Synapse's own check_media_file_for_spam module can never see E2EE
attachment content - only the client ever holds the decryption key.
Adds two hooks that call a self-hosted scan service
(https://axion1337.chat/_scan, deployed separately in the gitops repo):
- DecryptFile.ts: scans every decrypted attachment (image/audio/video/
file all funnel through this one function via MediaEventHelper)
before returning it as a Blob.
- ContentMessages.ts: scans plaintext before encryption/upload in
uploadFile(), the shared function behind all attachment uploads
(main file, thumbnails, voice messages), regardless of room
encryption state.
New ContentScanRejectedError surfaces through the existing error-
rendering paths (MediaProcessingError, upload failure dialog) using
the same pattern as DecryptError/DownloadError/UploadFailedError.
Live-tested: EICAR blocked pre-upload in encrypted rooms and DMs;
receive-side hook also blocks EICAR sent by an unpatched client
(app.element.io), confirming it isn't just self-protection for our
own uploads. Fails open on scanner errors so an outage can't block
all uploads/downloads.
Thore Cimbal
42285021cb