Add a `remote_mirrors` project API

This API can be used to gather information on a project's push mirrors
and their status.

lib/api/api.rb

@@ -156,6 +156,7 @@ module API
     mount ::API::ProtectedTags
     mount ::API::Releases
     mount ::API::Release::Links
+    mount ::API::RemoteMirrors
     mount ::API::Repositories
     mount ::API::Runner
     mount ::API::Runners

lib/api/entities.rb

@@ -166,6 +166,18 @@ module API
       end
     end
 
+    class RemoteMirror < Grape::Entity
+      expose :id
+      expose :enabled
+      expose :safe_url, as: :url
+      expose :update_status
+      expose :last_update_at
+      expose :last_update_started_at
+      expose :last_successful_update_at
+      expose :last_error
+      expose :only_protected_branches
+    end
+
     class ProjectImportStatus < ProjectIdentity
       expose :import_status
 

lib/api/remote_mirrors.rb

+# frozen_string_literal: true
+
+module API
+  class RemoteMirrors < Grape::API
+    include PaginationParams
+
+    before do
+      # TODO: Remove flag: https://gitlab.com/gitlab-org/gitlab/issues/38121
+      not_found! unless Feature.enabled?(:remote_mirrors_api, user_project)
+    end
+
+    params do
+      requires :id, type: String, desc: 'The ID of a project'
+    end
+    resource :projects, requirements: API::NAMESPACE_OR_PROJECT_REQUIREMENTS do
+      desc "List the project's remote mirrors" do
+        success Entities::RemoteMirror
+      end
+      params do
+        use :pagination
+      end
+      get ':id/remote_mirrors' do
+        unauthorized! unless can?(current_user, :admin_remote_mirror, user_project)
+
+        present paginate(user_project.remote_mirrors),
+          with: Entities::RemoteMirror
+      end
+    end
+  end
+end

spec/fixtures/api/schemas/remote_mirror.json

+{
+  "type": "object",
+  "required": [
+    "id",
+    "enabled",
+    "url",
+    "update_status",
+    "last_update_at",
+    "last_update_started_at",
+    "last_successful_update_at",
+    "last_error",
+    "only_protected_branches"
+    ],
+  "properties": {
+    "id": { "type": "integer" },
+    "enabled": { "type": "boolean" },
+    "url": { "type": "string" },
+    "update_status": { "type": "string" },
+    "last_update_at": { "type": ["string", "null"] },
+    "last_update_started_at": { "type": ["string", "null"] },
+    "last_successful_update_at": { "type": ["string", "null"] },
+    "last_error": { "type": ["string", "null"] },
+    "only_protected_branches": { "type": "boolean" }
+  },
+  "additionalProperties": false
+}

spec/fixtures/api/schemas/remote_mirrors.json

+{
+  "type": "array",
+  "items": { "$ref": "remote_mirror.json" }
+}

spec/requests/api/remote_mirrors_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe API::RemoteMirrors do
+  let_it_be(:user) { create(:user) }
+  let_it_be(:project) { create(:project, :repository, :remote_mirror) }
+
+  describe 'GET /projects/:id/remote_mirrors' do
+    let(:route) { "/projects/#{project.id}/remote_mirrors" }
+
+    it 'requires `admin_remote_mirror` permission' do
+      project.add_developer(user)
+
+      get api(route, user)
+
+      expect(response).to have_gitlab_http_status(:unauthorized)
+    end
+
+    it 'returns a list of remote mirrors' do
+      project.add_maintainer(user)
+
+      get api(route, user)
+
+      expect(response).to have_gitlab_http_status(:success)
+      expect(response).to match_response_schema('remote_mirrors')
+    end
+
+    context 'with the `remote_mirrors_api` feature disabled' do
+      before do
+        stub_feature_flags(remote_mirrors_api: false)
+      end
+
+      it 'responds with `not_found`' do
+        get api(route, user)
+
+        expect(response).to have_gitlab_http_status(:not_found)
+      end
+    end
+  end
+end