Full Resolution SVG Fails to Display in E2E Encrypted Rooms

[SethFalco]

Description

When sharing an SVG via chat, the thumbnail will always display correctly.
When sharing an SVG in an encrypted chat room, the full resolution version of the SVG fails to load.

I've attempted to peek around a little, and I believe it's because in an encrypted room, the full resolution image is retrieved with the Content-Type as octet-stream, unlike in unencrypted rooms, it correctly has the type svg+xml.

Steps to reproduce

• Upload any SVG file to an E2E encrypted room.
• Click the thumbnail to view the "full resolution" image.
• Observe a dead image.

I'd expect this to work the same as when an SVG is opened in an unencrypted chat room.

Logs being sent: yes

Version information

• Platform: Web and Desktop

For the web app:

• Browser: Firefox
• OS: Ubuntu 18.04
• URL: develop.element.io

For the desktop app:

• OS: Ubuntu 18.04
• Version: 1.7.5

[t3chguy]

So we specifically filter out svg+xml for security reasons to prevent XSS
https://github.com/matrix-org/matrix-react-sdk/blob/ce226ab5346b405b4f21a4938f87eb2ef6c748f9/src/utils/DecryptFile.js#L54

[t3chguy]

The same comment claims it should work regardless however:
https://github.com/matrix-org/matrix-react-sdk/blob/ce226ab5346b405b4f21a4938f87eb2ef6c748f9/src/utils/DecryptFile.js#L42-L45

[t3chguy]

@hex-m unrelated to this issue - #2581