Add support for paginating partial collections in SynchronizeFollowersService (#34277)

app/models/account.rb

@@ -153,7 +153,7 @@ class Account < ApplicationRecord
   scope :not_excluded_by_account, ->(account) { where.not(id: account.excluded_from_timeline_account_ids) }
   scope :not_domain_blocked_by_account, ->(account) { where(arel_table[:domain].eq(nil).or(arel_table[:domain].not_in(account.excluded_from_timeline_domains))) }
   scope :dormant, -> { joins(:account_stat).merge(AccountStat.without_recent_activity) }
-  scope :with_username, ->(value) { where arel_table[:username].lower.eq(value.to_s.downcase) }
+  scope :with_username, ->(value) { value.is_a?(Array) ? where(arel_table[:username].lower.in(value.map { |x| x.to_s.downcase })) : where(arel_table[:username].lower.eq(value.to_s.downcase)) }
   scope :with_domain, ->(value) { where arel_table[:domain].lower.eq(value&.to_s&.downcase) }
   scope :without_memorial, -> { where(memorial: false) }
   scope :duplicate_uris, -> { select(:uri, Arel.star.count).group(:uri).having(Arel.star.count.gt(1)) }

app/services/activitypub/synchronize_followers_service.rb

@@ -4,32 +4,46 @@ class ActivityPub::SynchronizeFollowersService < BaseService
   include JsonLdHelper
   include Payloadable
 
+  MAX_COLLECTION_PAGES = 10
+
   def call(account, partial_collection_url)
     @account = account
+    @expected_followers_ids = []
 
-    items = collection_items(partial_collection_url)
-    return if items.nil?
-
-    # There could be unresolved accounts (hence the call to .compact) but this
-    # should never happen in practice, since in almost all cases we keep an
-    # Account record, and should we not do that, we should have sent a Delete.
-    # In any case there is not much we can do if that occurs.
-    @expected_followers = items.filter_map { |uri| ActivityPub::TagManager.instance.uri_to_resource(uri, Account) }
+    return unless process_collection!(partial_collection_url)
 
     remove_unexpected_local_followers!
-    handle_unexpected_outgoing_follows!
   end
 
   private
 
+  def process_page!(items)
+    page_expected_followers = extract_local_followers(items)
+    @expected_followers_ids.concat(page_expected_followers.pluck(:id))
+
+    handle_unexpected_outgoing_follows!(page_expected_followers)
+  end
+
+  def extract_local_followers(items)
+    # There could be unresolved accounts (hence the call to .filter_map) but this
+    # should never happen in practice, since in almost all cases we keep an
+    # Account record, and should we not do that, we should have sent a Delete.
+    # In any case there is not much we can do if that occurs.
+
+    # TODO: this will need changes when switching to numeric IDs
+
+    usernames = items.filter_map { |uri| ActivityPub::TagManager.instance.uri_to_local_id(uri, :username)&.downcase }
+    Account.local.with_username(usernames)
+  end
+
   def remove_unexpected_local_followers!
-    @account.followers.local.where.not(id: @expected_followers.map(&:id)).reorder(nil).find_each do |unexpected_follower|
+    @account.followers.local.where.not(id: @expected_followers_ids).reorder(nil).find_each do |unexpected_follower|
       UnfollowService.new.call(unexpected_follower, @account)
     end
   end
 
-  def handle_unexpected_outgoing_follows!
-    @expected_followers.each do |expected_follower|
+  def handle_unexpected_outgoing_follows!(expected_followers)
+    expected_followers.each do |expected_follower|
       next if expected_follower.following?(@account)
 
       if expected_follower.requested?(@account)
@@ -50,21 +64,33 @@ class ActivityPub::SynchronizeFollowersService < BaseService
     Oj.dump(serialize_payload(follow, ActivityPub::UndoFollowSerializer))
   end
 
-  def collection_items(collection_or_uri)
-    collection = fetch_collection(collection_or_uri)
-    return unless collection.is_a?(Hash)
+  # Only returns true if the whole collection has been processed
+  def process_collection!(collection_uri, max_pages: MAX_COLLECTION_PAGES)
+    collection = fetch_collection(collection_uri)
+    return false unless collection.is_a?(Hash)
 
     collection = fetch_collection(collection['first']) if collection['first'].present?
-    return unless collection.is_a?(Hash)
 
-    # Abort if we'd have to paginate through more than one page of followers
-    return if collection['next'].present?
+    while collection.is_a?(Hash)
+      process_page!(as_array(collection_page_items(collection)))
 
+      max_pages -= 1
+
+      return true if collection['next'].blank? # We reached the end of the collection
+      return false if max_pages <= 0 # We reached our pages limit
+
+      collection = fetch_collection(collection['next'])
+    end
+
+    false
+  end
+
+  def collection_page_items(collection)
     case collection['type']
     when 'Collection', 'CollectionPage'
-      as_array(collection['items'])
+      collection['items']
     when 'OrderedCollection', 'OrderedCollectionPage'
-      as_array(collection['orderedItems'])
+      collection['orderedItems']
     end
   end
 

spec/services/activitypub/synchronize_followers_service_spec.rb

@@ -10,7 +10,7 @@ RSpec.describe ActivityPub::SynchronizeFollowersService do
   let(:bob)            { Fabricate(:account, username: 'bob') }
   let(:eve)            { Fabricate(:account, username: 'eve') }
   let(:mallory)        { Fabricate(:account, username: 'mallory') }
-  let(:collection_uri) { 'http://example.com/partial-followers' }
+  let(:collection_uri) { 'https://example.com/partial-followers' }
 
   let(:items) do
     [alice, eve, mallory].map do |account|
@@ -97,7 +97,76 @@ RSpec.describe ActivityPub::SynchronizeFollowersService do
       it_behaves_like 'synchronizes followers'
     end
 
-    context 'when the endpoint is a paginated Collection of actor URIs with a next page' do
+    context 'when the endpoint is a paginated Collection of actor URIs split across multiple pages' do
+      before do
+        stub_request(:get, 'https://example.com/partial-followers')
+          .to_return(status: 200, headers: { 'Content-Type': 'application/activity+json' }, body: Oj.dump({
+            '@context': 'https://www.w3.org/ns/activitystreams',
+            type: 'Collection',
+            id: 'https://example.com/partial-followers',
+            first: 'https://example.com/partial-followers/1',
+          }))
+
+        stub_request(:get, 'https://example.com/partial-followers/1')
+          .to_return(status: 200, headers: { 'Content-Type': 'application/activity+json' }, body: Oj.dump({
+            '@context': 'https://www.w3.org/ns/activitystreams',
+            type: 'CollectionPage',
+            id: 'https://example.com/partial-followers/1',
+            partOf: 'https://example.com/partial-followers',
+            next: 'https://example.com/partial-followers/2',
+            items: [alice, eve].map { |account| ActivityPub::TagManager.instance.uri_for(account) },
+          }))
+
+        stub_request(:get, 'https://example.com/partial-followers/2')
+          .to_return(status: 200, headers: { 'Content-Type': 'application/activity+json' }, body: Oj.dump({
+            '@context': 'https://www.w3.org/ns/activitystreams',
+            type: 'CollectionPage',
+            id: 'https://example.com/partial-followers/2',
+            partOf: 'https://example.com/partial-followers',
+            items: ActivityPub::TagManager.instance.uri_for(mallory),
+          }))
+      end
+
+      it_behaves_like 'synchronizes followers'
+    end
+
+    context 'when the endpoint is a paginated Collection of actor URIs split across, but one page errors out' do
+      before do
+        stub_request(:get, 'https://example.com/partial-followers')
+          .to_return(status: 200, headers: { 'Content-Type': 'application/activity+json' }, body: Oj.dump({
+            '@context': 'https://www.w3.org/ns/activitystreams',
+            type: 'Collection',
+            id: 'https://example.com/partial-followers',
+            first: 'https://example.com/partial-followers/1',
+          }))
+
+        stub_request(:get, 'https://example.com/partial-followers/1')
+          .to_return(status: 200, headers: { 'Content-Type': 'application/activity+json' }, body: Oj.dump({
+            '@context': 'https://www.w3.org/ns/activitystreams',
+            type: 'CollectionPage',
+            id: 'https://example.com/partial-followers/1',
+            partOf: 'https://example.com/partial-followers',
+            next: 'https://example.com/partial-followers/2',
+            items: [mallory].map { |account| ActivityPub::TagManager.instance.uri_for(account) },
+          }))
+
+        stub_request(:get, 'https://example.com/partial-followers/2')
+          .to_return(status: 404)
+      end
+
+      it 'confirms pending follow request but does not remove extra followers' do
+        previous_follower_ids = actor.followers.pluck(:id)
+
+        subject.call(actor, collection_uri)
+
+        expect(previous_follower_ids - actor.followers.reload.pluck(:id))
+          .to be_empty
+        expect(mallory)
+          .to be_following(actor)
+      end
+    end
+
+    context 'when the endpoint is a paginated Collection of actor URIs with more pages than we allow' do
       let(:payload) do
         {
           '@context': 'https://www.w3.org/ns/activitystreams',
@@ -113,12 +182,19 @@ RSpec.describe ActivityPub::SynchronizeFollowersService do
       end
 
       before do
+        stub_const('ActivityPub::SynchronizeFollowersService::MAX_COLLECTION_PAGES', 1)
         stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
-      it 'does not change followers' do
-        expect { subject.call(actor, collection_uri) }
-          .to_not(change { actor.followers.reload.reorder(id: :asc).pluck(:id) })
+      it 'confirms pending follow request but does not remove extra followers' do
+        previous_follower_ids = actor.followers.pluck(:id)
+
+        subject.call(actor, collection_uri)
+
+        expect(previous_follower_ids - actor.followers.reload.pluck(:id))
+          .to be_empty
+        expect(mallory)
+          .to be_following(actor)
       end
     end
   end