WrapDialContext and WrapConn registered the dial and the connection
independently, so a sweep landing between the dial finishing and WrapConn
cancelled only the dial registration: the connection dialed on the old
network entered the fresh registry and survived the network change.
Replace the pair with a Dial handle. Sweep marks pending dials under the
sweeper mutex, and WrapConn decides under the same mutex: a swept dial's
connection is closed and ErrSwept returned, so the caller redials on the
new network; otherwise the connection transfers to the registry with no
window in between.
On a network switch (e.g. cellular to WiFi) the management, signal and
relay sockets stay bound to the old network and look alive until the OS
tears them down — measured at 5 seconds of dead air on Android, while
the UI kept claiming Connected. The Android client papered over this
with a full engine restart, paying for it with a torn-down TUN device
and discarded peer state.
Introduce client/netsweep: connections register on dial and deregister
on close, and a sweep closes everything registered while aborting
in-flight dials through sweep-cancellable dial contexts. The aborted
dials matter: a relay dial started on the dying network would otherwise
hold the reconnect loop hostage for the QUIC handshake timeout. After a
sweep every failure surfaces as an ordinary read/write error and the
existing retry loops redial immediately on the new network.
The sweeper reaches the three long-lived connections through the same
options that carry the netstate gate: a gRPC dial option wraps the
management and signal transports (reconnects included), and the relay
client wraps its connection in one place for the picker, the guard and
foreign relays alike. Everything is nil-safe; platforms that inject no
sweeper are untouched.
Mobile clients expose the sweep as NotifyNetworkChange. Measured on
Android against the engine restart it replaces: recovery in 1.6s
instead of 3.2s, no Disconnected flash, and the TUN device, WireGuard
config and peer state survive.
Zoltán Papp