addSlash isn't a thing in twisted.web

src/allmydata/web/common.py

@@ -101,7 +101,7 @@ def parse_offset_arg(offset):
 def get_root(ctx_or_req):
     req = IRequest(ctx_or_req)
     # the addSlash=True gives us one extra (empty) segment
-    depth = len(req.prepath) + len(req.postpath) - 1
+    depth = len(req.prepath) + len(req.postpath)
     link = "/".join([".."] * depth)
     return link
 

src/allmydata/web/directory.py

@@ -91,7 +91,6 @@ def make_handler_for(node, client, parentnode=None, name=None):
 # support ?t=json but I don't know that all the variants already *did*
 # support that..
 class DirectoryNodeHandler(ReplaceMeMixin, Resource, object):
-    addSlash = True
 
     def __init__(self, client, node, parentnode=None, name=None):
         super(DirectoryNodeHandler, self).__init__()