Re: [quicwg/base-drafts] Allow CONNECTION_CLOSE in 0-RTT (#3440)

[Mike Bishop <[e-mail]>]

MikeBishop commented on this pull request.

This feels a little sticky:
- App-level CLOSE MUST only be sent in 0-RTT or 1-RTT
- If you're sending a CLOSE in 0-RTT, you OUGHT TO repeat it in an Initial packet, except that you can't if it's application-level.

Does that explicitly mean sending two different error codes at the two levels?

> -client has Handshake keys.  Under these circumstances, a server SHOULD send a
-CONNECTION_CLOSE frame in both Handshake and Initial packets to ensure that at
-least one of them is processable by the client.  Similarly, a peer might be
-unable to read 1-RTT packets, so an endpoint SHOULD send CONNECTION_CLOSE in
-Handshake and 1-RTT packets prior to confirming the handshake.  These packets
-can be coalesced into a single UDP datagram; see {{packet-coalesce}}.
+* A client will always know whether the server has Handshake keys (see
+  {{discard-initial}}), but it is possible that a server does not know whether
+  the client has Handshake keys.  Under these circumstances, a server SHOULD
+  send a CONNECTION_CLOSE frame in both Handshake and Initial packets to ensure
+  that at least one of them is processable by the client.
+
+* A client that sends CONNECTION_CLOSE in a 0-RTT packet cannot be assured of
+  the server has accepted 0-RTT and so sending a CONNECTION_CLOSE frame of type
+  0x1c in an Initial packet makes it more likely that the server can receive
+  the close signal, even if the application error code might not be received.

In a handshake that requires multiple flights (HRR, client certs, etc.), the client might also have Handshake keys but not 1-RTT keys.  This isn't the common case, but I believe it's still permitted?

Also, why are the other two SHOULDs, while this is merely a statement about likely outcomes?

> @@ -5680,10 +5689,10 @@ Reason Phrase:
   This SHOULD be a UTF-8 encoded string {{!RFC3629}}.
 
 The application-specific variant of CONNECTION_CLOSE (type 0x1d) can only be
-sent using an 1-RTT packet ({{QUIC-TLS}}, Section 4).  When an application
-wishes to abandon a connection during the handshake, an endpoint can send a
-CONNECTION_CLOSE frame (type 0x1c) with an error code of 0x15a ("user_canceled"
-alert; see {{?TLS13}}) in an Initial or a Handshake packet.
+sent using 0-RTT or 1-RTT packets ({{QUIC-TLS}}, Section 4).  When an
+application wishes to abandon a connection during the handshake, an endpoint
+can send a CONNECTION_CLOSE frame (type 0x1c) with an error code of 0x15a
+("user_canceled" alert; see {{?TLS13}}) in an Initial or a Handshake packet.

This feels slightly at odds with the above advice to repeat the frame in both 0-RTT and Initial.

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