := newTCPConn(fd)
+	if ln.lc.KeepAlive >= 0 {
+		setKeepAlive(fd, true)
+		ka := ln.lc.KeepAlive
+		if ln.lc.KeepAlive == 0 {
+			ka = 3 * time.Minute
+		}
+		setKeepAlivePeriod(fd, ka)
+	}
+	return tc, nil
 }
 
 func (ln *TCPListener) close() error {
@@ -160,5 +170,5 @@ func (sl *sysListener) listenTCP(ctx context.Context, laddr *TCPAddr) (*TCPListe
 	if err != nil {
 		return nil, err
 	}
-	return &TCPListener{fd}, nil
+	return &TCPListener{fd: fd, lc: sl.ListenConfig}, nil
 }