Fix followers synchronization mechanism not working when URI has empty path (#16510)

* Fix followers synchronization mechanism not working when URI has empty path

To my knowledge, there is no current implementation on the fediverse
that can use bare domains (e.g., actor is at https://example.org instead of
something like https://example.org/actor) that also plans to support the
followers synchronization mechanism. However, Mastodon's current implementation
would exclude such accounts from followers list.

Also adds tests and rename them to reflect the proper method names.

* Move url prefix regexp to its own constant

app/models/account.rb

@@ -60,6 +60,7 @@ class Account < ApplicationRecord
 
   USERNAME_RE   = /[a-z0-9_]+([a-z0-9_\.-]+[a-z0-9_]+)?/i
   MENTION_RE    = /(?<=^|[^\/[:word:]])@((#{USERNAME_RE})(?:@[[:word:]\.\-]+[[:word:]]+)?)/i
+  URL_PREFIX_RE = /\Ahttp(s?):\/\/[^\/]+/
 
   include AccountAssociations
   include AccountAvatar
@@ -379,7 +380,7 @@ class Account < ApplicationRecord
   def synchronization_uri_prefix
     return 'local' if local?
 
-    @synchronization_uri_prefix ||= uri[/http(s?):\/\/[^\/]+\//]
+    @synchronization_uri_prefix ||= "#{uri[URL_PREFIX_RE]}/"
   end
 
   class Field < ActiveModelSerializers::Model

app/models/concerns/account_interactions.rb

@@ -251,10 +251,13 @@ module AccountInteractions
          .where('users.current_sign_in_at > ?', User::ACTIVE_DURATION.ago)
   end
 
-  def remote_followers_hash(url_prefix)
-    Rails.cache.fetch("followers_hash:#{id}:#{url_prefix}") do
+  def remote_followers_hash(url)
+    url_prefix = url[Account::URL_PREFIX_RE]
+    return if url_prefix.blank?
+
+    Rails.cache.fetch("followers_hash:#{id}:#{url_prefix}/") do
       digest = "\x00" * 32
-      followers.where(Account.arel_table[:uri].matches(url_prefix + '%', false, true)).pluck_each(:uri) do |uri|
+      followers.where(Account.arel_table[:uri].matches("#{Account.sanitize_sql_like(url_prefix)}/%", false, true)).or(followers.where(uri: url_prefix)).pluck_each(:uri) do |uri|
         Xorcist.xor!(digest, Digest::SHA256.digest(uri))
       end
       digest.unpack('H*')[0]

app/workers/activitypub/delivery_worker.rb

@@ -44,11 +44,7 @@ class ActivityPub::DeliveryWorker
   end
 
   def synchronization_header
-    "collectionId=\"#{account_followers_url(@source_account)}\", digest=\"#{@source_account.remote_followers_hash(inbox_url_prefix)}\", url=\"#{account_followers_synchronization_url(@source_account)}\""
-  end
-
-  def inbox_url_prefix
-    @inbox_url[/http(s?):\/\/[^\/]+\//]
+    "collectionId=\"#{account_followers_url(@source_account)}\", digest=\"#{@source_account.remote_followers_hash(@inbox_url)}\", url=\"#{account_followers_synchronization_url(@source_account)}\""
   end
 
   def perform_request

spec/models/concerns/account_interactions_spec.rb

@@ -539,46 +539,57 @@ describe AccountInteractions do
     end
   end
 
-  describe '#followers_hash' do
+  describe '#remote_followers_hash' do
     let(:me) { Fabricate(:account, username: 'Me') }
     let(:remote_1) { Fabricate(:account, username: 'alice', domain: 'example.org', uri: 'https://example.org/users/alice') }
     let(:remote_2) { Fabricate(:account, username: 'bob', domain: 'example.org', uri: 'https://example.org/users/bob') }
-    let(:remote_3) { Fabricate(:account, username: 'eve', domain: 'foo.org', uri: 'https://foo.org/users/eve') }
+    let(:remote_3) { Fabricate(:account, username: 'instance-actor', domain: 'example.org', uri: 'https://example.org') }
+    let(:remote_4) { Fabricate(:account, username: 'eve', domain: 'foo.org', uri: 'https://foo.org/users/eve') }
 
     before do
       remote_1.follow!(me)
       remote_2.follow!(me)
       remote_3.follow!(me)
+      remote_4.follow!(me)
       me.follow!(remote_1)
     end
 
-    context 'on a local user' do
-      it 'returns correct hash for remote domains' do
-        expect(me.remote_followers_hash('https://example.org/')).to eq '707962e297b7bd94468a21bc8e506a1bcea607a9142cd64e27c9b106b2a5f6ec'
-        expect(me.remote_followers_hash('https://foo.org/')).to eq 'ccb9c18a67134cfff9d62c7f7e7eb88e6b803446c244b84265565f4eba29df0e'
-      end
-
-      it 'invalidates cache as needed when removing or adding followers' do
-        expect(me.remote_followers_hash('https://example.org/')).to eq '707962e297b7bd94468a21bc8e506a1bcea607a9142cd64e27c9b106b2a5f6ec'
-        remote_1.unfollow!(me)
-        expect(me.remote_followers_hash('https://example.org/')).to eq '241b00794ce9b46aa864f3220afadef128318da2659782985bac5ed5bd436bff'
-        remote_1.follow!(me)
-        expect(me.remote_followers_hash('https://example.org/')).to eq '707962e297b7bd94468a21bc8e506a1bcea607a9142cd64e27c9b106b2a5f6ec'
-      end
+    it 'returns correct hash for remote domains' do
+      expect(me.remote_followers_hash('https://example.org/')).to eq '20aecbe774b3d61c25094370baf370012b9271c5b172ecedb05caff8d79ef0c7'
+      expect(me.remote_followers_hash('https://foo.org/')).to eq 'ccb9c18a67134cfff9d62c7f7e7eb88e6b803446c244b84265565f4eba29df0e'
+      expect(me.remote_followers_hash('https://foo.org.evil.com/')).to eq '0000000000000000000000000000000000000000000000000000000000000000'
+      expect(me.remote_followers_hash('https://foo')).to eq '0000000000000000000000000000000000000000000000000000000000000000'
     end
 
-    context 'on a remote user' do
-      it 'returns correct hash for remote domains' do
-        expect(remote_1.local_followers_hash).to eq Digest::SHA256.hexdigest(ActivityPub::TagManager.instance.uri_for(me))
-      end
+    it 'invalidates cache as needed when removing or adding followers' do
+      expect(me.remote_followers_hash('https://example.org/')).to eq '20aecbe774b3d61c25094370baf370012b9271c5b172ecedb05caff8d79ef0c7'
+      remote_3.unfollow!(me)
+      expect(me.remote_followers_hash('https://example.org/')).to eq '707962e297b7bd94468a21bc8e506a1bcea607a9142cd64e27c9b106b2a5f6ec'
+      remote_1.unfollow!(me)
+      expect(me.remote_followers_hash('https://example.org/')).to eq '241b00794ce9b46aa864f3220afadef128318da2659782985bac5ed5bd436bff'
+      remote_1.follow!(me)
+      expect(me.remote_followers_hash('https://example.org/')).to eq '707962e297b7bd94468a21bc8e506a1bcea607a9142cd64e27c9b106b2a5f6ec'
+    end
+  end
 
-      it 'invalidates cache as needed when removing or adding followers' do
-        expect(remote_1.local_followers_hash).to eq Digest::SHA256.hexdigest(ActivityPub::TagManager.instance.uri_for(me))
-        me.unfollow!(remote_1)
-        expect(remote_1.local_followers_hash).to eq '0000000000000000000000000000000000000000000000000000000000000000'
-        me.follow!(remote_1)
-        expect(remote_1.local_followers_hash).to eq Digest::SHA256.hexdigest(ActivityPub::TagManager.instance.uri_for(me))
-      end
+  describe '#local_followers_hash' do
+    let(:me) { Fabricate(:account, username: 'Me') }
+    let(:remote_1) { Fabricate(:account, username: 'alice', domain: 'example.org', uri: 'https://example.org/users/alice') }
+
+    before do
+      me.follow!(remote_1)
+    end
+
+    it 'returns correct hash for local users' do
+      expect(remote_1.local_followers_hash).to eq Digest::SHA256.hexdigest(ActivityPub::TagManager.instance.uri_for(me))
+    end
+
+    it 'invalidates cache as needed when removing or adding followers' do
+      expect(remote_1.local_followers_hash).to eq Digest::SHA256.hexdigest(ActivityPub::TagManager.instance.uri_for(me))
+      me.unfollow!(remote_1)
+      expect(remote_1.local_followers_hash).to eq '0000000000000000000000000000000000000000000000000000000000000000'
+      me.follow!(remote_1)
+      expect(remote_1.local_followers_hash).to eq Digest::SHA256.hexdigest(ActivityPub::TagManager.instance.uri_for(me))
     end
   end
 

spec/workers/activitypub/delivery_worker_spec.rb

@@ -11,7 +11,7 @@ describe ActivityPub::DeliveryWorker do
   let(:payload) { 'test' }
 
   before do
-    allow_any_instance_of(Account).to receive(:remote_followers_hash).with('https://example.com/').and_return('somehash')
+    allow_any_instance_of(Account).to receive(:remote_followers_hash).with('https://example.com/api').and_return('somehash')
   end
 
   describe 'perform' do