add fetch callbacks

config/initializers/diaspora_federation.rb

@@ -110,6 +110,15 @@ DiasporaFederation.configure do |config|
       # TODO
     end
 
+    on :fetch_public_entity do |entity_type, guid|
+      entity = entity_type.constantize.find_by(guid: guid, public: true)
+      Diaspora::Federation.post(entity) if entity.is_a? Post
+    end
+
+    on :fetch_person_url_to do |diaspora_id, path|
+      Person.find_by(diaspora_handle: diaspora_id).send(:url_to, path)
+    end
+
     on :update_pod do
       # TODO
     end

spec/federation_callbacks_spec.rb

@@ -296,4 +296,57 @@ describe "diaspora federation callbacks" do
       expect(result).to be_falsey
     end
   end
+
+  describe ":fetch_public_entity" do
+    it "fetches a Post" do
+      post = FactoryGirl.create(:status_message, author: alice.person, public: true)
+      entity = DiasporaFederation.callbacks.trigger(:fetch_public_entity, "Post", post.guid)
+
+      expect(entity.guid).to eq(post.guid)
+      expect(entity.author).to eq(alice.diaspora_handle)
+      expect(entity.public).to be_truthy
+    end
+
+    it "fetches a StatusMessage" do
+      post = FactoryGirl.create(:status_message, author: alice.person, public: true)
+      entity = DiasporaFederation.callbacks.trigger(:fetch_public_entity, "StatusMessage", post.guid)
+
+      expect(entity.guid).to eq(post.guid)
+      expect(entity.author).to eq(alice.diaspora_handle)
+      expect(entity.public).to be_truthy
+    end
+
+    it "fetches a Reshare" do
+      post = FactoryGirl.create(:reshare, author: alice.person, public: true)
+      entity = DiasporaFederation.callbacks.trigger(:fetch_public_entity, "Reshare", post.guid)
+
+      expect(entity.guid).to eq(post.guid)
+      expect(entity.author).to eq(alice.diaspora_handle)
+      expect(entity.public).to be_truthy
+    end
+
+    it "does not fetch a private post" do
+      post = FactoryGirl.create(:status_message, author: alice.person, public: false)
+
+      expect(
+        DiasporaFederation.callbacks.trigger(:fetch_public_entity, "StatusMessage", post.guid)
+      ).to be_nil
+    end
+
+    it "returns nil, if the post is unknown" do
+      expect(
+        DiasporaFederation.callbacks.trigger(:fetch_public_entity, "Post", "unknown-guid")
+      ).to be_nil
+    end
+  end
+
+  describe ":fetch_person_url_to" do
+    it "returns the url with with the pod of the person" do
+      person = FactoryGirl.create(:person, url: "https://example.org")
+
+      expect(
+        DiasporaFederation.callbacks.trigger(:fetch_person_url_to, person.diaspora_handle, "/path/on/pod")
+      ).to eq("https://example.org/path/on/pod")
+    end
+  end
 end