trim_whitespace meddleware plugin

Our HTML output is very verbose (=whitespacy) as our templates are
written with an 80 char limit and lots of newlines between blocks,
variables etc....

This is a plugin that naively strips of all but the first whitespace
from the HTML response. We might want to have an all-fancy html tidy
interface here at some point, but it nicely decreases the HTML size
about a third on some simple pages.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

diff --git a/mediagoblin/plugins/trim_whitespace/README.rst b/mediagoblin/plugins/trim_whitespace/README.rst
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+=======================
+ Trim whitespace plugin
+=======================
+
+Mediagoblin templates are written with 80 char limit for better
+readability. However that means that the html output is very verbose
+containing LOTS of whitespace. This plugin inserts a Middleware that
+filters out whitespace from the returned HTML in the Response() objects.
+
+Simply enable this plugin by putting it somewhere where python can reach it and put it's path into the [plugins] section of your mediagoblin.ini or mediagoblin_local.ini like for example this:
+
+    [plugins]
+    [[mediagoblin.plugins.trim_whitespace]]
+
+There is no further configuration required. If this plugin is enabled,
+all text/html documents should not have lots of whitespace in between
+elements, although it does a very naive filtering right now (just keep
+the first whitespace and delete all subsequent ones).
+
+Nonetheless, it is a useful plugin that might serve as inspiration for
+other plugin writers.
+
+It was originally conceived by Sebastian Spaeth. It is licensed under
+the GNU AGPL v3 (or any later version) license.
+

diff --git a/mediagoblin/plugins/trim_whitespace/__init__.py b/mediagoblin/plugins/trim_whitespace/__init__.py
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+# GNU MediaGoblin -- federated, autonomous media hosting
+# Copyright (C) 2011, 2012 MediaGoblin contributors.  See AUTHORS.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+from __future__ import unicode_literals
+import logging
+import re
+
+from mediagoblin import meddleware
+
+_log = logging.getLogger(__name__)
+
+class TrimWhiteSpaceMeddleware(meddleware.BaseMeddleware):
+    _setup_plugin_called = 0
+    RE_MULTI_WHITESPACE = re.compile(b'(\s)\s+', re.M)
+
+    def process_response(self, request, response):
+        """Perform very naive html tidying by removing multiple whitespaces"""
+        # werkzeug.BaseResponse has no content_type attr, this comes via
+        # werkzeug.wrappers.CommonRequestDescriptorsMixin (part of
+        # wrappers.Response)
+        if getattr(response ,'content_type', None) != 'text/html':
+            return
+
+        # This is a tad more complex than needed to be able to handle
+        # response.data and response.body, depending on whether we have
+        # a werkzeug Resonse or a webob one. Let's kill webob soon!
+        if hasattr(response, 'body') and not hasattr(response, 'data'):
+            # Old-style webob Response object.
+            # TODO: Remove this once we transition away from webob
+            resp_attr = 'body'
+        else:
+            resp_attr = 'data'
+            # Don't flatten iterator to list when we fudge the response body
+            # (see werkzeug.Response documentation)
+            response.implicit_sequence_conversion = False
+
+        # Set the tidied text. Very naive tidying for now, just strip all
+        # subsequent whitespaces (this preserves most newlines)
+        setattr(response, resp_attr, re.sub(
+                TrimWhiteSpaceMeddleware.RE_MULTI_WHITESPACE, br'\1',
+                getattr(response, resp_attr)))
+
+    @classmethod
+    def setup_plugin(cls):
+        """Set up this meddleware as a plugin during 'setup' hook"""
+        global _log
+        if cls._setup_plugin_called:
+            _log.info('Trim whitespace plugin was already set up.')
+            return
+
+        _log.debug('Trim whitespace plugin set up.')
+        cls._setup_plugin_called += 1
+
+        # Append ourselves to the list of enabled Meddlewares
+        meddleware.ENABLED_MEDDLEWARE.append(
+            '{0}:{1}'.format(cls.__module__, cls.__name__))
+
+
+hooks = {
+    'setup': TrimWhiteSpaceMeddleware.setup_plugin
+    }