client: always enable TCP keepalives with OS defaults (#6834)

benchmark/benchmain/main.go

@@ -67,6 +67,7 @@ import (
 	"google.golang.org/grpc/credentials/insecure"
 	"google.golang.org/grpc/experimental"
 	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/internal"
 	"google.golang.org/grpc/internal/channelz"
 	"google.golang.org/grpc/keepalive"
 	"google.golang.org/grpc/metadata"
@@ -373,7 +374,7 @@ func makeClients(bf stats.Features) ([]testgrpc.BenchmarkServiceClient, func())
 			logger.Fatalf("Failed to listen: %v", err)
 		}
 		opts = append(opts, grpc.WithContextDialer(func(ctx context.Context, address string) (net.Conn, error) {
-			return nw.ContextDialer((&net.Dialer{KeepAlive: time.Duration(-1)}).DialContext)(ctx, "tcp", lis.Addr().String())
+			return nw.ContextDialer((internal.NetDialerWithTCPKeepalive().DialContext))(ctx, "tcp", lis.Addr().String())
 		}))
 	}
 	lis = nw.Listener(lis)

dialoptions.go

@@ -401,10 +401,12 @@ func WithTimeout(d time.Duration) DialOption {
 // returned by f, gRPC checks the error's Temporary() method to decide if it
 // should try to reconnect to the network address.
 //
-// Note: As of Go 1.21, the standard library overrides the OS defaults for
-// TCP keepalive time and interval to 15s.
-// To retain OS defaults, use a net.Dialer with the KeepAlive field set to a
-// negative value.
+// Note: All supported releases of Go (as of December 2023) override the OS
+// defaults for TCP keepalive time and interval to 15s. To enable TCP keepalive
+// with OS defaults for keepalive time and interval, use a net.Dialer that sets
+// the KeepAlive field to a negative value, and sets the SO_KEEPALIVE socket
+// option to true from the Control field. For a concrete example of how to do
+// this, see internal.NetDialerWithTCPKeepalive().
 //
 // For more information, please see [issue 23459] in the Go github repo.
 //

internal/tcp_keepalive.go

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2023 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package internal
+
+import (
+	"net"
+	"syscall"
+	"time"
+)
+
+// NetDialerWithTCPKeepalive returns a net.Dialer that enables TCP keepalives on
+// the underlying connection with OS default values for keepalive parameters.
+//
+// TODO: Once https://github.com/golang/go/issues/62254 lands, and the
+// appropriate Go version becomes less than our least supported Go version, we
+// should look into using the new API to make things more straightforward.
+func NetDialerWithTCPKeepalive() *net.Dialer {
+	return &net.Dialer{
+		// Setting a negative value here prevents the Go stdlib from overriding
+		// the values of TCP keepalive time and interval. It also prevents the
+		// Go stdlib from enabling TCP keepalives by default.
+		KeepAlive: time.Duration(-1),
+		// This method is called after the underlying network socket is created,
+		// but before dialing the socket (or calling its connect() method). The
+		// combination of unconditionally enabling TCP keepalives here, and
+		// disabling the overriding of TCP keepalive parameters by setting the
+		// KeepAlive field to a negative value above, results in OS defaults for
+		// the TCP keealive interval and time parameters.
+		Control: func(_, _ string, c syscall.RawConn) error {
+			return c.Control(func(fd uintptr) {
+				syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_KEEPALIVE, 1)
+			})
+		},
+	}
+}

internal/transport/http2_client.go

@@ -36,6 +36,7 @@ import (
 	"golang.org/x/net/http2/hpack"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/internal"
 	"google.golang.org/grpc/internal/channelz"
 	icredentials "google.golang.org/grpc/internal/credentials"
 	"google.golang.org/grpc/internal/grpclog"
@@ -43,7 +44,7 @@ import (
 	"google.golang.org/grpc/internal/grpcutil"
 	imetadata "google.golang.org/grpc/internal/metadata"
 	istatus "google.golang.org/grpc/internal/status"
-	"google.golang.org/grpc/internal/syscall"
+	isyscall "google.golang.org/grpc/internal/syscall"
 	"google.golang.org/grpc/internal/transport/networktype"
 	"google.golang.org/grpc/keepalive"
 	"google.golang.org/grpc/metadata"
@@ -176,9 +177,7 @@ func dial(ctx context.Context, fn func(context.Context, string) (net.Conn, error
 	if networkType == "tcp" && useProxy {
 		return proxyDial(ctx, address, grpcUA)
 	}
-	// KeepAlive is set to a negative value to prevent Go's override of the TCP
-	// keepalive time and interval; retain the OS default.
-	return (&net.Dialer{KeepAlive: time.Duration(-1)}).DialContext(ctx, networkType, address)
+	return internal.NetDialerWithTCPKeepalive().DialContext(ctx, networkType, address)
 }
 
 func isTemporary(err error) bool {
@@ -264,7 +263,7 @@ func newHTTP2Client(connectCtx, ctx context.Context, addr resolver.Address, opts
 	}
 	keepaliveEnabled := false
 	if kp.Time != infinity {
-		if err = syscall.SetTCPUserTimeout(conn, kp.Timeout); err != nil {
+		if err = isyscall.SetTCPUserTimeout(conn, kp.Timeout); err != nil {
 			return nil, connectionErrorf(false, err, "transport: failed to set TCP_USER_TIMEOUT: %v", err)
 		}
 		keepaliveEnabled = true

internal/transport/proxy.go

@@ -28,7 +28,8 @@ import (
 	"net/http"
 	"net/http/httputil"
 	"net/url"
-	"time"
+
+	"google.golang.org/grpc/internal"
 )
 
 const proxyAuthHeaderKey = "Proxy-Authorization"
@@ -113,7 +114,7 @@ func doHTTPConnectHandshake(ctx context.Context, conn net.Conn, backendAddr stri
 // proxyDial dials, connecting to a proxy first if necessary. Checks if a proxy
 // is necessary, dials, does the HTTP CONNECT handshake, and returns the
 // connection.
-func proxyDial(ctx context.Context, addr string, grpcUA string) (conn net.Conn, err error) {
+func proxyDial(ctx context.Context, addr string, grpcUA string) (net.Conn, error) {
 	newAddr := addr
 	proxyURL, err := mapAddress(addr)
 	if err != nil {
@@ -123,15 +124,15 @@ func proxyDial(ctx context.Context, addr string, grpcUA string) (conn net.Conn,
 		newAddr = proxyURL.Host
 	}
 
-	conn, err = (&net.Dialer{KeepAlive: time.Duration(-1)}).DialContext(ctx, "tcp", newAddr)
+	conn, err := internal.NetDialerWithTCPKeepalive().DialContext(ctx, "tcp", newAddr)
 	if err != nil {
-		return
+		return nil, err
 	}
-	if proxyURL != nil {
+	if proxyURL == nil {
 		// proxy is disabled if proxyURL is nil.
-		conn, err = doHTTPConnectHandshake(ctx, conn, addr, proxyURL, grpcUA)
+		return conn, err
 	}
-	return
+	return doHTTPConnectHandshake(ctx, conn, addr, proxyURL, grpcUA)
 }
 
 func sendHTTPRequest(ctx context.Context, req *http.Request, conn net.Conn) error {

server.go

@@ -814,14 +814,17 @@ func (l *listenSocket) Close() error {
 // this method returns.
 // Serve will return a non-nil error unless Stop or GracefulStop is called.
 //
-// Note: As of Go 1.21, the standard library overrides the OS defaults for
-// TCP keepalive time and interval to 15s.
-// To retain OS defaults, pass a net.Listener created by calling the Listen method
-// on a net.ListenConfig with the `KeepAlive` field set to a negative value.
-//
-// For more information, please see [issue 23459] in the Go github repo.
-//
-// [issue 23459]: https://github.com/golang/go/issues/23459
+// Note: All supported releases of Go (as of December 2023) override the OS
+// defaults for TCP keepalive time and interval to 15s. To enable TCP keepalive
+// with OS defaults for keepalive time and interval, callers need to do the
+// following two things:
+//   - pass a net.Listener created by calling the Listen method on a
+//     net.ListenConfig with the `KeepAlive` field set to a negative value. This
+//     will result in the Go standard library not overriding OS defaults for TCP
+//     keepalive interval and time. But this will also result in the Go standard
+//     library not enabling TCP keepalives by default.
+//   - override the Accept method on the passed in net.Listener and set the
+//     SO_KEEPALIVE socket option to enable TCP keepalives, with OS defaults.
 func (s *Server) Serve(lis net.Listener) error {
 	s.mu.Lock()
 	s.printf("serving")