A gateway with the selected Ethernet cable unplugged can still open an
AF_PACKET socket and join the relay room. That makes clients see a connected LAN
gateway even though DHCP and LAN discovery cannot make the physical round trip.
Check the selected Linux interface's sysfs carrier file before creating the raw
socket. If sysfs reports carrier 0, fail before the gateway joins the relay.
Missing or unrecognized carrier files remain allowed so this does not reject
interfaces where the kernel cannot expose link state in that form. README and
TESTING now document the preflight and the operator fix.
Test Plan:
All cargo commands used these environment variables:
RUSTUP_HOME=/tmp/softlan-vpn-rustup
CARGO_HOME=/tmp/softlan-vpn-cargo
- cargo test -p lanparty-gateway \
packet::tests::detects_disconnected_interfaces_from_sysfs_carrier
- cargo test -p lanparty-gateway
- cargo fmt --check
- cargo test --workspace
- cargo clippy --workspace --all-targets -- -D warnings
- git diff --check
Refs: PLAN.md wired Ethernet gateway requirement
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