text: # vim: tabstop=4 shiftwidth=4 softtabstop=4
  
  # Copyright 2010 United States Government as represented by the
  # Administrator of the National Aeronautics and Space Administration.
  # 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.
  
  """Metadata request handler."""
  import os
  
  import webob.dec
  import webob.exc
  
  from nova.api.metadata import base
  from nova import exception
  from nova import flags
  from nova.openstack.common import log as logging
  from nova import wsgi
  
  LOG = logging.getLogger(__name__)
  FLAGS = flags.FLAGS
  flags.DECLARE('use_forwarded_for', 'nova.api.auth')
  
  if FLAGS.memcached_servers:
      import memcache
  else:
      from nova.common import memorycache as memcache
  
  
  class MetadataRequestHandler(wsgi.Application):
      """Serve metadata."""
  
      def __init__(self):
          self._cache = memcache.Client(FLAGS.memcached_servers, debug=0)
  
      def get_metadata(self, address):
          if not address:
              raise exception.FixedIpNotFoundForAddress(address=address)
  
          cache_key = 'metadata-%s' % address
          data = self._cache.get(cache_key)
          if data:
              return data
  
          try:
              data = base.get_metadata_by_address(address)
          except exception.NotFound:
              return None
  
          self._cache.set(cache_key, data, 15)
  
          return data
  
      @webob.dec.wsgify(RequestClass=wsgi.Request)
      def __call__(self, req):
          remote_address = req.remote_addr
          if FLAGS.use_forwarded_for:
              remote_address = req.headers.get('X-Forwarded-For', remote_address)
  
          if os.path.normpath("/" + req.path_info) == "/":
              return(base.ec2_md_print(base.VERSIONS + ["latest"]))
  
          try:
              meta_data = self.get_metadata(remote_address)
          except Exception:
              LOG.exception(_('Failed to get metadata for ip: %s'),
                            remote_address)
              msg = _('An unknown error has occurred. '
                      'Please try your request again.')
              exc = webob.exc.HTTPInternalServerError(explanation=unicode(msg))
              return exc
          if meta_data is None:
              LOG.error(_('Failed to get metadata for ip: %s'), remote_address)
              raise webob.exc.HTTPNotFound()
  
          try:
              data = meta_data.lookup(req.path_info)
          except base.InvalidMetadataPath:
              raise webob.exc.HTTPNotFound()
  
          return base.ec2_md_print(data)
  