client: set TCP_USER_TIMEOUT socket option for linux (#2307)

Implements proposal A18 (https://github.com/grpc/proposal/blob/master/A18-tcp-user-timeout.md).

gRPC Core issue for reference: https://github.com/grpc/grpc/issues/15889

internal/syscall/syscall_linux.go

@@ -23,7 +23,10 @@
 package syscall
 
 import (
+	"fmt"
+	"net"
 	"syscall"
+	"time"
 
 	"golang.org/x/sys/unix"
 	"google.golang.org/grpc/grpclog"
@@ -65,3 +68,47 @@ func CPUTimeDiff(first *Rusage, latest *Rusage) (float64, float64) {
 
 	return uTimeElapsed, sTimeElapsed
 }
+
+// SetTCPUserTimeout sets the TCP user timeout on a connection's socket
+func SetTCPUserTimeout(conn net.Conn, timeout time.Duration) error {
+	tcpconn, ok := conn.(*net.TCPConn)
+	if !ok {
+		// not a TCP connection. exit early
+		return nil
+	}
+	rawConn, err := tcpconn.SyscallConn()
+	if err != nil {
+		return fmt.Errorf("error getting raw connection: %v", err)
+	}
+	err = rawConn.Control(func(fd uintptr) {
+		err = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_TCP, unix.TCP_USER_TIMEOUT, int(timeout/time.Millisecond))
+	})
+	if err != nil {
+		return fmt.Errorf("error setting option on socket: %v", err)
+	}
+
+	return nil
+}
+
+// GetTCPUserTimeout gets the TCP user timeout on a connection's socket
+func GetTCPUserTimeout(conn net.Conn) (opt int, err error) {
+	tcpconn, ok := conn.(*net.TCPConn)
+	if !ok {
+		err = fmt.Errorf("conn is not *net.TCPConn. got %T", conn)
+		return
+	}
+	rawConn, err := tcpconn.SyscallConn()
+	if err != nil {
+		err = fmt.Errorf("error getting raw connection: %v", err)
+		return
+	}
+	err = rawConn.Control(func(fd uintptr) {
+		opt, err = syscall.GetsockoptInt(int(fd), syscall.IPPROTO_TCP, unix.TCP_USER_TIMEOUT)
+	})
+	if err != nil {
+		err = fmt.Errorf("error getting option on socket: %v", err)
+		return
+	}
+
+	return
+}

internal/syscall/syscall_nonlinux.go

@@ -20,7 +20,12 @@
 
 package syscall
 
-import "google.golang.org/grpc/grpclog"
+import (
+	"net"
+	"time"
+
+	"google.golang.org/grpc/grpclog"
+)
 
 func init() {
 	grpclog.Info("CPU time info is unavailable on non-linux or appengine environment.")
@@ -45,3 +50,14 @@ func GetRusage() (rusage *Rusage) {
 func CPUTimeDiff(first *Rusage, latest *Rusage) (float64, float64) {
 	return 0, 0
 }
+
+// SetTCPUserTimeout is a no-op function under non-linux or appengine environments
+func SetTCPUserTimeout(conn net.Conn, timeout time.Duration) error {
+	return nil
+}
+
+// GetTCPUserTimeout is a no-op function under non-linux or appengine environments
+// a negative return value indicates the operation is not supported
+func GetTCPUserTimeout(conn net.Conn) (int, error) {
+	return -1, nil
+}

internal/transport/http2_client.go

@@ -36,6 +36,7 @@ import (
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/internal/channelz"
+	"google.golang.org/grpc/internal/syscall"
 	"google.golang.org/grpc/keepalive"
 	"google.golang.org/grpc/metadata"
 	"google.golang.org/grpc/peer"
@@ -166,6 +167,21 @@ func newHTTP2Client(connectCtx, ctx context.Context, addr TargetInfo, opts Conne
 			conn.Close()
 		}
 	}(conn)
+	kp := opts.KeepaliveParams
+	// Validate keepalive parameters.
+	if kp.Time == 0 {
+		kp.Time = defaultClientKeepaliveTime
+	}
+	if kp.Timeout == 0 {
+		kp.Timeout = defaultClientKeepaliveTimeout
+	}
+	keepaliveEnabled := false
+	if kp.Time != infinity {
+		if err = syscall.SetTCPUserTimeout(conn, kp.Timeout); err != nil {
+			return nil, connectionErrorf(false, err, "transport: failed to set TCP_USER_TIMEOUT: %v", err)
+		}
+		keepaliveEnabled = true
+	}
 	var (
 		isSecure bool
 		authInfo credentials.AuthInfo
@@ -189,14 +205,6 @@ func newHTTP2Client(connectCtx, ctx context.Context, addr TargetInfo, opts Conne
 		}
 		isSecure = true
 	}
-	kp := opts.KeepaliveParams
-	// Validate keepalive parameters.
-	if kp.Time == 0 {
-		kp.Time = defaultClientKeepaliveTime
-	}
-	if kp.Timeout == 0 {
-		kp.Timeout = defaultClientKeepaliveTimeout
-	}
 	dynamicWindow := true
 	icwz := int32(initialWindowSize)
 	if opts.InitialConnWindowSize >= defaultWindowSize {
@@ -240,6 +248,7 @@ func newHTTP2Client(connectCtx, ctx context.Context, addr TargetInfo, opts Conne
 		czData:                new(channelzData),
 		onGoAway:              onGoAway,
 		onClose:               onClose,
+		keepaliveEnabled:      keepaliveEnabled,
 	}
 	t.controlBuf = newControlBuffer(t.ctxDone)
 	if opts.InitialWindowSize >= defaultWindowSize {
@@ -268,8 +277,7 @@ func newHTTP2Client(connectCtx, ctx context.Context, addr TargetInfo, opts Conne
 	if channelz.IsOn() {
 		t.channelzID = channelz.RegisterNormalSocket(t, opts.ChannelzParentID, fmt.Sprintf("%s -> %s", t.localAddr, t.remoteAddr))
 	}
-	if t.kp.Time != infinity {
+	if t.keepaliveEnabled {
-		t.keepaliveEnabled = true
 		go t.keepalive()
 	}
 	// Start the reader goroutine for incoming message. Each transport has

internal/transport/transport_test.go

@@ -41,6 +41,7 @@ import (
 	"golang.org/x/net/http2/hpack"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/internal/leakcheck"
+	"google.golang.org/grpc/internal/syscall"
 	"google.golang.org/grpc/keepalive"
 	"google.golang.org/grpc/status"
 )
@@ -2317,3 +2318,61 @@ func TestHeaderTblSize(t *testing.T) {
 		t.Fatalf("expected len(limits) = 2 within 10s, got != 2")
 	}
 }
+
+// TestTCPUserTimeout tests that the TCP_USER_TIMEOUT socket option is set to the
+// keepalive timeout, as detailed in proposal A18
+func TestTCPUserTimeout(t *testing.T) {
+	tests := []struct {
+		time    time.Duration
+		timeout time.Duration
+	}{
+		{
+			10 * time.Second,
+			10 * time.Second,
+		},
+		{
+			0,
+			0,
+		},
+	}
+	for _, tt := range tests {
+		server, client, cancel := setUpWithOptions(
+			t,
+			0,
+			&ServerConfig{
+				KeepaliveParams: keepalive.ServerParameters{
+					Time:    tt.timeout,
+					Timeout: tt.timeout,
+				},
+			},
+			normal,
+			ConnectOptions{
+				KeepaliveParams: keepalive.ClientParameters{
+					Time:    tt.time,
+					Timeout: tt.timeout,
+				},
+			},
+		)
+		defer cancel()
+		defer server.stop()
+		defer client.Close()
+
+		stream, err := client.NewStream(context.Background(), &CallHdr{})
+		if err != nil {
+			t.Fatalf("Client failed to create RPC request: %v", err)
+		}
+		client.closeStream(stream, io.EOF, true, http2.ErrCodeCancel, nil, nil, false)
+
+		opt, err := syscall.GetTCPUserTimeout(client.conn)
+		if err != nil {
+			t.Fatalf("GetTCPUserTimeout error: %v", err)
+		}
+		if opt < 0 {
+			t.Skipf("skipping test on unsupported environment")
+		}
+		if timeoutMS := int(tt.timeout / time.Millisecond); timeoutMS != opt {
+			t.Fatalf("wrong TCP_USER_TIMEOUT set on conn. expected %d. got %d",
+				timeoutMS, opt)
+		}
+	}
+}