1// Copyright 2017 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// +build darwin dragonfly freebsd linux netbsd openbsd solaris
6
7package net
8
9import (
10	"bytes"
11	"syscall"
12	"testing"
13	"time"
14)
15
16// Test that a client can't trigger an endless loop of write system
17// calls on the server by shutting down the write side on the client.
18// Possibility raised in the discussion of https://golang.org/cl/71973.
19func TestEndlessWrite(t *testing.T) {
20	t.Parallel()
21	c := make(chan bool)
22	server := func(cs *TCPConn) error {
23		cs.CloseWrite()
24		<-c
25		return nil
26	}
27	client := func(ss *TCPConn) error {
28		// Tell the server to return when we return.
29		defer close(c)
30
31		// Loop writing to the server. The server is not reading
32		// anything, so this will eventually block, and then time out.
33		b := bytes.Repeat([]byte{'a'}, 8192)
34		cagain := 0
35		for {
36			n, err := ss.conn.fd.pfd.WriteOnce(b)
37			if n > 0 {
38				cagain = 0
39			}
40			switch err {
41			case nil:
42			case syscall.EAGAIN:
43				if cagain == 0 {
44					// We've written enough data to
45					// start blocking. Set a deadline
46					// so that we will stop.
47					ss.SetWriteDeadline(time.Now().Add(5 * time.Millisecond))
48				}
49				cagain++
50				if cagain > 20 {
51					t.Error("looping on EAGAIN")
52					return nil
53				}
54				if err = ss.conn.fd.pfd.WaitWrite(); err != nil {
55					t.Logf("client WaitWrite: %v", err)
56					return nil
57				}
58			default:
59				// We expect to eventually get an error.
60				t.Logf("client WriteOnce: %v", err)
61				return nil
62			}
63		}
64	}
65	withTCPConnPair(t, client, server)
66}
67