refactor wiki and added spec

ee/lib/ee/gitlab/geo_git_access.rb

+module EE
+  module Gitlab
+    module GeoGitAccess
+      GEO_SERVER_DOCS_URL = 'https://docs.gitlab.com/ee/gitlab-geo/using_a_geo_server.html'.freeze
+
+      private
+
+      def push_to_read_only_message
+        message = super
+
+        if ::Gitlab::Geo.primary_node
+          primary_url = ActionController::Base.helpers.link_to('primary node', ::Gitlab::Geo.primary_node.url)
+          message += " Please use the Primary node URL: #{primary_url.html_safe}. Documentation: #{GEO_SERVER_DOCS_URL}"
+        end
+
+        message
+      end
+    end
+  end
+end

lib/gitlab/git_access_wiki.rb

 module Gitlab
   class GitAccessWiki < GitAccess
+    prepend EE::Gitlab::GeoGitAccess
+
     ERROR_MESSAGES = {
       read_only:     "You can't push code to a read-only GitLab instance.",
       write_to_wiki: "You are not allowed to write to this project's wiki."
@@ -19,10 +21,14 @@ module Gitlab
       end
 
       if Gitlab::Database.read_only?
-        raise UnauthorizedError, ERROR_MESSAGES[:read_only]
+        raise UnauthorizedError, push_to_read_only_message
       end
 
       true
     end
+
+    def push_to_read_only_message
+      ERROR_MESSAGES[:read_only]
+    end
   end
 end

spec/ee/spec/lib/ee/gitlab/git_access_wiki_spec.rb

+require 'spec_helper'
+
+describe Gitlab::GitAccessWiki do
+  let(:access) { described_class.new(user, project, 'web', authentication_abilities: authentication_abilities, redirected_path: redirected_path) }
+  let(:project) { create(:project, :repository) }
+  let(:user) { create(:user) }
+  let(:changes) { ['6f6d7e7ed 570e7b2ab refs/heads/master'] }
+  let(:redirected_path) { nil }
+  let(:authentication_abilities) do
+    [
+        :read_project,
+        :download_code,
+        :push_code
+    ]
+  end
+
+  subject { access.check('git-receive-pack', changes) }
+
+  context "when in a read-only GitLab instance" do
+    before do
+      create(:protected_branch, name: 'feature', project: project)
+      allow(Gitlab::Database).to receive(:read_only?) { true }
+    end
+
+    it 'denies push access' do
+      project.add_master(user)
+
+      expect { subject }.to raise_unauthorized("You can't push code to a read-only GitLab instance.")
+    end
+
+    it 'denies push access with primary present' do
+      error_message = "You can't push code to a read-only GitLab instance. Please use the Primary node URL:"\
+" <a href=\"https://localhost:3000/gitlab/\">primary node</a>. Documentation: https://docs.gitlab.com/ee/gitlab-geo/using_a_geo_server.html"
+
+      primary_node = create(:geo_node, :primary, url: 'https://localhost:3000/gitlab')
+      allow(Gitlab::Geo).to receive(:primary).and_return(primary_node)
+
+      project.add_master(user)
+
+      expect { subject }.to raise_unauthorized(error_message)
+    end
+  end
+
+  private
+
+  def raise_unauthorized(message)
+    raise_error(Gitlab::GitAccess::UnauthorizedError, message)
+  end
+end