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

5 files changed, 48 insertions, 37 deletions

diff --git a/app/models/account.rb b/app/models/account.rb
index f7a7f4a7b..2c2840ee4 100644
--- a/app/models/account.rb
+++ b/app/models/account.rb
@@ -58,8 +58,9 @@ class Account < ApplicationRecord
     hub_url
   )
 
-  USERNAME_RE = /[a-z0-9_]+([a-z0-9_\.-]+[a-z0-9_]+)?/i
-  MENTION_RE  = /(?<=^|[^\/[:word:]])@((#{USERNAME_RE})(?:@[[:word:]\.\-]+[a-z0-9]+)?)/i
+  USERNAME_RE   = /[a-z0-9_]+([a-z0-9_\.-]+[a-z0-9_]+)?/i
+  MENTION_RE    = /(?<=^|[^\/[:word:]])@((#{USERNAME_RE})(?:@[[:word:]\.\-]+[a-z0-9]+)?)/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
diff --git a/app/models/concerns/account_interactions.rb b/app/models/concerns/account_interactions.rb
index 4bf62539c..8f19176a7 100644
--- a/app/models/concerns/account_interactions.rb
+++ b/app/models/concerns/account_interactions.rb
@@ -254,10 +254,13 @@ 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]
diff --git a/app/workers/activitypub/delivery_worker.rb b/app/workers/activitypub/delivery_worker.rb
index 6c5a576a7..788f2cf80 100644
--- a/app/workers/activitypub/delivery_worker.rb
+++ b/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
diff --git a/spec/models/concerns/account_interactions_spec.rb b/spec/models/concerns/account_interactions_spec.rb
index 85fbf7e79..ca243ebc5 100644
--- a/spec/models/concerns/account_interactions_spec.rb
+++ b/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 '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
 
-      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 '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
 
-    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
+  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') }
 
-      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
+    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
 
diff --git a/spec/workers/activitypub/delivery_worker_spec.rb b/spec/workers/activitypub/delivery_worker_spec.rb
index f4633731e..d39393d50 100644
--- a/spec/workers/activitypub/delivery_worker_spec.rb
+++ b/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