Messages sent while offline disappear after connection is regained if the user closes/reopen app - Reported by: @Santhosh-Sellavel

[isagoico]

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Action Performed:

1. Make sure you are offline.
2. Send some messages to any user.
3. Refresh the page on the web. Close & open the app on mobile.
4. Now you can still the messages.
5. Now enable internet
6. Repeat step 3 or switch between chats.

Expected Result:

Messages that were sent while offline should be sent to the other user

Actual Result:

Messages are displayed on chat but disappear once the user regains the connection.

Workaround:

None, sent messages while offline are lost.

Platform:

Where is this issue occurring?

• Web
• iOS
• Android
• Desktop App
• Mobile Web

Version Number: 1.1.8-8

Reproducible in staging?: Yes
Reproducible in production?: Yes

Logs: https://stackoverflow.com/c/expensify/questions/4856

Notes/Photos/Videos: Any additional supporting documentation

WhatsApp.Video.2021-10-21.at.6.49.54.PM.mp4

Expensify/Expensify Issue URL:

Issue reported by: @Santhosh-Sellavel
Slack conversation: https://expensify.slack.com/archives/C01GTK53T8Q/p1634765287021500

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[MelvinBot]

Triggered auto assignment to @johnmlee101 (Engineering), see https://stackoverflow.com/c/expensify/questions/4319 for more details.

[MelvinBot]

@johnmlee101 Whoops! This issue is 2 days overdue. Let's get this updated quick!

[MelvinBot]

@johnmlee101 Huh... This is 4 days overdue. Who can take care of this?

[MelvinBot]

@johnmlee101 6 days overdue. This is scarier than being forced to listen to Vogon poetry!

[MelvinBot]

@johnmlee101 10 days overdue. I'm getting more depressed than Marvin.

[MelvinBot]

@johnmlee101 12 days overdue. Walking. Toward. The. Light...

[kidroca]

"Add Comment" requests are persisted to storage when we're offline
But when we regain connectivity they are read, removed from storage and kept only in memory
Making a refresh/exit before they are complete would make the app "forget" about them

1. Persisted request getting cleared when they're added to the in-memory queue

App/src/libs/Network.js

Lines 55 to 59 in b12eb5f

	// Merge the persisted requests with the requests in memory then clear out the queue as we only need to load
	// this once when the app initializes
	networkRequestQueue = [...networkRequestQueue, ...persistedRequests];
	Onyx.set(ONYXKEYS.NETWORK_REQUEST_QUEUE, []);
	didLoadPersistedRequests = true;

2. Persisted requests getting cleared by the queue itself

App/src/libs/Network.js

Lines 215 to 220 in b12eb5f

	// We should clear the NETWORK_REQUEST_QUEUE when we have loaded the persisted requests & they are processed.
	// As multiple client will be sharing the same Queue and NETWORK_REQUEST_QUEUE is synchronized among clients,
	// we only ask Leader client to clear the queue
	if (ActiveClientManager.isClientTheLeader() && didLoadPersistedRequests) {
	Onyx.set(ONYXKEYS.NETWORK_REQUEST_QUEUE, []);
	}

The request are only moved in memory, they are initiated but not completed - making a browser refresh (or closing the app) after the above code has emptied persistent storage would lose the data when the request didn't complete

[kidroca]

In theory it should be possible to recreate this with shorter steps like

1. Make sure you are offline.
2. Send some messages to any user.
3. Regain connectivity
4. Very shortly after refresh or close the page / quit the app
   When you open the app again you should see the messages briefly and then they would disappear (These were the optimistic messages created and stored. They get cleared since we receive the latest data from the server and it is supposed to replace them with the actual messages, but since requests never made it they're just removed)

Considering that it's very specific window of time that will cause the issue it's less likely to happen often

IRL cases that this bug can happen are:

• User have been offline for an extended period of time and has accumulated many requests. They decide to quit/terminate the app, but by coincidence they regain connectivity right before they quit
• User with accumulated requests regains connectivity. Something causes the app to refresh - like an app update
• User with accumulated requests regains connectivity. Something causes the app to crash
• User with accumulated requests regains connectivity. Something causes a logout

All of these are the case of: A persisted request is moved to memory and executed but something unexpected happens

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IMO we're only trying to "bend" the network queue to fit this "process persisted requests" functionality
Due to the cyclic nature of the default queue and that it has no context of what's already running we're forced to clear persisted requests otherwise they'll get repeated - Onyx.set(ONYXKEYS.NETWORK_REQUEST_QUEUE, [])
Instead a separate queue should be processing persisted requests

• it would not be interval based - it's only needed when we have persisted requests - it's triggered when we regain connectivity
• it would clear requests from storage as they complete, and not when they are moved to the queue
• the default queue is relieved

[johnmlee101]

Looking now!

[johnmlee101]

Hmm, I would also say that a separate queue should have a maximum timeout, so we should keep that data with the requests. However, I like the idea. Do you know which files would need to be modified, or some psuedo code to represent this change?