Android re-establishes the VpnService interface on every route change, which
replaces tun0 with a fresh device. The file drop listeners are bound to the
overlay address of the interface being swapped out: the IPv4 one dies with
accept4: invalid argument and never comes back, so a peer dialing the overlay
IPv4 address gets an RST. Restart the receiver once the new device is in place.
Files move directly between peers over the overlay, with no server in the
path. The receiver listens on the WireGuard address only, so the port is
unreachable from outside the tunnel, and every offer is matched to a known
peer before anything is read.
Consent is the default: an offer carries metadata alone, and no payload
moves until the receiver accepts. Policy is per profile and device-local —
off, ask, or auto-accept, with per-sender exceptions on top.
Policy and history live in the profile's preferences, so removing a profile
takes its file drop state with it. Transfers interrupted by a restart are
settled on load; nothing survives to finish them, and left alone they would
sit in the log as permanently pending.
The Android bindings pull payload bytes through a chunk-returning stream:
gomobile copies a []byte argument into a fresh Java array and never copies
it back, so a fill-my-buffer method would hand back the right length with
no data.
