From c605ada3ddc7569ebfc153b07db12a21b30d0569 Mon Sep 17 00:00:00 2001
From: Robin Jarry <robin@jarry.cc>
Date: Mon, 6 Dec 2021 23:53:39 +0100
Subject: 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 | 44 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 41 insertions(+), 3 deletions(-)

(limited to 'worker')

diff --git a/worker/imap/worker.go b/worker/imap/worker.go
index 0f1c38d..4e6bc52 100644
--- a/worker/imap/worker.go
+++ b/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()
+			}
 		}
 	}
 }
-- 
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