imap: attempt automatic reconnection on error

Attempt to reconnect to the server when there is an unexpected
disconnection or network error.

Use the Client.LoggedOut() channel which is closed when the connection
is closed.

This patch is rather flaky and is certainly bugged. However, it is
a start.

Signed-off-by: Robin Jarry <robin@jarry.cc>

worker/imap/worker.go

@@ -56,6 +56,10 @@ type IMAPWorker struct {
 	worker   *types.Worker
 	// Map of sequence numbers to UIDs, index 0 is seq number 1
 	seqMap []uint32
+	// automatic reconnect
+	loggingOut   bool
+	loggedOut    <-chan struct{}
+	reconnecting bool
 }
 
 func NewIMAPWorker(worker *types.Worker) (types.Backend, error) {
@@ -69,7 +73,10 @@ func NewIMAPWorker(worker *types.Worker) (types.Backend, error) {
 
 func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
 	if w.client != nil && w.client.State() == imap.SelectedState {
-		close(w.idleStop)
+		if w.idleStop != nil {
+			close(w.idleStop)
+			w.idleStop = nil
+		}
 		if err := <-w.idleDone; err != nil {
 			w.worker.PostMessage(&types.Error{Error: err}, nil)
 		}
@@ -155,21 +162,27 @@ func (w *IMAPWorker) handleMessage(msg types.WorkerMessage) error {
 			}
 		}
 	case *types.Connect:
-		if w.client != nil && w.client.State() == imap.SelectedState {
+		if w.client != nil && w.client.State() == imap.SelectedState && !w.reconnecting {
 			return fmt.Errorf("Already connected")
 		}
+		w.loggingOut = false
 		c, err := w.connect()
 		if err != nil {
+			if !w.reconnecting {
+				go w.tryReconnect()
+			}
 			return err
 		}
-
 		c.Updates = w.updates
+		w.loggedOut = c.LoggedOut()
 		w.client = &imapClient{c, sortthread.NewThreadClient(c), sortthread.NewSortClient(c)}
 		w.worker.PostMessage(&types.Done{types.RespondTo(msg)}, nil)
 	case *types.Disconnect:
+		w.reconnecting = false
 		if w.client == nil || w.client.State() != imap.SelectedState {
 			return fmt.Errorf("Not connected")
 		}
+		w.loggingOut = true
 		if err := w.client.Logout(); err != nil {
 			return err
 		}
@@ -378,6 +391,25 @@ func (w *IMAPWorker) setKeepaliveParameters(conn *net.TCPConn) error {
 	return err
 }
 
+func (w *IMAPWorker) tryReconnect() {
+	w.reconnecting = true
+	for w.reconnecting {
+		w.worker.Logger.Printf("IMAP reconnection in 2 seconds...\n")
+		time.Sleep(2 * time.Second)
+		c := make(chan types.WorkerMessage)
+		w.worker.PostAction(&types.Connect{}, func(m types.WorkerMessage) {
+			c <- m
+		})
+		result := <-c
+		switch result.(type) {
+		case *types.Done:
+			w.reconnecting = false
+		case *types.Error:
+			w.worker.Logger.Printf("IMAP connection failed\n")
+		}
+	}
+}
+
 func (w *IMAPWorker) Run() {
 	for {
 		select {
@@ -395,6 +427,12 @@ func (w *IMAPWorker) Run() {
 			}
 		case update := <-w.updates:
 			w.handleImapUpdate(update)
+		case <-w.loggedOut:
+			w.loggedOut = nil
+			if !w.loggingOut && !w.reconnecting {
+				w.reconnecting = true
+				go w.tryReconnect()
+			}
 		}
 	}
 }