mastodon/app/services/activitypub/fetch_replies_service.rb

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# frozen_string_literal: true
class ActivityPub::FetchRepliesService < BaseService
include JsonLdHelper
def call(parent_status, collection_or_uri, allow_synchronous_requests = true)
@account = parent_status.account
@allow_synchronous_requests = allow_synchronous_requests
@items = collection_items(collection_or_uri)
return if @items.nil?
FetchReplyWorker.push_bulk(filtered_replies)
@items
end
private
def collection_items(collection_or_uri)
collection = fetch_collection(collection_or_uri)
return unless collection.is_a?(Hash)
collection = fetch_collection(collection['first']) if collection['first'].present?
return unless collection.is_a?(Hash)
case collection['type']
when 'Collection', 'CollectionPage'
collection['items']
when 'OrderedCollection', 'OrderedCollectionPage'
collection['orderedItems']
end
end
def fetch_collection(collection_or_uri)
return collection_or_uri if collection_or_uri.is_a?(Hash)
return unless @allow_synchronous_requests
return if invalid_origin?(collection_or_uri)
fetch_resource_without_id_validation(collection_or_uri, nil, true)
end
def filtered_replies
# Only fetch replies to the same server as the original status to avoid
# amplification attacks.
# Also limit to 5 fetched replies to limit potential for DoS.
@items.map { |item| value_or_id(item) }.reject { |uri| invalid_origin?(uri) }.take(5)
end
def invalid_origin?(url)
return true if unsupported_uri_scheme?(url)
needle = Addressable::URI.parse(url).host
haystack = Addressable::URI.parse(@account.uri).host
!haystack.casecmp(needle).zero?
end
end