A node behind a NAT is reachable only through A's relay. When the reachable node C dials it through the relay, the relayed node dials C back directly (C is public) and the relayed connection is upgraded to a direct one.

This is a unilateral reversal — only the NATed node dials, because C is public. It is not a coordinated hole punch; see ../hole-punch for the both-NATed case.

Topology

node B ──── lan ──── router (NAT) ──── wan ──── bootstrap A (relay)
                                        └────── node C (reachable)

bootstrap A — public node on the wan, autonat + relay server.
router — lan -> wan masquerade and no inbound forward.
node B — nat=auto, on the lan. NotReachable, takes a relay reservation on A. When C reaches it through the relay, its hole-punching handler dials C back directly and closes the relayed connection.
node C — nat=auto, directly on the wan, so it is Reachable. It dials B through the relay.

Run

make testNatIntegration \
  STORAGE_INTEGRATION_TEST_INCLUDES=tests/integration/nat/connection-reversal/testconnectionreversal.nim

Builds the shared image and brings the compose topology up and down. Rootless, but needs the host netfilter modules — if the router fails on iptables: sudo modprobe iptable_nat nf_conntrack.

Expected result

B is NotReachable behind the relay, C is Reachable. C downloads from B through the relay, which opens a relayed connection; B then dials C back directly. The direct upgrade has no REST surface, so the test asserts on B's log line Direct connection created..

Per-run container logs (router, bootstrap, client, node) are written before teardown to tests/integration/logs/<timestamp>__NAT_connection_reversal/<test>/<service>.log.