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]
+
 - Also handle resource resolver errors gracefully in the GracefulResourceRenderer.
   [thet]
 

webresource/_api.py

@@ -738,7 +738,7 @@ 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 = []
 
@@ -751,6 +751,8 @@ 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
@@ -768,4 +770,6 @@ def render(self):
                         error_message
                     ))
                     logger.exception(error_message)
+                    if error_callback:
+                        error_callback(error_message)
         return u'\n'.join(lines)

webresource/tests.py

@@ -7,19 +7,23 @@
     ResourceConfig,
     ResourceMixin
 )
+import logging
 import os
 import shutil
 import tempfile
 import unittest
 import webresource as wr
 
-
 try:
     FileNotFoundError
 except NameError:  # pragma: nocover
     FileNotFoundError = EnvironmentError
 
 
+# Get log level to restore it later
+original_log_level = logging.getLogger().getEffectiveLevel()
+
+
 def temp_directory(fn):
     def wrapper(*a, **kw):
         tempdir = tempfile.mkdtemp()
@@ -812,10 +816,6 @@ def test_GracefulResourceRenderer(self):
         ))
 
     def test_GreacefulResourceRenderer_resolver_errors(self):
-        # Get log level to restore it later
-        import logging
-        original_log_level = logging.getLogger().getEffectiveLevel()
-
         # Create a resource with a circular dependency
         resource = Resource(name='res1', resource='res1.ext', depends='res1')
 
@@ -840,6 +840,61 @@ def test_GreacefulResourceRenderer_resolver_errors(self):
         # interactible.
         self.assertEqual(rendered, "")
 
+    def test_GreacefulResourceRenderer_callback_resolver(self):
+        # Callback which should be called on error
+        error_message = []
+
+        def callback(message):
+            error_message.append(message)
+
+        # Create a resource with a circular dependency
+        resource = Resource(name='res1', resource='res1.ext', depends='res1')
+
+        resolver = wr.ResourceResolver([resource])
+        renderer = wr.GracefulResourceRenderer(resolver)
+
+        # Supress error traceback in logs
+        logging.disable(logging.CRITICAL)
+        renderer.render(error_callback=callback)
+        # Restore logging level
+        logging.disable(original_log_level)
+
+        self.assertEqual(len(error_message), 1)
+        self.assertEqual(
+            error_message[-1],
+            "Resources define circular dependencies: "
+            """[<Resource name="res1", depends="['res1']">]"""
+        )
+
+    def test_GreacefulResourceRenderer_callback_render(self):
+        # Callback which should be called on error
+        error_message = []
+
+        def callback(message):
+            error_message.append(message)
+
+        # Create a resource with a circular dependency
+        resource = wr.ScriptResource(
+            name='res1',
+            resource='res1.ext',
+            unique=True
+        )
+
+        resolver = wr.ResourceResolver([resource])
+        renderer = wr.GracefulResourceRenderer(resolver)
+
+        # Supress error traceback in logs
+        logging.disable(logging.CRITICAL)
+        renderer.render(error_callback=callback)
+        # Restore logging level
+        logging.disable(original_log_level)
+
+        self.assertEqual(len(error_message), 1)
+        self.assertEqual(
+            error_message[-1],
+            """No directory set on resource <ScriptResource name="res1">"""
+        )
+
 
 if __name__ == '__main__':
     unittest.main()