When doing xfr, do not compare with expiration if it is None.

[Issue #390]

diff --git a/dns/query.py b/dns/query.py
index fd8988ec81d10f811d771091d3a03bf99d78c4d2..ac15895ae1cac270186bcdf949ce10ea0c51d0bc 100644 (file)
--- 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)