idler: improve the imap idler

Rewrite the imap idler to make it more fault tolerant and prevent hangs
(and possibly short writes).

Fixes: https://todo.sr.ht/~rjarry/aerc/208
Signed-off-by: Koni Marti <koni.marti@gmail.com>
Tested-by: Karel Balej <balejk@matfyz.cz>
Acked-by: Robin Jarry <robin@jarry.cc>

5 files changed, 177 insertions, 137 deletions

diff --git a/worker/imap/configure.go b/worker/imap/configure.go
index 49464689..9d4a02de 100644
--- a/worker/imap/configure.go
+++ b/worker/imap/configure.go
@@ -166,7 +166,7 @@ func (w *IMAPWorker) handleConfigure(msg *types.Configure) error {
 	if w.config.cacheEnabled {
 		w.initCacheDb(msg.Config.Name)
 	}
-	w.idler = newIdler(w.config, w.worker)
+	w.idler = newIdler(w.config, w.worker, w.executeIdle)
 	w.observer = newObserver(w.config, w.worker)
 
 	if name, ok := msg.Config.Params["folder-map"]; ok {
diff --git a/worker/imap/extensions/xgmext/client.go b/worker/imap/extensions/xgmext/client.go
index 3107e642..62d081b2 100644
--- a/worker/imap/extensions/xgmext/client.go
+++ b/worker/imap/extensions/xgmext/client.go
@@ -46,7 +46,13 @@ func (h handler) fetchThreadIds(uids []uint32) ([]string, error) {
 	go func() {
 		defer log.PanicHandler()
 		for msg := range messages {
-			m[msg.Items[thriditem].(string)] = struct{}{}
+			if msg == nil {
+				continue
+			}
+			item, ok := msg.Items[thriditem].(string)
+			if ok {
+				m[item] = struct{}{}
+			}
 		}
 		done <- nil
 	}()
diff --git a/worker/imap/idler.go b/worker/imap/idler.go
index aa61776d..369ebd2e 100644
--- a/worker/imap/idler.go
+++ b/worker/imap/idler.go
@@ -2,156 +2,131 @@ package imap
 
 import (
 	"fmt"
-	"sync"
 	"time"
 
 	"git.sr.ht/~rjarry/aerc/log"
 	"git.sr.ht/~rjarry/aerc/worker/types"
 	"github.com/emersion/go-imap"
-	"github.com/emersion/go-imap/client"
 )
 
-var (
-	errIdleTimeout   = fmt.Errorf("idle timeout")
-	errIdleModeHangs = fmt.Errorf("idle mode hangs; waiting to reconnect")
-)
+var errIdleTimeout = fmt.Errorf("idle timeout")
 
 // idler manages the idle mode of the imap server. Enter idle mode if there's
 // no other task and leave idle mode when a new task arrives. Idle mode is only
 // used when the client is ready and connected. After a connection loss, make
 // sure that idling returns gracefully and the worker remains responsive.
 type idler struct {
-	sync.Mutex
-	config  imapConfig
-	client  *imapClient
-	worker  types.WorkerInteractor
-	stop    chan struct{}
-	done    chan error
-	waiting bool
-	idleing bool
+	client    *imapClient
+	debouncer *time.Timer
+	debounce  time.Duration
+	timeout   time.Duration
+	worker    types.WorkerInteractor
+	stop      chan struct{}
+	start     chan struct{}
+	done      chan error
 }
 
-func newIdler(cfg imapConfig, w types.WorkerInteractor) *idler {
-	return &idler{config: cfg, worker: w, done: make(chan error)}
+func newIdler(cfg imapConfig, w types.WorkerInteractor, startIdler chan struct{}) *idler {
+	return &idler{
+		debouncer: nil,
+		debounce:  cfg.idle_debounce,
+		timeout:   cfg.idle_timeout,
+		worker:    w,
+		stop:      make(chan struct{}),
+		start:     startIdler,
+		done:      make(chan error),
+	}
 }
 
 func (i *idler) SetClient(c *imapClient) {
-	i.Lock()
 	i.client = c
-	i.Unlock()
 }
 
-func (i *idler) setWaiting(wait bool) {
-	i.Lock()
-	i.waiting = wait
-	i.Unlock()
-}
-
-func (i *idler) isWaiting() bool {
-	i.Lock()
-	defer i.Unlock()
-	return i.waiting
-}
-
-func (i *idler) isReady() bool {
-	i.Lock()
-	defer i.Unlock()
-	return (!i.waiting && i.client != nil &&
-		i.client.State() == imap.SelectedState)
-}
-
-func (i *idler) setIdleing(v bool) {
-	i.Lock()
-	defer i.Unlock()
-	i.idleing = v
-}
-
-func (i *idler) isIdleing() bool {
-	i.Lock()
-	defer i.Unlock()
-	return i.idleing
+func (i *idler) ready() bool {
+	return (i.client != nil && i.client.State() == imap.SelectedState)
 }
 
 func (i *idler) Start() {
-	switch {
-	case i.isReady():
-		i.stop = make(chan struct{})
-
-		go func() {
-			defer log.PanicHandler()
-			select {
-			case <-i.stop:
-				// debounce idle
-				i.done <- nil
-			case <-time.After(i.config.idle_debounce):
-				// enter idle mode
-				i.setIdleing(true)
-				now := time.Now()
-				err := i.client.Idle(i.stop,
-					&client.IdleOptions{
-						LogoutTimeout: 0,
-						PollInterval:  0,
-					})
-				i.setIdleing(false)
-				i.done <- err
-				i.log("elapsed idle time: %v", time.Since(now))
-			}
-		}()
-
-	case i.isWaiting():
-		i.log("not started: wait for idle to exit")
-	default:
-		i.log("not started: client not ready")
+	if !i.ready() {
+		return
 	}
-}
 
-func (i *idler) Stop() error {
-	var reterr error
-	switch {
-	case i.isReady():
+	select {
+	case <-i.stop:
+		// stop channel is nil (probably after a debounce), we don't
+		// want to close it
+	default:
 		close(i.stop)
+	}
+
+	// create new stop channel
+	i.stop = make(chan struct{})
+
+	// clear done channel
+	clearing := true
+	for clearing {
 		select {
-		case err := <-i.done:
-			if err != nil {
-				i.log("<=(idle) with err: %v", err)
-			}
-			reterr = nil
-		case <-time.After(i.config.idle_timeout):
-			i.worker.PostMessage(&types.Done{
-				Message: types.RespondTo(&types.Disconnect{}),
-			}, nil)
-
-			i.waitOnIdle()
-
-			reterr = errIdleTimeout
+		case <-i.done:
+			continue
+		default:
+			clearing = false
 		}
-	case i.isWaiting():
-		reterr = errIdleModeHangs
-	default:
-		reterr = nil
 	}
-	return reterr
+
+	i.worker.Tracef("idler (start): start idle after debounce")
+	i.debouncer = time.AfterFunc(i.debounce, func() {
+		i.start <- struct{}{}
+		i.worker.Tracef("idler (start): started")
+	})
 }
 
-func (i *idler) waitOnIdle() {
-	i.setWaiting(true)
+func (i *idler) Execute() {
+	if !i.ready() {
+		return
+	}
+
+	// we need to call client.Idle in a goroutine since it is blocking call
+	// and we still want to receive messages
 	go func() {
 		defer log.PanicHandler()
-		err := <-i.done
-		if err == nil {
-			i.worker.PostMessage(&types.Done{
-				Message: types.RespondTo(&types.Connect{}),
-			}, nil)
-		} else {
-			i.log("<=(idle) waited; with err: %v", err)
+
+		start := time.Now()
+		err := i.client.Idle(i.stop, nil)
+		if err != nil {
+			i.worker.Errorf("idle returned error: %v", err)
 		}
-		i.setWaiting(false)
-		i.stop = make(chan struct{})
-		i.Start()
+		i.worker.Tracef("idler (execute): idleing for %s", time.Since(start))
+
+		i.done <- err
 	}()
 }
 
-func (i *idler) log(format string, v ...interface{}) {
-	msg := fmt.Sprintf(format, v...)
-	i.worker.Tracef("idler (%p) [idle:%t,wait:%t] %s", i, i.isIdleing(), i.isWaiting(), msg)
+func (i *idler) Stop() error {
+	if !i.ready() {
+		return nil
+	}
+
+	select {
+	case <-i.stop:
+		i.worker.Debugf("idler (stop): idler already stopped?")
+		return nil
+	default:
+		close(i.stop)
+	}
+
+	if i.debouncer != nil {
+		if i.debouncer.Stop() {
+			i.worker.Tracef("idler (stop): debounced")
+			return nil
+		}
+	}
+
+	select {
+	case err := <-i.done:
+		i.worker.Tracef("idler (stop): idle stopped: %v", err)
+		return err
+	case <-time.After(i.timeout):
+		i.worker.Errorf("idler (stop): cannot stop idle (timeout)")
+		return errIdleTimeout
+	}
 }
diff --git a/worker/imap/observer.go b/worker/imap/observer.go
index 7367ff58..7a604a1a 100644
--- a/worker/imap/observer.go
+++ b/worker/imap/observer.go
@@ -105,9 +105,6 @@ func (o *observer) Stop() {
 }
 
 func (o *observer) DelayedReconnect() error {
-	if o.client == nil {
-		return nil
-	}
 	var wait time.Duration
 	var reterr error
 
diff --git a/worker/imap/worker.go b/worker/imap/worker.go
index 7ef759d4..391f365a 100644
--- a/worker/imap/worker.go
+++ b/worker/imap/worker.go
@@ -80,29 +80,37 @@ type IMAPWorker struct {
 
 	threadAlgorithm sortthread.ThreadAlgorithm
 	liststatus      bool
+
+	executeIdle chan struct{}
 }
 
 func NewIMAPWorker(worker *types.Worker) (types.Backend, error) {
 	return &IMAPWorker{
-		updates:  make(chan client.Update, 50),
-		worker:   worker,
-		selected: &imap.MailboxStatus{},
-		idler:    newIdler(imapConfig{}, worker),
-		observer: newObserver(imapConfig{}, worker),
-		caps:     &models.Capabilities{},
+		updates:     make(chan client.Update, 50),
+		worker:      worker,
+		selected:    &imap.MailboxStatus{},
+		idler:       nil, // will be set in configure()
+		observer:    nil, // will be set in configure()
+		caps:        &models.Capabilities{},
+		executeIdle: make(chan struct{}),
 	}, nil
 }
 
 func (w *IMAPWorker) newClient(c *client.Client) {
-	c.Updates = w.updates
+	c.Updates = nil
 	w.client = &imapClient{
 		c,
 		sortthread.NewThreadClient(c),
 		sortthread.NewSortClient(c),
 		extensions.NewListStatusClient(c),
 	}
-	w.idler.SetClient(w.client)
-	w.observer.SetClient(w.client)
+	if w.idler != nil {
+		w.idler.SetClient(w.client)
+		c.Updates = w.updates
+	}
+	if w.observer != nil {
+		w.observer.SetClient(w.client)
+	}
 	sort, err := w.client.sort.SupportSort()
 	if err == nil && sort {
 		w.caps.Sort = true
@@ -125,7 +133,7 @@ func (w *IMAPWorker) newClient(c *client.Client) {
 	xgmext, err := w.client.Support("X-GM-EXT-1")
 	if err == nil && xgmext && w.config.useXGMEXT {
 		w.worker.Debugf("Server Capability found: X-GM-EXT-1")
-		w.worker = middleware.NewGmailWorker(w.worker, w.client.Client, w.idler)
+		w.worker = middleware.NewGmailWorker(w.worker, w.client.Client)
 	}
 	if err == nil && !xgmext && w.config.useXGMEXT {
 		w.worker.Infof("X-GM-EXT-1 requested, but it is not supported")
@@ -133,13 +141,6 @@ func (w *IMAPWorker) newClient(c *client.Client) {
 }
 
 func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
-	defer func() {
-		w.idler.Start()
-	}()
-	if err := w.idler.Stop(); err != nil {
-		return err
-	}
-
 	var reterr error // will be returned at the end, needed to support idle
 
 	// when client is nil allow only certain messages to be handled
@@ -200,12 +201,14 @@ func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
 	case *types.Disconnect:
 		w.observer.SetAutoReconnect(false)
 		w.observer.Stop()
-		if w.client == nil || w.client.State() != imap.SelectedState {
+
+		if w.client == nil || (w.client != nil && w.client.State() != imap.SelectedState) {
 			reterr = errNotConnected
 			break
 		}
 
 		if err := w.client.Logout(); err != nil {
+			w.terminate()
 			reterr = err
 			break
 		}
@@ -298,10 +301,64 @@ func (w *IMAPWorker) handleImapUpdate(update client.Update) {
 	}
 }
 
+func (w *IMAPWorker) terminate() {
+	if w.observer != nil {
+		w.observer.Stop()
+		w.observer.SetClient(nil)
+	}
+
+	if w.client != nil {
+		w.client.Updates = nil
+		if err := w.client.Terminate(); err != nil {
+			w.worker.Errorf("could not terminate connection: %v", err)
+		}
+	}
+
+	w.client = nil
+	w.selected = &imap.MailboxStatus{}
+
+	if w.idler != nil {
+		w.idler.SetClient(nil)
+	}
+}
+
+func (w *IMAPWorker) stopIdler() error {
+	if w.idler == nil {
+		return nil
+	}
+
+	if err := w.idler.Stop(); err != nil {
+		w.terminate()
+		w.observer.EmitIfNotConnected()
+		w.worker.Errorf("idler stopped with error:%v", err)
+		return err
+	}
+
+	return nil
+}
+
+func (w *IMAPWorker) startIdler() {
+	if w.idler == nil {
+		return
+	}
+
+	w.idler.Start()
+}
+
 func (w *IMAPWorker) Run() {
 	for {
 		select {
 		case msg := <-w.worker.Actions():
+
+			if err := w.stopIdler(); err != nil {
+				w.worker.PostMessage(&types.Error{
+					Message: types.RespondTo(msg),
+					Error:   err,
+				}, nil)
+				break
+			}
+			w.worker.Tracef("ready to handle %T", msg)
+
 			msg = w.worker.ProcessAction(msg)
 
 			if err := w.handleMessage(msg); errors.Is(err, errUnsupported) {
@@ -315,8 +372,13 @@ func (w *IMAPWorker) Run() {
 				}, nil)
 			}
 
+			w.startIdler()
+
 		case update := <-w.updates:
 			w.handleImapUpdate(update)
+
+		case <-w.executeIdle:
+			w.idler.Execute()
 		}
 	}
 }