cmd/vidforward: add watchdog notifier

This change adds a "watchdog notifier" utility which tracks the
health of request handlers and notifies an external systemd
watchdog if everything looks good. This allows us to cause a
termination if any request handlers get hung.

cmd/vidforward/main.go

@@ -86,13 +86,35 @@ type broadcastManager struct {
 	broadcasts       map[MAC]Broadcast
 	slateExitSignals map[MAC]chan struct{} // Used to signal to stop writing slate image.
 	log              logging.Logger
+	dogNotifier      *watchdogNotifier
 	mu               sync.Mutex
 }
 
 // newBroadcastManager returns a new broadcastManager with the provided logger.
-func newBroadcastManager(l logging.Logger) *broadcastManager {
+func newBroadcastManager(l logging.Logger) (*broadcastManager, error) {
-	return &broadcastManager{log: l, broadcasts: make(map[MAC]Broadcast), slateExitSignals: make(map[MAC]chan struct{})}
+	m := &broadcastManager{
+		log:              l,
+		broadcasts:       make(map[MAC]Broadcast),
+		slateExitSignals: make(map[MAC]chan struct{}),
 	}
+	notifier, err := newWatchdogNotifier(l, func() {
+		err := m.save()
+		if err != nil {
+			m.log.Error("could not save on notifier termination signal", "error", err)
+			return
+		}
+		m.log.Info("successfully saved broadcast manager state on termination signal")
+	})
+	m.dogNotifier = notifier
+	if err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+// save is currently just a stub, but will eventually save the broadcastManager's
+// state to file.
+func (b *broadcastManager) save() error { return nil }
 
 // recvHandler handles recv requests for video forwarding. The MAC is firstly
 // checked to ensure it is "active" i.e. should be sending data, and then the
@@ -100,6 +122,9 @@ func newBroadcastManager(l logging.Logger) *broadcastManager {
 // corresponding to said MAC.
 // Clips of MPEG-TS h264 are the only accepted format and codec.
 func (m *broadcastManager) recv(w http.ResponseWriter, r *http.Request) {
+	done := m.dogNotifier.handlerInvoked("recv")
+	defer done()
+
 	m.log.Debug("recv handler")
 	q := r.URL.Query()
 	ma := MAC(q.Get("ma"))
@@ -171,6 +196,9 @@ func (m *broadcastManager) recv(w http.ResponseWriter, r *http.Request) {
 
 // control handles control API requests.
 func (m *broadcastManager) control(w http.ResponseWriter, r *http.Request) {
+	done := m.dogNotifier.handlerInvoked("control")
+	defer done()
+
 	m.log.Info("control request", "method", r.Method)
 	switch r.Method {
 	case http.MethodPut:
@@ -359,8 +387,14 @@ func main() {
 	// lumberjack and netloggers.
 	log := logging.New(logVerbosity, io.MultiWriter(fileLog, netLog), logSuppress)
 
-	bm := newBroadcastManager(log)
+	m, err := newBroadcastManager(log)
-	http.HandleFunc("/recv", bm.recv)
+	if err != nil {
-	http.HandleFunc("/control", bm.control)
+		log.Fatal("could not create new broadcast manager", "error", err)
+	}
+	http.HandleFunc("/recv", m.recv)
+	http.HandleFunc("/control", m.control)
+
+	go m.dogNotifier.notify()
+
 	http.ListenAndServe(*host+":"+*port, nil)
 }

cmd/vidforward/notifier.go

@@ -0,0 +1,171 @@
+/*
+DESCRIPTION
+  notifier.go provides a tool for notifying a systemd watchdog under healthy
+  operation of the vidforward service.
+
+AUTHORS
+  Saxon A. Nelson-Milton <saxon@ausocean.org>
+
+LICENSE
+  Copyright (C) 2022 the Australian Ocean Lab (AusOcean)
+
+  It is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+  for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
+*/
+
+package main
+
+import (
+	"log"
+	"os"
+	"os/signal"
+	"sync"
+	"syscall"
+	"time"
+
+	"bitbucket.org/ausocean/utils/logging"
+	"github.com/coreos/go-systemd/daemon"
+)
+
+// By default we assume we should be notifying a systemd watchdog. This can be
+// toggled off by using the nowatchdog build tag (see nowatchdog.go file).
+var notifyWatchdog = true
+
+// watchdogNotifier keeps track of the watchdog interval from the external
+// sysd service settings, the currently active request handlers and a curId
+// field that is is incremented to generate new handler ids for storage.
+type watchdogNotifier struct {
+	watchdogInterval time.Duration
+	activeHandlers   map[int]handlerInfo
+	curId            int
+	termCallback     func()
+	log              logging.Logger
+	mu               sync.Mutex
+}
+
+// handlerInfo keeps track of a handlers name (for any logging purposes) and
+// time at which the handler was invoked, which is later used to calculate time
+// active and therefore heatlh.
+type handlerInfo struct {
+	name string
+	time time.Time
+}
+
+// newWatchdogNotifier creates a new watchdogNotifier with the provided logger
+// and termination callback that is called if a SIGINT or SIGTERM signal is
+// received. Recommended use of this is an attempted state save.
+func newWatchdogNotifier(l logging.Logger, termCallback func()) (*watchdogNotifier, error) {
+	var (
+		interval = 1 * time.Minute
+		err      error
+	)
+
+	if notifyWatchdog {
+		const clearEnvVars = false
+		interval, err = daemon.SdWatchdogEnabled(clearEnvVars)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return &watchdogNotifier{
+		activeHandlers:   make(map[int]handlerInfo),
+		watchdogInterval: interval,
+		log:              l,
+		termCallback:     termCallback,
+	}, nil
+}
+
+// notify is to be called as a routine. This is responsible for checking if the
+// handlers are healthy and then notifying the watchdog if so, otherwise we
+// wait, continue and check again until they are. If the handlers take too long to
+// become healthy, we risk exceeding the watchdog interval causing a process restart.
+// notify also starts a routine to monitor for any SIGINT or SIGTERM, upon which
+// a callback that's provided at initialisation is called.
+func (n *watchdogNotifier) notify() {
+	notifyTicker := time.NewTicker(n.watchdogInterval / 2)
+
+	go func() {
+		sigs := make(chan os.Signal, 1)
+		signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
+		sig := <-sigs
+		n.log.Warning("received termination signal, calling termination callback", "signal", sig.String())
+		n.termCallback()
+	}()
+
+	for {
+		if n.handlersUnhealthy() {
+			const unhealthyHandlerWait = 1 * time.Second
+			time.Sleep(unhealthyHandlerWait)
+			continue
+		}
+
+		<-notifyTicker.C
+
+		if !notifyWatchdog {
+			continue
+		}
+
+		// If this fails for any reason it indicates a systemd service configuration
+		// issue, and therefore programmer error, so do fatal log to cause crash.
+		supported, err := daemon.SdNotify(false, daemon.SdNotifyWatchdog)
+		if err != nil {
+			n.log.Fatal("error from systemd watchdog notify", "error", err)
+		}
+
+		if !supported {
+			n.log.Fatal("watchdog notification not supported")
+		}
+	}
+}
+
+// handlersUnhealthy returns true if it is detected that any handlers are unhealthy,
+// that is, if they have been handling for longer than the unhealthyHandleDuration.
+func (n *watchdogNotifier) handlersUnhealthy() bool {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+	for _, info := range n.activeHandlers {
+		const unhealthyHandleDuration = 30 * time.Second
+		if time.Now().Sub(info.time) > unhealthyHandleDuration {
+			n.log.Warning("handler unhealthy", "name", info.name)
+			return true
+		}
+	}
+	return false
+}
+
+// handlerInvoked is to be called at the start of a request handler to indicate
+// that handling has begun. The name and start time of the handler is recorded
+// in the active handlers map with a unique ID as the key. A function is returned
+// that must be called at exit of the handler to indicate that handling has
+// finished. It is recommended this be done using a defer statement immediately
+// after receiveing it.
+func (n *watchdogNotifier) handlerInvoked(name string) func() {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+
+	id := n.curId
+	n.curId++
+	n.activeHandlers[id] = handlerInfo{time: time.Now(), name: name}
+
+	return func() {
+		n.mu.Lock()
+		defer n.mu.Unlock()
+
+		if _, ok := n.activeHandlers[id]; !ok {
+			log.Fatal("handler id not in map", "name", name)
+		}
+
+		delete(n.activeHandlers, id)
+	}
+}

cmd/vidforward/nowatchdog.go

@@ -0,0 +1,32 @@
+//go:build nowatchdog
+// +build nowatchdog
+
+/*
+DESCRIPTION
+  nowatchdog.go sets the notifyWatchdog global to false.
+
+AUTHORS
+  Saxon A. Nelson-Milton <saxon@ausocean.org>
+
+LICENSE
+  Copyright (C) 2022 the Australian Ocean Lab (AusOcean)
+
+  It is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+  for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
+*/
+
+package main
+
+func init() {
+	notifyWatchdog = false
+}

go.mod

@@ -6,6 +6,7 @@ require (
 	bitbucket.org/ausocean/iot v1.3.3
 	bitbucket.org/ausocean/utils v1.3.2
 	github.com/Comcast/gots v0.0.0-20190305015453-8d56e473f0f7
+	github.com/coreos/go-systemd v0.0.0-20191104093116-d3cd4ed1dbcf
 	github.com/go-audio/audio v0.0.0-20181013203223-7b2a6ca21480
 	github.com/go-audio/wav v0.0.0-20181013172942-de841e69b884
 	github.com/google/go-cmp v0.4.1

go.sum

@@ -26,6 +26,8 @@ github.com/boombuler/barcode v1.0.1/go.mod h1:paBWMcWSl3LHKBqUq+rly7CNSldXjb2rDl
 github.com/cheekybits/is v0.0.0-20150225183255-68e9c0620927/go.mod h1:h/aW8ynjgkuj+NQRlZcDbAbM1ORAbXjXX77sX7T289U=
 github.com/cocoonlife/goalsa v0.0.0-20160812085113-b711ae6f3eff/go.mod h1:5aLO409bJnd+jCw0t/SB/DhHkVBhPAE31lnHJnYQxy0=
 github.com/cocoonlife/testify v0.0.0-20160218172820-792cc1faeb64/go.mod h1:LoCAz53rbPcqs8Da2BjB/yDy4gxMtiSQmqnYI/DGH+U=
+github.com/coreos/go-systemd v0.0.0-20191104093116-d3cd4ed1dbcf h1:iW4rZ826su+pqaw19uhpSCzhj44qo35pNgKFGqzDKkU=
+github.com/coreos/go-systemd v0.0.0-20191104093116-d3cd4ed1dbcf/go.mod h1:F5haX7vjVVG0kc13fIWeqUViNPyEJxv/OmvnBo0Yme4=
 github.com/cryptix/wav v0.0.0-20180415113528-8bdace674401/go.mod h1:knK8fd+KPlGGqSUWogv1DQzGTwnfUvAi0cIoWyOG7+U=
 github.com/d2r2/go-dht v0.0.0-20200119175940-4ba96621a218/go.mod h1:AzSqP4S4/6pINOKg3VC79WC7YY3zskQcrXMFzphCry0=
 github.com/d2r2/go-logger v0.0.0-20210606094344-60e9d1233e22/go.mod h1:eSx+YfcVy5vCjRZBNIhpIpfCGFMQ6XSOSQkDk7+VCpg=