A peer that has lost connection state (crash, restart, route change)
signals so by sending a "Stateless Reset" datagram — bytes shaped like
a short-header packet whose trailing 16 bytes equal a
`stateless_reset_token` previously communicated by the peer.
Pre-fix the tokens were stored (via NEW_CONNECTION_ID into the
[PathValidator] pool, and via the peer's `statelessResetToken`
transport parameter) but never matched against arriving datagrams —
a peer's stateless reset looked indistinguishable from noise and the
connection lingered until idle timeout, or worse, an attacker could
spam look-like-noise packets toward our integrity counter.
Implementation:
* `QuicConnection.isStatelessReset(datagram)` — short-header-form
+ size + trailing-16-bytes comparison. Matches against the peer's
advertised token AND every unused entry in `pathValidator`'s
pool. Constant-time per-token compare per §10.3.1 to avoid
leaking token bits via timing.
* `PathValidator.unusedTokenForSequence(seq)` — accessor for the
above to walk the pool.
* Parser pre-empts AEAD/HP parsing: `feedDatagramInner` checks every
short-header-form datagram before the loop. False-positive rate
of a real short-header packet (whose trailing 16 bytes are the
AEAD tag) matching a known token is 2^-128, negligible in
practice. Defense-in-depth: the AEAD-failure branch in
`feedShortHeaderPacket` retains a redundant check for
second-packet-of-coalesced edge cases.
* On match, `markClosedExternally("stateless reset received from
peer")` transitions silently to CLOSED — no CONNECTION_CLOSE
emission per §10.3.1.
Limitation: tokens for an actively-used DCID we migrated to via
`PathValidator.tryStartValidation` are lost when the entry leaves
the unused pool. Acceptable for the audio-rooms scope (no migration);
documented in the kdoc.
Test: `StatelessResetDetectionTest` (5 cases) covers token-match
silent-close, unknown-trailer no-close, pool-stored token match,
long-header form rejected, too-short datagram rejected.
https://claude.ai/code/session_01XGmmaVuy2wsSZQx2AqN2ik
Claude
50ea477426