Compress response's content according to client's accepted encoding

Currently Glance ignores the Accept-Encoding header and returns
responses as they are regardless the client accepts gzip or other type
of compression.

This patch adds this capability to glance (by using a middleware)
supporting just gzip for now.

Important note:
    - The patch uses a lazy compression for Content-Type
    application/octet-stream but in order to do that, the
    content-length has to be unset which means that when an image is
    downloaded the content-length will be unknown to the client.

Fixes bug: 1150380

Change-Id: Ieb65837d4e3fe310f97d9666882ecc572b14956a

etc/glance-api-paste.ini

@@ -55,3 +55,6 @@ paste.filter_factory = glance.api.middleware.context:UnauthenticatedContextMiddl
 [filter:authtoken]
 paste.filter_factory = keystoneclient.middleware.auth_token:filter_factory
 delay_auth_decision = true
+
+[filter:gzip]
+paste.filter_factory = glance.api.middleware.gzip:GzipMiddleware.factory

glance/api/middleware/gzip.py

@@ -0,0 +1,65 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2013 Red Hat, Inc.
+# 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.
+
+"""
+Use gzip compression if the client accepts it.
+"""
+
+import re
+
+from glance.common import wsgi
+import glance.openstack.common.log as logging
+
+LOG = logging.getLogger(__name__)
+
+
+class GzipMiddleware(wsgi.Middleware):
+
+    re_zip = re.compile(r'\bgzip\b')
+
+    def __init__(self, app):
+        LOG.info(_("Initialized gzip middleware"))
+        super(GzipMiddleware, self).__init__(app)
+
+    def process_response(self, response):
+        request = response.request
+        accept_encoding = request.headers.get('Accept-Encoding', '')
+
+        if self.re_zip.search(accept_encoding):
+            # NOTE(flaper87): Webob removes the content-md5 when
+            # app_iter is called. We'll keep it and reset it later
+            checksum = response.headers.get("Content-MD5")
+
+            # NOTE(flaper87): We'll use lazy for images so
+            # that they can be compressed without reading
+            # the whole content in memory. Notice that using
+            # lazy will set response's content-length to 0.
+            content_type = response.headers["Content-Type"]
+            lazy = content_type == "application/octet-stream"
+
+            # NOTE(flaper87): Webob takes care of the compression
+            # process, it will replace the body either with a
+            # compressed body or a generator - used for lazy com
+            # pression - depending on the lazy value.
+            #
+            # Webob itself will set the Content-Encoding header.
+            response.encode_content(lazy=lazy)
+
+            if checksum:
+                response.headers['Content-MD5'] = checksum
+
+        return response

glance/common/wsgi.py

@@ -548,6 +548,7 @@ class Resource(object):
     may raise a webob.exc exception or return a dict, which will be
     serialized by requested content type.
     """
+
     def __init__(self, controller, deserializer=None, serializer=None):
         """
         :param controller: object that implement methods created by routes lib

glance/tests/functional/__init__.py

@@ -354,24 +354,25 @@ enable_v2_api= %(enable_v2_api)s
 flavor = %(deployment_flavor)s
 """
         self.paste_conf_base = """[pipeline:glance-api]
-pipeline = versionnegotiation unauthenticated-context rootapp
+pipeline = versionnegotiation gzip unauthenticated-context rootapp
 
 [pipeline:glance-api-caching]
-pipeline = versionnegotiation unauthenticated-context cache rootapp
+pipeline = versionnegotiation gzip unauthenticated-context cache rootapp
 
 [pipeline:glance-api-cachemanagement]
 pipeline =
     versionnegotiation
+    gzip
     unauthenticated-context
     cache
     cache_manage
     rootapp
 
 [pipeline:glance-api-fakeauth]
-pipeline = versionnegotiation fakeauth context rootapp
+pipeline = versionnegotiation gzip fakeauth context rootapp
 
 [pipeline:glance-api-noauth]
-pipeline = versionnegotiation context rootapp
+pipeline = versionnegotiation gzip context rootapp
 
 [composite:rootapp]
 paste.composite_factory = glance.api:root_app_factory
@@ -392,6 +393,9 @@ paste.app_factory = glance.api.v2.router:API.factory
 paste.filter_factory =
  glance.api.middleware.version_negotiation:VersionNegotiationFilter.factory
 
+[filter:gzip]
+paste.filter_factory = glance.api.middleware.gzip:GzipMiddleware.factory
+
 [filter:cache]
 paste.filter_factory = glance.api.middleware.cache:CacheFilter.factory
 

glance/tests/functional/test_gzip_middleware.py

@@ -0,0 +1,50 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2013 Red Hat, Inc
+# 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.
+
+"""Tests gzip middleware."""
+
+import httplib2
+
+from glance.tests import functional
+from glance.tests import utils
+
+
+class GzipMiddlewareTest(functional.FunctionalTest):
+
+    @utils.skip_if_disabled
+    def test_gzip_requests(self):
+        self.cleanup()
+        self.start_servers(**self.__dict__.copy())
+
+        def request(path, headers=None):
+            # We don't care what version we're using here so,
+            # sticking with latest
+            url = 'http://127.0.0.1:%s/v2/%s' % (self.api_port, path)
+            http = httplib2.Http()
+            return http.request(url, 'GET', headers=headers)
+
+        # Accept-Encoding: Identity
+        headers = {'Accept-Encoding': 'identity'}
+        response, content = request('images', headers=headers)
+        self.assertEqual(response.get("-content-encoding"), None)
+
+        # Accept-Encoding: gzip
+        headers = {'Accept-Encoding': 'gzip'}
+        response, content = request('images', headers=headers)
+        self.assertEqual(response.get("-content-encoding"), 'gzip')
+
+        self.stop_servers()