"Request failed" error when message is Deleted with "Show Next Message..." option is enabled

[SergeyMosin]

Describe the bug
When the "Show Next Message..." option is enabled and a message is deleted the "Request Failed" screen is briefly shown. This error mostly happens when connection between Snappymail and the Mail server is slow. This is somewhat an edge case to have slow connection server side but it does help with flushing out bugs

To Reproduce
Steps to reproduce the behavior:

1. Slow connection (ex: install SnappyMail locally and connect to a remote IMAP/SMTP server)
2. Enable "Show next message when (re)move current message" option
3. Delete a message
4. 💥 "Request failed" error pops up and the next message is not loaded

Possible Solution
The problem seems to be two fold:

1. 'AbortError' is not properly handled
2. Double requests are sent which causes the 'AbortError'

Abort handling error:

1. controler.abort is called here:

   snappymail/dev/Remote/AbstractFetch.js

   Lines 37 to 40 in 99d68bc

   	if (controller) {
   	clearTimeout(controller.timeoutId);
   	bClearOnly || controller.abort(sReason || 'AbortError');
   	}

2. And is caught as a type string not type error here:

   snappymail/dev/Remote/AbstractFetch.js

   Lines 61 to 66 in 99d68bc

   	}).catch(err => {
   	clearTimeout(controller.timeoutId);
   	err.aborted = signal.aborted;
   	err.reason = signal.reason;
   	return Promise.reject(err);
   	});

3. But because 'err' is type string line 63 throws 'not an object error`
   One possible way to fix this is:

...
	}).catch(err => {
		clearTimeout(controller.timeoutId);
		// controller.abort(sReason || 'AbortError'); sends the err as string
		// and also sets signal.reason = sReason || 'AbortError'
		if (typeof err === 'string') {
			const _msg=err
			err = new Error(_msg);
			// there is err.name == 'AbortError' check in the request() function
			// maybe the check should be err.aborted === true instead
			err.name = _msg;
		}
		err.aborted = signal.aborted;
		err.reason = signal.reason;
		return Promise.reject(err);
	});
...

This way the error will be properly propagated to here:

snappymail/dev/Remote/AbstractFetch.js

Lines 165 to 171 in 99d68bc

	.catch(err => {
	console.error({fetchError:err});
	fCallback && fCallback(
	'TimeoutError' == err.reason ? 3 : (err.name == 'AbortError' ? 2 : 1),
	err
	);
	});

and the fCallback will have the proper iError code, which will skip the 'Request failed` screen here:

snappymail/dev/Common/UtilsUser.js

Lines 296 to 301 in 99d68bc

	if (iError) {
	if (Notifications.RequestAborted !== iError && !popup) {
	MessageUserStore.message(null);
	MessageUserStore.error(getNotification(iError));
	}
	} else {

Double Requests
On slower connections there are duplicate requests under certain conditions that actually cause the AbortError.
The first request is properly initiated from here:

snappymail/dev/Stores/User/Messagelist.js

Lines 454 to 464 in 99d68bc

	// Select next email https://github.com/the-djmaze/snappymail/issues/968
	if (currentMessage && 1 == messages.length && SettingsUserStore.showNextMessage()) {
	let next = MessagelistUserStore.indexOf(currentMessage) + 1;
	if (0 < next && (next = MessagelistUserStore()[next])) {
	currentMessage = null;
	fireEvent('mailbox.message.show', {
	folder: next.folder,
	uid: next.uid
	});
	}
	}

The second request can be initiated by the remove() call from here sometime:

snappymail/dev/Stores/User/Messagelist.js

Line 475 in 99d68bc

setTimeout(() => messages.forEach(item => MessagelistUserStore.remove(item)), 350);

because on slow connection it will pass this.autoSelect() check here:

snappymail/dev/Common/Selector.js

Lines 65 to 71 in 99d68bc

	this.listChecked.subscribe(items => {
	if (items.length) {
	koSelectedItem() ? koSelectedItem(null) : koSelectedItem.valueHasMutated?.();
	} else if (this.autoSelect()) {
	koSelectedItem(koFocusedItem());
	}
	});

It is possible to fix the this.autoSelect() check like so

MessagelistUserStore.canAutoSelect = () =>
	!/is:unseen/.test(MessagelistUserStore.mainSearch())
	&& !disableAutoSelect()
	&& SettingsUserStore.usePreviewPane()
	// When the 'Show Next Message...' option is enable, the next message is "selected"
	// in a different request. This will prevent duplicate requests and 'AbortError'
	// under some conditions on slow connections
	&& !SettingsUserStore.showNextMessage();

here:

snappymail/dev/Stores/User/Messagelist.js

Lines 167 to 172 in 99d68bc

	MessagelistUserStore.canAutoSelect = () =>
	!/is:unseen/.test(MessagelistUserStore.mainSearch())
	&& !disableAutoSelect()
	&& SettingsUserStore.usePreviewPane();

@the-djmaze I can submit a PR as well.

Thanks for all the work you put into this app btw

[the-djmaze]

The handling of controller.abort() was interpreted incorrectly because i misread the documentation.
https://developer.mozilla.org/en-US/docs/Web/API/AbortController/abort#parameters

If not specified, the reason is set to "AbortError" DOMException.

I thought it was a string, but it is a DOMException object.
So i've changed the code to always use DOMException.

[SergeyMosin]

Thanks for fixing this.

BTW, the Double Requests possible fix in essagelistUserStore.canAutoSelect will not work. It breaks keyboard navigation.

[the-djmaze]

On slower connections there are duplicate requests under certain conditions that actually cause the AbortError.

The main reason why this happens is disableAutoSelect.
It is set to true on MessagelistUserStore.reload and goes back to false after 500 milliseconds.

After 'MessageMove' or 'MessageDelete' it does:

MessagelistUserStore.reload(!MessagelistUserStore.length)

But there are some caveats due to uncheck/removal/page changes that cause multiple autoSelect and MessageList requests.

So now i made big changes to handle them

[the-djmaze]

Solved, or do you still see this issue?