Re: [quicwg/base-drafts] enforce the active_connection_id_limit (#3201)

[Jana Iyengar <[e-mail]>]

janaiyengar commented on this pull request.

Having chatted about this with @erickinnear and @kazuho, I'm ok with this set of changes. A few suggestions.

> @@ -999,8 +999,10 @@ retired are considered active; any active connection ID can be used.
 An endpoint SHOULD ensure that its peer has a sufficient number of available and
 unused connection IDs.  Endpoints store received connection IDs for future use
 and advertise the number of connection IDs they are willing to store with the
-active_connection_id_limit transport parameter.  An endpoint SHOULD NOT provide
-more connection IDs than the peer's limit.
+active_connection_id_limit transport parameter.  An endpoint MUST NOT provide
+more connection IDs than the peer's limit.  An endpoint that receives more
+connection IDs than its advertised active_connection_id_limit MUST close the
+connection with an error of type CONNECTION_ID_LIMIT_ERROR.

I'm ok with this being a MUST. I would suggest that you explicitly add a note saying that an endpoint is expected to store enough information all received CIDs to be able to generate this error. It might be redundant, but that's ok.

> @@ -999,12 +999,15 @@ retired are considered active; any active connection ID can be used.
 An endpoint SHOULD ensure that its peer has a sufficient number of available and
 unused connection IDs.  Endpoints store received connection IDs for future use
 and advertise the number of connection IDs they are willing to store with the
-active_connection_id_limit transport parameter.  An endpoint SHOULD NOT provide
-more connection IDs than the peer's limit.
-
-An endpoint SHOULD supply a new connection ID when it receives a packet with a
-previously unused connection ID or when the peer retires one, unless providing
-the new connection ID would exceed the peer's limit.  An endpoint MAY limit the
+active_connection_id_limit transport parameter.  An endpoint MUST NOT provide
+more connection IDs than the peer's limit.  An endpoint that receives more
+connection IDs than its advertised active_connection_id_limit MUST close the
+connection with an error of type CONNECTION_ID_LIMIT_ERROR.
+
+An endpoint SHOULD supply a new connection ID when the peer retires a connection
+ID. If an endpoint provided fewer connection IDs than the peer's
+active_connection_id_limit, it MAY supply a new connection ID when it receives
+a packet with a previously unused connection ID.  An endpoint MAY limit the

Is this MAY necessary? It's certainly not disallowed. I understand how this could be useful, but it seems like a purely server-side optimization, which doesn't need to be specified. Alternatively, how about something like: "An endpoint can but is not required to send as many connection IDs as the peer can store."

> @@ -4590,8 +4595,14 @@ preferred_address (0x000d):
 active_connection_id_limit (0x000e):
 
 : The maximum number of connection IDs from the peer that an endpoint is willing
-  to store. This value includes only connection IDs sent in NEW_CONNECTION_ID
-  frames. If this parameter is absent, a default of 0 is assumed.
+  to store. This value includes connection IDs sent in NEW_CONNECTION_ID frames,
+  the connection ID used during the handshake as well as the connection ID
+  provided in the preferred_address transport parameter.

Suggested edit: "This value includes the connection ID received during the handshake, that received in the preferred_address transport parameter, and those received in NEW_CONNECTION_ID frames."

> @@ -4590,8 +4595,14 @@ preferred_address (0x000d):
 active_connection_id_limit (0x000e):
 
 : The maximum number of connection IDs from the peer that an endpoint is willing
-  to store. This value includes only connection IDs sent in NEW_CONNECTION_ID
-  frames. If this parameter is absent, a default of 0 is assumed.
+  to store. This value includes connection IDs sent in NEW_CONNECTION_ID frames,
+  the connection ID used during the handshake as well as the connection ID
+  provided in the preferred_address transport parameter.
+  Unless a zero-length connection ID is being used, the value of the
+  active_connection_id_limit parameter MUST be no less than 2. If this
+  transport parameter is absent, a default of 2 is assumed.
+  When a zero-length connection ID is being used, the active_connection_id_limit
+  parameter MUST NOT be sent.

I said detrimental because we used to not encode values on the wire that were illegal ... but we've walked away from that in other places too :-/ I'm ok with this.

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