Asynchronous verification fails on missing header

[Nikita Sychev]

Hello!

Thanks for your library!

I'm trying to switch my old project from older dkimpy version and I decided to try new async functions.

Unfortunately, when I tried to send myself an e-mail without DKIM-Signature header at all, it failed. Here is the stacktrace:

  File "/usr/lib/python3.10/site-packages/aiosmtpd/smtp.py", line 741, in _handle_client
    await method(arg)
  File "/usr/lib/python3.10/site-packages/aiosmtpd/smtp.py", line 1460, in smtp_DATA
    status = await self._call_handler_hook('DATA')
  File "/usr/lib/python3.10/site-packages/aiosmtpd/smtp.py", line 473, in _call_handler_hook
    status = await hook(self, self.session, self.envelope, *args)
  File "/usr/lib/python3.10/site-packages/aiosmtpd/handlers.py", line 228, in handle_DATA
    await self.handle_message(message)
  File "<hidden>", line 26, in handle_message
    dkim_result = await dkim.verify_async(message.as_bytes())
  File "/usr/lib/python3.10/site-packages/dkim/asyncsupport.py", line 119, in verify_async
    return await d.verify(dnsfunc=dnsfunc)
  File "/usr/lib/python3.10/site-packages/dkim/asyncsupport.py", line 97, in verify
    sig, include_headers, sigheaders = self.verify_headerprep(idx=0)
TypeError: cannot unpack non-iterable bool object

Now I just catch TypeError on my side, but actually here the patch:

--- dkim/asyncsupport.py 2023-02-27 23:31:56.605726566 +0600
+++ dkim/asyncsupport.py.patched 2023-02-27 23:39:38.526180586 +0600
@@ -94,7 +94,10 @@

   async def verify(self,idx=0,dnsfunc=get_txt_async):
- sig, include_headers, sigheaders = self.verify_headerprep(idx=0)
+ prep = self.verify_headerprep(idx=0)
+ if not prep:
+ return False
+ sig, include_headers, sigheaders = prep
     return await self.verify_sig(sig, include_headers, sigheaders[idx], dnsfunc)

I didn't find a better way to send patches here, so I hope it's OK to do it here.

[Scott Kitterman (kitterman)]

Thanks. I'll look into it and plan to fix it for the next release.

[Scott Kitterman (kitterman)]

That looks mostly correct. I did it slightly differently in the non-async version of verify. The only issue I see is that the prep = line should have (idx) vice (idx=0) as the idx=0 will override any idx value passed into the function. Thanks. I fixed it to be like the non-async version.

Your patch made it super easy to pinpoint what to do. Very much appreciated. Fix committed to git for the next release.