1 files changed, 62 insertions, 0 deletions
diff --git a/actionpack/lib/action_dispatch/middleware/show_exceptions.rb b/actionpack/lib/action_dispatch/middleware/show_exceptions.rb
new file mode 100644
index 0000000000..3c88afd4d3
--- /dev/null
+++ b/actionpack/lib/action_dispatch/middleware/show_exceptions.rb
@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+require "action_dispatch/http/request"
+require "action_dispatch/middleware/exception_wrapper"
+
+module ActionDispatch
+  # This middleware rescues any exception returned by the application
+  # and calls an exceptions app that will wrap it in a format for the end user.
+  #
+  # The exceptions app should be passed as parameter on initialization
+  # of ShowExceptions. Every time there is an exception, ShowExceptions will
+  # store the exception in env["action_dispatch.exception"], rewrite the
+  # PATH_INFO to the exception status code and call the Rack app.
+  #
+  # If the application returns a "X-Cascade" pass response, this middleware
+  # will send an empty response as result with the correct status code.
+  # If any exception happens inside the exceptions app, this middleware
+  # catches the exceptions and returns a FAILSAFE_RESPONSE.
+  class ShowExceptions
+    FAILSAFE_RESPONSE = [500, { "Content-Type" => "text/plain" },
+      ["500 Internal Server Error\n" \
+       "If you are the administrator of this website, then please read this web " \
+       "application's log file and/or the web server's log file to find out what " \
+       "went wrong."]]
+
+    def initialize(app, exceptions_app)
+      @app = app
+      @exceptions_app = exceptions_app
+    end
+
+    def call(env)
+      request = ActionDispatch::Request.new env
+      @app.call(env)
+    rescue Exception => exception
+      if request.show_exceptions?
+        render_exception(request, exception)
+      else
+        raise exception
+      end
+    end
+
+    private
+
+      def render_exception(request, exception)
+        backtrace_cleaner = request.get_header "action_dispatch.backtrace_cleaner"
+        wrapper = ExceptionWrapper.new(backtrace_cleaner, exception)
+        status  = wrapper.status_code
+        request.set_header "action_dispatch.exception", wrapper.exception
+        request.set_header "action_dispatch.original_path", request.path_info
+        request.path_info = "/#{status}"
+        response = @exceptions_app.call(request.env)
+        response[1]["X-Cascade"] == "pass" ? pass_response(status) : response
+      rescue Exception => failsafe_error
+        $stderr.puts "Error during failsafe response: #{failsafe_error}\n  #{failsafe_error.backtrace * "\n  "}"
+        FAILSAFE_RESPONSE
+      end
+
+      def pass_response(status)
+        [status, { "Content-Type" => "text/html; charset=#{Response.default_charset}", "Content-Length" => "0" }, []]
+      end
+  end
+end