Implements the client side of connection migration so a path that
stops receiving ACKs (NAT rebind, route flap, dead peer) can be
recovered without a fresh handshake:
1. NEW_CONNECTION_ID frames from the server are stored in a
PathValidator pool (was: parsed and dropped).
2. After PATH_PROBE_PTO_THRESHOLD consecutive PTOs, the driver
calls triggerPathMigrationLocked(); the validator picks an
unused CID and queues a PATH_CHALLENGE with a CSPRNG payload.
3. The writer drains the challenge into the next outbound 1-RTT
packet using the new DCID; a RecoveryToken.PathChallenge is
attached so loss recovery can re-queue on packet drop.
4. Inbound PATH_RESPONSE that byte-equals the outstanding payload
promotes destinationConnectionId to the new bytes and queues
RETIRE_CONNECTION_ID for the prior sequence.
5. RFC 9000 §8.2.4: validation is abandoned after 3 * PTO;
timeout transitions to PathValidationState.Failed for retry.
Spec coverage:
- §5.1.1 initial DCID is sequence 0
- §5.1.2 retire_prior_to enforcement (clamping per §19.15
reordering rule, force-retire of cached entries below
watermark)
- §8.2.2 byte-equal payload match
- §8.2.4 3 * PTO abandonment
- §19.15 frame-encoding error checks (retire_prior_to >
sequence_number, invalid CID/token length)
- §19.16 RETIRE_CONNECTION_ID frame codec + protocol-violation
close on retire of an unissued sequence
Observability: QlogObserver gains onPathValidationStarted /
Succeeded / Failed and onConnectionIdActivated / Retired hooks
for qvis sequence diagrams.
Tests: PathValidatorTest (state-machine unit) +
ClientPathMigrationTest (full round-trip through InMemoryQuicPipe:
NEW_CONNECTION_ID -> trigger -> PATH_CHALLENGE -> PATH_RESPONSE ->
DCID rotated + RETIRE_CONNECTION_ID emitted). Existing
PathValidationTest (peer-initiated PATH_CHALLENGE echo) continues
to pass unchanged.
https://claude.ai/code/session_01PVVhSQXvw4K4oQ46FzpgaT
Claude
435c49bae9