Change GET /invite/:invite_code to return a JSON document when JSON is requested

app/controllers/api/v1/invites_controller.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+class Api::V1::InvitesController < Api::BaseController
+  include RegistrationHelper
+
+  skip_before_action :require_authenticated_user!
+  skip_around_action :set_locale
+
+  before_action :set_invite
+  before_action :check_enabled_registrations!
+
+  # Override `current_user` to avoid reading session cookies
+  def current_user; end
+
+  def show
+    render json: { invite_code: params[:invite_code], instance_api_url: api_v2_instance_url }, status: 200
+  end
+
+  private
+
+  def set_invite
+    @invite = Invite.find_by!(code: params[:invite_code])
+  end
+
+  def check_enabled_registrations!
+    return render json: { error: I18n.t('invites.invalid') }, status: 401 unless @invite.valid_for_use?
+
+    raise Mastodon::NotPermittedError unless allowed_registration?(request.remote_ip, @invite)
+  end
+end

config/locales/en.yml

@@ -1368,6 +1368,7 @@ en:
       '86400': 1 day
     expires_in_prompt: Never
     generate: Generate invite link
+    invalid: This invite is not valid
     invited_by: 'You were invited by:'
     max_uses:
       one: 1 use

config/routes.rb

@@ -81,6 +81,8 @@ Rails.application.routes.draw do
     resource :outbox, only: [:show], module: :activitypub
   end
 
+  get '/invite/:invite_code', constraints: ->(req) { req.format == :json }, to: 'api/v1/invites#show'
+
   devise_scope :user do
     get '/invite/:invite_code', to: 'auth/registrations#new', as: :public_invite
 

spec/requests/invite_spec.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe 'invites' do
+  let(:invite) { Fabricate(:invite) }
+
+  context 'when requesting a JSON document' do
+    it 'returns a JSON document with expected attributes' do
+      get "/invite/#{invite.code}", headers: { 'Accept' => 'application/activity+json' }
+
+      expect(response).to have_http_status(200)
+      expect(response.media_type).to eq 'application/json'
+
+      expect(body_as_json[:invite_code]).to eq invite.code
+    end
+  end
+
+  context 'when not requesting a JSON document' do
+    it 'returns an HTML page' do
+      get "/invite/#{invite.code}"
+
+      expect(response).to have_http_status(200)
+      expect(response.media_type).to eq 'text/html'
+    end
+  end
+end