backends: send MessageInfoError on header fetching error

When an error is encountered fetching a header, the backends respond
with a type.Error worker message. On receipt of this message, the UI
deletes all pending headers. The headers are all requested again as they
remain on the screen, resulting in an infinite request loop - and an
infinite logging loop. The user only ever sees the spinner unless they
check the logs.

A previous commit intended to fix this, however it introduced a
regression where any message that was part of the fetch request would
also be marked as erroneous. This commit is reverted with commit
2aad2fea7d36 ("msgstore: revert 9fdc7acf5b48").

Send an erroneous message info message from the backend when an error is
encountered for a specific UID.

Fixes: 01f80721e2 ("msgstore: post MessageInfo on erroneous fetch")
Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
Acked-by: Robin Jarry <robin@jarry.cc>

worker/imap/fetch.go

@@ -50,10 +50,7 @@ func (imapw *IMAPWorker) handleFetchMessageHeaders(
 			if err != nil {
 				logging.Errorf(
 					"message %d: could not read header: %v", _msg.Uid, err)
-				imapw.worker.PostMessage(&types.Error{
-					Message: types.RespondTo(msg),
-					Error:   err,
-				}, nil)
+				imapw.worker.PostMessageInfoError(msg, _msg.Uid, err)
 				return nil
 			}
 			header := &mail.Header{Header: message.Header{Header: textprotoHeader}}

worker/maildir/worker.go

@@ -479,7 +479,7 @@ func (w *Worker) handleFetchMessageHeaders(
 		info, err := w.msgInfoFromUid(uid)
 		if err != nil {
 			logging.Errorf("could not get message info: %w", err)
-			w.err(msg, err)
+			w.worker.PostMessageInfoError(msg, uid, err)
 			continue
 		}
 		w.worker.PostMessage(&types.MessageInfo{

worker/mbox/worker.go

@@ -152,7 +152,7 @@ func (w *mboxWorker) handleMessage(msg types.WorkerMessage) error {
 			}
 			msgInfo, err := lib.MessageInfo(m)
 			if err != nil {
-				reterr = err
+				w.worker.PostMessageInfoError(msg, uid, err)
 				break
 			} else {
 				w.worker.PostMessage(&types.MessageInfo{

worker/notmuch/worker.go

@@ -315,13 +315,13 @@ func (w *worker) handleFetchMessageHeaders(
 		m, err := w.msgFromUid(uid)
 		if err != nil {
 			logging.Errorf("could not get message: %w", err)
-			w.err(msg, err)
+			w.w.PostMessageInfoError(msg, uid, err)
 			continue
 		}
 		err = w.emitMessageInfo(m, msg)
 		if err != nil {
 			logging.Errorf("could not emit message info: %w", err)
-			w.err(msg, err)
+			w.w.PostMessageInfoError(msg, uid, err)
 			continue
 		}
 	}

worker/types/worker.go

@@ -4,6 +4,7 @@ import (
 	"sync/atomic"
 
 	"git.sr.ht/~rjarry/aerc/logging"
+	"git.sr.ht/~rjarry/aerc/models"
 )
 
 var lastId int64 = 1 // access via atomic
@@ -104,3 +105,17 @@ func (worker *Worker) ProcessAction(msg WorkerMessage) WorkerMessage {
 	}
 	return msg
 }
+
+// PostMessageInfoError posts a MessageInfo message to the worker when an
+// error was encountered fetching the message header
+func (worker *Worker) PostMessageInfoError(msg WorkerMessage, uid uint32, err error) {
+	worker.PostMessage(&MessageInfo{
+		Info: &models.MessageInfo{
+			Envelope: &models.Envelope{},
+			Flags:    []models.Flag{models.SeenFlag},
+			Uid:      uid,
+			Error:    err,
+		},
+		Message: RespondTo(msg),
+	}, nil)
+}