[quicwg/base-drafts] Method for associating stateless resets with connections is unclear (#2591)

[Benjamin Saunders <[e-mail]>]

Relevant sections:
[§10.4](https://quicwg.org/base-drafts/draft-ietf-quic-transport.html#stateless-reset):
> An endpoint that receives a packet where removal of packet protection fails MUST check the last 16 bytes of that packet

[§10.4.1](https://quicwg.org/base-drafts/draft-ietf-quic-transport.html#detecting-a-stateless-reset)
> An endpoint detects a potential stateless reset when a incoming packet with a short header either cannot be associated with a connection, cannot be decrypted, or is marked as a duplicate packet. The endpoint then compares the last 16 bytes of the packet with the Stateless Reset Token provided by its peer

There is no single token that a packet which cannot be associated with a connection can be compared against, and although §10.4 could be read as a suggestion that decryption should be attempted first, this is impossible if the associated connection is unknown. Connections with non-zero-length IDs cannot be identified by remote address, as multiple connections may share the same remote address.

The obvious approach here is to maintain a look-up table mapping stateless reset tokens to connections, and consult it on receipt of a packet that cannot be associated with a connection, perhaps after first ensuring that the packet originates from a known remote address. Should this be made explicit?

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