Summary:
Draft-19 onwards effectively punted version negotiation to QUICv2. Now receiving version negotiation on clients is treated as an immediate termination of the connection.
The transport parameter format has also changed to no longer include any reference to the QUIC version. To avoid us (Facebook) having to turn off QUIC traffic in production, our server needs to be able to parse these transport parameters from our older clients. To achieve this when parsing the transport parameters we will, as a temporary measure, check for the Facebook QUIC version to determine which transport parameter format we are parsing. Luckily for us the version we chose maps nicely to an implausible length for the transport parameters (0xface).
Note that this diff still has the client send the old transport parameter format, so that the rollout can be staged.
Reviewed By: yangchi
Differential Revision: D15203481
fbshipit-source-id: dfaaddc3acc76434461b04430b82a0902138c060
