Mark files that have been deleted on the server.

[YamatoRyou]

Your use case

What would you like to do?

If a file is deleted on the server, but still exists in the room's stream, use a flag to inform the user that the file no longer exists on the server.
When the user tries to download the file, somehow inform the user that the file cannot be downloaded, instead of popping up a select path dialog.

Why would you like to do it?

The current handling of such files is somewhat ugly: even if the file has been deleted by the server, the user can still download the file forcibly, and the file just contains JSON like this:
{"errcode":"M_NOT_FOUND","error":"Not found [b'*******************.com', b'EfbkyHNJEXrwRFAzxHjnbIhJ']"}

How would you like to achieve it?

n/a

Have you considered any alternatives?

Use another external file transfer service, such as Jirafeau or PsiTrasnfer. An external file transfer service can solve the following problems:

1. Synapse fails to upload large files inexplicably (Weirdly large file upload failed. matrix-org/synapse#12937);
2. An additional note can be attached to inform the user of the expiration date of the document;
3. Batch download;
4. The size of the remaining disk space will affect the download of large files. element-web#22369

Additional context

n/a

[t3chguy]

This would require a HEAD request to each and every bit of media to check if it is still present, which would be a significant privacy leak as then your server would know exactly where your client is scrolling