Port middleware error handler from ceilometer API

Change-Id: I159923338e0447347d1c4bed4a80586ad6c06fcc

ironic/api/app.py

@@ -22,6 +22,7 @@ import pecan
 from ironic.api import acl
 from ironic.api import config
 from ironic.api import hooks
+from ironic.api import middleware
 
 auth_opts = [
     cfg.StrOpt('auth_strategy',
@@ -55,7 +56,6 @@ def setup_app(pecan_config=None, extra_hooks=None):
 
     pecan.configuration.set_config(dict(pecan_config), overwrite=True)
 
-# TODO(deva): add middleware.ParsableErrorMiddleware from Ceilometer
     app = pecan.make_app(
         pecan_config.app.root,
         static_root=pecan_config.app.static_root,
@@ -63,6 +63,7 @@ def setup_app(pecan_config=None, extra_hooks=None):
         debug=CONF.debug,
         force_canonical=getattr(pecan_config.app, 'force_canonical', True),
         hooks=app_hooks,
+        wrap_app=middleware.ParsableErrorMiddleware,
     )
 
     if pecan_config.app.enable_acl:

ironic/api/middleware.py

@@ -0,0 +1,91 @@
+# -*- encoding: utf-8 -*-
+#
+# Copyright © 2012 New Dream Network, LLC (DreamHost)
+#
+# Author: Doug Hellmann <doug.hellmann@dreamhost.com>
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+"""
+Middleware to replace the plain text message body of an error
+response with one formatted so the client can parse it.
+
+Based on pecan.middleware.errordocument
+"""
+
+import json
+import webob
+from xml import etree as et
+
+from ironic.openstack.common import log
+
+LOG = log.getLogger(__name__)
+
+
+class ParsableErrorMiddleware(object):
+    """Replace error body with something the client can parse.
+    """
+    def __init__(self, app):
+        self.app = app
+
+    def __call__(self, environ, start_response):
+        # Request for this state, modified by replace_start_response()
+        # and used when an error is being reported.
+        state = {}
+
+        def replacement_start_response(status, headers, exc_info=None):
+            """Overrides the default response to make errors parsable.
+            """
+            try:
+                status_code = int(status.split(' ')[0])
+                state['status_code'] = status_code
+            except (ValueError, TypeError):  # pragma: nocover
+                raise Exception((
+                    'ErrorDocumentMiddleware received an invalid '
+                    'status %s' % status
+                ))
+            else:
+                if (state['status_code'] / 100) not in (2, 3):
+                    # Remove some headers so we can replace them later
+                    # when we have the full error message and can
+                    # compute the length.
+                    headers = [(h, v)
+                               for (h, v) in headers
+                               if h not in ('Content-Length', 'Content-Type')
+                               ]
+                # Save the headers in case we need to modify them.
+                state['headers'] = headers
+                return start_response(status, headers, exc_info)
+
+        app_iter = self.app(environ, replacement_start_response)
+        if (state['status_code'] / 100) not in (2, 3):
+            req = webob.Request(environ)
+            if (req.accept.best_match(['application/json', 'application/xml'])
+                == 'application/xml'):
+                try:
+                    # simple check xml is valid
+                    body = [et.ElementTree.tostring(
+                            et.ElementTree.fromstring('<error_message>'
+                                                      + '\n'.join(app_iter)
+                                                      + '</error_message>'))]
+                except et.ElementTree.ParseError as err:
+                    LOG.error('Error parsing HTTP response: %s' % err)
+                    body = ['<error_message>%s' % state['status_code']
+                            + '</error_message>']
+                state['headers'].append(('Content-Type', 'application/xml'))
+            else:
+                body = [json.dumps({'error_message': '\n'.join(app_iter)})]
+                state['headers'].append(('Content-Type', 'application/json'))
+            state['headers'].append(('Content-Length', len(body[0])))
+        else:
+            body = app_iter
+        return body