Split out create_resource_tree to a separate file

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)