Add metadata provider for ActivityPub alternate links

Signed-off-by: marcin mikołajczak <git@mkljczk.pl>

changelog.d/activity-pub-metadata.add

@@ -0,0 +1 @@
+Add metadata provider for ActivityPub alternate links

lib/pleroma/web/metadata.ex

@@ -7,6 +7,7 @@ defmodule Pleroma.Web.Metadata do
 
   def build_tags(params) do
     providers = [
+      Pleroma.Web.Metadata.Providers.ActivityPub,
       Pleroma.Web.Metadata.Providers.RelMe,
       Pleroma.Web.Metadata.Providers.RestrictIndexing
       | activated_providers()

lib/pleroma/web/metadata/providers/activity_pub.ex

@@ -0,0 +1,19 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2024 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.Metadata.Providers.ActivityPub do
+  alias Pleroma.Web.Metadata.Providers.Provider
+
+  @behaviour Provider
+
+  @impl Provider
+  def build_tags(%{object: %{data: %{"id" => object_id}}}) do
+    [{:link, [rel: "alternate", type: "application/activity+json", href: object_id], []}]
+  end
+
+  @impl Provider
+  def build_tags(%{user: user}) do
+    [{:link, [rel: "alternate", type: "application/activity+json", href: user.ap_id], []}]
+  end
+end

test/pleroma/web/metadata/providers/activity_pub_test.exs

@@ -0,0 +1,34 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2024 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.Metadata.Providers.ActivityPubTest do
+  use Pleroma.DataCase
+  import Pleroma.Factory
+
+  alias Pleroma.Web.CommonAPI
+  alias Pleroma.Web.Metadata.Providers.ActivityPub
+
+  setup do: clear_config([Pleroma.Web.Metadata, :unfurl_nsfw])
+
+  test "it renders a link for user info" do
+    user = insert(:user)
+    res = ActivityPub.build_tags(%{user: user})
+
+    assert res == [
+             {:link, [rel: "alternate", type: "application/activity+json", href: user.ap_id], []}
+           ]
+  end
+
+  test "it renders a link for a post" do
+    user = insert(:user)
+    {:ok, %{id: activity_id, object: object}} = CommonAPI.post(user, %{status: "hi"})
+
+    result = ActivityPub.build_tags(%{object: object, user: user, activity_id: activity_id})
+
+    assert [
+             {:link,
+              [rel: "alternate", type: "application/activity+json", href: object.data["id"]], []}
+           ] == result
+  end
+end