1/*
2 * Copyright (c) 2015, Yawning Angel <yawning at schwanenlied dot me>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are met:
7 *
8 *  * Redistributions of source code must retain the above copyright notice,
9 *    this list of conditions and the following disclaimer.
10 *
11 *  * Redistributions in binary form must reproduce the above copyright notice,
12 *    this list of conditions and the following disclaimer in the documentation
13 *    and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
16 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
19 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
20 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
21 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
22 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
23 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
24 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
25 * POSSIBILITY OF SUCH DAMAGE.
26 */
27
28package main
29
30import (
31	"io"
32	"io/ioutil"
33	"os"
34	"os/signal"
35	"runtime"
36	"syscall"
37	"time"
38
39	"gitlab.com/yawning/obfs4.git/common/log"
40)
41
42var termMonitorOSInit func(*termMonitor) error
43
44type termMonitor struct {
45	sigChan     chan os.Signal
46	handlerChan chan int
47	numHandlers int
48}
49
50func (m *termMonitor) onHandlerStart() {
51	m.handlerChan <- 1
52}
53
54func (m *termMonitor) onHandlerFinish() {
55	m.handlerChan <- -1
56}
57
58func (m *termMonitor) wait(termOnNoHandlers bool) os.Signal {
59	// Block until a signal has been received, or (optionally) the
60	// number of pending handlers has hit 0.  In the case of the
61	// latter, treat it as if a SIGTERM has been received.
62	for {
63		select {
64		case n := <-m.handlerChan:
65			m.numHandlers += n
66		case sig := <-m.sigChan:
67			return sig
68		}
69		if termOnNoHandlers && m.numHandlers == 0 {
70			return syscall.SIGTERM
71		}
72	}
73}
74
75func (m *termMonitor) termOnStdinClose() {
76	_, err := io.Copy(ioutil.Discard, os.Stdin)
77
78	// io.Copy() will return a nil on EOF, since reaching EOF is
79	// expected behavior.  No matter what, if this unblocks, assume
80	// that stdin is closed, and treat that as having received a
81	// SIGTERM.
82	log.Noticef("Stdin is closed or unreadable: %v", err)
83	m.sigChan <- syscall.SIGTERM
84}
85
86func (m *termMonitor) termOnPPIDChange(ppid int) {
87	// Under most if not all U*IX systems, the parent PID will change
88	// to that of init once the parent dies.  There are several notable
89	// exceptions (Slowlaris/Android), but the parent PID changes
90	// under those platforms as well.
91	//
92	// Naturally we lose if the parent has died by the time when the
93	// Getppid() call was issued in our parent, but, this is better
94	// than nothing.
95	const ppidPollInterval = 1 * time.Second
96	for ppid == os.Getppid() {
97		time.Sleep(ppidPollInterval)
98	}
99
100	// Treat the parent PID changing as the same as having received
101	// a SIGTERM.
102	log.Noticef("Parent pid changed: %d (was %d)", os.Getppid(), ppid)
103	m.sigChan <- syscall.SIGTERM
104}
105
106func newTermMonitor() (m *termMonitor) {
107	ppid := os.Getppid()
108	m = new(termMonitor)
109	m.sigChan = make(chan os.Signal)
110	m.handlerChan = make(chan int)
111	signal.Notify(m.sigChan, syscall.SIGINT, syscall.SIGTERM)
112
113	// If tor supports feature #15435, we can use Stdin being closed as an
114	// indication that tor has died, or wants the PT to shutdown for any
115	// reason.
116	if ptShouldExitOnStdinClose() {
117		go m.termOnStdinClose()
118	} else {
119		// Instead of feature #15435, use various kludges and hacks:
120		//  * Linux - Platform specific code that should always work.
121		//  * Other U*IX - Somewhat generic code, that works unless the
122		//    parent dies before the monitor is initialized.
123		if termMonitorOSInit != nil {
124			// Errors here are non-fatal, since it might still be
125			// possible to fall back to a generic implementation.
126			if err := termMonitorOSInit(m); err == nil {
127				return
128			}
129		}
130		if runtime.GOOS != "windows" {
131			go m.termOnPPIDChange(ppid)
132		}
133	}
134	return
135}
136