Capture exceptions happening in API layer

Added the faulwrapper around EC2 api so that it captures any unseen
exceptions and return a graceful error back. Also changed the openstack
exception message. The actual exception message will be printed in the
logs and would not return back the user.
Removed openstack wsgi dependency from
EC2 fault wrapper. Added unit tests for
EC2 fault wrapper
Fixes bug 869132.

Change-Id: I03d18f321f141ae96f1add99ea0b70e736253c89

2 files changed, 78 insertions, 0 deletions

diff --git a/nova/api/ec2/__init__.py b/nova/api/ec2/__init__.py
index ebb8c7bff..db92ca053 100644
--- a/nova/api/ec2/__init__.py
+++ b/nova/api/ec2/__init__.py
@@ -36,6 +36,7 @@ from nova import utils
 from nova import wsgi
 from nova.api.ec2 import apirequest
 from nova.api.ec2 import ec2utils
+from nova.api.ec2 import faults
 from nova.auth import manager
 
 FLAGS = flags.FLAGS
@@ -49,6 +50,19 @@ flags.DEFINE_integer('lockout_window', 15,
 flags.DECLARE('use_forwarded_for', 'nova.api.auth')
 
 
+## Fault Wrapper around all EC2 requests ##
+class FaultWrapper(wsgi.Middleware):
+    """Calls the middleware stack, captures any exceptions into faults."""
+
+    @webob.dec.wsgify(RequestClass=wsgi.Request)
+    def __call__(self, req):
+        try:
+            return req.get_response(self.application)
+        except Exception as ex:
+            LOG.exception(_("FaultWrapper: %s"), unicode(ex))
+            return faults.Fault(webob.exc.HTTPInternalServerError())
+
+
 class RequestLogging(wsgi.Middleware):
     """Access-Log akin logging for all EC2 API requests."""
 
diff --git a/nova/api/ec2/faults.py b/nova/api/ec2/faults.py
new file mode 100644
index 000000000..9e47702d9
--- /dev/null
+++ b/nova/api/ec2/faults.py
@@ -0,0 +1,64 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+#    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.
+
+import webob.dec
+import webob.exc
+
+from nova import utils
+from nova import context
+from nova import flags
+
+FLAGS = flags.FLAGS
+
+
+class Fault(webob.exc.HTTPException):
+    """Captures exception and return REST Response."""
+
+    def __init__(self, exception):
+        """Create a response for the given webob.exc.exception."""
+        self.wrapped_exc = exception
+
+    @webob.dec.wsgify
+    def __call__(self, req):
+        """Generate a WSGI response based on the exception passed to ctor."""
+        code = self.wrapped_exc.status_int
+        message = self.wrapped_exc.explanation
+
+        if code == 501:
+            message = "The requested function is not supported"
+        code = str(code)
+
+        if 'AWSAccessKeyId' not in req.params:
+            raise webob.exc.HTTPBadRequest()
+        user_id, _sep, project_id = req.params['AWSAccessKeyId'].partition(':')
+        project_id = project_id or user_id
+        remote_address = getattr(req, 'remote_address', '127.0.0.1')
+        if FLAGS.use_forwarded_for:
+            remote_address = req.headers.get('X-Forwarded-For', remote_address)
+
+        ctxt = context.RequestContext(user_id,
+                                      project_id,
+                                      remote_address=remote_address)
+
+        resp = webob.Response()
+        resp.status = self.wrapped_exc.status_int
+        resp.headers['Content-Type'] = 'text/xml'
+        resp.body = str('<?xml version="1.0"?>\n'
+                         '<Response><Errors><Error><Code>%s</Code>'
+                         '<Message>%s</Message></Error></Errors>'
+                         '<RequestID>%s</RequestID></Response>' %
+                         (utils.utf8(code), utils.utf8(message),
+                         utils.utf8(ctxt.request_id)))
+
+        return resp