// Copyright 2009 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 net

import (
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"runtime"
	"sync"
	"testing"
	"time"
)

func init() {
	// Install a hook to ensure that a 1ns timeout will always
	// be exceeded by the time Dial gets to the relevant system call.
	//
	// Without this, systems with a very large timer granularity — such as
	// Windows — may be able to accept connections without measurably exceeding
	// even an implausibly short deadline.
	testHookStepTime = func() {
		now := time.Now()
		for time.Since(now) == 0 {
			time.Sleep(1 * time.Nanosecond)
		}
	}
}

var dialTimeoutTests = []struct {
	initialTimeout time.Duration
	initialDelta   time.Duration // for deadline
}{
	// Tests that dial timeouts, deadlines in the past work.
	{-5 * time.Second, 0},
	{0, -5 * time.Second},
	{-5 * time.Second, 5 * time.Second}, // timeout over deadline
	{-1 << 63, 0},
	{0, -1 << 63},

	{1 * time.Millisecond, 0},
	{0, 1 * time.Millisecond},
	{1 * time.Millisecond, 5 * time.Second}, // timeout over deadline
}

func TestDialTimeout(t *testing.T) {
	switch runtime.GOOS {
	case "plan9":
		t.Skipf("not supported on %s", runtime.GOOS)
	}

	t.Parallel()

	ln := newLocalListener(t, "tcp")
	defer func() {
		if err := ln.Close(); err != nil {
			t.Error(err)
		}
	}()

	for _, tt := range dialTimeoutTests {
		t.Run(fmt.Sprintf("%v/%v", tt.initialTimeout, tt.initialDelta), func(t *testing.T) {
			// We don't run these subtests in parallel because we don't know how big
			// the kernel's accept queue is, and we don't want to accidentally saturate
			// it with concurrent calls. (That could cause the Dial to fail with
			// ECONNREFUSED or ECONNRESET instead of a timeout error.)
			d := Dialer{Timeout: tt.initialTimeout}
			delta := tt.initialDelta

			var (
				beforeDial time.Time
				afterDial  time.Time
				err        error
			)
			for {
				if delta != 0 {
					d.Deadline = time.Now().Add(delta)
				}

				beforeDial = time.Now()

				var c Conn
				c, err = d.Dial(ln.Addr().Network(), ln.Addr().String())
				afterDial = time.Now()

				if err != nil {
					break
				}

				// Even though we're not calling Accept on the Listener, the kernel may
				// spuriously accept connections on its behalf. If that happens, we will
				// close the connection (to try to get it out of the kernel's accept
				// queue) and try a shorter timeout.
				//
				// We assume that we will reach a point where the call actually does
				// time out, although in theory (since this socket is on a loopback
				// address) a sufficiently clever kernel could notice that no Accept
				// call is pending and bypass both the queue and the timeout to return
				// another error immediately.
				t.Logf("closing spurious connection from Dial")
				c.Close()

				if delta <= 1 && d.Timeout <= 1 {
					t.Fatalf("can't reduce Timeout or Deadline")
				}
				if delta > 1 {
					delta /= 2
					t.Logf("reducing Deadline delta to %v", delta)
				}
				if d.Timeout > 1 {
					d.Timeout /= 2
					t.Logf("reducing Timeout to %v", d.Timeout)
				}
			}

			if d.Deadline.IsZero() || afterDial.Before(d.Deadline) {
				delay := afterDial.Sub(beforeDial)
				if delay < d.Timeout {
					t.Errorf("Dial returned after %v; want ≥%v", delay, d.Timeout)
				}
			}

			if perr := parseDialError(err); perr != nil {
				t.Errorf("unexpected error from Dial: %v", perr)
			}
			if nerr, ok := err.(Error); !ok || !nerr.Timeout() {
				t.Errorf("Dial: %v, want timeout", err)
			}
		})
	}
}

func TestDialTimeoutMaxDuration(t *testing.T) {
	ln := newLocalListener(t, "tcp")
	defer func() {
		if err := ln.Close(); err != nil {
			t.Error(err)
		}
	}()

	for _, tt := range []struct {
		timeout time.Duration
		delta   time.Duration // for deadline
	}{
		// Large timeouts that will overflow an int64 unix nanos.
		{1<<63 - 1, 0},
		{0, 1<<63 - 1},
	} {
		t.Run(fmt.Sprintf("timeout=%s/delta=%s", tt.timeout, tt.delta), func(t *testing.T) {
			d := Dialer{Timeout: tt.timeout}
			if tt.delta != 0 {
				d.Deadline = time.Now().Add(tt.delta)
			}
			c, err := d.Dial(ln.Addr().Network(), ln.Addr().String())
			if err != nil {
				t.Fatal(err)
			}
			if err := c.Close(); err != nil {
				t.Error(err)
			}
		})
	}
}

func TestAcceptTimeout(t *testing.T) {
	t.Parallel()

	switch runtime.GOOS {
	case "plan9":
		t.Skipf("not supported on %s", runtime.GOOS)
	}

	timeouts := []time.Duration{
		-5 * time.Second,
		10 * time.Millisecond,
	}

	for _, timeout := range timeouts {
		timeout := timeout
		t.Run(fmt.Sprintf("%v", timeout), func(t *testing.T) {
			t.Parallel()

			ln := newLocalListener(t, "tcp")
			defer ln.Close()

			if timeout >= 0 {
				// Don't dial the listener at all, so that Accept will hang.
			} else {
				// A deadline in the past should cause Accept to fail even if there are
				// incoming connections available. Try to make one available before the
				// call to Accept happens. (It's ok if the timing doesn't always work
				// out that way, though: the test should pass regardless.)
				ctx, cancel := context.WithCancel(context.Background())
				dialDone := make(chan struct{})

				// Ensure that our background Dial returns before we close the listener.
				// Otherwise, the listener's port could be reused immediately and we
				// might spuriously Dial some completely unrelated socket, causing some
				// other test to see an unexpected extra connection.
				defer func() {
					cancel()
					<-dialDone
				}()

				go func() {
					defer close(dialDone)
					d := Dialer{}
					c, err := d.DialContext(ctx, ln.Addr().Network(), ln.Addr().String())
					if err != nil {
						// If the timing didn't work out, it is possible for this Dial
						// to return an error (depending on the kernel's buffering behavior).
						// In https://go.dev/issue/65240 we saw failures with ECONNREFUSED
						// and ECONNRESET.
						//
						// What this test really cares about is the behavior of Accept, not
						// Dial, so just log the error and ignore it.
						t.Logf("DialContext: %v", err)
						return
					}
					t.Logf("Dialed %v -> %v", c.LocalAddr(), c.RemoteAddr())
					c.Close()
				}()

				time.Sleep(10 * time.Millisecond)
			}

			if err := ln.(*TCPListener).SetDeadline(time.Now().Add(timeout)); err != nil {
				t.Fatal(err)
			}
			t.Logf("ln.SetDeadline(time.Now().Add(%v))", timeout)

			c, err := ln.Accept()
			if err == nil {
				c.Close()
			}
			t.Logf("ln.Accept: %v", err)

			if perr := parseAcceptError(err); perr != nil {
				t.Error(perr)
			}
			if !isDeadlineExceeded(err) {
				t.Error("wanted deadline exceeded")
			}
		})
	}
}

func TestAcceptTimeoutMustReturn(t *testing.T) {
	t.Parallel()

	switch runtime.GOOS {
	case "plan9":
		t.Skipf("not supported on %s", runtime.GOOS)
	}

	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	if err := ln.(*TCPListener).SetDeadline(noDeadline); err != nil {
		t.Error(err)
	}
	if err := ln.(*TCPListener).SetDeadline(time.Now().Add(10 * time.Millisecond)); err != nil {
		t.Error(err)
	}
	c, err := ln.Accept()
	if err == nil {
		c.Close()
	}

	if perr := parseAcceptError(err); perr != nil {
		t.Error(perr)
	}
	if !isDeadlineExceeded(err) {
		t.Fatal(err)
	}
}

func TestAcceptTimeoutMustNotReturn(t *testing.T) {
	t.Parallel()

	switch runtime.GOOS {
	case "plan9":
		t.Skipf("not supported on %s", runtime.GOOS)
	}

	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	maxch := make(chan *time.Timer)
	ch := make(chan error)
	go func() {
		if err := ln.(*TCPListener).SetDeadline(time.Now().Add(-5 * time.Second)); err != nil {
			t.Error(err)
		}
		if err := ln.(*TCPListener).SetDeadline(noDeadline); err != nil {
			t.Error(err)
		}
		maxch <- time.NewTimer(100 * time.Millisecond)
		_, err := ln.Accept()
		ch <- err
	}()

	max := <-maxch
	defer max.Stop()

	select {
	case err := <-ch:
		if perr := parseAcceptError(err); perr != nil {
			t.Error(perr)
		}
		t.Fatalf("expected Accept to not return, but it returned with %v", err)
	case <-max.C:
		ln.Close()
		<-ch // wait for tester goroutine to stop
	}
}

var readTimeoutTests = []struct {
	timeout time.Duration
	xerrs   [2]error // expected errors in transition
}{
	// Tests that read deadlines work, even if there's data ready
	// to be read.
	{-5 * time.Second, [2]error{os.ErrDeadlineExceeded, os.ErrDeadlineExceeded}},

	{50 * time.Millisecond, [2]error{nil, os.ErrDeadlineExceeded}},
}

// There is a very similar copy of this in os/timeout_test.go.
func TestReadTimeout(t *testing.T) {
	handler := func(ls *localServer, ln Listener) {
		c, err := ln.Accept()
		if err != nil {
			t.Error(err)
			return
		}
		c.Write([]byte("READ TIMEOUT TEST"))
		defer c.Close()
	}
	ls := newLocalServer(t, "tcp")
	defer ls.teardown()
	if err := ls.buildup(handler); err != nil {
		t.Fatal(err)
	}

	c, err := Dial(ls.Listener.Addr().Network(), ls.Listener.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer c.Close()

	for i, tt := range readTimeoutTests {
		if err := c.SetReadDeadline(time.Now().Add(tt.timeout)); err != nil {
			t.Fatalf("#%d: %v", i, err)
		}
		var b [1]byte
		for j, xerr := range tt.xerrs {
			for {
				n, err := c.Read(b[:])
				if xerr != nil {
					if perr := parseReadError(err); perr != nil {
						t.Errorf("#%d/%d: %v", i, j, perr)
					}
					if !isDeadlineExceeded(err) {
						t.Fatalf("#%d/%d: %v", i, j, err)
					}
				}
				if err == nil {
					time.Sleep(tt.timeout / 3)
					continue
				}
				if n != 0 {
					t.Fatalf("#%d/%d: read %d; want 0", i, j, n)
				}
				break
			}
		}
	}
}

// There is a very similar copy of this in os/timeout_test.go.
func TestReadTimeoutMustNotReturn(t *testing.T) {
	t.Parallel()

	switch runtime.GOOS {
	case "plan9":
		t.Skipf("not supported on %s", runtime.GOOS)
	}

	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	c, err := Dial(ln.Addr().Network(), ln.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer c.Close()

	maxch := make(chan *time.Timer)
	ch := make(chan error)
	go func() {
		if err := c.SetDeadline(time.Now().Add(-5 * time.Second)); err != nil {
			t.Error(err)
		}
		if err := c.SetWriteDeadline(time.Now().Add(-5 * time.Second)); err != nil {
			t.Error(err)
		}
		if err := c.SetReadDeadline(noDeadline); err != nil {
			t.Error(err)
		}
		maxch <- time.NewTimer(100 * time.Millisecond)
		var b [1]byte
		_, err := c.Read(b[:])
		ch <- err
	}()

	max := <-maxch
	defer max.Stop()

	select {
	case err := <-ch:
		if perr := parseReadError(err); perr != nil {
			t.Error(perr)
		}
		t.Fatalf("expected Read to not return, but it returned with %v", err)
	case <-max.C:
		c.Close()
		err := <-ch // wait for tester goroutine to stop
		if perr := parseReadError(err); perr != nil {
			t.Error(perr)
		}
		if nerr, ok := err.(Error); !ok || nerr.Timeout() || nerr.Temporary() {
			t.Fatal(err)
		}
	}
}

var readFromTimeoutTests = []struct {
	timeout time.Duration
	xerrs   [2]error // expected errors in transition
}{
	// Tests that read deadlines work, even if there's data ready
	// to be read.
	{-5 * time.Second, [2]error{os.ErrDeadlineExceeded, os.ErrDeadlineExceeded}},

	{50 * time.Millisecond, [2]error{nil, os.ErrDeadlineExceeded}},
}

func TestReadFromTimeout(t *testing.T) {
	ch := make(chan Addr)
	defer close(ch)
	handler := func(ls *localPacketServer, c PacketConn) {
		if dst, ok := <-ch; ok {
			c.WriteTo([]byte("READFROM TIMEOUT TEST"), dst)
		}
	}
	ls := newLocalPacketServer(t, "udp")
	defer ls.teardown()
	if err := ls.buildup(handler); err != nil {
		t.Fatal(err)
	}

	host, _, err := SplitHostPort(ls.PacketConn.LocalAddr().String())
	if err != nil {
		t.Fatal(err)
	}
	c, err := ListenPacket(ls.PacketConn.LocalAddr().Network(), JoinHostPort(host, "0"))
	if err != nil {
		t.Fatal(err)
	}
	defer c.Close()
	ch <- c.LocalAddr()

	for i, tt := range readFromTimeoutTests {
		if err := c.SetReadDeadline(time.Now().Add(tt.timeout)); err != nil {
			t.Fatalf("#%d: %v", i, err)
		}
		var b [1]byte
		for j, xerr := range tt.xerrs {
			for {
				n, _, err := c.ReadFrom(b[:])
				if xerr != nil {
					if perr := parseReadError(err); perr != nil {
						t.Errorf("#%d/%d: %v", i, j, perr)
					}
					if !isDeadlineExceeded(err) {
						t.Fatalf("#%d/%d: %v", i, j, err)
					}
				}
				if err == nil {
					time.Sleep(tt.timeout / 3)
					continue
				}
				if nerr, ok := err.(Error); ok && nerr.Timeout() && n != 0 {
					t.Fatalf("#%d/%d: read %d; want 0", i, j, n)
				}
				break
			}
		}
	}
}

var writeTimeoutTests = []struct {
	timeout time.Duration
	xerrs   [2]error // expected errors in transition
}{
	// Tests that write deadlines work, even if there's buffer
	// space available to write.
	{-5 * time.Second, [2]error{os.ErrDeadlineExceeded, os.ErrDeadlineExceeded}},

	{10 * time.Millisecond, [2]error{nil, os.ErrDeadlineExceeded}},
}

// There is a very similar copy of this in os/timeout_test.go.
func TestWriteTimeout(t *testing.T) {
	t.Parallel()

	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	for i, tt := range writeTimeoutTests {
		c, err := Dial(ln.Addr().Network(), ln.Addr().String())
		if err != nil {
			t.Fatal(err)
		}
		defer c.Close()

		if err := c.SetWriteDeadline(time.Now().Add(tt.timeout)); err != nil {
			t.Fatalf("#%d: %v", i, err)
		}
		for j, xerr := range tt.xerrs {
			for {
				n, err := c.Write([]byte("WRITE TIMEOUT TEST"))
				if xerr != nil {
					if perr := parseWriteError(err); perr != nil {
						t.Errorf("#%d/%d: %v", i, j, perr)
					}
					if !isDeadlineExceeded(err) {
						t.Fatalf("#%d/%d: %v", i, j, err)
					}
				}
				if err == nil {
					time.Sleep(tt.timeout / 3)
					continue
				}
				if n != 0 {
					t.Fatalf("#%d/%d: wrote %d; want 0", i, j, n)
				}
				break
			}
		}
	}
}

// There is a very similar copy of this in os/timeout_test.go.
func TestWriteTimeoutMustNotReturn(t *testing.T) {
	t.Parallel()

	switch runtime.GOOS {
	case "plan9":
		t.Skipf("not supported on %s", runtime.GOOS)
	}

	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	c, err := Dial(ln.Addr().Network(), ln.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer c.Close()

	maxch := make(chan *time.Timer)
	ch := make(chan error)
	go func() {
		if err := c.SetDeadline(time.Now().Add(-5 * time.Second)); err != nil {
			t.Error(err)
		}
		if err := c.SetReadDeadline(time.Now().Add(-5 * time.Second)); err != nil {
			t.Error(err)
		}
		if err := c.SetWriteDeadline(noDeadline); err != nil {
			t.Error(err)
		}
		maxch <- time.NewTimer(100 * time.Millisecond)
		var b [1024]byte
		for {
			if _, err := c.Write(b[:]); err != nil {
				ch <- err
				break
			}
		}
	}()

	max := <-maxch
	defer max.Stop()

	select {
	case err := <-ch:
		if perr := parseWriteError(err); perr != nil {
			t.Error(perr)
		}
		t.Fatalf("expected Write to not return, but it returned with %v", err)
	case <-max.C:
		c.Close()
		err := <-ch // wait for tester goroutine to stop
		if perr := parseWriteError(err); perr != nil {
			t.Error(perr)
		}
		if nerr, ok := err.(Error); !ok || nerr.Timeout() || nerr.Temporary() {
			t.Fatal(err)
		}
	}
}

func TestWriteToTimeout(t *testing.T) {
	t.Parallel()

	c1 := newLocalPacketListener(t, "udp")
	defer c1.Close()

	host, _, err := SplitHostPort(c1.LocalAddr().String())
	if err != nil {
		t.Fatal(err)
	}

	timeouts := []time.Duration{
		-5 * time.Second,
		10 * time.Millisecond,
	}

	for _, timeout := range timeouts {
		t.Run(fmt.Sprint(timeout), func(t *testing.T) {
			c2, err := ListenPacket(c1.LocalAddr().Network(), JoinHostPort(host, "0"))
			if err != nil {
				t.Fatal(err)
			}
			defer c2.Close()

			if err := c2.SetWriteDeadline(time.Now().Add(timeout)); err != nil {
				t.Fatalf("SetWriteDeadline: %v", err)
			}
			backoff := 1 * time.Millisecond
			nDeadlineExceeded := 0
			for j := 0; nDeadlineExceeded < 2; j++ {
				n, err := c2.WriteTo([]byte("WRITETO TIMEOUT TEST"), c1.LocalAddr())
				t.Logf("#%d: WriteTo: %d, %v", j, n, err)
				if err == nil && timeout >= 0 && nDeadlineExceeded == 0 {
					// If the timeout is nonnegative, some number of WriteTo calls may
					// succeed before the timeout takes effect.
					t.Logf("WriteTo succeeded; sleeping %v", timeout/3)
					time.Sleep(timeout / 3)
					continue
				}
				if isENOBUFS(err) {
					t.Logf("WriteTo: %v", err)
					// We're looking for a deadline exceeded error, but if the kernel's
					// network buffers are saturated we may see ENOBUFS instead (see
					// https://go.dev/issue/49930). Give it some time to unsaturate.
					time.Sleep(backoff)
					backoff *= 2
					continue
				}
				if perr := parseWriteError(err); perr != nil {
					t.Errorf("failed to parse error: %v", perr)
				}
				if !isDeadlineExceeded(err) {
					t.Errorf("error is not 'deadline exceeded'")
				}
				if n != 0 {
					t.Errorf("unexpectedly wrote %d bytes", n)
				}
				if !t.Failed() {
					t.Logf("WriteTo timed out as expected")
				}
				nDeadlineExceeded++
			}
		})
	}
}

const (
	// minDynamicTimeout is the minimum timeout to attempt for
	// tests that automatically increase timeouts until success.
	//
	// Lower values may allow tests to succeed more quickly if the value is close
	// to the true minimum, but may require more iterations (and waste more time
	// and CPU power on failed attempts) if the timeout is too low.
	minDynamicTimeout = 1 * time.Millisecond

	// maxDynamicTimeout is the maximum timeout to attempt for
	// tests that automatically increase timeouts until success.
	//
	// This should be a strict upper bound on the latency required to hit a
	// timeout accurately, even on a slow or heavily-loaded machine. If a test
	// would increase the timeout beyond this value, the test fails.
	maxDynamicTimeout = 4 * time.Second
)

// timeoutUpperBound returns the maximum time that we expect a timeout of
// duration d to take to return the caller.
func timeoutUpperBound(d time.Duration) time.Duration {
	switch runtime.GOOS {
	case "openbsd", "netbsd":
		// NetBSD and OpenBSD seem to be unable to reliably hit deadlines even when
		// the absolute durations are long.
		// In https://build.golang.org/log/c34f8685d020b98377dd4988cd38f0c5bd72267e,
		// we observed that an openbsd-amd64-68 builder took 4.090948779s for a
		// 2.983020682s timeout (37.1% overhead).
		// (See https://go.dev/issue/50189 for further detail.)
		// Give them lots of slop to compensate.
		return d * 3 / 2
	}
	// Other platforms seem to hit their deadlines more reliably,
	// at least when they are long enough to cover scheduling jitter.
	return d * 11 / 10
}

// nextTimeout returns the next timeout to try after an operation took the given
// actual duration with a timeout shorter than that duration.
func nextTimeout(actual time.Duration) (next time.Duration, ok bool) {
	if actual >= maxDynamicTimeout {
		return maxDynamicTimeout, false
	}
	// Since the previous attempt took actual, we can't expect to beat that
	// duration by any significant margin. Try the next attempt with an arbitrary
	// factor above that, so that our growth curve is at least exponential.
	next = actual * 5 / 4
	if next > maxDynamicTimeout {
		return maxDynamicTimeout, true
	}
	return next, true
}

// There is a very similar copy of this in os/timeout_test.go.
func TestReadTimeoutFluctuation(t *testing.T) {
	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	c, err := Dial(ln.Addr().Network(), ln.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer c.Close()

	d := minDynamicTimeout
	b := make([]byte, 256)
	for {
		t.Logf("SetReadDeadline(+%v)", d)
		t0 := time.Now()
		deadline := t0.Add(d)
		if err = c.SetReadDeadline(deadline); err != nil {
			t.Fatalf("SetReadDeadline(%v): %v", deadline, err)
		}
		var n int
		n, err = c.Read(b)
		t1 := time.Now()

		if n != 0 || err == nil || !err.(Error).Timeout() {
			t.Errorf("Read did not return (0, timeout): (%d, %v)", n, err)
		}
		if perr := parseReadError(err); perr != nil {
			t.Error(perr)
		}
		if !isDeadlineExceeded(err) {
			t.Errorf("Read error is not DeadlineExceeded: %v", err)
		}

		actual := t1.Sub(t0)
		if t1.Before(deadline) {
			t.Errorf("Read took %s; expected at least %s", actual, d)
		}
		if t.Failed() {
			return
		}
		if want := timeoutUpperBound(d); actual > want {
			next, ok := nextTimeout(actual)
			if !ok {
				t.Fatalf("Read took %s; expected at most %v", actual, want)
			}
			// Maybe this machine is too slow to reliably schedule goroutines within
			// the requested duration. Increase the timeout and try again.
			t.Logf("Read took %s (expected %s); trying with longer timeout", actual, d)
			d = next
			continue
		}

		break
	}
}

// There is a very similar copy of this in os/timeout_test.go.
func TestReadFromTimeoutFluctuation(t *testing.T) {
	c1 := newLocalPacketListener(t, "udp")
	defer c1.Close()

	c2, err := Dial(c1.LocalAddr().Network(), c1.LocalAddr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer c2.Close()

	d := minDynamicTimeout
	b := make([]byte, 256)
	for {
		t.Logf("SetReadDeadline(+%v)", d)
		t0 := time.Now()
		deadline := t0.Add(d)
		if err = c2.SetReadDeadline(deadline); err != nil {
			t.Fatalf("SetReadDeadline(%v): %v", deadline, err)
		}
		var n int
		n, _, err = c2.(PacketConn).ReadFrom(b)
		t1 := time.Now()

		if n != 0 || err == nil || !err.(Error).Timeout() {
			t.Errorf("ReadFrom did not return (0, timeout): (%d, %v)", n, err)
		}
		if perr := parseReadError(err); perr != nil {
			t.Error(perr)
		}
		if !isDeadlineExceeded(err) {
			t.Errorf("ReadFrom error is not DeadlineExceeded: %v", err)
		}

		actual := t1.Sub(t0)
		if t1.Before(deadline) {
			t.Errorf("ReadFrom took %s; expected at least %s", actual, d)
		}
		if t.Failed() {
			return
		}
		if want := timeoutUpperBound(d); actual > want {
			next, ok := nextTimeout(actual)
			if !ok {
				t.Fatalf("ReadFrom took %s; expected at most %s", actual, want)
			}
			// Maybe this machine is too slow to reliably schedule goroutines within
			// the requested duration. Increase the timeout and try again.
			t.Logf("ReadFrom took %s (expected %s); trying with longer timeout", actual, d)
			d = next
			continue
		}

		break
	}
}

func TestWriteTimeoutFluctuation(t *testing.T) {
	switch runtime.GOOS {
	case "plan9":
		t.Skipf("not supported on %s", runtime.GOOS)
	}

	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	c, err := Dial(ln.Addr().Network(), ln.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer c.Close()

	d := minDynamicTimeout
	for {
		t.Logf("SetWriteDeadline(+%v)", d)
		t0 := time.Now()
		deadline := t0.Add(d)
		if err := c.SetWriteDeadline(deadline); err != nil {
			t.Fatalf("SetWriteDeadline(%v): %v", deadline, err)
		}
		var n int64
		var err error
		for {
			var dn int
			dn, err = c.Write([]byte("TIMEOUT TRANSMITTER"))
			n += int64(dn)
			if err != nil {
				break
			}
		}
		t1 := time.Now()
		// Inv: err != nil
		if !err.(Error).Timeout() {
			t.Fatalf("Write did not return (any, timeout): (%d, %v)", n, err)
		}
		if perr := parseWriteError(err); perr != nil {
			t.Error(perr)
		}
		if !isDeadlineExceeded(err) {
			t.Errorf("Write error is not DeadlineExceeded: %v", err)
		}

		actual := t1.Sub(t0)
		if t1.Before(deadline) {
			t.Errorf("Write took %s; expected at least %s", actual, d)
		}
		if t.Failed() {
			return
		}
		if want := timeoutUpperBound(d); actual > want {
			if n > 0 {
				// SetWriteDeadline specifies a time “after which I/O operations fail
				// instead of blocking”. However, the kernel's send buffer is not yet
				// full, we may be able to write some arbitrary (but finite) number of
				// bytes to it without blocking.
				t.Logf("Wrote %d bytes into send buffer; retrying until buffer is full", n)
				if d <= maxDynamicTimeout/2 {
					// We don't know how long the actual write loop would have taken if
					// the buffer were full, so just guess and double the duration so that
					// the next attempt can make twice as much progress toward filling it.
					d *= 2
				}
			} else if next, ok := nextTimeout(actual); !ok {
				t.Fatalf("Write took %s; expected at most %s", actual, want)
			} else {
				// Maybe this machine is too slow to reliably schedule goroutines within
				// the requested duration. Increase the timeout and try again.
				t.Logf("Write took %s (expected %s); trying with longer timeout", actual, d)
				d = next
			}
			continue
		}

		break
	}
}

// There is a very similar copy of this in os/timeout_test.go.
func TestVariousDeadlines(t *testing.T) {
	t.Parallel()
	testVariousDeadlines(t)
}

// There is a very similar copy of this in os/timeout_test.go.
func TestVariousDeadlines1Proc(t *testing.T) {
	// Cannot use t.Parallel - modifies global GOMAXPROCS.
	if testing.Short() {
		t.Skip("skipping in short mode")
	}
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
	testVariousDeadlines(t)
}

// There is a very similar copy of this in os/timeout_test.go.
func TestVariousDeadlines4Proc(t *testing.T) {
	// Cannot use t.Parallel - modifies global GOMAXPROCS.
	if testing.Short() {
		t.Skip("skipping in short mode")
	}
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
	testVariousDeadlines(t)
}

func testVariousDeadlines(t *testing.T) {
	handler := func(ls *localServer, ln Listener) {
		for {
			c, err := ln.Accept()
			if err != nil {
				break
			}
			c.Read(make([]byte, 1)) // wait for client to close connection
			c.Close()
		}
	}
	ls := newLocalServer(t, "tcp")
	defer ls.teardown()
	if err := ls.buildup(handler); err != nil {
		t.Fatal(err)
	}

	for _, timeout := range []time.Duration{
		1 * time.Nanosecond,
		2 * time.Nanosecond,
		5 * time.Nanosecond,
		50 * time.Nanosecond,
		100 * time.Nanosecond,
		200 * time.Nanosecond,
		500 * time.Nanosecond,
		750 * time.Nanosecond,
		1 * time.Microsecond,
		5 * time.Microsecond,
		25 * time.Microsecond,
		250 * time.Microsecond,
		500 * time.Microsecond,
		1 * time.Millisecond,
		5 * time.Millisecond,
		100 * time.Millisecond,
		250 * time.Millisecond,
		500 * time.Millisecond,
		1 * time.Second,
	} {
		numRuns := 3
		if testing.Short() {
			numRuns = 1
			if timeout > 500*time.Microsecond {
				continue
			}
		}
		for run := 0; run < numRuns; run++ {
			name := fmt.Sprintf("%v %d/%d", timeout, run, numRuns)
			t.Log(name)

			c, err := Dial(ls.Listener.Addr().Network(), ls.Listener.Addr().String())
			if err != nil {
				t.Fatal(err)
			}

			t0 := time.Now()
			if err := c.SetDeadline(t0.Add(timeout)); err != nil {
				t.Error(err)
			}
			n, err := io.Copy(io.Discard, c)
			dt := time.Since(t0)
			c.Close()

			if nerr, ok := err.(Error); ok && nerr.Timeout() {
				t.Logf("%v: good timeout after %v; %d bytes", name, dt, n)
			} else {
				t.Fatalf("%v: Copy = %d, %v; want timeout", name, n, err)
			}
		}
	}
}

// TestReadWriteProlongedTimeout tests concurrent deadline
// modification. Known to cause data races in the past.
func TestReadWriteProlongedTimeout(t *testing.T) {
	t.Parallel()

	switch runtime.GOOS {
	case "plan9":
		t.Skipf("not supported on %s", runtime.GOOS)
	}

	handler := func(ls *localServer, ln Listener) {
		c, err := ln.Accept()
		if err != nil {
			t.Error(err)
			return
		}
		defer c.Close()

		var wg sync.WaitGroup
		wg.Add(2)
		go func() {
			defer wg.Done()
			var b [1]byte
			for {
				if err := c.SetReadDeadline(time.Now().Add(time.Hour)); err != nil {
					if perr := parseCommonError(err); perr != nil {
						t.Error(perr)
					}
					t.Error(err)
					return
				}
				if _, err := c.Read(b[:]); err != nil {
					if perr := parseReadError(err); perr != nil {
						t.Error(perr)
					}
					return
				}
			}
		}()
		go func() {
			defer wg.Done()
			var b [1]byte
			for {
				if err := c.SetWriteDeadline(time.Now().Add(time.Hour)); err != nil {
					if perr := parseCommonError(err); perr != nil {
						t.Error(perr)
					}
					t.Error(err)
					return
				}
				if _, err := c.Write(b[:]); err != nil {
					if perr := parseWriteError(err); perr != nil {
						t.Error(perr)
					}
					return
				}
			}
		}()
		wg.Wait()
	}
	ls := newLocalServer(t, "tcp")
	defer ls.teardown()
	if err := ls.buildup(handler); err != nil {
		t.Fatal(err)
	}

	c, err := Dial(ls.Listener.Addr().Network(), ls.Listener.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer c.Close()

	var b [1]byte
	for i := 0; i < 1000; i++ {
		c.Write(b[:])
		c.Read(b[:])
	}
}

// There is a very similar copy of this in os/timeout_test.go.
func TestReadWriteDeadlineRace(t *testing.T) {
	t.Parallel()

	N := 1000
	if testing.Short() {
		N = 50
	}

	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	c, err := Dial(ln.Addr().Network(), ln.Addr().String())
	if err != nil {
		t.Fatal(err)
	}
	defer c.Close()

	var wg sync.WaitGroup
	wg.Add(3)
	go func() {
		defer wg.Done()
		tic := time.NewTicker(2 * time.Microsecond)
		defer tic.Stop()
		for i := 0; i < N; i++ {
			if err := c.SetReadDeadline(time.Now().Add(2 * time.Microsecond)); err != nil {
				if perr := parseCommonError(err); perr != nil {
					t.Error(perr)
				}
				break
			}
			if err := c.SetWriteDeadline(time.Now().Add(2 * time.Microsecond)); err != nil {
				if perr := parseCommonError(err); perr != nil {
					t.Error(perr)
				}
				break
			}
			<-tic.C
		}
	}()
	go func() {
		defer wg.Done()
		var b [1]byte
		for i := 0; i < N; i++ {
			c.Read(b[:]) // ignore possible timeout errors
		}
	}()
	go func() {
		defer wg.Done()
		var b [1]byte
		for i := 0; i < N; i++ {
			c.Write(b[:]) // ignore possible timeout errors
		}
	}()
	wg.Wait() // wait for tester goroutine to stop
}

// Issue 35367.
func TestConcurrentSetDeadline(t *testing.T) {
	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	const goroutines = 8
	const conns = 10
	const tries = 100

	var c [conns]Conn
	for i := 0; i < conns; i++ {
		var err error
		c[i], err = Dial(ln.Addr().Network(), ln.Addr().String())
		if err != nil {
			t.Fatal(err)
		}
		defer c[i].Close()
	}

	var wg sync.WaitGroup
	wg.Add(goroutines)
	now := time.Now()
	for i := 0; i < goroutines; i++ {
		go func(i int) {
			defer wg.Done()
			// Make the deadlines steadily earlier,
			// to trigger runtime adjusttimers calls.
			for j := tries; j > 0; j-- {
				for k := 0; k < conns; k++ {
					c[k].SetReadDeadline(now.Add(2*time.Hour + time.Duration(i*j*k)*time.Second))
					c[k].SetWriteDeadline(now.Add(1*time.Hour + time.Duration(i*j*k)*time.Second))
				}
			}
		}(i)
	}
	wg.Wait()
}

// isDeadlineExceeded reports whether err is or wraps os.ErrDeadlineExceeded.
// We also check that the error implements net.Error, and that the
// Timeout method returns true.
func isDeadlineExceeded(err error) bool {
	nerr, ok := err.(Error)
	if !ok {
		return false
	}
	if !nerr.Timeout() {
		return false
	}
	if !errors.Is(err, os.ErrDeadlineExceeded) {
		return false
	}
	return true
}