- Fixed problem with header folding that caused the first line to be

folded too long (Updated test test_add_body_length since l= tag is no
      longer at the beginning of a line

dkim/__init__.py

@@ -299,7 +299,7 @@ def text(s):
     if type(s) is str: return s
     return s.encode('ascii')
 
-def fold(header):
+def fold(header, namelen=0):
     """Fold a header line into multiple crlf-separated lines at column 72.
 
     >>> text(fold(b'foo'))
@@ -318,14 +318,18 @@ def fold(header):
         i += 3
         pre = header[:i]
         header = header[i:]
-    while len(header) > 72:
-        i = header[:72].rfind(b" ")
+    # 72 is the max line length we actually want, but the header field name
+    # has to fit in the first line too (See Debian Bug #863690).
+    maxleng = 72 - namelen
+    while len(header) > maxleng:
+        i = header[:maxleng].rfind(b" ")
         if i == -1:
-            j = 72
+            j = maxleng
         else:
             j = i + 1
         pre += header[:j] + b"\r\n "
         header = header[j:]
+        namelen = 0
     return pre + header
 
 def load_pk_from_dns(name, dnsfunc=get_txt):
@@ -485,7 +489,7 @@ class DomainSigner(object):
 
     header_value = b"; ".join(b"=".join(x) for x in fields)
     if not standardize:
-      header_value = fold(header_value)
+      header_value = fold(header_value, namelen=len(header_name))
     header_value = RE_BTAG.sub(b'\\1',header_value)
     header = (header_name, b' ' + header_value)
     h = HashThrough(self.hasher())
@@ -510,7 +514,7 @@ class DomainSigner(object):
     header_value = b"; ".join(b"=".join(x) for x in fields) + b"\r\n"
 
     if not standardize:
-      header_value = fold(header_value)
+      header_value = fold(header_value, namelen=len(header_name))
 
     return header_value
 

dkim/tests/test_dkim.py

@@ -103,7 +103,7 @@ Y+vtSBczUiKERHv1yRbcaQtZFh5wtiRrN04BLUTD21MycBX5jYchHjPY/wIDAQAB"""
         sig = dkim.sign(
             self.message, b"test", b"example.com", self.key, length=True)
         msg = email.message_from_string(self.message.decode('utf-8'))
-        self.assertIn('\n l=%s' % len(msg.get_payload() + '\n'), sig.decode('utf-8'))
+        self.assertIn('; l=%s' % len(msg.get_payload() + '\n'), sig.decode('utf-8'))
         res = dkim.verify(sig + self.message, dnsfunc=self.dnsfunc)
         self.assertTrue(res)