Add Middleware for correlation_id

The middleware generates the 'correlation_id' if it is not already present
in the request header. This 'correlation_id' can be used to enable more
effective debugging of requests that span multiple services.

Implements: blueprint create-a-unified-correlation-id

Change-Id: Ibc06a5b05b628e0b640e9299c79127ecbf9c684e

3 files changed, 91 insertions, 0 deletions

diff --git a/openstack/common/middleware/correlation_id.py b/openstack/common/middleware/correlation_id.py
new file mode 100644
index 0000000..a3efe34
--- /dev/null
+++ b/openstack/common/middleware/correlation_id.py
@@ -0,0 +1,29 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright (c) 2013 Rackspace Hosting
+# All Rights Reserved.
+#
+#    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 that attaches a correlation id to WSGI request"""
+
+from openstack.common import uuidutils
+from openstack.common import wsgi
+
+
+class CorrelationIdMiddleware(wsgi.Middleware):
+
+    def process_request(self, req):
+        correlation_id = (req.headers.get("X_CORRELATION_ID") or
+                          uuidutils.generate_uuid())
+        req.headers['X_CORRELATION_ID'] = correlation_id
diff --git a/openstack/common/wsgi.py b/openstack/common/wsgi.py
index d184963..80d4b9b 100644
--- a/openstack/common/wsgi.py
+++ b/openstack/common/wsgi.py
@@ -172,6 +172,17 @@ class Middleware(object):
     behavior.
     """
 
+    @classmethod
+    def factory(cls, global_conf, **local_conf):
+        """
+        Factory method for paste.deploy
+        """
+
+        def filter(app):
+            return cls(app)
+
+        return filter
+
     def __init__(self, application):
         self.application = application
 
diff --git a/tests/unit/middleware/test_correlation_id.py b/tests/unit/middleware/test_correlation_id.py
new file mode 100644
index 0000000..070c23e
--- /dev/null
+++ b/tests/unit/middleware/test_correlation_id.py
@@ -0,0 +1,51 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright (c) 2013 Rackspace Hosting
+# All Rights Reserved.
+#
+#    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 mock
+
+from openstack.common.middleware import correlation_id
+from openstack.common import uuidutils
+from tests import utils
+
+
+class CorrelationIdMiddlewareTest(utils.BaseTestCase):
+
+    def test_process_request(self):
+        app = mock.Mock()
+        req = mock.Mock()
+        req.headers = {}
+        original_method = uuidutils.generate_uuid
+        mock_generate_uuid = mock.Mock()
+        mock_generate_uuid.return_value = "fake_uuid"
+        uuidutils.generate_uuid = mock_generate_uuid
+
+        middleware = correlation_id.CorrelationIdMiddleware(app)
+        middleware(req)
+        uuidutils.generate_uuid = original_method
+
+        self.assertEquals(req.headers.get("X_CORRELATION_ID"), "fake_uuid")
+
+    def test_process_request_should_not_regenerate_correlation_id(self):
+        app = mock.Mock()
+        req = mock.Mock()
+        req.headers = {"X_CORRELATION_ID": "correlation_id"}
+
+        middleware = correlation_id.CorrelationIdMiddleware(app)
+        middleware(req)
+
+        self.assertEquals(req.headers.get("X_CORRELATION_ID"),
+                          "correlation_id")