Add API hook for enriching the Error result metadata.

Fixes #590

huey/api.py

@@ -389,17 +389,8 @@ def _execute(self, task, timestamp):
 
         if self.results and not isinstance(task, PeriodicTask):
             if exception is not None:
-                try:
-                    tb = traceback.format_exc()
-                except AttributeError:  # Seems to only happen on 3.4.
-                    tb = '- unable to resolve traceback on Python 3.4 -'
-
-                self.put_result(task.id, Error({
-                    'error': repr(exception),
-                    'retries': task.retries,
-                    'traceback': tb,
-                    'task_id': task.id,
-                }))
+                error = self.build_error_result(task, exception)
+                self.put_result(task.id, error)
             elif task_value is not None or self.store_none:
                 self.put_result(task.id, task_value)
 
@@ -456,6 +447,19 @@ def _run_post_execute(self, task, task_value, exception):
                 logger.exception('Unhandled exception calling post-execute '
                                  'hook %s for %s.', name, task)
 
+    def build_error_result(self, task, exception):
+        try:
+            tb = traceback.format_exc()
+        except AttributeError:  # Seems to only happen on 3.4.
+            tb = '- unable to resolve traceback on Python 3.4 -'
+
+        return Error({
+            'error': repr(exception),
+            'retries': task.retries,
+            'traceback': tb,
+            'task_id': task.id,
+        })
+
     def _task_key(self, task_class, key):
         return ':'.join((key, self._registry.task_to_string(task_class)))
 

huey/tests/test_api.py

@@ -1286,3 +1286,33 @@ def ptask():
 
         self.assertEqual(inspect.getdoc(add), 'Adds two numbers.')
         self.assertEqual(inspect.getdoc(ptask), 'Sample periodic task.')
+
+
+class TestCustomErrorMetadata(BaseTestCase):
+    def get_huey(self):
+        class CustomError(MemoryHuey):
+            def build_error_result(self, task, exc):
+                err = super(CustomError, self).build_error_result(task, exc)
+                err.metadata['name'] = task.name
+                err.metadata['args'] = task.args
+                return err
+        return CustomError(utc=False)
+
+    def test_custom_error(self):
+        @self.huey.task()
+        def task_e(n):
+            raise TestError('uh-oh')
+
+        re = task_e(0)
+        self.assertTrue(self.execute_next() is None)
+        self.assertEqual(self.huey.result_count(), 1)  # Error result present.
+
+        # Resolves the result handle, which re-raises the error.
+        err = self.trap_exception(re)
+        self.assertEqual(err.metadata['error'], 'TestError(uh-oh)')
+        self.assertEqual(err.metadata['retries'], 0)
+        self.assertEqual(err.metadata['name'], 'task_e')
+        self.assertEqual(err.metadata['args'], (0,))
+
+        self.assertEqual(self.huey.result_count(), 0)
+        self.assertEqual(len(self.huey), 0)