Recently edited message from the past is not visible

[Anderas]

Steps to reproduce

1. Open a room where some message from the past has not yet been loaded via pagination
2. Edit this message on another client
3. Paginate to this message on the first device

=> The message is not shown at all

The root cause of this behaviour is the implementation of replay attack prevention. Given that the original event as well as the edit event now have the same content, Olm will recieve the same ciphertext and return the same message index. We now have two identical decrypted messages, one of which will be ignored by the replay attack prevention. If the first event happens to be the edit and the second the original, the client will never show any message at all, because it is ignored.

Outcome

What did you expect?

The edited message is visible

What happened instead?

The edited message is missing

Your phone model

No response

Operating system version

No response

Application version

No response

Homeserver

No response

Will you send logs?

No

[Anderas]

Partially related to #4329