diff --git a/synapse/util/httpresourcetree.py b/synapse/util/httpresourcetree.py
new file mode 100644
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--- /dev/null
+++ b/synapse/util/httpresourcetree.py
@@ -0,0 +1,98 @@
+# Copyright 2016 OpenMarket Ltd
+#
+# 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.
+
+from twisted.web.resource import Resource
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+def create_resource_tree(desired_tree, root_resource):
+ """Create the resource tree for this Home Server.
+
+ This in unduly complicated because Twisted does not support putting
+ child resources more than 1 level deep at a time.
+
+ Args:
+ web_client (bool): True to enable the web client.
+ root_resource (twisted.web.resource.Resource): The root
+ resource to add the tree to.
+ Returns:
+ twisted.web.resource.Resource: the ``root_resource`` with a tree of
+ child resources added to it.
+ """
+
+ # ideally we'd just use getChild and putChild but getChild doesn't work
+ # unless you give it a Request object IN ADDITION to the name :/ So
+ # instead, we'll store a copy of this mapping so we can actually add
+ # extra resources to existing nodes. See self._resource_id for the key.
+ resource_mappings = {}
+ for full_path, res in desired_tree.items():
+ logger.info("Attaching %s to path %s", res, full_path)
+ last_resource = root_resource
+ for path_seg in full_path.split('/')[1:-1]:
+ if path_seg not in last_resource.listNames():
+ # resource doesn't exist, so make a "dummy resource"
+ child_resource = Resource()
+ last_resource.putChild(path_seg, child_resource)
+ res_id = _resource_id(last_resource, path_seg)
+ resource_mappings[res_id] = child_resource
+ last_resource = child_resource
+ else:
+ # we have an existing Resource, use that instead.
+ res_id = _resource_id(last_resource, path_seg)
+ last_resource = resource_mappings[res_id]
+
+ # ===========================
+ # now attach the actual desired resource
+ last_path_seg = full_path.split('/')[-1]
+
+ # if there is already a resource here, thieve its children and
+ # replace it
+ res_id = _resource_id(last_resource, last_path_seg)
+ if res_id in resource_mappings:
+ # there is a dummy resource at this path already, which needs
+ # to be replaced with the desired resource.
+ existing_dummy_resource = resource_mappings[res_id]
+ for child_name in existing_dummy_resource.listNames():
+ child_res_id = _resource_id(
+ existing_dummy_resource, child_name
+ )
+ child_resource = resource_mappings[child_res_id]
+ # steal the children
+ res.putChild(child_name, child_resource)
+
+ # finally, insert the desired resource in the right place
+ last_resource.putChild(last_path_seg, res)
+ res_id = _resource_id(last_resource, last_path_seg)
+ resource_mappings[res_id] = res
+
+ return root_resource
+
+
+def _resource_id(resource, path_seg):
+ """Construct an arbitrary resource ID so you can retrieve the mapping
+ later.
+
+ If you want to represent resource A putChild resource B with path C,
+ the mapping should looks like _resource_id(A,C) = B.
+
+ Args:
+ resource (Resource): The *parent* Resourceb
+ path_seg (str): The name of the child Resource to be attached.
+ Returns:
+ str: A unique string which can be a key to the child Resource.
+ """
+ return "%s-%s" % (resource, path_seg)
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