1 files changed, 43 insertions, 0 deletions
diff --git a/lib/gitlab/exceptions_app.rb b/lib/gitlab/exceptions_app.rb
new file mode 100644
index 00000000000..de07b788fb9
--- /dev/null
+++ b/lib/gitlab/exceptions_app.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require_relative 'utils/override'
+
+module Gitlab
+  class ExceptionsApp < ActionDispatch::PublicExceptions
+    extend ::Gitlab::Utils::Override
+
+    REQUEST_ID_PLACEHOLDER = '<!-- REQUEST_ID -->'
+    REQUEST_ID_PARAGRAPH = '<p>Request ID: <code>%s</code></p>'
+
+    override :call
+    def call(env)
+      status, headers, body = super
+
+      if html_rendered? && body.first&.include?(REQUEST_ID_PLACEHOLDER)
+        body = [insert_request_id(env, body.first)]
+        headers['X-GitLab-Custom-Error'] = '1'
+      end
+
+      [status, headers, body]
+    end
+
+    private
+
+    override :render_html
+    def render_html(status)
+      @html_rendered = true
+
+      super
+    end
+
+    def html_rendered?
+      !!@html_rendered
+    end
+
+    def insert_request_id(env, body)
+      request_id = ERB::Util.html_escape(ActionDispatch::Request.new(env).request_id)
+
+      body.gsub(REQUEST_ID_PLACEHOLDER, REQUEST_ID_PARAGRAPH % [request_id])
+    end
+  end
+end