circuitv2: clarify what to do when data limit is reached (#526)

This documents the rust-libp2p behaviour when more data than is allowed is transferred over a relayed connection.  js-libp2p will take the same approach.  go-libp2p may need to be updated.

---------

Co-authored-by: Max Inden <[email protected]>
Co-authored-by: Prithvi Shahi <[email protected]>

Author: 3 people

relay/circuit-v2.md

@@ -4,7 +4,7 @@ This is the version 2 of the libp2p Circuit Relay protocol.
 
 | Lifecycle Stage | Maturity       | Status | Latest Revision |
 | --------------- | -------------- | ------ | --------------- |
-| 3A              | Recommendation | Active | r2, 2023-01-31  |
+| 3A              | Recommendation | Active | r3, 2023-02-28  |
 
 Authors: [@vyzo]
 
@@ -255,6 +255,16 @@ accidental termination according to its connection management policy.
 If a relay server becomes overloaded however, it may still drop a
 connection with reservations in order to maintain its resource quotas.
 
+If more data than the limit specified in the `data` field is transferred
+over the relayed connection, or the relayed connection has been open for
+longer than `duration`, the relay should reset the stream to the source
+and the stream to the destination.
+
+If the reservation for the connection has expired then the relay may
+apply any connection management policy to the connection as normal otherwise
+it should retain the connection, unless doing so would prevent it from
+maintaining its resource quotas.
+
 ***Note: Implementations _should not_ accept reservations over already relayed connections.***
 
 #### Connection Initiation