Trac #1734
This is implemented by bouncing uploaded file links through a view
that checks authentication and redirects to an expiring S3 URL.
This makes file uploads return a domain-relative URI. The client converts
this to an absolute URI when it's in the composebox, then back to relative
when it's submitted to the server.
We need the relative URI because the same message may be viewed across
{staging,www,zephyr}.zulip.com, which have different cookies.
(imported from commit 33acb2abaa3002325f389d5198fb20ee1b30f5fa)
We have to read the data anyway, and we don't have a convenient file
handle for uploads from attachments sent through the e-mail gateway.
(imported from commit 86260a4eaceef85c82707929a80558e11dc54ef6)
This needs to be deployed to both staging and prod at the same
off-peak time (and the schema migration run).
At the time it is deployed, we need to make a few changes directly in
the database:
(1) UPDATE django_content_type set app_label='zerver' where app_label='zephyr';
(2) UPDATE south_migrationhistory set app_name='zerver' where app_name='zephyr';
(imported from commit eb3fd719571740189514ef0b884738cb30df1320)