Re: [quicwg/base-drafts] Application close should be disallowed in Initial or Handshake (#3158)

[Kazuho Oku <[e-mail]>]

@nibanks 
>> The problem is that then there would be two requirements:
>> * Application protocols MUST define a generic error code that can be exposed unencrypted.
>> * QUIC stacks need to provide an API that tells the application if a CONNECTION_CLOSE frame is going to be sent using Initial packets. Each application needs to consult that in order to determine the error code to be sent.
> 
> For the first bullet, that's a decision for the application protocols.

At the very least, the transport draft needs to suggest that, otherwise an application protocol might leak information through APPLICATION_CLOSE frames carried in Initial packets.

> For the second, I'd argue you don't need any special API. If the app terminates the connection before the "handshake complete" notification then any error code it would pass down to the QUIC API would not be sent in a 1-RTT packet. That state is enough for the app to make an intelligent decision. Another option is to have an API flag that indicate the application close is allowed to be send unencrypted.

Requiring such interaction seems more complicated than just forbidding the use of APPLICATION_CLOSE in Initial and Handshake packets in favor of CONNECTION_CLOSE(user_canceled). How a QUIC stack enforces that is an implementation issue, but for example, when an application instructs the QUIC stack to close the connection, the stack can decide which of the two frames to send based on the current state.

> If you assume this is not the common case, then I don't think we need optimize for it. The app just closes the connection after the handshake completes.

I'd dispute that this is an optimization. This is about addressing a security concern that we have so far left open.

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