From e3b1d4f536029fa383cde5746b37af862ac8c72b Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Thu, 22 Oct 2020 07:17:52 -0400
Subject: [PATCH] enforce the type requirement

---
 src/allmydata/web/common.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/allmydata/web/common.py b/src/allmydata/web/common.py
index bcdf21581..d970cc918 100644
--- a/src/allmydata/web/common.py
+++ b/src/allmydata/web/common.py
@@ -21,6 +21,9 @@ from twisted.web import (
     resource,
     template,
 )
+from twisted.web.iweb import (
+    IRequest,
+)
 from twisted.web.template import (
     tags,
 )
@@ -163,6 +166,10 @@ def get_root(req):
     :return: A string like ``../../..`` with the correct number of segments to
         reach the root.
     """
+    if not IRequest.providedBy(req):
+        raise TypeError(
+            "get_root requires IRequest provider, got {!r}".format(req),
+        )
     depth = len(req.prepath) + len(req.postpath)
     link = "/".join([".."] * depth)
     return link