Add support for FEP-2c59 (#38239)

app/helpers/context_helper.rb

@@ -4,6 +4,7 @@ module ContextHelper
   NAMED_CONTEXT_MAP = {
     activitystreams: 'https://www.w3.org/ns/activitystreams',
     security: 'https://w3id.org/security/v1',
+    webfinger: 'https://purl.archive.org/socialweb/webfinger',
   }.freeze
 
   CONTEXT_EXTENSION_MAP = {

app/serializers/activitypub/actor_serializer.rb

@@ -4,7 +4,7 @@ class ActivityPub::ActorSerializer < ActivityPub::Serializer
   include RoutingHelper
   include FormattingHelper
 
-  context :security
+  context :security, :webfinger
 
   context_extensions :manually_approves_followers, :featured, :also_known_as,
                      :moved_to, :property_value, :discoverable, :suspended,
@@ -55,6 +55,10 @@ class ActivityPub::ActorSerializer < ActivityPub::Serializer
     ActivityPub::TagManager.instance.uri_for(object)
   end
 
+  def webfinger
+    object.local_username_and_domain
+  end
+
   def type
     if object.instance_actor?
       'Application'

app/services/activitypub/fetch_remote_actor_service.rb

@@ -27,11 +27,23 @@ class ActivityPub::FetchRemoteActorService < BaseService
     raise Error, "Unsupported JSON-LD context for document #{uri}" unless supported_context?
     raise Error, "Unexpected object type for actor #{uri} (expected any of: #{SUPPORTED_TYPES})" unless expected_type?
     raise Error, "Actor #{uri} has moved to #{@json['movedTo']}" if break_on_redirect && @json['movedTo'].present?
-    raise Error, "Actor #{uri} has no 'preferredUsername', which is a requirement for Mastodon compatibility" if @json['preferredUsername'].blank?
+    raise Error, "Actor #{uri} has neither 'preferredUsername' nor `webfinger`, which is a requirement for Mastodon compatibility" if @json['preferredUsername'].blank? && @json['webfinger'].blank?
 
-    @uri      = @json['id']
-    @username = @json['preferredUsername']
-    @domain   = Addressable::URI.parse(@uri).normalized_host
+    @uri = @json['id']
+
+    # FEP-2c59 defines a `webfinger` attribute that makes things more explicit and spares an extra request in some cases.
+    # It supersedes `preferredUsername`.
+    if @json['webfinger'].present? && @json['webfinger'].is_a?(String)
+      @username, @domain = split_acct(@json['webfinger'])
+      Rails.logger.debug { "Actor #{uri} has an invalid `webfinger` value, falling back to `preferredUsername`" }
+    end
+
+    if @username.blank? || @domain.blank?
+      raise "Actor #{uri} has no `preferredUsername`, and either a bogus or missing `webfinger`, which is a requirement for Mastodon compatibility" if @json['preferredUsername'].blank?
+
+      @username = @json['preferredUsername']
+      @domain   = Addressable::URI.parse(@uri).normalized_host
+    end
 
     check_webfinger! unless only_key
 

config/initializers/json_ld_webfinger.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require 'json/ld'
+
+class JSON::LD::Context
+  add_preloaded("http://purl.archive.org/socialweb/webfinger") do
+    new(processingMode: "json-ld-1.0", term_definitions: {
+      "webfinger" => TermDefinition.new("webfinger", id: "https://purl.archive.org/socialweb/webfinger#webfinger", type_mapping: "http://www.w3.org/2001/XMLSchema#string"),
+      "wf" => TermDefinition.new("wf", id: "https://purl.archive.org/socialweb/webfinger#", simple: true, prefix: true),
+      "xsd" => TermDefinition.new("xsd", id: "http://www.w3.org/2001/XMLSchema#", simple: true, prefix: true)
+    })
+  end
+  alias_preloaded("https://purl.archive.org/socialweb/webfinger", "http://purl.archive.org/socialweb/webfinger")
+end

spec/services/activitypub/fetch_remote_actor_service_spec.rb

@@ -133,5 +133,97 @@ RSpec.describe ActivityPub::FetchRemoteActorService do
         expect(subject.call('https://fake.address/@foo', prefetched_body: actor.to_json)).to be_nil
       end
     end
+
+    context 'when the actor uses the webfinger propery from FEP-2c59' do
+      before do
+        actor[:webfinger] = acct
+      end
+
+      context 'when URI and WebFinger share the same host' do
+        let(:acct) { 'alice@example.com' }
+        let!(:webfinger) { { subject: "acct:#{acct}", links: [{ rel: 'self', href: 'https://example.com/alice', type: 'application/activity+json' }] } }
+
+        before do
+          stub_request(:get, 'https://example.com/alice').to_return(body: actor.to_json, headers: { 'Content-Type': 'application/activity+json' })
+          stub_request(:get, "https://example.com/.well-known/webfinger?resource=acct:#{acct}").to_return(body: webfinger.to_json, headers: { 'Content-Type': 'application/jrd+json' })
+        end
+
+        it 'fetches resource and looks up webfinger and sets values' do
+          account
+
+          expect(a_request(:get, 'https://example.com/alice')).to have_been_made.once
+          expect(a_request(:get, "https://example.com/.well-known/webfinger?resource=acct:#{acct}")).to have_been_made.once
+
+          expect(account.username).to eq 'alice'
+          expect(account.domain).to eq 'example.com'
+        end
+
+        it_behaves_like 'sets profile data'
+      end
+
+      context 'when WebFinger returns a different URI' do
+        let(:acct) { 'alice@example.com' }
+        let!(:webfinger) { { subject: "acct:#{acct}", links: [{ rel: 'self', href: 'https://example.com/bob', type: 'application/activity+json' }] } }
+
+        before do
+          stub_request(:get, 'https://example.com/alice').to_return(body: actor.to_json, headers: { 'Content-Type': 'application/activity+json' })
+          stub_request(:get, "https://example.com/.well-known/webfinger?resource=acct:#{acct}").to_return(body: webfinger.to_json, headers: { 'Content-Type': 'application/jrd+json' })
+        end
+
+        it 'fetches resource and looks up webfinger and does not create account' do
+          expect(account).to be_nil
+
+          expect(a_request(:get, 'https://example.com/alice')).to have_been_made.once
+          expect(a_request(:get, "https://example.com/.well-known/webfinger?resource=acct:#{acct}")).to have_been_made.once
+        end
+      end
+
+      context 'when WebFinger is at another domain' do
+        let(:acct) { 'alice@iscool.af' }
+        let!(:webfinger) { { subject: "acct:#{acct}", links: [{ rel: 'self', href: 'https://example.com/alice', type: 'application/activity+json' }] } }
+
+        before do
+          stub_request(:get, 'https://example.com/alice').to_return(body: actor.to_json, headers: { 'Content-Type': 'application/activity+json' })
+          stub_request(:get, "https://iscool.af/.well-known/webfinger?resource=acct:#{acct}").to_return(body: webfinger.to_json, headers: { 'Content-Type': 'application/jrd+json' })
+        end
+
+        it 'fetches resource and looks up webfinger and follows redirect and sets values' do
+          account
+
+          expect(a_request(:get, 'https://example.com/alice')).to have_been_made.once
+          expect(a_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com')).to_not have_been_made
+          expect(a_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af')).to have_been_made.once
+
+          expect(account.username).to eq 'alice'
+          expect(account.domain).to eq 'iscool.af'
+        end
+
+        it_behaves_like 'sets profile data'
+      end
+
+      context 'when WebFinger is at another domain and redirects back' do
+        let(:acct) { 'alice@iscool.af' }
+        let!(:webfinger) { { subject: 'acct:alice@example.com', links: [{ rel: 'self', href: 'https://example.com/alice', type: 'application/activity+json' }] } }
+
+        before do
+          stub_request(:get, 'https://example.com/alice').to_return(body: actor.to_json, headers: { 'Content-Type': 'application/activity+json' })
+          stub_request(:get, "https://iscool.af/.well-known/webfinger?resource=acct:#{acct}").to_return(body: webfinger.to_json, headers: { 'Content-Type': 'application/jrd+json' })
+          stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: webfinger.to_json, headers: { 'Content-Type': 'application/jrd+json' })
+        end
+
+        it 'fetches resource and looks up webfinger and follows redirect and sets values' do
+          account
+
+          expect(a_request(:get, 'https://example.com/alice')).to have_been_made.once
+          expect(a_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af')).to have_been_made.once
+          expect(a_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com')).to have_been_made
+
+          expect(account.username).to eq 'alice'
+          expect(account.domain).to eq 'example.com'
+        end
+
+        it_behaves_like 'sets profile data'
+      end
+    end
   end
 end