Handle Unicode in get_txt.

dkim/__init__.py

@@ -356,14 +356,8 @@ def verify(message, logger=None, dnsfunc=get_txt):
             (base64.b64encode(bodyhash), sig[b'bh']))
         return False
 
-    # dnstxt wants Unicode
-    try:
-        selector = sig[b's'].decode('ascii')
-        domain = sig[b'd'].decode('ascii')
-    except UnicodeDecodeError:
-        return False
-    name = "%s._domainkey.%s." % (selector, domain)
-    s = dnsfunc(name).encode('utf-8')
+    name = sig[b's'] + b"._domainkey." + sig[b'd'] + b"."
+    s = dnsfunc(name)
     if not s:
         return False
     try:

dkim/dns.py

@@ -49,7 +49,20 @@ def get_txt_pydns(name):
 # Prefer dnspython if it's there, otherwise use pydns.
 try:
     import dns.resolver
-    get_txt = get_txt_dnspython
+    _get_txt = get_txt_dnspython
 except ImportError:
     import DNS
-    get_txt = get_txt_pydns
+    _get_txt = get_txt_pydns
+
+
+def get_txt(name):
+    """Return a TXT record associated with a DNS name.
+
+    @param name: The bytestring domain name to look up.
+    """
+    # pydns needs Unicode, but DKIM's d= is ASCII (already punycoded).
+    try:
+        unicode_name = name.decode('ascii')
+    except UnicodeDecodeError:
+        return None
+    return _get_txt(unicode_name).decode('utf-8')

dkim/tests/test_dkim.py

@@ -53,8 +53,12 @@ class TestSignAndVerify(unittest.TestCase):
         self.key = read_test_data("test.private")
 
     def dnsfunc(self, domain):
+        try:
+            domain = domain.decode('ascii')
+        except UnicodeDecodeError:
+            return None
         self.assertEqual('test._domainkey.example.com.', domain)
-        return read_test_data("test.txt").decode('utf-8')
+        return read_test_data("test.txt")
 
     def test_verifies(self):
         # A message verifies after being signed.