Add header flag to prevent overriding error responses

Currently for an non-200 page, Slimmer will replace the response body with templates from Static. This certain apps like email-alert-frontend need to present custom error page (e.g. 422). This allows an app to tell Slimmer not to replace the body.
alphagov · Apr 7, 2020 · 4a5172a · 4a5172a
1 parent 47001b1
commit 4a5172a
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Showing 4 changed files with 53 additions and 15 deletions.
diff --git a/lib/slimmer/app.rb b/lib/slimmer/app.rb
@@ -64,6 +64,10 @@ def skip_slimmer_header?(response)
       !!response.headers[Headers::SKIP_HEADER]
     end
 
+    def ignore_error_header?(response)
+      !!response.headers[Headers::IGNORE_ERROR_HEADER]
+    end
+
     def s(body)
       return body.to_s unless body.respond_to?(:each)
 
@@ -84,26 +88,32 @@ def rewrite_response(env, response)
       # Store the request id so it can be passed on with any template requests
       GovukRequestId.value = env["HTTP_GOVUK_REQUEST_ID"]
 
-      rewritten_body = case response.status
-                       when 200
-                         @skin.success request, response, s(response.body)
-                       when 403
-                         @skin.error "403", s(response.body), request.env
-                       when 404
-                         @skin.error "404", s(response.body), request.env
-                       when 410
-                         @skin.error "410", s(response.body), request.env
-                       else
-                         @skin.error "500", s(response.body), request.env
-                       end
-
-      rewritten_body = [rewritten_body] unless rewritten_body.respond_to?(:each)
-      response.body = rewritten_body
+      body = rewritten_body(request, response)
+
+      body = [body] unless body.respond_to?(:each)
+      response.body = body
       response.headers["Content-Length"] = content_length(response.body)
 
       response.finish
     end
 
+    def rewritten_body(request, response)
+      return @skin.success request, response, s(response.body) if ignore_error_header?(response)
+
+      case response.status
+      when 200
+        @skin.success request, response, s(response.body)
+      when 403
+        @skin.error "403", s(response.body), request.env
+      when 404
+        @skin.error "404", s(response.body), request.env
+      when 410
+        @skin.error "410", s(response.body), request.env
+      else
+        @skin.error "500", s(response.body), request.env
+      end
+    end
+
     def strip_slimmer_headers(headers)
       headers.reject { |k, _v| k =~ /\A#{Headers::HEADER_PREFIX}/ }
     end

diff --git a/lib/slimmer/headers.rb b/lib/slimmer/headers.rb
@@ -20,6 +20,7 @@ module Headers
       skip:                 "Skip",
       template:             "Template",
       remove_search:        "Remove-Search",
+      ignore_error:         "Ignore-Error",
     }.freeze
 
     # @private
@@ -55,10 +56,15 @@ module Headers
     # @private
     REMOVE_SEARCH_HEADER = "#{HEADER_PREFIX}-#{SLIMMER_HEADER_MAPPING[:remove_search]}".freeze
 
+    # @private
+    IGNORE_ERROR_HEADER = "#{HEADER_PREFIX}-#{SLIMMER_HEADER_MAPPING[:ignore_error]}".freeze
+
+
     # Set the "slimmer headers" to configure the page
     #
     # @param hash [Hash] the options
     # @option hash [String] application_name
+    # @option hash [String] ignore_error
     # @option hash [String] format
     # @option hash [String] organisations
     # @option hash [String] page_owner

diff --git a/test/test_helper.rb b/test/test_helper.rb
@@ -84,6 +84,7 @@ def given_response(code, body, headers = {}, app_options = {})
 
     template_name = case code
                     when 200 then "core_layout"
+                    when 422 then "core_layout"
                     when 404 then "404"
                     when 410 then "410"
                     else          "500"

diff --git a/test/typical_usage_test.rb b/test/typical_usage_test.rb
@@ -295,6 +295,27 @@ def test_should_replace_the_title_using_the_app_response
     end
   end
 
+  class IgnoreErrorTest < SlimmerIntegrationTest
+    given_response 422, %{
+      <html>
+      <head><title>422 Session expired</title>
+      <meta name="something" content="yes">
+      <script src="blah.js"></script>
+      <link href="app.css" rel="stylesheet" type="text/css">
+      </head>
+      <body class="body_class">
+      <div id="wrapper"><p class='message'>Your session expired</p></div>
+      </body>
+      </html>
+      <html>
+    }, "X-Slimmer-Ignore-Error" => "true"
+
+
+    def test_should_include_the_existing_error_message
+      assert_rendered_in_template "p.message", /^Your session expired/
+    end
+  end
+
   class ArbitraryWrapperIdTest < SlimmerIntegrationTest
     given_response 200, %{
       <html>