Move termmon code from main into its own package

2 files changed, 185 insertions, 0 deletions

diff --git a/common/termmon/termmon.go b/common/termmon/termmon.go
new file mode 100644
index 0000000..0968817
--- /dev/null
+++ b/common/termmon/termmon.go
@@ -0,0 +1,136 @@
+/*
+ * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *  * Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *
+ *  * Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package termmon
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+	"os/signal"
+	"runtime"
+	"syscall"
+	"time"
+
+	"github.com/OperatorFoundation/obfs4/common/log"
+	"github.com/OperatorFoundation/obfs4/common/pt_extras"
+)
+
+var TermMonitorOSInit func(*TermMonitor) error
+
+type TermMonitor struct {
+	sigChan     chan os.Signal
+	handlerChan chan int
+	numHandlers int
+}
+
+func (m *TermMonitor) OnHandlerStart() {
+	m.handlerChan <- 1
+}
+
+func (m *TermMonitor) OnHandlerFinish() {
+	m.handlerChan <- -1
+}
+
+func (m *TermMonitor) Wait(termOnNoHandlers bool) os.Signal {
+	// Block until a signal has been received, or (optionally) the
+	// number of pending handlers has hit 0.  In the case of the
+	// latter, treat it as if a SIGTERM has been received.
+	for {
+		select {
+		case n := <-m.handlerChan:
+			m.numHandlers += n
+		case sig := <-m.sigChan:
+			return sig
+		}
+		if termOnNoHandlers && m.numHandlers == 0 {
+			return syscall.SIGTERM
+		}
+	}
+}
+
+func (m *TermMonitor) termOnStdinClose() {
+	_, err := io.Copy(ioutil.Discard, os.Stdin)
+
+	// io.Copy() will return a nil on EOF, since reaching EOF is
+	// expected behavior.  No matter what, if this unblocks, assume
+	// that stdin is closed, and treat that as having received a
+	// SIGTERM.
+	log.Noticef("Stdin is closed or unreadable: %v", err)
+	m.sigChan <- syscall.SIGTERM
+}
+
+func (m *TermMonitor) termOnPPIDChange(ppid int) {
+	// Under most if not all U*IX systems, the parent PID will change
+	// to that of init once the parent dies.  There are several notable
+	// exceptions (Slowlaris/Android), but the parent PID changes
+	// under those platforms as well.
+	//
+	// Naturally we lose if the parent has died by the time when the
+	// Getppid() call was issued in our parent, but, this is better
+	// than nothing.
+	const ppidPollInterval = 1 * time.Second
+	for ppid == os.Getppid() {
+		time.Sleep(ppidPollInterval)
+	}
+
+	// Treat the parent PID changing as the same as having received
+	// a SIGTERM.
+	log.Noticef("Parent pid changed: %d (was %d)", os.Getppid(), ppid)
+	m.sigChan <- syscall.SIGTERM
+}
+
+func NewTermMonitor() (m *TermMonitor) {
+	ppid := os.Getppid()
+	m = new(TermMonitor)
+	m.sigChan = make(chan os.Signal)
+	m.handlerChan = make(chan int)
+	signal.Notify(m.sigChan, syscall.SIGINT, syscall.SIGTERM)
+
+	// If tor supports feature #15435, we can use Stdin being closed as an
+	// indication that tor has died, or wants the PT to shutdown for any
+	// reason.
+	if pt_extras.PtShouldExitOnStdinClose() {
+		go m.termOnStdinClose()
+	} else {
+		// Instead of feature #15435, use various kludges and hacks:
+		//  * Linux - Platform specific code that should always work.
+		//  * Other U*IX - Somewhat generic code, that works unless the
+		//    parent dies before the monitor is initialized.
+		if TermMonitorOSInit != nil {
+			// Errors here are non-fatal, since it might still be
+			// possible to fall back to a generic implementation.
+			if err := TermMonitorOSInit(m); err == nil {
+				return
+			}
+		}
+		if runtime.GOOS != "windows" {
+			go m.termOnPPIDChange(ppid)
+		}
+	}
+	return
+}
diff --git a/common/termmon/termmon_linux.go b/common/termmon/termmon_linux.go
new file mode 100644
index 0000000..5540562
--- /dev/null
+++ b/common/termmon/termmon_linux.go
@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *  * Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *
+ *  * Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package main
+
+import (
+	"fmt"
+	"syscall"
+)
+
+func TermMonitorInitLinux(m *TermMonitor) error {
+	// Use prctl() to have the kernel deliver a SIGTERM if the parent
+	// process dies.  This beats anything else that can be done before
+	// #15435 is implemented.
+	_, _, errno := syscall.Syscall(syscall.SYS_PRCTL, syscall.PR_SET_PDEATHSIG, uintptr(syscall.SIGTERM), 0)
+	if errno != 0 {
+		var err error = errno
+		return fmt.Errorf("prctl(PR_SET_PDEATHSIG, SIGTERM) returned: %s", err)
+	}
+	return nil
+}
+
+func init() {
+	TermMonitorOSInit = TermMonitorInitLinux
+}