Add support for dereferencing objects through bearcaps (mastodon#14683)

app/lib/activitypub/activity.rb

@@ -71,7 +71,15 @@ def account_from_uri(uri)
   end
 
   def object_uri
-    @object_uri ||= value_or_id(@object)
+    @object_uri ||= begin
+      str = value_or_id(@object)
+
+      if str.start_with?('bear:')
+        Addressable::URI.parse(str).query_values['u']
+      else
+        str
+      end
+    end
   end
 
   def unsupported_object_type?
@@ -159,12 +167,10 @@ def status_from_object
 
   def dereference_object!
     return unless @object.is_a?(String)
-    return if invalid_origin?(@object)
 
-    object = fetch_resource(@object, true, signed_fetch_account)
-    return unless object.present? && object.is_a?(Hash) && supported_context?(object)
+    dereferencer = ActivityPub::Dereferencer.new(@object, permitted_origin: @account.uri, signature_account: signed_fetch_account)
 
-    @object = object
+    @object = dereferencer.object unless dereferencer.object.nil?
   end
 
   def signed_fetch_account

app/lib/activitypub/activity/create.rb

@@ -15,7 +15,7 @@ def perform
   private
 
   def create_encrypted_message
-    return reject_payload! if invalid_origin?(@object['id']) || @options[:delivered_to_account_id].blank?
+    return reject_payload! if invalid_origin?(object_uri) || @options[:delivered_to_account_id].blank?
 
     target_account = Account.find(@options[:delivered_to_account_id])
     target_device  = target_account.devices.find_by(device_id: @object.dig('to', 'deviceId'))
@@ -43,7 +43,7 @@ def message_franking
   end
 
   def create_status
-    return reject_payload! if unsupported_object_type? || invalid_origin?(@object['id']) || Tombstone.exists?(uri: @object['id']) || !related_to_local_activity?
+    return reject_payload! if unsupported_object_type? || invalid_origin?(object_uri) || tombstone_exists? || !related_to_local_activity?
 
     RedisLock.acquire(lock_options) do |lock|
       if lock.acquired?
@@ -90,7 +90,7 @@ def process_status
     fetch_replies(@status)
     check_for_spam
     distribute(@status)
-    forward_for_reply if @status.distributable?
+    forward_for_reply
   end
 
   def find_existing_status
@@ -102,8 +102,8 @@ def find_existing_status
   def process_status_params
     @params = begin
       {
-        uri: @object['id'],
-        url: object_url || @object['id'],
+        uri: object_uri,
+        url: object_url || object_uri,
         account: @account,
         text: text_from_content || '',
         language: detected_language,
@@ -313,7 +313,7 @@ def poll_vote!
     RedisLock.acquire(poll_lock_options) do |lock|
       if lock.acquired?
         already_voted = poll.votes.where(account: @account).exists?
-        poll.votes.create!(account: @account, choice: poll.options.index(@object['name']), uri: @object['id'])
+        poll.votes.create!(account: @account, choice: poll.options.index(@object['name']), uri: object_uri)
       else
         raise Mastodon::RaceConditionError
       end
@@ -385,7 +385,7 @@ def in_reply_to_uri
   end
 
   def text_from_content
-    return Formatter.instance.linkify([[text_from_name, text_from_summary.presence].compact.join("\n\n"), object_url || @object['id']].join(' ')) if converted_object_type?
+    return Formatter.instance.linkify([[text_from_name, text_from_summary.presence].compact.join("\n\n"), object_url || object_uri].join(' ')) if converted_object_type?
 
     if @object['content'].present?
       @object['content']
@@ -484,12 +484,16 @@ def addresses_local_accounts?
     Account.local.where(username: local_usernames).exists?
   end
 
+  def tombstone_exists?
+    Tombstone.exists?(uri: object_uri)
+  end
+
   def check_for_spam
     SpamCheck.perform(@status)
   end
 
   def forward_for_reply
-    return unless @json['signature'].present? && reply_to_local?
+    return unless @status.distributable? && @json['signature'].present? && reply_to_local?
 
     ActivityPub::RawDistributionWorker.perform_async(Oj.dump(@json), replied_to_status.account_id, [@account.preferred_inbox_url])
   end
@@ -507,7 +511,7 @@ def increment_voters_count!
   end
 
   def lock_options
-    { redis: Redis.current, key: "create:#{@object['id']}" }
+    { redis: Redis.current, key: "create:#{object_uri}" }
   end
 
   def poll_lock_options

app/lib/activitypub/dereferencer.rb

@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+class ActivityPub::Dereferencer
+  include JsonLdHelper
+
+  def initialize(uri, permitted_origin: nil, signature_account: nil)
+    @uri               = uri
+    @permitted_origin  = permitted_origin
+    @signature_account = signature_account
+  end
+
+  def object
+    @object ||= fetch_object!
+  end
+
+  private
+
+  def bear_cap?
+    @uri.start_with?('bear:')
+  end
+
+  def fetch_object!
+    if bear_cap?
+      fetch_with_token!
+    else
+      fetch_with_signature!
+    end
+  end
+
+  def fetch_with_token!
+    perform_request(bear_cap['u'], headers: { 'Authorization' => "Bearer #{bear_cap['t']}" })
+  end
+
+  def fetch_with_signature!
+    perform_request(@uri)
+  end
+
+  def bear_cap
+    @bear_cap ||= Addressable::URI.parse(@uri).query_values
+  end
+
+  def perform_request(uri, headers: nil)
+    return if invalid_origin?(uri)
+
+    req = Request.new(:get, uri)
+
+    req.add_headers('Accept' => 'application/activity+json, application/ld+json')
+    req.add_headers(headers) if headers
+    req.on_behalf_of(@signature_account) if @signature_account
+
+    req.perform do |res|
+      if res.code == 200
+        json = body_to_json(res.body_with_limit)
+        json if json.present? && json['id'] == uri
+      else
+        raise Mastodon::UnexpectedResponseError, res unless response_successful?(res) || response_error_unsalvageable?(res)
+      end
+    end
+  end
+
+  def invalid_origin?(uri)
+    return true if unsupported_uri_scheme?(uri)
+
+    needle   = Addressable::URI.parse(uri).host
+    haystack = Addressable::URI.parse(@permitted_origin).host
+
+    !haystack.casecmp(needle).zero?
+  end
+end

spec/lib/activitypub/dereferencer_spec.rb

@@ -0,0 +1,73 @@
+require 'rails_helper'
+
+RSpec.describe ActivityPub::Dereferencer do
+  describe '#object' do
+    let(:object) { { '@context': 'https://www.w3.org/ns/activitystreams', id: 'https://example.com/foo', type: 'Note', content: 'Hoge' } }
+    let(:permitted_origin) { 'https://example.com' }
+    let(:signature_account) { nil }
+    let(:uri) { nil }
+
+    subject { described_class.new(uri, permitted_origin: permitted_origin, signature_account: signature_account).object }
+
+    before do
+      stub_request(:get, 'https://example.com/foo').to_return(body: Oj.dump(object), headers: { 'Content-Type' => 'application/activity+json' })
+    end
+
+    context 'with a URI' do
+      let(:uri) { 'https://example.com/foo' }
+
+      it 'returns object' do
+        expect(subject.with_indifferent_access).to eq object.with_indifferent_access
+      end
+
+      context 'with signature account' do
+        let(:signature_account) { Fabricate(:account) }
+
+        it 'makes signed request' do
+          subject
+          expect(a_request(:get, 'https://example.com/foo').with { |req| req.headers['Signature'].present? }).to have_been_made
+        end
+      end
+
+      context 'with different origin' do
+        let(:uri) { 'https://other-example.com/foo' }
+
+        it 'does not make request' do
+          subject
+          expect(a_request(:get, 'https://other-example.com/foo')).to_not have_been_made
+        end
+      end
+    end
+
+    context 'with a bearcap' do
+      let(:uri) { 'bear:?t=hoge&u=https://example.com/foo' }
+
+      it 'makes request with Authorization header' do
+        subject
+        expect(a_request(:get, 'https://example.com/foo').with(headers: { 'Authorization' => 'Bearer hoge' })).to have_been_made
+      end
+
+      it 'returns object' do
+        expect(subject.with_indifferent_access).to eq object.with_indifferent_access
+      end
+
+      context 'with signature account' do
+        let(:signature_account) { Fabricate(:account) }
+
+        it 'makes signed request' do
+          subject
+          expect(a_request(:get, 'https://example.com/foo').with { |req| req.headers['Signature'].present? && req.headers['Authorization'] == 'Bearer hoge' }).to have_been_made
+        end
+      end
+
+      context 'with different origin' do
+        let(:uri) { 'bear:?t=hoge&u=https://other-example.com/foo' }
+
+        it 'does not make request' do
+          subject
+          expect(a_request(:get, 'https://other-example.com/foo')).to_not have_been_made
+        end
+      end
+    end
+  end
+end