Allow to dereference Follow object for ActivityPub (#5772)

* Allow to dereference Follow object for ActivityPub

* Accept IRI as object representation for Accept activity

app/controllers/activitypub/follows_controller.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class ActivityPub::FollowsController < Api::BaseController
+  include SignatureVerification
+
+  def show
+    render(
+      json: FollowRequest.includes(:account).references(:account).find_by!(
+        id: params.require(:id),
+        accounts: { domain: nil, username: params.require(:account_username) },
+        target_account: signed_request_account
+      ),
+      serializer: ActivityPub::FollowSerializer,
+      adapter: ActivityPub::Adapter,
+      content_type: 'application/activity+json'
+    )
+  end
+end

app/lib/activitypub/activity/accept.rb

@@ -2,16 +2,18 @@
 
 class ActivityPub::Activity::Accept < ActivityPub::Activity
   def perform
-    case @object['type']
-    when 'Follow'
-      accept_follow
+    if @object.respond_to?(:[]) &&
+       @object['type'] == 'Follow' && @object['actor'].present?
+      accept_follow_from @object['actor']
+    else
+      accept_follow_object @object
     end
   end
 
   private
 
-  def accept_follow
-    target_account = account_from_uri(target_uri)
+  def accept_follow_from(actor)
+    target_account = account_from_uri(value_or_id(actor))
 
     return if target_account.nil? || !target_account.local?
 
@@ -19,7 +21,8 @@ class ActivityPub::Activity::Accept < ActivityPub::Activity
     follow_request&.authorize!
   end
 
-  def target_uri
-    @target_uri ||= value_or_id(@object['actor'])
+  def accept_follow_object(object)
+    follow_request = ActivityPub::TagManager.instance.uri_to_resource(value_or_id(object), FollowRequest)
+    follow_request&.authorize!
   end
 end

app/lib/activitypub/tag_manager.rb

@@ -28,6 +28,8 @@ class ActivityPub::TagManager
     return target.uri if target.respond_to?(:local?) && !target.local?
 
     case target.object_type
+    when :follow
+      account_follow_url(target.account.username, target)
     when :person
       account_url(target)
     when :note, :comment, :activity
@@ -97,6 +99,12 @@ class ActivityPub::TagManager
       case klass.name
       when 'Account'
         klass.find_local(uri_to_local_id(uri, :username))
+      when 'FollowRequest'
+        params = Rails.application.routes.recognize_path(uri)
+        klass.joins(:account).find_by!(
+          accounts: { domain: nil, username: params[:account_username] },
+          id: params[:id]
+        )
       else
         StatusFinder.new(uri).status
       end

app/models/follow_request.rb

@@ -21,6 +21,10 @@ class FollowRequest < ApplicationRecord
 
   validates :account_id, uniqueness: { scope: :target_account_id }
 
+  def object_type
+    :follow
+  end
+
   def authorize!
     account.follow!(target_account, reblogs: show_reblogs)
     MergeWorker.perform_async(target_account.id, account.id)

app/serializers/activitypub/follow_serializer.rb

@@ -1,11 +1,12 @@
 # frozen_string_literal: true
 
 class ActivityPub::FollowSerializer < ActiveModel::Serializer
-  attributes :id, :type, :actor
+  attributes :type, :actor
+  attribute :id, if: :dereferencable?
   attribute :virtual_object, key: :object
 
   def id
-    [ActivityPub::TagManager.instance.uri_for(object.account), '#follows/', object.id].join
+    ActivityPub::TagManager.instance.uri_for(object)
   end
 
   def type
@@ -19,4 +20,8 @@ class ActivityPub::FollowSerializer < ActiveModel::Serializer
   def virtual_object
     ActivityPub::TagManager.instance.uri_for(object.target_account)
   end
+
+  def dereferencable?
+    object.respond_to?(:object_type)
+  end
 end

app/views/accounts/_header.html.haml

@@ -8,7 +8,7 @@
               = fa_icon 'user-times'
               = t('accounts.unfollow')
           - else
-            = link_to account_follow_path(account), data: { method: :post }, class: 'icon-button' do
+            = link_to account_follows_path(account), data: { method: :post }, class: 'icon-button' do
               = fa_icon 'user-plus'
               = t('accounts.follow')
       - elsif !user_signed_in?

config/routes.rb

@@ -54,7 +54,8 @@ Rails.application.routes.draw do
 
     resources :followers, only: [:index], controller: :follower_accounts
     resources :following, only: [:index], controller: :following_accounts
-    resource :follow, only: [:create], controller: :account_follow
+    resources :follows, only: [:show], module: :activitypub
+    resource :follow, only: [:create], controller: :account_follow, as: :follows
     resource :unfollow, only: [:create], controller: :account_unfollow
     resource :outbox, only: [:show], module: :activitypub
     resource :inbox, only: [:create], module: :activitypub

spec/controllers/activitypub/follows_controller_spec.rb

@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe ActivityPub::FollowsController, type: :controller do
+  let(:follow_request) { Fabricate(:follow_request, account: account) }
+
+  render_views
+
+  context 'with local account' do
+    let(:account) { Fabricate(:account, domain: nil) }
+
+    it 'returns follow request' do
+      signed_request = Request.new(:get, account_follow_url(account, follow_request))
+      signed_request.on_behalf_of(follow_request.target_account)
+      request.headers.merge! signed_request.headers
+
+      get :show, params: { id: follow_request, account_username: account.username }
+
+      expect(body_as_json[:id]).to eq ActivityPub::TagManager.instance.uri_for(follow_request)
+      expect(response).to have_http_status :success
+    end
+
+    it 'returns http 404 without signature' do
+      get :show, params: { id: follow_request, account_username: account.username }
+      expect(response).to have_http_status 404
+    end
+  end
+
+  context 'with remote account' do
+    let(:account) { Fabricate(:account, domain: Faker::Internet.domain_name) }
+
+    it 'returns http 404' do
+      signed_request = Request.new(:get, account_follow_url(account, follow_request))
+      signed_request.on_behalf_of(follow_request.target_account)
+      request.headers.merge! signed_request.headers
+
+      get :show, params: { id: follow_request, account_username: account.username }
+
+      expect(response).to have_http_status 404
+    end
+  end
+end

spec/lib/activitypub/activity/accept_spec.rb

@@ -3,36 +3,49 @@ require 'rails_helper'
 RSpec.describe ActivityPub::Activity::Accept do
   let(:sender)    { Fabricate(:account) }
   let(:recipient) { Fabricate(:account) }
-
-  let(:json) do
-    {
-      '@context': 'https://www.w3.org/ns/activitystreams',
-      id: 'foo',
-      type: 'Accept',
-      actor: ActivityPub::TagManager.instance.uri_for(sender),
-      object: {
-        id: 'bar',
-        type: 'Follow',
-        actor: ActivityPub::TagManager.instance.uri_for(recipient),
-        object: ActivityPub::TagManager.instance.uri_for(sender),
-      },
-    }.with_indifferent_access
-  end
+  let!(:follow_request) { Fabricate(:follow_request, account: recipient, target_account: sender) }
 
   describe '#perform' do
     subject { described_class.new(json, sender) }
 
     before do
-      Fabricate(:follow_request, account: recipient, target_account: sender)
       subject.perform
     end
 
-    it 'creates a follow relationship' do
-      expect(recipient.following?(sender)).to be true
+    context 'with concerete object representation' do
+      let(:json) do
+        {
+          '@context': 'https://www.w3.org/ns/activitystreams',
+          id: 'foo',
+          type: 'Accept',
+          actor: ActivityPub::TagManager.instance.uri_for(sender),
+          object: {
+            type: 'Follow',
+            actor: ActivityPub::TagManager.instance.uri_for(recipient),
+            object: ActivityPub::TagManager.instance.uri_for(sender),
+          },
+        }.with_indifferent_access
+      end
+
+      it 'creates a follow relationship' do
+        expect(recipient.following?(sender)).to be true
+      end
     end
 
-    it 'removes the follow request' do
-      expect(recipient.requested?(sender)).to be false
+    context 'with object represented by id' do
+      let(:json) do
+        {
+          '@context': 'https://www.w3.org/ns/activitystreams',
+          id: 'foo',
+          type: 'Accept',
+          actor: ActivityPub::TagManager.instance.uri_for(sender),
+          object: ActivityPub::TagManager.instance.uri_for(follow_request),
+        }.with_indifferent_access
+      end
+
+      it 'creates a follow relationship' do
+        expect(recipient.following?(sender)).to be true
+      end
     end
   end
 end

spec/models/follow_request_spec.rb

@@ -27,4 +27,12 @@ RSpec.describe FollowRequest, type: :model do
       expect(follow_request.account.muting_reblogs?(target)).to be true
     end
   end
+
+  describe '#object_type' do
+    let(:follow_request) { Fabricate(:follow_request) }
+
+    it 'equals to :follow' do
+      expect(follow_request.object_type).to eq :follow
+    end
+  end
 end