add a PING frame, when acknowledging packets during the handshake

[marten-seemann]

When acknowledging packets during the handshake, we should add a PING frame to the packet if otherwise we'd just send an ACK frame. This commonly happens when the ClientHello is split across two packets, and one of them is lost.

This will allow the server to generate an RTT sample, speeding up the rest of the handshake.

[marten-seemann]

@SahibYar You were asking for good first issue you could pick up. Want to take a look at this one?
Let me know if you need any pointers.

[SahibYar]

Sure, thank you @marten-seemann, let me see this.

[SahibYar]

@marten-seemann Adding these lines inside handleAckFrame() in connection.go will be sufficient ?

if s.perspective == protocol.PerspectiveClient && !s.handshakeConfirmed {
   s.handleHandshakeConfirmed()
   
   // See https://github.com/quic-go/quic-go/issues/3851 for details
   // This is not strictly necessary, but it speeds up the handshake.
   s.queueControlFrame(&wire.PingFrame{})
}

[marten-seemann]

handleAckFrame is called when we receive an ACK frame. This needs to be part of the packet packer, probably somewhere in the PackCoalescedPacket code path.

[SahibYar]

@marten-seemann you got the chance to review this PR ?

[marten-seemann]

Sorry, pretty busy right now. I haven't forgotten about it.