nettest/conntest.go - net - Git at Google

 // Copyright 2016 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package nettest

 import (
 	"bytes"
 	"encoding/binary"
 	"io"
 	"io/ioutil"
 	"math/rand"
 	"net"
 	"runtime"
 	"sync"
 	"testing"
 	"time"
 )

 // MakePipe creates a connection between two endpoints and returns the pair
 // as c1 and c2, such that anything written to c1 is read by c2 and vice-versa.
 // The stop function closes all resources, including c1, c2, and the underlying
 // net.Listener (if there is one), and should not be nil.
 type MakePipe func() (c1, c2 net.Conn, stop func(), err error)

 // TestConn tests that a net.Conn implementation properly satisfies the interface.
 // The tests should not produce any false positives, but may experience
 // false negatives. Thus, some issues may only be detected when the test is
 // run multiple times. For maximal effectiveness, run the tests under the
 // race detector.
 func TestConn(t *testing.T, mp MakePipe) {
 	t.Run("BasicIO", func(t *testing.T) { timeoutWrapper(t, mp, testBasicIO) })
 	t.Run("PingPong", func(t *testing.T) { timeoutWrapper(t, mp, testPingPong) })
 	t.Run("RacyRead", func(t *testing.T) { timeoutWrapper(t, mp, testRacyRead) })
 	t.Run("RacyWrite", func(t *testing.T) { timeoutWrapper(t, mp, testRacyWrite) })
 	t.Run("ReadTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testReadTimeout) })
 	t.Run("WriteTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testWriteTimeout) })
 	t.Run("PastTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testPastTimeout) })
 	t.Run("PresentTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testPresentTimeout) })
 	t.Run("FutureTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testFutureTimeout) })
 	t.Run("CloseTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testCloseTimeout) })
 	t.Run("ConcurrentMethods", func(t *testing.T) { timeoutWrapper(t, mp, testConcurrentMethods) })
 }

 type connTester func(t *testing.T, c1, c2 net.Conn)

 func timeoutWrapper(t *testing.T, mp MakePipe, f connTester) {
 	t.Helper()
 	c1, c2, stop, err := mp()
 	if err != nil {
 		t.Fatalf("unable to make pipe: %v", err)
 	}
 	var once sync.Once
 	defer once.Do(func() { stop() })
 	timer := time.AfterFunc(time.Minute, func() {
 		once.Do(func() {
 			t.Error("test timed out; terminating pipe")
 			stop()
 		})
 	})
 	defer timer.Stop()
 	f(t, c1, c2)
 }

 // testBasicIO tests that the data sent on c1 is properly received on c2.
 func testBasicIO(t *testing.T, c1, c2 net.Conn) {
 	want := make([]byte, 1<<20)
 	rand.New(rand.NewSource(0)).Read(want)

 	dataCh := make(chan []byte)
 	go func() {
 		rd := bytes.NewReader(want)
 		if err := chunkedCopy(c1, rd); err != nil {
 			t.Errorf("unexpected c1.Write error: %v", err)
 		}
 		if err := c1.Close(); err != nil {
 			t.Errorf("unexpected c1.Close error: %v", err)
 		}
 	}()

 	go func() {
 		wr := new(bytes.Buffer)
 		if err := chunkedCopy(wr, c2); err != nil {
 			t.Errorf("unexpected c2.Read error: %v", err)
 		}
 		if err := c2.Close(); err != nil {
 			t.Errorf("unexpected c2.Close error: %v", err)
 		}
 		dataCh <- wr.Bytes()
 	}()

 	if got := <-dataCh; !bytes.Equal(got, want) {
 		t.Error("transmitted data differs")
 	}
 }

 // testPingPong tests that the two endpoints can synchronously send data to
 // each other in a typical request-response pattern.
 func testPingPong(t *testing.T, c1, c2 net.Conn) {
 	var wg sync.WaitGroup
 	defer wg.Wait()

 	pingPonger := func(c net.Conn) {
 		defer wg.Done()
 		buf := make([]byte, 8)
 		var prev uint64
 		for {
 			if _, err := io.ReadFull(c, buf); err != nil {
 				if err == io.EOF {
 					break
 				}
 				t.Errorf("unexpected Read error: %v", err)
 			}

 			v := binary.LittleEndian.Uint64(buf)
 			binary.LittleEndian.PutUint64(buf, v+1)
 			if prev != 0 && prev+2 != v {
 				t.Errorf("mismatching value: got %d, want %d", v, prev+2)
 			}
 			prev = v
 			if v == 1000 {
 				break
 			}

 			if _, err := c.Write(buf); err != nil {
 				t.Errorf("unexpected Write error: %v", err)
 				break
 			}
 		}
 		if err := c.Close(); err != nil {
 			t.Errorf("unexpected Close error: %v", err)
 		}
 	}

 	wg.Add(2)
 	go pingPonger(c1)
 	go pingPonger(c2)

 	// Start off the chain reaction.
 	if _, err := c1.Write(make([]byte, 8)); err != nil {
 		t.Errorf("unexpected c1.Write error: %v", err)
 	}
 }

 // testRacyRead tests that it is safe to mutate the input Read buffer
 // immediately after cancelation has occurred.
 func testRacyRead(t *testing.T, c1, c2 net.Conn) {
 	go chunkedCopy(c2, rand.New(rand.NewSource(0)))

 	var wg sync.WaitGroup
 	defer wg.Wait()

 	c1.SetReadDeadline(time.Now().Add(time.Millisecond))
 	for i := 0; i < 10; i++ {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()

 			b1 := make([]byte, 1024)
 			b2 := make([]byte, 1024)
 			for j := 0; j < 100; j++ {
 				_, err := c1.Read(b1)
 				copy(b1, b2) // Mutate b1 to trigger potential race
 				if err != nil {
 					checkForTimeoutError(t, err)
 					c1.SetReadDeadline(time.Now().Add(time.Millisecond))
 				}
 			}
 		}()
 	}
 }

 // testRacyWrite tests that it is safe to mutate the input Write buffer
 // immediately after cancelation has occurred.
 func testRacyWrite(t *testing.T, c1, c2 net.Conn) {
 	go chunkedCopy(ioutil.Discard, c2)

 	var wg sync.WaitGroup
 	defer wg.Wait()

 	c1.SetWriteDeadline(time.Now().Add(time.Millisecond))
 	for i := 0; i < 10; i++ {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()

 			b1 := make([]byte, 1024)
 			b2 := make([]byte, 1024)
 			for j := 0; j < 100; j++ {
 				_, err := c1.Write(b1)
 				copy(b1, b2) // Mutate b1 to trigger potential race
 				if err != nil {
 					checkForTimeoutError(t, err)
 					c1.SetWriteDeadline(time.Now().Add(time.Millisecond))
 				}
 			}
 		}()
 	}
 }

 // testReadTimeout tests that Read timeouts do not affect Write.
 func testReadTimeout(t *testing.T, c1, c2 net.Conn) {
 	go chunkedCopy(ioutil.Discard, c2)

 	c1.SetReadDeadline(aLongTimeAgo)
 	_, err := c1.Read(make([]byte, 1024))
 	checkForTimeoutError(t, err)
 	if _, err := c1.Write(make([]byte, 1024)); err != nil {
 		t.Errorf("unexpected Write error: %v", err)
 	}
 }

 // testWriteTimeout tests that Write timeouts do not affect Read.
 func testWriteTimeout(t *testing.T, c1, c2 net.Conn) {
 	go chunkedCopy(c2, rand.New(rand.NewSource(0)))

 	c1.SetWriteDeadline(aLongTimeAgo)
 	_, err := c1.Write(make([]byte, 1024))
 	checkForTimeoutError(t, err)
 	if _, err := c1.Read(make([]byte, 1024)); err != nil {
 		t.Errorf("unexpected Read error: %v", err)
 	}
 }

 // testPastTimeout tests that a deadline set in the past immediately times out
 // Read and Write requests.
 func testPastTimeout(t *testing.T, c1, c2 net.Conn) {
 	go chunkedCopy(c2, c2)

 	testRoundtrip(t, c1)

 	c1.SetDeadline(aLongTimeAgo)
 	n, err := c1.Write(make([]byte, 1024))
 	if n != 0 {
 		t.Errorf("unexpected Write count: got %d, want 0", n)
 	}
 	checkForTimeoutError(t, err)
 	n, err = c1.Read(make([]byte, 1024))
 	if n != 0 {
 		t.Errorf("unexpected Read count: got %d, want 0", n)
 	}
 	checkForTimeoutError(t, err)

 	testRoundtrip(t, c1)
 }

 // testPresentTimeout tests that a past deadline set while there are pending
 // Read and Write operations immediately times out those operations.
 func testPresentTimeout(t *testing.T, c1, c2 net.Conn) {
 	var wg sync.WaitGroup
 	defer wg.Wait()
 	wg.Add(3)

 	deadlineSet := make(chan bool, 1)
 	go func() {
 		defer wg.Done()
 		time.Sleep(100 * time.Millisecond)
 		deadlineSet <- true
 		c1.SetReadDeadline(aLongTimeAgo)
 		c1.SetWriteDeadline(aLongTimeAgo)
 	}()
 	go func() {
 		defer wg.Done()
 		n, err := c1.Read(make([]byte, 1024))
 		if n != 0 {
 			t.Errorf("unexpected Read count: got %d, want 0", n)
 		}
 		checkForTimeoutError(t, err)
 		if len(deadlineSet) == 0 {
 			t.Error("Read timed out before deadline is set")
 		}
 	}()
 	go func() {
 		defer wg.Done()
 		var err error
 		for err == nil {
 			_, err = c1.Write(make([]byte, 1024))
 		}
 		checkForTimeoutError(t, err)
 		if len(deadlineSet) == 0 {
 			t.Error("Write timed out before deadline is set")
 		}
 	}()
 }

 // testFutureTimeout tests that a future deadline will eventually time out
 // Read and Write operations.
 func testFutureTimeout(t *testing.T, c1, c2 net.Conn) {
 	var wg sync.WaitGroup
 	wg.Add(2)

 	c1.SetDeadline(time.Now().Add(100 * time.Millisecond))
 	go func() {
 		defer wg.Done()
 		_, err := c1.Read(make([]byte, 1024))
 		checkForTimeoutError(t, err)
 	}()
 	go func() {
 		defer wg.Done()
 		var err error
 		for err == nil {
 			_, err = c1.Write(make([]byte, 1024))
 		}
 		checkForTimeoutError(t, err)
 	}()
 	wg.Wait()

 	go chunkedCopy(c2, c2)
 	resyncConn(t, c1)
 	testRoundtrip(t, c1)
 }

 // testCloseTimeout tests that calling Close immediately times out pending
 // Read and Write operations.
 func testCloseTimeout(t *testing.T, c1, c2 net.Conn) {
 	go chunkedCopy(c2, c2)

 	var wg sync.WaitGroup
 	defer wg.Wait()
 	wg.Add(3)

 	// Test for cancelation upon connection closure.
 	c1.SetDeadline(neverTimeout)
 	go func() {
 		defer wg.Done()
 		time.Sleep(100 * time.Millisecond)
 		c1.Close()
 	}()
 	go func() {
 		defer wg.Done()
 		var err error
 		buf := make([]byte, 1024)
 		for err == nil {
 			_, err = c1.Read(buf)
 		}
 	}()
 	go func() {
 		defer wg.Done()
 		var err error
 		buf := make([]byte, 1024)
 		for err == nil {
 			_, err = c1.Write(buf)
 		}
 	}()
 }

 // testConcurrentMethods tests that the methods of net.Conn can safely
 // be called concurrently.
 func testConcurrentMethods(t *testing.T, c1, c2 net.Conn) {
 	if runtime.GOOS == "plan9" {
 		t.Skip("skipping on plan9; see https://golang.org/issue/20489")
 	}
 	go chunkedCopy(c2, c2)

 	// The results of the calls may be nonsensical, but this should
 	// not trigger a race detector warning.
 	var wg sync.WaitGroup
 	for i := 0; i < 100; i++ {
 		wg.Add(7)
 		go func() {
 			defer wg.Done()
 			c1.Read(make([]byte, 1024))
 		}()
 		go func() {
 			defer wg.Done()
 			c1.Write(make([]byte, 1024))
 		}()
 		go func() {
 			defer wg.Done()
 			c1.SetDeadline(time.Now().Add(10 * time.Millisecond))
 		}()
 		go func() {
 			defer wg.Done()
 			c1.SetReadDeadline(aLongTimeAgo)
 		}()
 		go func() {
 			defer wg.Done()
 			c1.SetWriteDeadline(aLongTimeAgo)
 		}()
 		go func() {
 			defer wg.Done()
 			c1.LocalAddr()
 		}()
 		go func() {
 			defer wg.Done()
 			c1.RemoteAddr()
 		}()
 	}
 	wg.Wait() // At worst, the deadline is set 10ms into the future

 	resyncConn(t, c1)
 	testRoundtrip(t, c1)
 }

 // checkForTimeoutError checks that the error satisfies the Error interface
 // and that Timeout returns true.
 func checkForTimeoutError(t *testing.T, err error) {
 	t.Helper()
 	if nerr, ok := err.(net.Error); ok {
 		if !nerr.Timeout() {
 			if runtime.GOOS == "windows" && runtime.GOARCH == "arm64" && t.Name() == "TestTestConn/TCP/RacyRead" {
 				t.Logf("ignoring known failure mode on windows/arm64; see https://go.dev/issue/52893")
 			} else {
 				t.Errorf("got error: %v, want err.Timeout() = true", nerr)
 			}
 		}
 	} else {
 		t.Errorf("got %T: %v, want net.Error", err, err)
 	}
 }

 // testRoundtrip writes something into c and reads it back.
 // It assumes that everything written into c is echoed back to itself.
 func testRoundtrip(t *testing.T, c net.Conn) {
 	t.Helper()
 	if err := c.SetDeadline(neverTimeout); err != nil {
 		t.Errorf("roundtrip SetDeadline error: %v", err)
 	}

 	const s = "Hello, world!"
 	buf := []byte(s)
 	if _, err := c.Write(buf); err != nil {
 		t.Errorf("roundtrip Write error: %v", err)
 	}
 	if _, err := io.ReadFull(c, buf); err != nil {
 		t.Errorf("roundtrip Read error: %v", err)
 	}
 	if string(buf) != s {
 		t.Errorf("roundtrip data mismatch: got %q, want %q", buf, s)
 	}
 }

 // resyncConn resynchronizes the connection into a sane state.
 // It assumes that everything written into c is echoed back to itself.
 // It assumes that 0xff is not currently on the wire or in the read buffer.
 func resyncConn(t *testing.T, c net.Conn) {
 	t.Helper()
 	c.SetDeadline(neverTimeout)
 	errCh := make(chan error)
 	go func() {
 		_, err := c.Write([]byte{0xff})
 		errCh <- err
 	}()
 	buf := make([]byte, 1024)
 	for {
 		n, err := c.Read(buf)
 		if n > 0 && bytes.IndexByte(buf[:n], 0xff) == n-1 {
 			break
 		}
 		if err != nil {
 			t.Errorf("unexpected Read error: %v", err)
 			break
 		}
 	}
 	if err := <-errCh; err != nil {
 		t.Errorf("unexpected Write error: %v", err)
 	}
 }

 // chunkedCopy copies from r to w in fixed-width chunks to avoid
 // causing a Write that exceeds the maximum packet size for packet-based
 // connections like "unixpacket".
 // We assume that the maximum packet size is at least 1024.
 func chunkedCopy(w io.Writer, r io.Reader) error {
 	b := make([]byte, 1024)
 	_, err := io.CopyBuffer(struct{ io.Writer }{w}, struct{ io.Reader }{r}, b)
 	return err
 }
	// Copyright 2016 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package nettest

	import (
	"bytes"
	"encoding/binary"
	"io"
	"io/ioutil"
	"math/rand"
	"net"
	"runtime"
	"sync"
	"testing"
	"time"
	)

	// MakePipe creates a connection between two endpoints and returns the pair
	// as c1 and c2, such that anything written to c1 is read by c2 and vice-versa.
	// The stop function closes all resources, including c1, c2, and the underlying
	// net.Listener (if there is one), and should not be nil.
	type MakePipe func() (c1, c2 net.Conn, stop func(), err error)

	// TestConn tests that a net.Conn implementation properly satisfies the interface.
	// The tests should not produce any false positives, but may experience
	// false negatives. Thus, some issues may only be detected when the test is
	// run multiple times. For maximal effectiveness, run the tests under the
	// race detector.
	func TestConn(t *testing.T, mp MakePipe) {
	t.Run("BasicIO", func(t *testing.T) { timeoutWrapper(t, mp, testBasicIO) })
	t.Run("PingPong", func(t *testing.T) { timeoutWrapper(t, mp, testPingPong) })
	t.Run("RacyRead", func(t *testing.T) { timeoutWrapper(t, mp, testRacyRead) })
	t.Run("RacyWrite", func(t *testing.T) { timeoutWrapper(t, mp, testRacyWrite) })
	t.Run("ReadTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testReadTimeout) })
	t.Run("WriteTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testWriteTimeout) })
	t.Run("PastTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testPastTimeout) })
	t.Run("PresentTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testPresentTimeout) })
	t.Run("FutureTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testFutureTimeout) })
	t.Run("CloseTimeout", func(t *testing.T) { timeoutWrapper(t, mp, testCloseTimeout) })
	t.Run("ConcurrentMethods", func(t *testing.T) { timeoutWrapper(t, mp, testConcurrentMethods) })
	}

	type connTester func(t *testing.T, c1, c2 net.Conn)

	func timeoutWrapper(t *testing.T, mp MakePipe, f connTester) {
	t.Helper()
	c1, c2, stop, err := mp()
	if err != nil {
	t.Fatalf("unable to make pipe: %v", err)
	}
	var once sync.Once
	defer once.Do(func() { stop() })
	timer := time.AfterFunc(time.Minute, func() {
	once.Do(func() {
	t.Error("test timed out; terminating pipe")
	stop()
	})
	})
	defer timer.Stop()
	f(t, c1, c2)
	}

	// testBasicIO tests that the data sent on c1 is properly received on c2.
	func testBasicIO(t *testing.T, c1, c2 net.Conn) {
	want := make([]byte, 1<<20)
	rand.New(rand.NewSource(0)).Read(want)

	dataCh := make(chan []byte)
	go func() {
	rd := bytes.NewReader(want)
	if err := chunkedCopy(c1, rd); err != nil {
	t.Errorf("unexpected c1.Write error: %v", err)
	}
	if err := c1.Close(); err != nil {
	t.Errorf("unexpected c1.Close error: %v", err)
	}
	}()

	go func() {
	wr := new(bytes.Buffer)
	if err := chunkedCopy(wr, c2); err != nil {
	t.Errorf("unexpected c2.Read error: %v", err)
	}
	if err := c2.Close(); err != nil {
	t.Errorf("unexpected c2.Close error: %v", err)
	}
	dataCh <- wr.Bytes()
	}()

	if got := <-dataCh; !bytes.Equal(got, want) {
	t.Error("transmitted data differs")
	}
	}

	// testPingPong tests that the two endpoints can synchronously send data to
	// each other in a typical request-response pattern.
	func testPingPong(t *testing.T, c1, c2 net.Conn) {
	var wg sync.WaitGroup
	defer wg.Wait()

	pingPonger := func(c net.Conn) {
	defer wg.Done()
	buf := make([]byte, 8)
	var prev uint64
	for {
	if _, err := io.ReadFull(c, buf); err != nil {
	if err == io.EOF {
	break
	}
	t.Errorf("unexpected Read error: %v", err)
	}

	v := binary.LittleEndian.Uint64(buf)
	binary.LittleEndian.PutUint64(buf, v+1)
	if prev != 0 && prev+2 != v {
	t.Errorf("mismatching value: got %d, want %d", v, prev+2)
	}
	prev = v
	if v == 1000 {
	break
	}

	if _, err := c.Write(buf); err != nil {
	t.Errorf("unexpected Write error: %v", err)
	break
	}
	}
	if err := c.Close(); err != nil {
	t.Errorf("unexpected Close error: %v", err)
	}
	}

	wg.Add(2)
	go pingPonger(c1)
	go pingPonger(c2)

	// Start off the chain reaction.
	if _, err := c1.Write(make([]byte, 8)); err != nil {
	t.Errorf("unexpected c1.Write error: %v", err)
	}
	}

	// testRacyRead tests that it is safe to mutate the input Read buffer
	// immediately after cancelation has occurred.
	func testRacyRead(t *testing.T, c1, c2 net.Conn) {
	go chunkedCopy(c2, rand.New(rand.NewSource(0)))

	var wg sync.WaitGroup
	defer wg.Wait()

	c1.SetReadDeadline(time.Now().Add(time.Millisecond))
	for i := 0; i < 10; i++ {
	wg.Add(1)
	go func() {
	defer wg.Done()

	b1 := make([]byte, 1024)
	b2 := make([]byte, 1024)
	for j := 0; j < 100; j++ {
	_, err := c1.Read(b1)
	copy(b1, b2) // Mutate b1 to trigger potential race
	if err != nil {
	checkForTimeoutError(t, err)
	c1.SetReadDeadline(time.Now().Add(time.Millisecond))
	}
	}
	}()
	}
	}

	// testRacyWrite tests that it is safe to mutate the input Write buffer
	// immediately after cancelation has occurred.
	func testRacyWrite(t *testing.T, c1, c2 net.Conn) {
	go chunkedCopy(ioutil.Discard, c2)

	var wg sync.WaitGroup
	defer wg.Wait()

	c1.SetWriteDeadline(time.Now().Add(time.Millisecond))
	for i := 0; i < 10; i++ {
	wg.Add(1)
	go func() {
	defer wg.Done()

	b1 := make([]byte, 1024)
	b2 := make([]byte, 1024)
	for j := 0; j < 100; j++ {
	_, err := c1.Write(b1)
	copy(b1, b2) // Mutate b1 to trigger potential race
	if err != nil {
	checkForTimeoutError(t, err)
	c1.SetWriteDeadline(time.Now().Add(time.Millisecond))
	}
	}
	}()
	}
	}

	// testReadTimeout tests that Read timeouts do not affect Write.
	func testReadTimeout(t *testing.T, c1, c2 net.Conn) {
	go chunkedCopy(ioutil.Discard, c2)

	c1.SetReadDeadline(aLongTimeAgo)
	_, err := c1.Read(make([]byte, 1024))
	checkForTimeoutError(t, err)
	if _, err := c1.Write(make([]byte, 1024)); err != nil {
	t.Errorf("unexpected Write error: %v", err)
	}
	}

	// testWriteTimeout tests that Write timeouts do not affect Read.
	func testWriteTimeout(t *testing.T, c1, c2 net.Conn) {
	go chunkedCopy(c2, rand.New(rand.NewSource(0)))

	c1.SetWriteDeadline(aLongTimeAgo)
	_, err := c1.Write(make([]byte, 1024))
	checkForTimeoutError(t, err)
	if _, err := c1.Read(make([]byte, 1024)); err != nil {
	t.Errorf("unexpected Read error: %v", err)
	}
	}

	// testPastTimeout tests that a deadline set in the past immediately times out
	// Read and Write requests.
	func testPastTimeout(t *testing.T, c1, c2 net.Conn) {
	go chunkedCopy(c2, c2)

	testRoundtrip(t, c1)

	c1.SetDeadline(aLongTimeAgo)
	n, err := c1.Write(make([]byte, 1024))
	if n != 0 {
	t.Errorf("unexpected Write count: got %d, want 0", n)
	}
	checkForTimeoutError(t, err)
	n, err = c1.Read(make([]byte, 1024))
	if n != 0 {
	t.Errorf("unexpected Read count: got %d, want 0", n)
	}
	checkForTimeoutError(t, err)

	testRoundtrip(t, c1)
	}

	// testPresentTimeout tests that a past deadline set while there are pending
	// Read and Write operations immediately times out those operations.
	func testPresentTimeout(t *testing.T, c1, c2 net.Conn) {
	var wg sync.WaitGroup
	defer wg.Wait()
	wg.Add(3)

	deadlineSet := make(chan bool, 1)
	go func() {
	defer wg.Done()
	time.Sleep(100 * time.Millisecond)
	deadlineSet <- true
	c1.SetReadDeadline(aLongTimeAgo)
	c1.SetWriteDeadline(aLongTimeAgo)
	}()
	go func() {
	defer wg.Done()
	n, err := c1.Read(make([]byte, 1024))
	if n != 0 {
	t.Errorf("unexpected Read count: got %d, want 0", n)
	}
	checkForTimeoutError(t, err)
	if len(deadlineSet) == 0 {
	t.Error("Read timed out before deadline is set")
	}
	}()
	go func() {
	defer wg.Done()
	var err error
	for err == nil {
	_, err = c1.Write(make([]byte, 1024))
	}
	checkForTimeoutError(t, err)
	if len(deadlineSet) == 0 {
	t.Error("Write timed out before deadline is set")
	}
	}()
	}

	// testFutureTimeout tests that a future deadline will eventually time out
	// Read and Write operations.
	func testFutureTimeout(t *testing.T, c1, c2 net.Conn) {
	var wg sync.WaitGroup
	wg.Add(2)

	c1.SetDeadline(time.Now().Add(100 * time.Millisecond))
	go func() {
	defer wg.Done()
	_, err := c1.Read(make([]byte, 1024))
	checkForTimeoutError(t, err)
	}()
	go func() {
	defer wg.Done()
	var err error
	for err == nil {
	_, err = c1.Write(make([]byte, 1024))
	}
	checkForTimeoutError(t, err)
	}()
	wg.Wait()

	go chunkedCopy(c2, c2)
	resyncConn(t, c1)
	testRoundtrip(t, c1)
	}

	// testCloseTimeout tests that calling Close immediately times out pending
	// Read and Write operations.
	func testCloseTimeout(t *testing.T, c1, c2 net.Conn) {
	go chunkedCopy(c2, c2)

	var wg sync.WaitGroup
	defer wg.Wait()
	wg.Add(3)

	// Test for cancelation upon connection closure.
	c1.SetDeadline(neverTimeout)
	go func() {
	defer wg.Done()
	time.Sleep(100 * time.Millisecond)
	c1.Close()
	}()
	go func() {
	defer wg.Done()
	var err error
	buf := make([]byte, 1024)
	for err == nil {
	_, err = c1.Read(buf)
	}
	}()
	go func() {
	defer wg.Done()
	var err error
	buf := make([]byte, 1024)
	for err == nil {
	_, err = c1.Write(buf)
	}
	}()
	}

	// testConcurrentMethods tests that the methods of net.Conn can safely
	// be called concurrently.
	func testConcurrentMethods(t *testing.T, c1, c2 net.Conn) {
	if runtime.GOOS == "plan9" {
	t.Skip("skipping on plan9; see https://golang.org/issue/20489")
	}
	go chunkedCopy(c2, c2)

	// The results of the calls may be nonsensical, but this should
	// not trigger a race detector warning.
	var wg sync.WaitGroup
	for i := 0; i < 100; i++ {
	wg.Add(7)
	go func() {
	defer wg.Done()
	c1.Read(make([]byte, 1024))
	}()
	go func() {
	defer wg.Done()
	c1.Write(make([]byte, 1024))
	}()
	go func() {
	defer wg.Done()
	c1.SetDeadline(time.Now().Add(10 * time.Millisecond))
	}()
	go func() {
	defer wg.Done()
	c1.SetReadDeadline(aLongTimeAgo)
	}()
	go func() {
	defer wg.Done()
	c1.SetWriteDeadline(aLongTimeAgo)
	}()
	go func() {
	defer wg.Done()
	c1.LocalAddr()
	}()
	go func() {
	defer wg.Done()
	c1.RemoteAddr()
	}()
	}
	wg.Wait() // At worst, the deadline is set 10ms into the future

	resyncConn(t, c1)
	testRoundtrip(t, c1)
	}

	// checkForTimeoutError checks that the error satisfies the Error interface
	// and that Timeout returns true.
	func checkForTimeoutError(t *testing.T, err error) {
	t.Helper()
	if nerr, ok := err.(net.Error); ok {
	if !nerr.Timeout() {
	if runtime.GOOS == "windows" && runtime.GOARCH == "arm64" && t.Name() == "TestTestConn/TCP/RacyRead" {
	t.Logf("ignoring known failure mode on windows/arm64; see https://go.dev/issue/52893")
	} else {
	t.Errorf("got error: %v, want err.Timeout() = true", nerr)
	}
	}
	} else {
	t.Errorf("got %T: %v, want net.Error", err, err)
	}
	}

	// testRoundtrip writes something into c and reads it back.
	// It assumes that everything written into c is echoed back to itself.
	func testRoundtrip(t *testing.T, c net.Conn) {
	t.Helper()
	if err := c.SetDeadline(neverTimeout); err != nil {
	t.Errorf("roundtrip SetDeadline error: %v", err)
	}

	const s = "Hello, world!"
	buf := []byte(s)
	if _, err := c.Write(buf); err != nil {
	t.Errorf("roundtrip Write error: %v", err)
	}
	if _, err := io.ReadFull(c, buf); err != nil {
	t.Errorf("roundtrip Read error: %v", err)
	}
	if string(buf) != s {
	t.Errorf("roundtrip data mismatch: got %q, want %q", buf, s)
	}
	}

	// resyncConn resynchronizes the connection into a sane state.
	// It assumes that everything written into c is echoed back to itself.
	// It assumes that 0xff is not currently on the wire or in the read buffer.
	func resyncConn(t *testing.T, c net.Conn) {
	t.Helper()
	c.SetDeadline(neverTimeout)
	errCh := make(chan error)
	go func() {
	_, err := c.Write([]byte{0xff})
	errCh <- err
	}()
	buf := make([]byte, 1024)
	for {
	n, err := c.Read(buf)
	if n > 0 && bytes.IndexByte(buf[:n], 0xff) == n-1 {
	break
	}
	if err != nil {
	t.Errorf("unexpected Read error: %v", err)
	break
	}
	}
	if err := <-errCh; err != nil {
	t.Errorf("unexpected Write error: %v", err)
	}
	}

	// chunkedCopy copies from r to w in fixed-width chunks to avoid
	// causing a Write that exceeds the maximum packet size for packet-based
	// connections like "unixpacket".
	// We assume that the maximum packet size is at least 1024.
	func chunkedCopy(w io.Writer, r io.Reader) error {
	b := make([]byte, 1024)
	_, err := io.CopyBuffer(struct{ io.Writer }{w}, struct{ io.Reader }{r}, b)
	return err
	}