da4443f392
We didn't have thumbnailing for images coming from data import and this
commit adds the functionality.
There are a few fundamental issues that the implementation needs to
solve.
1. The images come from an untrusted source and therefore we don't want
to just pass them through to thumbnailing without checking. For that
reason, we cannot just import ImageAttachment rows from the export
data, even for zulip=>zulip imports.
The right way to process images is to pass them to maybe_thumbail(),
which runs libvips_check_image() on them to verify we're okay with
thumbnailing, creates ImageAttachment rows for them and sends them
to the thumbnailing queue worker. This approach lets us handle both
zulip=>zulip and 3rd party=>zulip imports in the same way,
2. There is a somewhat circular dependency between the Message,
Attachment and ImageAttachment import process:
- ImageAttachments would ideally be created after importing
Attachments, but they need to already exist at the time of Message
import. Otherwise, the markdown processor doesn't know it has to add
HTML for image previews to messages that reference images. This would
mean that messages imported from 3rd party tools don't get image
previews.
- Attachments only get created after Message import however, due to the
many-to-many relationship between Message and Attachment.
This is solved by fixing up some data of Attachments pre-emptively, such
as the path_ids. This gives us the necessary information for creating
ImageAttachments before importing Messages.
While we generate ImageAttachment rows synchronously, the actual
thumbnailing job is sent to the queue worker. Theoretically, the worker
could be very backlogged and not process the thumbnails anytime soon.
This is fine - if the app is loaded and tries to display a message with
such a not-yet-generated thumbnail, the code in `serve_file` will
generate the thumbnails synchronously on the fly and the user will see
the image preview displayed normally. See:
1b47134d0d/zerver/views/upload.py (L333-L342)
Zulip overview
Zulip is an open-source team collaboration tool with unique topic-based threading that combines the best of email and chat to make remote work productive and delightful. Fortune 500 companies, leading open source projects, and thousands of other organizations use Zulip every day. Zulip is the only modern team chat app that is designed for both live and asynchronous conversations.
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