Add GET endpoints for remote subscription forms

There are two reasons for adding a GET endpoint:

0: Barely displaying the form does not change anything on the server.

1: It makes frontend development easier as they can now use a link,
instead of a form, to allow remote users to interact with local ones.

lib/pleroma/web/api_spec/operations/twitter_util_operation.ex

@@ -405,6 +405,16 @@ defmodule Pleroma.Web.ApiSpec.TwitterUtilOperation do
     }
   end
 
+  def show_subscribe_form_operation do
+    %Operation{
+      tags: ["Accounts"],
+      summary: "Show remote subscribe form",
+      operationId: "UtilController.show_subscribe_form",
+      parameters: [],
+      responses: %{200 => Operation.response("Web Page", "test/html", %Schema{type: :string})}
+    }
+  end
+
   defp delete_account_request do
     %Schema{
       title: "AccountDeleteRequest",

lib/pleroma/web/router.ex

@@ -337,6 +337,7 @@ defmodule Pleroma.Web.Router do
     pipe_through(:pleroma_html)
 
     post("/main/ostatus", UtilController, :remote_subscribe)
+    get("/main/ostatus", UtilController, :show_subscribe_form)
     get("/ostatus_subscribe", RemoteFollowController, :follow)
     post("/ostatus_subscribe", RemoteFollowController, :do_follow)
   end

lib/pleroma/web/twitter_api/controllers/util_controller.ex

@@ -17,8 +17,8 @@ defmodule Pleroma.Web.TwitterAPI.UtilController do
   alias Pleroma.Web.Plugs.OAuthScopesPlug
   alias Pleroma.Web.WebFinger
 
-  plug(Pleroma.Web.ApiSpec.CastAndValidate when action != :remote_subscribe)
+  plug(Pleroma.Web.ApiSpec.CastAndValidate when action != :remote_subscribe and action != :show_subscribe_form)
-  plug(Pleroma.Web.Plugs.FederatingPlug when action == :remote_subscribe)
+  plug(Pleroma.Web.Plugs.FederatingPlug when action == :remote_subscribe when action == :show_subscribe_form)
 
   plug(
     OAuthScopesPlug,
@@ -45,7 +45,7 @@ defmodule Pleroma.Web.TwitterAPI.UtilController do
 
   defdelegate open_api_operation(action), to: Pleroma.Web.ApiSpec.TwitterUtilOperation
 
-  def remote_subscribe(conn, %{"nickname" => nick, "profile" => _}) do
+  def show_subscribe_form(conn, %{"nickname" => nick}) do
     with %User{} = user <- User.get_cached_by_nickname(nick),
          avatar = User.avatar_url(user) do
       conn
@@ -60,7 +60,7 @@ defmodule Pleroma.Web.TwitterAPI.UtilController do
     end
   end
 
-  def remote_subscribe(conn, %{"status_id" => id, "profile" => _}) do
+  def show_subscribe_form(conn, %{"status_id" => id}) do
     with %Activity{} = activity <- Activity.get_by_id(id),
          %User{} = user <- User.get_cached_by_ap_id(activity.actor),
          avatar = User.avatar_url(user) do
@@ -81,6 +81,14 @@ defmodule Pleroma.Web.TwitterAPI.UtilController do
     end
   end
 
+  def remote_subscribe(conn, %{"nickname" => nick, "profile" => _}) do
+    show_subscribe_form(conn, %{"nickname" => nick})
+  end
+
+  def remote_subscribe(conn, %{"status_id" => id, "profile" => _}) do
+    show_subscribe_form(conn, %{"status_id" => id})
+  end
+
   def remote_subscribe(conn, %{"user" => %{"nickname" => nick, "profile" => profile}}) do
     with {:ok, %{"subscribe_address" => template}} <- WebFinger.finger(profile),
          %User{ap_id: ap_id} <- User.get_cached_by_nickname(nick) do

test/pleroma/web/twitter_api/util_controller_test.exs

@@ -297,6 +297,38 @@ defmodule Pleroma.Web.TwitterAPI.UtilControllerTest do
     end
   end
 
+  describe "GET /main/ostatus - show_subscribe_form/2" do
+    setup do: clear_config([:instance, :federating], true)
+
+    test "it works with users", %{conn: conn} do
+      user = insert(:user)
+
+      response =
+        conn
+        |> get("/main/ostatus", %{"nickname" => user.nickname})
+        |> response(:ok)
+
+      refute response =~ "Could not find user"
+      assert response =~ "Remotely follow #{user.nickname}"
+    end
+
+    test "it works with statuses", %{conn: conn} do
+      user = insert(:user)
+      status = insert(:note_activity, %{user: user})
+      status_id = status.id
+
+      assert is_binary(status_id)
+
+      response =
+        conn
+        |> get("/main/ostatus", %{"status_id" => status_id})
+        |> response(:ok)
+
+      refute response =~ "Could not find status"
+      assert response =~ "Interacting with"
+    end
+  end
+
   test "it returns new captcha", %{conn: conn} do
     with_mock Pleroma.Captcha,
       new: fn -> "test_captcha" end do