Dedupe now uses a three-level sharding directory structure to improve performance when many files are uploaded and stored on a filesystem instead of an object store. (note: Minio still affected as it still uses a traditional filesystem)
This does not help if you already have hundreds of thousands of files uploaded. The media URLs are permanently part of the activity so the files cannot be relocated. A motivated user could write a tool to move the files and perhaps write an Nginx or equivalent redirect to make the files still accessible, but that is beyond the scope of this change.
Validate the content-type of the response when fetching an object,
according to https://www.w3.org/TR/activitypub/#x3-2-retrieving-objects.
content-type headers had to be added to many mocks in order to support
this, some of this was done with a regex. While I did go over the
resulting files to check I didn't modify anything unrelated, there is a
possibility I missed something.
Closes pleroma#1948
