The main work here is about bytes vs. strings. This work was
confusing for several reasons:
* pymilter thinks that headers are all strings, but body is bytes
* dkimpy wants to deal with bytes objects generally (though it
accepts a string object as an ed25519 secret key for some reason,
despite requiring bytes as an RSA secret key)
* authres.AuthenticationResultsHeader object converts easily to a
string, but has no direct bytes conversion. meanwhile, it wants
its arguments as strings, but will accept them if they are bytes
and convert them with something like str(), which leaves weird
cruft like "header.a=b'ed25519-sha256'"
* dkimpy_milter/utils.py contains fold() which expects bytes
* self.fp needs to accumulate the on-the-wire version of the message
as a whole (so it needs to be bytes). That means converting the
headers. Header names and values are US-ASCII, per §2.2 of RFC
5322, so they should be convertible cleanly, but we still have to
convert them explicitly so that python knows the right thing to do.
At any rate, tests/runtests all passes with these changes, and the
output for both Authentication-Results: and DKIM-Signature headers
looks the same.
Daniel Kahn Gillmor
ea09bab1a8