The H2 developers are amazing. :-)

NoSuchAlgorithmExceptions. Key generation is *slow* - I guess that's a
good sign. ;-)

Modifying Protocol Buffers (or Thrift, or MessagePack, or any of the free ASN.1 implementations I could find) to support length constraints was more work than writing a custom serialisation format, so I wrote a custom format.

Protocol Buffers will be used for the wire protocol. As a quick test it's now used to serialize transport details when creating an invitation.