app slow to show configured servers on start-up

[ghost]

It takes around ~2 seconds before the server is shown, until that time this is what is shown:

Is there network activity at this stage? What is fetched? Why is it so slow? Why does it not happen in the background?

[dzolnai]

The server_list, and organization_list JSONs and their signatures are fetched, then verified against each other.
After that the JSON needs to be parsed, and the view should be updated. This should all happen under 1 sec in optimal circumstances, but on a slower connection or device it might take a bit longer.

[ghost]

organization_list.json should NEVER be fetched on (subsequent) start-up, only when choosing an organization, which typically only happens once... As for server_list.json that could easily be a background thread that doesn't impact the loading of the UI.

[ghost]

See also https://github.com/eduvpn/documentation/blob/v2/SERVER_DISCOVERY.md

[dzolnai]

Oh sorry, I thought this was the search screen, my mistake.
There the app waits for the server_list, but I have applied a fix to not wait if the user does not have an organization added.
Otherwise it will wait 3 seconds, because we have some retry-after-failure which checks again after 3 seconds.
This is required because sometimes it wants to refresh this list when coming back from a disconnect, and it needs some time to get a working connection again.

[dzolnai]

Should be better now.

[ghost]

It is not. Just showing a banner that it is refreshing the list is not okay. There should be no banner and no delay. There is no need for network activity at all! At least not on the main thread. If it can update in the background, fine.

[dzolnai]

Server list is cached now for one hour.

[ghost]

Actually you are not allowed to do that. The web server indicates information about caching!

Cache-Control: no-cache

See also: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control

[ghost]

Just to make it clear: no-cache does NOT mean that you can't cache it, just that you need to validate at the server before using it (again).

[dzolnai]

Okay, but that means that there has to be a network call, which you did not want:

Just showing a banner that it is refreshing the list is not okay. There should be no banner and no delay. There is no need for network activity at all!

[ghost]

We are only talking about server_list.json in this case, as that is the only file that is potentially retrieved when showing the servers. So technically you are correct. When you use server_list.json to extract the display_name of the configured servers you would need to make a network request when showing the server list.

Using a conditional request you can skip a lot of work if the file on the server didn't change though (304 response), no need to verify the signature, no need to parse the JSON, no need to update the model...

I don't recall exactly what gets called when though.

Edit: not to mention this could be done in the background, not needing to block at all :)

[dzolnai]

Using a conditional request you can skip a lot of work if the file on the server didn't change though (304 response), no need to verify the signature, no need to parse the JSON, no need to update the model...

That would be true if the models would be cached on that level (like they are since the last update).
But the HTTP cache works on the response level, so the only step we are saving here is fetching the response data. After that, the signature verification and JSON parsing still happen, because the app will not know if the response is a cached one or not (which it shouldn't).

Edit: not to mention this could be done in the background, not needing to block at all :)

All the processing already happens in the background. You see the loading bars until there is something to show, otherwise the user does not know why the list is empty.

[ghost]

Maybe this is the best we can do then. I'm just a bit worried about choosing a caching yourself, i.e. 1 hour, especially if the user cannot override this except by clearing browser cache (I guess)?

[dzolnai]

To clear it, the app data has to be cleared, which removes all other saved data as well. I can reduce the 1 hour though.