Programmatic probing of new paths

[levaitamas]

@nemethf and I have been trying to migrate a client connection. It seems, based on the example code, one just need to rebind the client endpoint to a new UDP socket. Is this the recommended approach?

Furthermore, RFC 9000 allows the client to validate a path even before migrating the connection. In quinn is it possible to validate a path before rewriting the endpoint address? This would allow us to migrate only when the server can be reached from the new address.

Thanks!