Add JsonErrorMixin:

This commit adds the JsonErrorMixin for formatting error message from a
given RequestHandler as JSON.

README.rst

@@ -24,12 +24,30 @@ Requirements
 
 Example
 -------
-This examples demonstrates how to use ``sprockets.mixins.json_error`` by ...
+This examples demonstrates how to use ``sprockets.mixins.json_error`` to format
+errors as JSON.
+
 .. code:: python
 
     from sprockets import mixins.json_error
+    from tornado import web
+
+    class MyRequestHandler(statsd.RequestMetricsMixin,
+                           web.RequestHandler):
+
+        def get(self, *args, **kwargs):
+            raise web.HTTPError(404, log_message='My reason')
+
+
+The response from the handler will automatically be formatted as:
+
+.. code:: json
+
+    {
+        "message": "My reason",
+        "type": "Not Found"
+    }
 
-    # Example here
 
 Version History
 ---------------

sprockets/mixins/json_error/__init__.py

@@ -4,5 +4,42 @@ mixins.json_error
 Handler mixin for writing JSON errors
 
 """
-version_info = (0, 0, 0)
+version_info = (1, 0, 0)
 __version__ = '.'.join(str(v) for v in version_info)
+
+
+class JsonErrorMixin(object):
+
+    def write_error(self, status_code, **kwargs):
+        """Suppress the automatic rendering of HTML code upon an error.
+
+           :param int status_code:
+                The HTTP status code the :class:`HTTPError` raised.
+
+           :param dict kwargs:
+                Automatically filled with exception information including
+                the error that was raised, the class of error raised, and an
+                object.
+
+        """
+        if kwargs.get('error'):
+            raised_error = kwargs.get('error')
+        else:
+            _, raised_error, _ = kwargs['exc_info']
+
+        error_message = getattr(
+            raised_error, 'log_message', 'Unexpected Error')
+        error_type = getattr(raised_error, 'error_type', self._reason)
+
+        self.error = {
+            'message': error_message,
+            'type': error_type,
+        }
+        if hasattr(raised_error, 'documentation_url'):
+            self.error['documentation_url'] = raised_error.documentation_url
+
+        error_status_code = getattr(raised_error, 'status_code', status_code)
+        self.set_status(error_status_code)
+
+        self.set_header('Content-Type', 'application/json; charset=UTF-8')
+        self.finish(self.error)

test-requirements.txt

@@ -1,3 +1,4 @@
 coverage>=3.7,<4
 coveralls>=0.4,<1
 nose>=1.3,<2
+tornado>=4.0,<5

tests.py

@@ -2,12 +2,75 @@
 Tests for the sprockets.mixins.json_error package
 
 """
-import mock
-try:
-    import unittest2 as unittest
-except ImportError:
-    import unittest
+import json
+
+from sprockets.mixins import json_error
+from tornado import testing, web
 
 
-class MyTest(unittest.TestCase):
-    pass
+class HTTPErrorRequestHandler(
+        json_error.JsonErrorMixin, web.RequestHandler):
+
+    def get(self):
+        raise web.HTTPError(400, 'Error Reason')
+
+
+class CustomExceptionRequestHandler(
+        json_error.JsonErrorMixin, web.RequestHandler):
+
+    class FailureError(Exception):
+
+        status_code = 400
+        log_message = 'Too much Foo'
+        error_type = 'FailureError'
+        documentation_url = 'http://www.example.com'
+
+    def get(self):
+        raise self.FailureError()
+
+
+class UnexpectedErrorRequestHandler(
+        json_error.JsonErrorMixin, web.RequestHandler):
+
+    def get(self):
+        raise Exception()
+
+
+class TestHTTPError(testing.AsyncHTTPTestCase):
+
+    def get_app(self):
+        return web.Application([('/', HTTPErrorRequestHandler)])
+
+    def test_tornado_thrown_exception(self):
+        response = self.fetch('/')
+        expected = {'message': 'Error Reason', 'type': 'Bad Request'}
+        self.assertEqual(json.loads(response.body), expected)
+
+
+class TestCustomExceptions(testing.AsyncHTTPTestCase):
+
+    def get_app(self):
+        return web.Application([('/', CustomExceptionRequestHandler)])
+
+    def test_tornado_custom_exception(self):
+        response = self.fetch('/')
+        expected = {
+            'message': 'Too much Foo',
+            'type': 'FailureError',
+            'documentation_url': 'http://www.example.com',
+        }
+        self.assertEqual(json.loads(response.body), expected)
+
+
+class TestUnexpectedError(testing.AsyncHTTPTestCase):
+
+    def get_app(self):
+        return web.Application([('/', UnexpectedErrorRequestHandler)])
+
+    def test_unexpected_exception(self):
+        response = self.fetch('/')
+        expected = {
+            'message': 'Unexpected Error',
+            'type': 'Internal Server Error'
+        }
+        self.assertEqual(json.loads(response.body), expected)