Re: [quicwg/base-drafts] When to send the SETTINGS frame (#2945)

[Nick Harper <[e-mail]>]

The asymmetry between having client send SETTINGS in an H3 frame and a server sending SETTINGS in TP doesn't bother me because those settings serve different purposes. The client's SETTINGS serves solely to indicate H3 configuration for the connection on which it was sent. The server's SETTINGS serves both that purpose and to indicate H3 configuration that will be accepted for early data sent on a future connection. We already have an asymmetry in the purpose of the two SETTINGS frames.

Why not consider the two use cases for the server's SETTINGS separately? The second use case (use these settings for early data on a future connection) would be better served if it were more tightly coupled to other information sent to the client about what to do on that future connection. That could be done by sending it in a NewSessionTicket extension; it could also be done by putting it in the TLS handshake (e.g. in EncryptedExtensions or in transport parameters).

If we consider the use cases completely separately, then we could have the server send an H3 SETTINGS frame for the current connection and put settings in NST or EE for use for the future connection. This leads to duplication of data sent (if n NSTs are sent, the settings are sent n+1 times), although it allows the server to specify different parameters for the current connection vs the future ones. Using EE instead of NST reduces the duplication when multiple NSTs are sent.

A design of both client and server sending SETTINGS as an H3 frame to apply for the current connection (and only that connection) meets the requirements for symmetry. The requirement for allowing non-default SETTINGS to apply in early data is solved by having the server signal the SETTINGS for early data of a future connection via some other mechanism, either in the NST or in EE. Is putting server SETTINGS in both an H3 frame and EE preferable to putting them just in EE?

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