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mastodon/app/services/activitypub/prepare_followers_synchroni...

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Add follower synchronization mechanism (#14510) * Add support for followers synchronization on the receiving end Check the `collectionSynchronization` attribute on `Create` and `Announce` activities and synchronize followers from provided collection if possible. * Add tests for followers synchronization on the receiving end * Add support for follower synchronization on the sender's end * Add tests for the sending end * Switch from AS attributes to HTTP header Replace the custom `collectionSynchronization` ActivityStreams attribute by an HTTP header (`X-AS-Collection-Synchronization`) with the same syntax as the `Signature` header and the following fields: - `collectionId` to specify which collection to synchronize - `digest` for the SHA256 hex-digest of the list of followers known on the receiving instance (where “receiving instance” is determined by accounts sharing the same host name for their ActivityPub actor `id`) - `url` of a collection that should be fetched by the instance actor Internally, move away from the webfinger-based `domain` attribute and use account `uri` prefix to group accounts. * Add environment variable to disable followers synchronization Since the whole mechanism relies on some new preconditions that, in some extremely rare cases, might not be met, add an environment variable (DISABLE_FOLLOWERS_SYNCHRONIZATION) to disable the mechanism altogether and avoid followers being incorrectly removed. The current conditions are: 1. all managed accounts' actor `id` and inbox URL have the same URI scheme and netloc. 2. all accounts whose actor `id` or inbox URL share the same URI scheme and netloc as a managed account must be managed by the same Mastodon instance as well. As far as Mastodon is concerned, breaking those preconditions require extensive configuration changes in the reverse proxy and might also cause other issues. Therefore, this environment variable provides a way out for people with highly unusual configurations, and can be safely ignored for the overwhelming majority of Mastodon administrators. * Only set follower synchronization header on non-public statuses This is to avoid unnecessary computations and allow Follow-related activities to be handled by the usual codepath instead of going through the synchronization mechanism (otherwise, any Follow/Undo/Accept activity would trigger the synchronization mechanism even if processing the activity itself would be enough to re-introduce synchronization) * Change how ActivityPub::SynchronizeFollowersService handles follow requests If the remote lists a local follower which we only know has sent a follow request, consider the follow request as accepted instead of sending an Undo. * Integrate review feeback - rename X-AS-Collection-Synchronization to Collection-Synchronization - various minor refactoring and code style changes * Only select required fields when computing followers_hash * Use actor URI rather than webfinger domain in synchronization endpoint * Change hash computation to be a XOR of individual hashes Makes it much easier to be memory-efficient, and avoid sorting discrepancy issues. * Marginally improve followers_hash computation speed * Further improve hash computation performances by using pluck_each
2020-10-21 16:04:09 +00:00
# frozen_string_literal: true
class ActivityPub::PrepareFollowersSynchronizationService < BaseService
include JsonLdHelper
def call(account, params)
@account = account
return if params['collectionId'] != @account.followers_url || invalid_origin?(params['url']) || @account.local_followers_hash == params['digest']
ActivityPub::FollowersSynchronizationWorker.perform_async(@account.id, params['url'])
end
end