MediaProxy returns 404 for valid image payloads labeled as octet-stream

[ntsklab]

Summary

MediaProxy can return 404 for remote media even when upstream is reachable and the payload is a valid image.

Example URL (affected)

• Hollo proxy URL:
  • https://hl.oyasumi.dev/proxy/jlCELzQVvO0-JNvkT2OVsQ/aHR0cHM6Ly9tZWRpYS5zb2NpYWwuZmVkaWZ5LmRldi9hdmF0YXJzL2FmNTk2ZmM4LWNmMDMtNGVkZC1hMGU5LTRiZGMwZjIwY2U1ZA
• Decoded upstream URL:
  • https://media.social.fedify.dev/avatars/af596fc8-cf03-4edd-a0e9-4bdc0f20ce5d

Observed behavior

• Hollo proxy URL responds with 404.
• Upstream URL responds with 200.
• Upstream uses Content-Type: application/octet-stream (or binary/octet-stream) in some cases.
• Payload bytes are valid image data.

Expected behavior

Valid safe image payloads should not be rejected as 404 solely because upstream labels MIME as octet-stream.

Impact

Avatars/media may appear missing in timelines for multiple remote accounts.

Environment

• Hollo 0.9.1
• MEDIA_PROXY=proxy
• REMOTE_MEDIA_THUMBNAILS=off

Additional note

A similar upstream MIME pattern was observed on hosting used by Hollo official account avatar media.

AI disclosure

This issue text was drafted with AI assistance (GPT-5.3 Codex) and reviewed by a human before submission.

[dahlia]

Fixed in Hollo 0.9.2.