imap: add debouncer to the idler

Add a debouncer to the idle mode. Avoid unnecessary idling when another
job arrives within a certain time frame.

For example, the ui sends three messages to the worker at the same time
when we open a message (FlagMessage, FetchMessageBodyPart, and the
FetchMessageHeaders). The debouncer prevents the unnecessary entering
and leaving of the idle mode between those messages.

Signed-off-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>

worker/imap/configure.go

@@ -45,7 +45,10 @@ func (w *IMAPWorker) handleConfigure(msg *types.Configure) error {
 
 	w.config.user = u.User
 	w.config.folders = msg.Config.Folders
+
 	w.config.idle_timeout = 10 * time.Second
+	w.config.idle_debounce = 10 * time.Millisecond
+
 	w.config.connection_timeout = 30 * time.Second
 	w.config.keepalive_period = 0 * time.Second
 	w.config.keepalive_probes = 3
@@ -63,6 +66,14 @@ func (w *IMAPWorker) handleConfigure(msg *types.Configure) error {
 					value, err)
 			}
 			w.config.idle_timeout = val
+		case "idle-debounce":
+			val, err := time.ParseDuration(value)
+			if err != nil || val < 0 {
+				return fmt.Errorf(
+					"invalid idle-debounce value %v: %v",
+					value, err)
+			}
+			w.config.idle_debounce = val
 		case "reconnect-maxwait":
 			val, err := time.ParseDuration(value)
 			if err != nil || val < 0 {

worker/imap/idler.go

@@ -25,6 +25,7 @@ type idler struct {
 	config  imapConfig
 	client  *imapClient
 	worker  *types.Worker
+	last    time.Time
 	stop    chan struct{}
 	done    chan error
 	waiting bool
@@ -63,8 +64,16 @@ func (i *idler) isReady() bool {
 func (i *idler) Start() {
 	if i.isReady() {
 		i.stop = make(chan struct{})
+
 		go func() {
 			defer logging.PanicHandler()
+			select {
+			case <-i.stop:
+				// debounce idle
+				i.log("=>(idle) [debounce]")
+				i.done <- nil
+			case <-time.After(i.config.idle_debounce):
+				// enter idle mode
 				i.idleing = true
 				i.log("=>(idle)")
 				now := time.Now()
@@ -75,8 +84,11 @@ func (i *idler) Start() {
 					})
 				i.idleing = false
 				i.done <- err
-			i.log("elapsed ideling time:", time.Since(now))
+				i.log("elapsed idle time:",
+					time.Since(now))
+			}
 		}()
+
 	} else if i.isWaiting() {
 		i.log("not started: wait for idle to exit")
 	} else {

worker/imap/worker.go

@@ -43,6 +43,7 @@ type imapConfig struct {
 	folders           []string
 	oauthBearer       lib.OAuthBearer
 	idle_timeout      time.Duration
+	idle_debounce     time.Duration
 	reconnect_maxwait time.Duration
 	// tcp connection parameters
 	connection_timeout time.Duration