FEATURE: Add support for image attachments

app/models/concerns/discourse_activity_pub/ap/identifier_validations.rb

@@ -4,21 +4,16 @@ module AP
     module IdentifierValidations
       extend ActiveSupport::Concern
       include JsonLd
+      include TypeValidations
 
       included do
-        before_validation :ensure_ap_type
         before_validation :ensure_ap_key, if: :local?
         before_validation :ensure_ap_id, if: :local?
 
-        validates :ap_type, presence: true
         validates :ap_key, uniqueness: true, allow_nil: true # foreign objects don't have keys
         validates :ap_id, uniqueness: true, presence: true
       end
 
-      def ap
-        @ap ||= DiscourseActivityPub::AP::Object.get_klass(ap_type)&.new(stored: self)
-      end
-
       def local?
         !!self.local
       end
@@ -27,27 +22,6 @@ def remote?
         !local?
       end
 
-      def _model
-        self.respond_to?(:model) ? self.model : self.actor.model
-      end
-
-      def ensure_ap_type
-        self.ap_type = _model.activity_pub_default_object_type if !self.ap_type
-
-        unless ap
-          self.errors.add(
-            :ap_type,
-            I18n.t(
-              "activerecord.errors.models.discourse_activity_pub_activity.attributes.ap_type.invalid",
-            ),
-          )
-
-          raise ActiveRecord::RecordInvalid
-        end
-
-        self.ap_type = ap.type
-      end
-
       def ensure_ap_key
         self.ap_key = generate_key if !self.ap_key
       end

app/models/concerns/discourse_activity_pub/ap/model_callbacks.rb

@@ -144,6 +144,20 @@ def update_activity_pub_activity_object
         if performing_activity.create? || performing_activity.update?
           performing_activity_object.name = self.activity_pub_name if self.activity_pub_name
           performing_activity_object.content = self.activity_pub_content
+
+          if self.activity_pub_attachments.present?
+            self.activity_pub_attachments.each do |attachment|
+              performing_activity_object.attachments.build(
+                object_id: performing_activity_object.id,
+                object_type: performing_activity_object.class.name,
+                ap_type: attachment.type,
+                url: attachment.url.href,
+                name: attachment.name,
+                media_type: attachment.media_type,
+              )
+            end
+          end
+
           performing_activity_object.save!
         end
       end

app/models/concerns/discourse_activity_pub/ap/type_validations.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+module DiscourseActivityPub
+  module AP
+    module TypeValidations
+      extend ActiveSupport::Concern
+
+      included do
+        before_validation :ensure_ap_type
+        validates :ap_type, presence: true
+      end
+
+      def ap
+        @ap ||= DiscourseActivityPub::AP::Object.get_klass(ap_type)&.new(stored: self)
+      end
+
+      def _model
+        self.respond_to?(:model) ? self.model : self.actor.model
+      end
+
+      def ensure_ap_type
+        self.ap_type = _model.activity_pub_default_object_type if !self.ap_type && _model.present?
+
+        unless ap
+          self.errors.add(
+            :ap_type,
+            I18n.t(
+              "activerecord.errors.models.discourse_activity_pub_activity.attributes.ap_type.invalid",
+            ),
+          )
+
+          raise ActiveRecord::RecordInvalid
+        end
+
+        self.ap_type = ap.type
+      end
+    end
+  end
+end

app/models/discourse_activity_pub_attachment.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+class DiscourseActivityPubAttachment < ActiveRecord::Base
+  include DiscourseActivityPub::AP::TypeValidations
+  include DiscourseActivityPub::AP::ObjectValidations
+
+  belongs_to :object, class_name: "DiscourseActivityPubObject", polymorphic: true
+
+  validate :validate_media_type
+
+  protected
+
+  def validate_media_type
+    unless MiniMime.lookup_by_content_type(self.media_type)
+      self.errors.add(
+        :media_type,
+        I18n.t(
+          "activerecord.errors.models.discourse_activity_pub_attachment.attributes.media_type.invalid",
+        ),
+      )
+      raise ActiveRecord::RecordInvalid
+    end
+  end
+end
+
+# == Schema Information
+#
+# Table name: discourse_activity_pub_attachments
+#
+#  id          :bigint           not null, primary key
+#  ap_type     :string           not null
+#  object_id   :bigint           not null
+#  object_type :string           not null
+#  url         :string
+#  name        :string
+#  media_type  :string(200)
+#  created_at  :datetime         not null
+#  updated_at  :datetime         not null
+#

app/models/discourse_activity_pub_object.rb

@@ -7,12 +7,21 @@ class DiscourseActivityPubObject < ActiveRecord::Base
 
   belongs_to :model, -> { unscope(where: :deleted_at) }, polymorphic: true, optional: true
   belongs_to :collection, class_name: "DiscourseActivityPubCollection", foreign_key: "collection_id"
+  belongs_to :reply_to,
+             class_name: "DiscourseActivityPubObject",
+             primary_key: "ap_id",
+             foreign_key: "reply_to_id"
+  belongs_to :attributed_to,
+             class_name: "DiscourseActivityPubActor",
+             primary_key: "ap_id",
+             foreign_key: "attributed_to_id"
 
-  has_many :activities, class_name: "DiscourseActivityPubActivity", foreign_key: "object_id"
   has_one :create_activity,
           -> { where(ap_type: DiscourseActivityPub::AP::Activity::Create.type) },
           class_name: "DiscourseActivityPubActivity",
           foreign_key: "object_id"
+
+  has_many :activities, class_name: "DiscourseActivityPubActivity", foreign_key: "object_id"
   has_many :announcements,
            class_name: "DiscourseActivityPubActivity",
            through: :activities,
@@ -21,20 +30,11 @@ class DiscourseActivityPubObject < ActiveRecord::Base
            -> { likes },
            class_name: "DiscourseActivityPubActivity",
            foreign_key: "object_id"
-
-  belongs_to :reply_to,
-             class_name: "DiscourseActivityPubObject",
-             primary_key: "ap_id",
-             foreign_key: "reply_to_id"
   has_many :replies,
            class_name: "DiscourseActivityPubObject",
            primary_key: "ap_id",
            foreign_key: "reply_to_id"
-
-  belongs_to :attributed_to,
-             class_name: "DiscourseActivityPubActor",
-             primary_key: "ap_id",
-             foreign_key: "attributed_to_id"
+  has_many :attachments, class_name: "DiscourseActivityPubAttachment", foreign_key: "object_id"
 
   def url
     if local?
@@ -159,6 +159,10 @@ def attributed_to
     end
   end
 
+  def attachment
+    self.attachments
+  end
+
   def likes_collection
     @likes_collection ||=
       begin

app/serializers/discourse_activity_pub/ap/object/article_serializer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class DiscourseActivityPub::AP::Object::ArticleSerializer < DiscourseActivityPub::AP::ObjectSerializer
-  attributes :content, :inReplyTo, :url, :updated
+  attributes :content, :inReplyTo, :url, :updated, :attachment
 
   def inReplyTo
     object.in_reply_to
@@ -18,4 +18,12 @@ def include_content?
   def deleted?
     !object.stored.model || object.stored.model.trashed?
   end
+
+  def attachment
+    object.attachment.map(&:json)
+  end
+
+  def include_attachment?
+    object.attachment.present?
+  end
 end

app/serializers/discourse_activity_pub/ap/object/document_serializer.rb

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+class DiscourseActivityPub::AP::Object::DocumentSerializer < DiscourseActivityPub::AP::ObjectSerializer
+  attributes :media_type
+end

app/serializers/discourse_activity_pub/ap/object/image_serializer.rb

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+class DiscourseActivityPub::AP::Object::ImageSerializer < DiscourseActivityPub::AP::ObjectSerializer
+  attributes :media_type
+end

app/serializers/discourse_activity_pub/ap/object/note_serializer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class DiscourseActivityPub::AP::Object::NoteSerializer < DiscourseActivityPub::AP::ObjectSerializer
-  attributes :content, :inReplyTo, :context
+  attributes :content, :inReplyTo, :context, :attachment
 
   def content
     content = object.content
@@ -30,4 +30,12 @@ def include_content?
   def deleted?
     !object.stored.model || object.stored.model.trashed?
   end
+
+  def attachment
+    object.attachment.map(&:json)
+  end
+
+  def include_attachment?
+    object.attachment.present?
+  end
 end

app/serializers/discourse_activity_pub/ap/object_serializer.rb

@@ -20,8 +20,9 @@ def attributes(*args)
     hash
   end
 
-  def context
-    object.context
+  def include_id?
+    return false if object.attachment?
+    object.id.present?
   end
 
   def include_context?

config/locales/server.en.yml

@@ -21,6 +21,10 @@ en:
             credentials:
               required: "are required"
               invalid: "is not valid"
+        discourse_activity_pub_attachment:
+          attributes:
+            media_type:
+              invalid: "is not valid"
         discourse_activity_pub:
           attributes:
             model_type:

db/migrate/20250319134150_create_discourse_activity_pub_attachments.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+class CreateDiscourseActivityPubAttachments < ActiveRecord::Migration[7.2]
+  def change
+    create_table :discourse_activity_pub_attachments do |t|
+      t.string :ap_type, null: false
+      t.bigint :object_id, null: false
+      t.string :object_type, null: false
+      t.string :url
+      t.string :name
+      t.string :media_type, limit: 200
+
+      t.timestamps
+    end
+  end
+end

lib/discourse_activity_pub/ap/link.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+module DiscourseActivityPub
+  module AP
+    class Link
+      attr_accessor :value
+
+      def initialize(value = nil)
+        @value = value
+      end
+
+      def type
+        "Link"
+      end
+
+      def href
+        return value if value.is_a?(String)
+        value[:href] if value.is_a?(Hash)
+      end
+
+      def media_type
+        value[:mediaType] if value.is_a?(Hash)
+      end
+
+      def name
+        value[:name] if value.is_a?(Hash)
+      end
+    end
+  end
+end

lib/discourse_activity_pub/ap/object.rb

@@ -7,6 +7,8 @@ class Object
       include HasErrors
       include Handlers
 
+      ATTACHMENT_TYPES = %w[Image Document]
+
       attr_writer :json
       attr_writer :attributed_to
       attr_writer :context
@@ -50,8 +52,16 @@ def actor?
         base_type == "Actor"
       end
 
+      def attachment?
+        ATTACHMENT_TYPES.include?(type)
+      end
+
       def url
-        stored.respond_to?(:url) && stored&.url
+        if stored
+          stored.respond_to?(:url) && stored&.url
+        elsif json.present?
+          Link.new(json[:url])
+        end
       end
 
       def audience
@@ -95,7 +105,11 @@ def summary
       end
 
       def name
-        stored.respond_to?(:name) && stored&.name
+        if stored.present?
+          stored.respond_to?(:name) && stored&.name
+        elsif json.present?
+          json[:name]
+        end
       end
 
       def context
@@ -110,6 +124,17 @@ def delivered_to
         @delivered_to ||= []
       end
 
+      def attachment
+        if stored.respond_to?(:attachment)
+          @attachment ||= (stored.attachment || []).map { |a| a.ap }
+        elsif json.present? && json[:attachment].present?
+          json[:attachment].each_with_object([]) do |attachment_json, result|
+            obj = AP::Object.factory(attachment_json)
+            result << obj if obj.present?
+          end
+        end
+      end
+
       def cache
         @cache ||= {}
       end