From 9fbf9b223dc26262b1cf23f623f89283ee9c8375 Mon Sep 17 00:00:00 2001
From: Bob Halley <halley@dnspython.org>
Date: Sun, 29 Sep 2019 13:39:41 -0700
Subject: [PATCH] When doing xfr, do not compare with expiration if it is None.
 [Issue #390]

---
 dns/query.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/dns/query.py b/dns/query.py
index fd8988ec..ac15895a 100644
--- a/dns/query.py
+++ b/dns/query.py
@@ -607,7 +607,8 @@ def xfr(where, zone, rdtype=dns.rdatatype.AXFR, rdclass=dns.rdataclass.IN,
     first = True
     while not done:
         mexpiration = _compute_expiration(timeout)
-        if mexpiration is None or mexpiration > expiration:
+        if mexpiration is None or \
+           (expiration is not None and mexpiration > expiration):
             mexpiration = expiration
         if use_udp:
             _wait_for_readable(s, expiration)
-- 
2.47.3