error_callback for GracefulResourceRenderer

Allow to pass an error_callback for the GracefulResourceRenderer.
This allows to run some code in an error case, e.g. to add a user-visible
status message.

Author: thet

CHANGES.rst

@@ -4,6 +4,11 @@ Changelog
 1.3 (unreleased)
 ----------------
 
+- Allow to pass an error_callback for the GracefulResourceRenderer.
+  This allows to run some code in an error case, e.g. to add a user-visible
+  status message.
+  [thet]
+
 - Improve the error messages for the GracefulResourceRenderer to give an admin
   better hints on what was going wrong.
   [thet]

webresource/_api.py

@@ -735,7 +735,7 @@ def render(self):
 class GracefulResourceRenderer(ResourceRenderer):
     """Resource renderer, which does not fail but logs an exception."""
 
-    def render(self):
+    def render(self, error_callback=None):
         lines = []
         resources = []
         try:
@@ -747,6 +747,8 @@ def render(self):
         ) as e:
             error_message = str(e)
             logger.exception(error_message)
+            if error_callback:
+                error_callback(error_message)
 
         for resource in resources:
             error_message = None
@@ -764,4 +766,6 @@ def render(self):
                         error_message
                     ))
                     logger.exception(error_message)
+                    if error_callback:
+                        error_callback(error_message)
         return u'\n'.join(lines)