net: unify TCP keepalive behavior

CL 107196 introduced a default TCP keepalive interval for Dialer and TCPListener (used by both ListenConfig and ListenTCP). Leaving DialTCP out was likely an oversight.

DialTCP's documentation says it "acts like Dial". Therefore it's natural to also expect DialTCP to enable TCP keepalive by default.

This commit addresses this disparity by moving the enablement logic down to the newTCPConn function, which is used by both dialer and listener.

Fixes #49345

Change-Id: I99c08b161c468ed0b993d1dbd2bd0d7e803f3826
GitHub-Last-Rev: 5c2f1cb
GitHub-Pull-Request: #56565
Reviewed-on: https://go-review.googlesource.com/c/go/+/447917
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

src/net/dial.go

@@ -437,21 +437,7 @@ func (d *Dialer) DialContext(ctx context.Context, network, address string) (Conn
 		primaries = addrs
 	}
 
-	c, err := sd.dialParallel(ctx, primaries, fallbacks)
-	if err != nil {
-		return nil, err
-	}
-
-	if tc, ok := c.(*TCPConn); ok && d.KeepAlive >= 0 {
-		setKeepAlive(tc.fd, true)
-		ka := d.KeepAlive
-		if d.KeepAlive == 0 {
-			ka = defaultTCPKeepAlive
-		}
-		setKeepAlivePeriod(tc.fd, ka)
-		testHookSetKeepAlive(ka)
-	}
-	return c, nil
+	return sd.dialParallel(ctx, primaries, fallbacks)
 }
 
 // dialParallel races two copies of dialSerial, giving the first a

src/net/file_plan9.go

@@ -100,7 +100,7 @@ func fileConn(f *os.File) (Conn, error) {
 
 	switch fd.laddr.(type) {
 	case *TCPAddr:
-		return newTCPConn(fd), nil
+		return newTCPConn(fd, defaultTCPKeepAlive, testHookSetKeepAlive), nil
 	case *UDPAddr:
 		return newUDPConn(fd), nil
 	}

src/net/file_unix.go

@@ -74,7 +74,7 @@ func fileConn(f *os.File) (Conn, error) {
 	}
 	switch fd.laddr.(type) {
 	case *TCPAddr:
-		return newTCPConn(fd), nil
+		return newTCPConn(fd, defaultTCPKeepAlive, testHookSetKeepAlive), nil
 	case *UDPAddr:
 		return newUDPConn(fd), nil
 	case *IPAddr:

src/net/tcpsock.go

@@ -217,10 +217,19 @@ func (c *TCPConn) SetNoDelay(noDelay bool) error {
 	return nil
 }
 
-func newTCPConn(fd *netFD) *TCPConn {
-	c := &TCPConn{conn{fd}}
-	setNoDelay(c.fd, true)
-	return c
+func newTCPConn(fd *netFD, keepAlive time.Duration, keepAliveHook func(time.Duration)) *TCPConn {
+	setNoDelay(fd, true)
+	if keepAlive == 0 {
+		keepAlive = defaultTCPKeepAlive
+	}
+	if keepAlive > 0 {
+		setKeepAlive(fd, true)
+		setKeepAlivePeriod(fd, keepAlive)
+		if keepAliveHook != nil {
+			keepAliveHook(keepAlive)
+		}
+	}
+	return &TCPConn{conn{fd}}
 }
 
 // DialTCP acts like Dial for TCP networks.

src/net/tcpsock_plan9.go

@@ -42,7 +42,7 @@ func (sd *sysDialer) doDialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCP
 	if err != nil {
 		return nil, err
 	}
-	return newTCPConn(fd), nil
+	return newTCPConn(fd, sd.Dialer.KeepAlive, testHookSetKeepAlive), nil
 }
 
 func (ln *TCPListener) ok() bool { return ln != nil && ln.fd != nil && ln.fd.ctl != nil }
@@ -52,16 +52,7 @@ func (ln *TCPListener) accept() (*TCPConn, error) {
 	if err != nil {
 		return nil, err
 	}
-	tc := newTCPConn(fd)
-	if ln.lc.KeepAlive >= 0 {
-		setKeepAlive(fd, true)
-		ka := ln.lc.KeepAlive
-		if ln.lc.KeepAlive == 0 {
-			ka = defaultTCPKeepAlive
-		}
-		setKeepAlivePeriod(fd, ka)
-	}
-	return tc, nil
+	return newTCPConn(fd, ln.lc.KeepAlive, nil), nil
 }
 
 func (ln *TCPListener) close() error {

src/net/tcpsock_posix.go

@@ -107,7 +107,7 @@ func (sd *sysDialer) doDialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCP
 	if err != nil {
 		return nil, err
 	}
-	return newTCPConn(fd), nil
+	return newTCPConn(fd, sd.Dialer.KeepAlive, testHookSetKeepAlive), nil
 }
 
 func selfConnect(fd *netFD, err error) bool {
@@ -149,16 +149,7 @@ func (ln *TCPListener) accept() (*TCPConn, error) {
 	if err != nil {
 		return nil, err
 	}
-	tc := newTCPConn(fd)
-	if ln.lc.KeepAlive >= 0 {
-		setKeepAlive(fd, true)
-		ka := ln.lc.KeepAlive
-		if ln.lc.KeepAlive == 0 {
-			ka = defaultTCPKeepAlive
-		}
-		setKeepAlivePeriod(fd, ka)
-	}
-	return tc, nil
+	return newTCPConn(fd, ln.lc.KeepAlive, nil), nil
 }
 
 func (ln *TCPListener) close() error {

src/net/tcpsock_test.go

@@ -808,3 +808,22 @@ func BenchmarkSetReadDeadline(b *testing.B) {
 		deadline = deadline.Add(1)
 	}
 }
+
+func TestDialTCPDefaultKeepAlive(t *testing.T) {
+	ln := newLocalListener(t, "tcp")
+	defer ln.Close()
+
+	got := time.Duration(-1)
+	testHookSetKeepAlive = func(d time.Duration) { got = d }
+	defer func() { testHookSetKeepAlive = func(time.Duration) {} }()
+
+	c, err := DialTCP("tcp", nil, ln.Addr().(*TCPAddr))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer c.Close()
+
+	if got != defaultTCPKeepAlive {
+		t.Errorf("got keepalive %v; want %v", got, defaultTCPKeepAlive)
+	}
+}