Images repeatedly re-fetched on Android

[gnprice]

Recently I've started seeing the following symptom, [reported yesterday in chat](#mobile > Pulling from sides blacks out avatars @ 💬) by Alex:

• Open a message list, say the combined feed.
• Navigate to another message list, say by tapping a recipient header to go to the conversation.
• Now navigate back.
• All the sender avatars on the screen blink out, then re-appear.
  • In fact they do this twice, if you use the Android "back" gesture of swiping in from the side: first, when you start to swipe, the avatars on the current screen do it. Then when the back animation completes, the avatars on the previous screen do it.
  • If there are messages on the screen that have image previews, then these seem to do the same thing.

Both I and Alex are seeing this on Android; I'm using a Pixel 8 running Android 16. I tried it on an iOS device and it didn't reproduce — neither with the "back" gesture of swiping in from the left, nor with the back button at top left.

I believe I started seeing this sometime in the last few weeks.

Next steps

Most likely this is some sort of regression in Flutter upstream, in the implementation of Image.network, which we use and is supposed to cache the images. I don't think we've changed any relevant code in our own tree.

I think the next steps for investigating this are therefore:

• Look in the upstream tracker for any matching issue. If one is found, go from there. Shouldn't spend more than like 15 minutes on this; because the issue seems to be new and is probably only in Flutter main and not stable yet, I think it's fairly likely there is no existing issue thread.
• Then bisect to find where the issue began.
  • First, bisect among our published release builds: https://github.com/zulip/zulip-flutter/releases
  • Then bisect among Git commits between the two successive releases where it appeared. For this step, take care to use the corresponding Flutter commit for each of our commits being tested, namely the commit that appears in a comment in pubspec.yaml next to the Flutter version bound.
  • Then if the commit of ours that introduced the issue was a Flutter upgrade (as I suspect it will be), bisect among Git commits in Flutter to find which upstream commit introduced it.
• Proceed using the result of the bisection. If it is indeed an upstream change, then use that in reporting an upstream issue. Potentially also send a PR for the issue.

References

• Chat thread: #mobile > Pulling from sides blacks out avatars @ 💬