Catch more ascii encoding errors to improve resilience against bad data

(LP: #1844189)

CHANGES

@@ -15,6 +15,8 @@
    conversion issues
  - Fix variable initialization so mailformed mails missing body From do not
    cause a traceback (LP: #1844161)
+ - Catch more ascii encoding errors to improve resilience against bad data
+   (LP: #1844189)
 
 1.1.0 2019-04-12
  - Add SubDomains option to enable signing for sub-domains (LP: #1811535)

dkimpy_milter/__init__.py

@@ -149,7 +149,11 @@ class dkimMilter(Milter.Base):
         elif lname == 'authentication-results':
             self.arheaders.append(val)
         if self.fp:
+            try:
                 self.fp.write(b"%s: %s\n" % (codecs.encode(name, 'ascii'), codecs.encode(val, 'ascii')))
+            except:
+                # Don't choke on header fields with non-ascii garbage in them.
+                pass
         return Milter.CONTINUE
 
     @Milter.noreply
@@ -305,8 +309,13 @@ class dkimMilter(Milter.Base):
                 self.header_i = codecs.decode(d.signature_fields.get(b'i'), 'ascii')
             except TypeError as x:
                 self.header_i = None
+            try:
                 self.header_d = codecs.decode(d.signature_fields.get(b'd'), 'ascii')
                 self.header_a = codecs.decode(d.signature_fields.get(b'a'), 'ascii')
+            except Exception as x:
+                self.dkim_comment = str(x)
+                if milterconfig.get('Syslog'):
+                    syslog.syslog("check_dkim: {0}".format(x))
             if res:
                 if (milterconfig.get('Syslog') and
                         (milterconfig.get('SyslogSuccess') or
@@ -326,7 +335,12 @@ class dkimMilter(Milter.Base):
                         syslog.syslog('DKIM: Fail (saved as {0})'
                                       .format(fname))
                 else:
-                    syslog.syslog('DKIM: Fail ({0})'.format(d.domain.lower()))
+                    if milterconfig.get('Syslog'):
+                        if d.domain:
+                            syslog.syslog('DKIM: Fail ({0})'
+                                          .format(d.domain.lower()))
+                        else:
+                            syslog.syslog('DKIM: Fail, unextractable domain'
             if res:
                 result = 'pass'
             else: