gitee.com/zhaochuninhefei/gmgo@v0.0.31-0.20240209061119-069254a02979/grpc/internal/transport/keepalive_test.go

/*
 *
 * Copyright 2019 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.
 *
 */

// This file contains tests related to the following proposals:
// https://github.com/grpc/proposal/blob/master/A8-client-side-keepalive.md
// https://github.com/grpc/proposal/blob/master/A9-server-side-conn-mgt.md
// https://github.com/grpc/proposal/blob/master/A18-tcp-user-timeout.md
package transport

import (
	"context"
	"fmt"
	"io"
	"net"
	"testing"
	"time"

	"gitee.com/zhaochuninhefei/gmgo/grpc/internal/syscall"
	"gitee.com/zhaochuninhefei/gmgo/grpc/keepalive"
	"gitee.com/zhaochuninhefei/gmgo/net/http2"
)

const defaultTestTimeout = 10 * time.Second

// TestMaxConnectionIdle tests that a server will send GoAway to an idle
// client. An idle client is one who doesn't make any RPC calls for a duration
// of MaxConnectionIdle time.
func (s) TestMaxConnectionIdle(t *testing.T) {
	serverConfig := &ServerConfig{
		KeepaliveParams: keepalive.ServerParameters{
			MaxConnectionIdle: 2 * time.Second,
		},
	}
	server, client, cancel := setUpWithOptions(t, 0, serverConfig, suspended, ConnectOptions{})
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	stream, err := client.NewStream(ctx, &CallHdr{})
	if err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}
	client.CloseStream(stream, io.EOF)

	// Wait for the server's MaxConnectionIdle timeout to kick in, and for it
	// to send a GoAway.
	timeout := time.NewTimer(time.Second * 4)
	select {
	case <-client.Error():
		if !timeout.Stop() {
			<-timeout.C
		}
		if reason, _ := client.GetGoAwayReason(); reason != GoAwayNoReason {
			t.Fatalf("GoAwayReason is %v, want %v", reason, GoAwayNoReason)
		}
	case <-timeout.C:
		t.Fatalf("MaxConnectionIdle timeout expired, expected a GoAway from the server.")
	}
}

// TestMaxConenctionIdleBusyClient tests that a server will not send GoAway to
// a busy client.
func (s) TestMaxConnectionIdleBusyClient(t *testing.T) {
	serverConfig := &ServerConfig{
		KeepaliveParams: keepalive.ServerParameters{
			MaxConnectionIdle: 2 * time.Second,
		},
	}
	server, client, cancel := setUpWithOptions(t, 0, serverConfig, suspended, ConnectOptions{})
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	_, err := client.NewStream(ctx, &CallHdr{})
	if err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}

	// Wait for double the MaxConnectionIdle time to make sure the server does
	// not send a GoAway, as the client has an open stream.
	timeout := time.NewTimer(time.Second * 4)
	select {
	case <-client.GoAway():
		if !timeout.Stop() {
			<-timeout.C
		}
		t.Fatalf("A non-idle client received a GoAway.")
	case <-timeout.C:
	}
}

// TestMaxConnectionAge tests that a server will send GoAway after a duration
// of MaxConnectionAge.
func (s) TestMaxConnectionAge(t *testing.T) {
	serverConfig := &ServerConfig{
		KeepaliveParams: keepalive.ServerParameters{
			MaxConnectionAge:      1 * time.Second,
			MaxConnectionAgeGrace: 1 * time.Second,
		},
	}
	server, client, cancel := setUpWithOptions(t, 0, serverConfig, suspended, ConnectOptions{})
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	_, err := client.NewStream(ctx, &CallHdr{})
	if err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}

	// Wait for the server's MaxConnectionAge timeout to kick in, and for it
	// to send a GoAway.
	timeout := time.NewTimer(4 * time.Second)
	select {
	case <-client.Error():
		if !timeout.Stop() {
			<-timeout.C
		}
		if reason, _ := client.GetGoAwayReason(); reason != GoAwayNoReason {
			t.Fatalf("GoAwayReason is %v, want %v", reason, GoAwayNoReason)
		}
	case <-timeout.C:
		t.Fatalf("MaxConnectionAge timeout expired, expected a GoAway from the server.")
	}
}

const (
	defaultWriteBufSize = 32 * 1024
	defaultReadBufSize  = 32 * 1024
)

// TestKeepaliveServerClosesUnresponsiveClient tests that a server closes
// the connection with a client that doesn't respond to keepalive pings.
//
// This test creates a regular net.Conn connection to the server and sends the
// clientPreface and the initial Settings frame, and then remains unresponsive.
func (s) TestKeepaliveServerClosesUnresponsiveClient(t *testing.T) {
	serverConfig := &ServerConfig{
		KeepaliveParams: keepalive.ServerParameters{
			Time:    1 * time.Second,
			Timeout: 1 * time.Second,
		},
	}
	server, client, cancel := setUpWithOptions(t, 0, serverConfig, suspended, ConnectOptions{})
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	addr := server.addr()
	conn, err := net.Dial("tcp", addr)
	if err != nil {
		t.Fatalf("net.Dial(tcp, %v) failed: %v", addr, err)
	}
	defer func(conn net.Conn) {
		_ = conn.Close()
	}(conn)

	if n, err := conn.Write(clientPreface); err != nil || n != len(clientPreface) {
		t.Fatalf("conn.Write(clientPreface) failed: n=%v, err=%v", n, err)
	}
	framer := newFramer(conn, defaultWriteBufSize, defaultReadBufSize, 0)
	if err := framer.fr.WriteSettings(http2.Setting{}); err != nil {
		t.Fatal("framer.WriteSettings(http2.Setting{}) failed:", err)
	}
	_ = framer.writer.Flush()

	// We read from the net.Conn till we get an error, which is expected when
	// the server closes the connection as part of the keepalive logic.
	errCh := make(chan error, 1)
	go func() {
		b := make([]byte, 24)
		for {
			if _, err = conn.Read(b); err != nil {
				errCh <- err
				return
			}
		}
	}()

	// Server waits for KeepaliveParams.Time seconds before sending out a ping,
	// and then waits for KeepaliveParams.Timeout for a ping ack.
	timeout := time.NewTimer(4 * time.Second)
	select {
	case err := <-errCh:
		if err != io.EOF {
			t.Fatalf("client.Read(_) = _,%v, want io.EOF", err)

		}
	case <-timeout.C:
		t.Fatalf("keepalive timeout expired, server should have closed the connection.")
	}
}

// TestKeepaliveServerWithResponsiveClient tests that a server doesn't close
// the connection with a client that responds to keepalive pings.
func (s) TestKeepaliveServerWithResponsiveClient(t *testing.T) {
	serverConfig := &ServerConfig{
		KeepaliveParams: keepalive.ServerParameters{
			Time:    1 * time.Second,
			Timeout: 1 * time.Second,
		},
	}
	server, client, cancel := setUpWithOptions(t, 0, serverConfig, suspended, ConnectOptions{})
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	// Give keepalive logic some time by sleeping.
	time.Sleep(4 * time.Second)

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	// Make sure the client transport is healthy.
	if _, err := client.NewStream(ctx, &CallHdr{}); err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}
}

// TestKeepaliveClientClosesUnresponsiveServer creates a server which does not
// respond to keepalive pings, and makes sure that the client closes the
// transport once the keepalive logic kicks in. Here, we set the
// `PermitWithoutStream` parameter to true which ensures that the keepalive
// logic is running even without any active streams.
func (s) TestKeepaliveClientClosesUnresponsiveServer(t *testing.T) {
	connCh := make(chan net.Conn, 1)
	client, cancel := setUpWithNoPingServer(t, ConnectOptions{KeepaliveParams: keepalive.ClientParameters{
		Time:                1 * time.Second,
		Timeout:             1 * time.Second,
		PermitWithoutStream: true,
	}}, connCh)
	defer cancel()
	defer client.Close(fmt.Errorf("closed manually by test"))

	conn, ok := <-connCh
	if !ok {
		t.Fatalf("Server didn't return connection object")
	}
	defer func(conn net.Conn) {
		_ = conn.Close()
	}(conn)

	// Sleep for keepalive to close the connection.
	time.Sleep(4 * time.Second)

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	// Make sure the client transport is not healthy.
	if _, err := client.NewStream(ctx, &CallHdr{}); err == nil {
		t.Fatal("client.NewStream() should have failed, but succeeded")
	}
}

// TestKeepaliveClientOpenWithUnresponsiveServer creates a server which does
// not respond to keepalive pings, and makes sure that the client does not
// close the transport. Here, we do not set the `PermitWithoutStream` parameter
// to true which ensures that the keepalive logic is turned off without any
// active streams, and therefore the transport stays open.
func (s) TestKeepaliveClientOpenWithUnresponsiveServer(t *testing.T) {
	connCh := make(chan net.Conn, 1)
	client, cancel := setUpWithNoPingServer(t, ConnectOptions{KeepaliveParams: keepalive.ClientParameters{
		Time:    1 * time.Second,
		Timeout: 1 * time.Second,
	}}, connCh)
	defer cancel()
	defer client.Close(fmt.Errorf("closed manually by test"))

	conn, ok := <-connCh
	if !ok {
		t.Fatalf("Server didn't return connection object")
	}
	defer func(conn net.Conn) {
		_ = conn.Close()
	}(conn)

	// Give keepalive some time.
	time.Sleep(4 * time.Second)

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	// Make sure the client transport is healthy.
	if _, err := client.NewStream(ctx, &CallHdr{}); err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}
}

// TestKeepaliveClientClosesWithActiveStreams creates a server which does not
// respond to keepalive pings, and makes sure that the client closes the
// transport even when there is an active stream.
func (s) TestKeepaliveClientClosesWithActiveStreams(t *testing.T) {
	connCh := make(chan net.Conn, 1)
	client, cancel := setUpWithNoPingServer(t, ConnectOptions{KeepaliveParams: keepalive.ClientParameters{
		Time:    1 * time.Second,
		Timeout: 1 * time.Second,
	}}, connCh)
	defer cancel()
	defer client.Close(fmt.Errorf("closed manually by test"))

	conn, ok := <-connCh
	if !ok {
		t.Fatalf("Server didn't return connection object")
	}
	defer func(conn net.Conn) {
		_ = conn.Close()
	}(conn)

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	// Create a stream, but send no data on it.
	if _, err := client.NewStream(ctx, &CallHdr{}); err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}

	// Give keepalive some time.
	time.Sleep(4 * time.Second)

	// Make sure the client transport is not healthy.
	if _, err := client.NewStream(ctx, &CallHdr{}); err == nil {
		t.Fatal("client.NewStream() should have failed, but succeeded")
	}
}

// TestKeepaliveClientStaysHealthyWithResponsiveServer creates a server which
// responds to keepalive pings, and makes sure than a client transport stays
// healthy without any active streams.
func (s) TestKeepaliveClientStaysHealthyWithResponsiveServer(t *testing.T) {
	server, client, cancel := setUpWithOptions(t, 0,
		&ServerConfig{
			KeepalivePolicy: keepalive.EnforcementPolicy{
				PermitWithoutStream: true,
			},
		},
		normal,
		ConnectOptions{
			KeepaliveParams: keepalive.ClientParameters{
				Time:                1 * time.Second,
				Timeout:             1 * time.Second,
				PermitWithoutStream: true,
			}})
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	// Give keepalive some time.
	time.Sleep(4 * time.Second)

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	// Make sure the client transport is healthy.
	if _, err := client.NewStream(ctx, &CallHdr{}); err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}
}

// TestKeepaliveClientFrequency creates a server which expects at most 1 client
// ping for every 1.2 seconds, while the client is configured to send a ping
// every 1 second. So, this configuration should end up with the client
// transport being closed. But we had a bug wherein the client was sending one
// ping every [Time+Timeout] instead of every [Time] period, and this test
// explicitly makes sure the fix works and the client sends a ping every [Time]
// period.
func (s) TestKeepaliveClientFrequency(t *testing.T) {
	serverConfig := &ServerConfig{
		KeepalivePolicy: keepalive.EnforcementPolicy{
			MinTime:             1200 * time.Millisecond, // 1.2 seconds
			PermitWithoutStream: true,
		},
	}
	clientOptions := ConnectOptions{
		KeepaliveParams: keepalive.ClientParameters{
			Time:                1 * time.Second,
			Timeout:             2 * time.Second,
			PermitWithoutStream: true,
		},
	}
	server, client, cancel := setUpWithOptions(t, 0, serverConfig, normal, clientOptions)
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	timeout := time.NewTimer(6 * time.Second)
	select {
	case <-client.Error():
		if !timeout.Stop() {
			<-timeout.C
		}
		if reason, _ := client.GetGoAwayReason(); reason != GoAwayTooManyPings {
			t.Fatalf("GoAwayReason is %v, want %v", reason, GoAwayTooManyPings)
		}
	case <-timeout.C:
		t.Fatalf("client transport still healthy; expected GoAway from the server.")
	}

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	// Make sure the client transport is not healthy.
	if _, err := client.NewStream(ctx, &CallHdr{}); err == nil {
		t.Fatal("client.NewStream() should have failed, but succeeded")
	}
}

// TestKeepaliveServerEnforcementWithAbusiveClientNoRPC verifies that the
// server closes a client transport when it sends too many keepalive pings
// (when there are no active streams), based on the configured
// EnforcementPolicy.
func (s) TestKeepaliveServerEnforcementWithAbusiveClientNoRPC(t *testing.T) {
	serverConfig := &ServerConfig{
		KeepalivePolicy: keepalive.EnforcementPolicy{
			MinTime: 2 * time.Second,
		},
	}
	clientOptions := ConnectOptions{
		KeepaliveParams: keepalive.ClientParameters{
			Time:                50 * time.Millisecond,
			Timeout:             1 * time.Second,
			PermitWithoutStream: true,
		},
	}
	server, client, cancel := setUpWithOptions(t, 0, serverConfig, normal, clientOptions)
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	timeout := time.NewTimer(4 * time.Second)
	select {
	case <-client.Error():
		if !timeout.Stop() {
			<-timeout.C
		}
		if reason, _ := client.GetGoAwayReason(); reason != GoAwayTooManyPings {
			t.Fatalf("GoAwayReason is %v, want %v", reason, GoAwayTooManyPings)
		}
	case <-timeout.C:
		t.Fatalf("client transport still healthy; expected GoAway from the server.")
	}

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	// Make sure the client transport is not healthy.
	if _, err := client.NewStream(ctx, &CallHdr{}); err == nil {
		t.Fatal("client.NewStream() should have failed, but succeeded")
	}
}

// TestKeepaliveServerEnforcementWithAbusiveClientWithRPC verifies that the
// server closes a client transport when it sends too many keepalive pings
// (even when there is an active stream), based on the configured
// EnforcementPolicy.
func (s) TestKeepaliveServerEnforcementWithAbusiveClientWithRPC(t *testing.T) {
	serverConfig := &ServerConfig{
		KeepalivePolicy: keepalive.EnforcementPolicy{
			MinTime: 2 * time.Second,
		},
	}
	clientOptions := ConnectOptions{
		KeepaliveParams: keepalive.ClientParameters{
			Time:    50 * time.Millisecond,
			Timeout: 1 * time.Second,
		},
	}
	server, client, cancel := setUpWithOptions(t, 0, serverConfig, suspended, clientOptions)
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	if _, err := client.NewStream(ctx, &CallHdr{}); err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}

	timeout := time.NewTimer(4 * time.Second)
	select {
	case <-client.Error():
		if !timeout.Stop() {
			<-timeout.C
		}
		if reason, _ := client.GetGoAwayReason(); reason != GoAwayTooManyPings {
			t.Fatalf("GoAwayReason is %v, want %v", reason, GoAwayTooManyPings)
		}
	case <-timeout.C:
		t.Fatalf("client transport still healthy; expected GoAway from the server.")
	}

	// Make sure the client transport is not healthy.
	if _, err := client.NewStream(ctx, &CallHdr{}); err == nil {
		t.Fatal("client.NewStream() should have failed, but succeeded")
	}
}

// TestKeepaliveServerEnforcementWithObeyingClientNoRPC verifies that the
// server does not close a client transport (with no active streams) which
// sends keepalive pings in accordance to the configured keepalive
// EnforcementPolicy.
func (s) TestKeepaliveServerEnforcementWithObeyingClientNoRPC(t *testing.T) {
	serverConfig := &ServerConfig{
		KeepalivePolicy: keepalive.EnforcementPolicy{
			MinTime:             100 * time.Millisecond,
			PermitWithoutStream: true,
		},
	}
	clientOptions := ConnectOptions{
		KeepaliveParams: keepalive.ClientParameters{
			Time:                101 * time.Millisecond,
			Timeout:             1 * time.Second,
			PermitWithoutStream: true,
		},
	}
	server, client, cancel := setUpWithOptions(t, 0, serverConfig, normal, clientOptions)
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	// Give keepalive enough time.
	time.Sleep(3 * time.Second)

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	// Make sure the client transport is healthy.
	if _, err := client.NewStream(ctx, &CallHdr{}); err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}
}

// TestKeepaliveServerEnforcementWithObeyingClientWithRPC verifies that the
// server does not close a client transport (with active streams) which
// sends keepalive pings in accordance to the configured keepalive
// EnforcementPolicy.
func (s) TestKeepaliveServerEnforcementWithObeyingClientWithRPC(t *testing.T) {
	serverConfig := &ServerConfig{
		KeepalivePolicy: keepalive.EnforcementPolicy{
			MinTime: 100 * time.Millisecond,
		},
	}
	clientOptions := ConnectOptions{
		KeepaliveParams: keepalive.ClientParameters{
			Time:    101 * time.Millisecond,
			Timeout: 1 * time.Second,
		},
	}
	server, client, cancel := setUpWithOptions(t, 0, serverConfig, suspended, clientOptions)
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	if _, err := client.NewStream(ctx, &CallHdr{}); err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}

	// Give keepalive enough time.
	time.Sleep(3 * time.Second)

	// Make sure the client transport is healthy.
	if _, err := client.NewStream(ctx, &CallHdr{}); err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}
}

// TestKeepaliveServerEnforcementWithDormantKeepaliveOnClient verifies that the
// server does not closes a client transport, which has been configured to send
// more pings than allowed by the server's EnforcementPolicy. This client
// transport does not have any active streams and `PermitWithoutStream` is set
// to false. This should ensure that the keepalive functionality on the client
// side enters a dormant state.
func (s) TestKeepaliveServerEnforcementWithDormantKeepaliveOnClient(t *testing.T) {
	serverConfig := &ServerConfig{
		KeepalivePolicy: keepalive.EnforcementPolicy{
			MinTime: 2 * time.Second,
		},
	}
	clientOptions := ConnectOptions{
		KeepaliveParams: keepalive.ClientParameters{
			Time:    50 * time.Millisecond,
			Timeout: 1 * time.Second,
		},
	}
	server, client, cancel := setUpWithOptions(t, 0, serverConfig, normal, clientOptions)
	defer func() {
		client.Close(fmt.Errorf("closed manually by test"))
		server.stop()
		cancel()
	}()

	// No active streams on the client. Give keepalive enough time.
	time.Sleep(5 * time.Second)

	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
	defer cancel()
	// Make sure the client transport is healthy.
	if _, err := client.NewStream(ctx, &CallHdr{}); err != nil {
		t.Fatalf("client.NewStream() failed: %v", err)
	}
}

// TestTCPUserTimeout tests that the TCP_USER_TIMEOUT socket option is set to
// the keepalive timeout, as detailed in proposal A18.
func (s) TestTCPUserTimeout(t *testing.T) {
	tests := []struct {
		time        time.Duration
		timeout     time.Duration
		wantTimeout time.Duration
	}{
		{
			10 * time.Second,
			10 * time.Second,
			10 * 1000 * time.Millisecond,
		},
		{
			0,
			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,
				},
			},
		)
		//goland:noinspection GoDeferInLoop
		defer func() {
			client.Close(fmt.Errorf("closed manually by test"))
			server.stop()
			cancel()
		}()

		ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
		//goland:noinspection GoDeferInLoop
		defer cancel()
		stream, err := client.NewStream(ctx, &CallHdr{})
		if err != nil {
			t.Fatalf("client.NewStream() failed: %v", err)
		}
		client.CloseStream(stream, io.EOF)

		opt, err := syscall.GetTCPUserTimeout(client.conn)
		if err != nil {
			t.Fatalf("syscall.GetTCPUserTimeout() failed: %v", err)
		}
		if opt < 0 {
			t.Skipf("skipping test on unsupported environment")
		}
		if gotTimeout := time.Duration(opt) * time.Millisecond; gotTimeout != tt.wantTimeout {
			t.Fatalf("syscall.GetTCPUserTimeout() = %d, want %d", gotTimeout, tt.wantTimeout)
		}
	}
}