element-desktop crashes when downloading large encrypted file

[ldot72]

Steps to reproduce

1. Start element desktop app. Open an encrypted room that has a large file uploaded to it. I tested with a 1.95GB .tar.
2. Click on download. Wait.

Outcome

What did you expect?

The file downloads and decrypts normally.

What happened instead?

The element desktop app crashes after downloading for some time. White window, RAM usage of the process drops to below 100MB and stays there. Closing and reopening the app needed to restore functionality.

Operating system

Windows 10

Application version

1.10.3

How did you install the app?

https://element.io/get-started#download Windows 64-bit

Homeserver

Synapse 1.52.0

Will you send logs?

No

[dbkr]

I'm assuming this is also specific to encrypted rooms?

[ldot72]

It is specific to encrypted rooms.
On further testing, the crash seems to happen with files that element-desktop is unable to upload to encrypted rooms. A 1.6GB file can be uploaded and downloaded without issue. Uploading a 1.95GB file causes element-desktop to increase RAM usage as expected, but it stops after increasing by a few GB and gives the file failed to upload error shortly afterwards. If the same file is uploaded with a different client and then downloaded with element-desktop, the element-desktop app crashes. I've used nheko for uploading files of that size. Downloading files uploaded with nheko does not otherwise lead to crashes.
Note that element-desktop fails the upload differently for files larger than at least 1.6GB but smaller than 2GB on the one hand, and files larger than 2GB on the other hand. Files larger than 2GB fail instantly without increase in RAM usage. This latter case is described in #21091

Some time after writing the above, further testing points in a somewhat different direction. Take a few files with 1.6GB size and a freshly started element-desktop instance. Start uploading one of the files to an encrypted room. Once RAM usage has plateaued, cancel the upload. Start uploading another file to the same room. Cancel once RAM usage has plateaued. Repeat until element-desktop crashes.
On the other hand, a freshly opened element-desktop instance seems to be able to upload files up to the 2GB hard limit, provided no other uploads are attempted before that.

[turt2live]

Duplicate of #4264