* Remove Salmon and PubSubHubbub endpoints

* Add error when trying to follow OStatus accounts

* Fix new accounts not being created in ResolveAccountService

* Change domain blocks to automatically support subdomains

If a more authoritative domain is blocked (example.com), then the
same block will be applied to a subdomain (foo.example.com)

* Match subdomains of existing accounts when blocking/unblocking domains

* Improve code style

* When serializing polls over OStatus, serialize poll options to text

* Do the same for RSS feeds

* Use “[ ] ” as a prefix for poll options instead of “- ”

* Create Redisable

* Use #redis instead of Redis.current

* Add silent column to mentions

* Save silent mentions in ActivityPub Create handler and optimize it

Move networking calls out of the database transaction

* Add "limited" visibility level masked as "private" in the API

Unlike DMs, limited statuses are pushed into home feeds. The access
control rules between direct and limited statuses is almost the same,
except for counter and conversation logic

* Ensure silent column is non-null, add spec

* Ensure filters don't check silent mentions for blocks/mutes

As those are "this person is also allowed to see" rather than "this
person is involved", therefore does not warrant filtering

* Clean up code

* Use Status#active_mentions to limit returned mentions

* Fix code style issues

* Use Status#active_mentions in Notification

And remove stream_entry eager-loading from Notification

* Fix URI not being sufficiently validated with prefetched JSON

* Add additional id validation to OStatus documents, when possible

An explicit error allows user agents to know the error and Sidekiq to
retry.

* If an OStatus message contains nsfw hashtag, mark it as sensitive

Undo parts of #7048

* Put nsfw hashtag on OStatus messages if they have any media

* Fix code style issues

* Revert "Fixes/do not override timestamps (#7331)"

This reverts commit 581a5c9d29.

* Document Snowflake ID corner-case a bit more

Snowflake IDs are used for two purposes: making object identifiers harder to
guess and ensuring they are in chronological order. For this reason, they
are based on the `created_at` attribute of the object.

Unfortunately, inserting items with older snowflakes IDs will break the
assumption of consumers of the paging APIs that new items will always have
a greater identifier than the last seen one.

* Add `override_timestamps` virtual attribute to not correlate snowflake ID with created_at

* Do not override timestamps for incoming toots

* Remove every reference to override_timestamps

Statuses are now created with the announced publishing date
and are only pushed to timelines if that date is at most
6 hours earlier than the time at which it is processed.

Fix #7011

Federate custom emojis with accounts

Up until now, the order seemed to be in the *opposite* order,
which caused the WebUI to populate mentions in reversed order
when replying to toots local to one's instance.

Fix #6821

* fix validation error (media only status)

* Incorporating review suggestions

* Reflect similar fix to OStatus side

* Fix not to include media in transaction

* Restore the limit of the number of media

* Fix not to return nil

Time window of 6 hours

* Skip ActivityPub Announces of non-public objects

* Skip OStatus reblogs of non-public statuses

This error occurred at least in development environment

- Rename Mastodon::TimestampIds into Mastodon::Snowflake for clarity
- Skip for statuses coming from inbox, aka delivered in real-time
- Skip for statuses that claim to be from the future

Additionally, ActivityPub::FetchRemoteStatusService no longer parses
activities.
OStatus::Activity::Creation no longer delegates to ActivityPub because
the provided ActivityPub representations are not signed while OStatus
representations are.

* Avoid races in incoming OStatus toots processing

* oops

* oops again

* Custom emoji

- In OStatus: `<link rel="emoji" name="coolcat" href="http://..." />`
- In ActivityPub: `{ type: "Emoji", name: ":coolcat:", href: "http://..." }`
- In REST API: Status object includes `emojis` array (`shortcode`, `url`)
- Domain blocks with reject media stop emojis
- Emoji file up to 50KB
- Web UI handles custom emojis
- Static pages render custom emojis as `<img />` tags

Side effects:

- Undo #4500 optimization, as I needed to modify it to restore
  shortcode handling in emojify()
- Formatter#plaintext should now make sure stripped out line-breaks
  and paragraphs are replaced with newlines

* Fix emoji at the start not being converted

* Decouple Status#local? from uri being nil

* Replace on-the-fly URI generation with stored URIs

- Generate URI in after_save hook for local statuses
- Use static value in TagManager when available, fallback to tag format
- Make TagManager use ActivityPub::TagManager to understand new format
- Adjust tests

* Use other heuristic for locality of old statuses, do not perform long query

* Exclude tombstone stream entries from Atom feed

* Prevent nil statuses from landing in Pubsubhubbub::DistributionWorker

* Fix URI not being saved (#4818)

* Add more specs for Status

* Save generated uri immediately

and also fix method order to minimize diff.

* Fix alternate HTML URL in Atom

* Fix tests

* Remove not-null constraint from statuses migration to speed it up

Currently, private / direct posts via OStatus from AP compatible instance will be dropped due to failing to fetch AP version.

So this fallbacks to OStatus handling:

* when failed to fetch ActivityPub version
* when status is neither :public nor :unlisted

Requires moving Atom rendering from DistributionWorker (where
`stream_entry.status` is already nil) to inline (where
`stream_entry.status.destroyed?` is true) and distributing that.

Unfortunately, such XML renderings can no longer be easily chained
together into one payload of n items.

* Wrap methods of ProcessFeedService::ProcessEntry in classes

This is a change same with 425acecfdb15093a265b191120fb2d4e4c4135c4, except
that it has the following changes:

* Revert irrelevant change in find_or_create_conversation
* Fix error handling for RemoteActivity

* Introduce Ostatus name space