A five hour flight is enough time to write several unit tests. So, yesterday I started working on the band sets for 2019 and I wrote tests and new library functions and fixed a latent bug in an old library function. And now we’re in Hawaii!
Today I learned a couple of things that they don’t tell you in the official documentation or on Stack Overflow. If you want to display some information in a table and that information updates and you want to display those updates, then you have to hook things up the hard way, and not the way everyone tells you to do it.
Several days and a lot of testing later, I think I have the answer: don’t try to build a play-by-email service in Google AppEngine. The limitations imposed by the environment make it a bad place to do a lot of email traffic that requires anything other than text/plain or text/html. Because Google has defined javax.mail.Transport to use the AppEngine mail service, you can’t choose to connect to a different SMTP host; if you specify an external SMTP server (such as SendGrid or Pobox) in the Session, Google’s Transport implementation ignores it and still uses the AppEngine mail service. When you try to use a web API to send your message through SendGrid, that screws up the MIME headers and your message won’t validate (if it’s even readable) at the receiver’s end.
That said, I have finally figured out how to prepare and send a PGP signed MIME message such that it arrives and validates properly. Since nobody else has written that down on the web (that I could find), I’ll detail the recipe here.