Convert any ChaliceViewError to a response

chalice/app.py

@@ -106,6 +106,14 @@ def __init__(self, connection_id):
 class ChaliceViewError(ChaliceError):
     STATUS_CODE = 500
 
+    def to_response(self):
+        return Response(
+            body={
+                'Code': self.__class__.__name__,
+                'Message': str(self)},
+            status_code=self.STATUS_CODE
+        )
+
 
 class ChaliceUnhandledError(ChaliceError):
     """This error is not caught from a Chalice view function.
@@ -1760,9 +1768,7 @@ def _get_view_function_response(self, view_function, function_args):
         except ChaliceViewError as e:
             # Any chalice view error should propagate.  These
             # get mapped to various HTTP status codes in API Gateway.
-            response = Response(body={'Code': e.__class__.__name__,
-                                      'Message': str(e)},
-                                status_code=e.STATUS_CODE)
+            response = e.to_response()
         except Exception:
             response = self._unhandled_exception_to_response()
         return response

docs/source/tutorials/basicrestapi.rst

@@ -211,6 +211,60 @@ You can import these directly from the ``chalice`` package:
 
     from chalice import UnauthorizedError
 
+Custom errors
+^^^^^^^^^^^^^
+
+You can create a custom response by implementing your own exception class.
+The response must be generated by the method ``to_response`` and be
+inherited from ``ChaliceViewError``. A sample custom error should look
+like this:
+
+.. code-block:: python
+
+    from chalice import ChaliceViewError, Response
+
+    class GoneCity(ChaliceViewError):
+        city = None
+        STATUS_CODE = 410
+
+        def __init__(self, city):
+            super().__init__()
+            self.city = city
+
+        def to_response(self):
+            return Response(
+                body=dict(
+                    error=self.__class__.__name__,
+                    message=f"The city of {self.city} has been abandoned",
+                    city=self.city,
+                ),
+                status_code=self.STATUS_CODE,
+            )
+
+    @app.route('/cities/{city}')
+    def state_of_city(city):
+        try:
+            if city in ABANDONED_CITIES:
+                raise GoneCity(city)
+            return {'state': CITIES_TO_STATE[city]}
+        except KeyError:
+            raise BadRequestError("Unknown city '%s', valid choices are: %s" % (
+                city, ', '.join(CITIES_TO_STATE.keys())))
+
+
+Save and deploy these changes::
+
+    $ chalice deploy
+    $ http https://endpoint/api/cities/petra
+    HTTP/1.1 410 Gone
+
+    {
+        "error": "Gone",
+        "message": "The city of Petra has been abandoned",
+        "city": "petra"
+    }
+
+
 
 Additional Routing
 ------------------

tests/unit/test_app.py

@@ -19,6 +19,7 @@
 from chalice.test import Client
 from chalice.app import (
     APIGateway,
+    ChaliceViewError,
     Request,
     Response,
     handle_extra_types,
@@ -1042,6 +1043,71 @@ def notfound():
     assert json_response_body(raw_response)['Code'] == 'NotFoundError'
 
 
+def test_chalice_view_custom_error_in_non_debug_mode(sample_app, create_event):
+    class CustomError(ChaliceViewError):
+        message = None
+
+        def __init__(self, code, message):
+            super().__init__()
+            self.STATUS_CODE = code
+            self.message = message
+
+        def to_response(self):
+            return Response(
+                body=dict(
+                    error=self.__class__.__name__,
+                    custom_msg=str(self.message)
+                ),
+                status_code=self.STATUS_CODE,
+            )
+
+    err_code = 503
+    err_msg = "Method not available"
+
+    @sample_app.route('/internalerr')
+    def internalerr():
+        raise CustomError(err_code, err_msg)
+
+    event = create_event('/internalerr', 'GET', {})
+    raw_response = sample_app(event, context=None)
+    assert raw_response['statusCode'] == err_code
+    assert json_response_body(raw_response)['error'] == 'CustomError'
+    assert json_response_body(raw_response)['custom_msg'] == err_msg
+
+
+def test_chalice_view_custom_error_in_debug_mode(sample_app, create_event):
+    class CustomError(ChaliceViewError):
+        message = None
+
+        def __init__(self, code, message):
+            super().__init__()
+            self.STATUS_CODE = code
+            self.message = message
+
+        def to_response(self):
+            return Response(
+                body=dict(
+                    error=self.__class__.__name__,
+                    custom_msg=str(self.message)
+                ),
+                status_code=self.STATUS_CODE,
+            )
+
+    err_code = 503
+    err_msg = "Method not available"
+
+    @sample_app.route('/internalerr')
+    def internalerr():
+        raise CustomError(err_code, err_msg)
+    sample_app.debug = True
+
+    event = create_event('/internalerr', 'GET', {})
+    raw_response = sample_app(event, context=None)
+    assert raw_response['statusCode'] == err_code
+    assert json_response_body(raw_response)['error'] == 'CustomError'
+    assert json_response_body(raw_response)['custom_msg'] == err_msg
+
+
 def test_case_insensitive_mapping():
     mapping = app.CaseInsensitiveMapping({'HEADER': 'Value'})