softlan-vpn/README.md

# softlan-vpn

Monorepo for a Layer 2 over QUIC LAN party bridge.

## Workspace crates

- `lanparty-proto`: shared frame format, MAC validation, MTU helpers.
- `lanparty-ctrl`: control-plane messages (join/hello/role/version).
- `lanparty-net`: shared relay endpoint parsing and resolution.
- `lanparty-obs`: shared diagnostics/logging event models.
- `lanparty-client-core`: platform-agnostic client session state.
- `lanparty-client-route`: Windows relay-route inspection.
- `lanparty-client-tap`: TAP-Windows6 adapter discovery and frame I/O.
- `lanparty-client-win`: Windows TAP + route/metric handling binary.
- `lanparty-gateway`: Linux AF_PACKET gateway binary.
- `lanparty-relay`: public QUIC relay binary.

### `lanparty-proto`

Transport-agnostic tunnel contract shared by all binaries:

- overlay datagram header encoding and decoding
- Ethernet frame header parsing
- MAC address parsing and identity validation
- QUIC datagram to TAP MTU budget helpers

### `lanparty-ctrl`

Reliable control-plane schema shared by the QUIC stream handlers:

- endpoint hello messages with role, room, MAC, and datagram budget
- server welcome mode, reject, peer lifecycle, stats, and disconnect messages
- initial room gateway-presence status in server welcomes
- room-code, role/MAC, peer-id, and effective-MTU validation
- length-prefixed JSON control frames for reliable QUIC streams

### `lanparty-obs`

Shared diagnostics and structured logging vocabulary:

- gateway/relay frame logs with MACs, ethertype, length, peer, and action
- tunnel counters shared by control messages and runtime diagnostics
- client connectivity/TAP diagnostics and user-facing status messages

### `lanparty-net`

Shared network address handling for tunnel binaries:

- relay DNS name, IP literal, and socket-address parsing
- UDP/443 default for bare relay hosts
- relay address resolution before tunnel interface activation

### `lanparty-client-core`

Platform-neutral remote client relay session:

- relay QUIC connection with pinned relay certificate trust
- client hello with room, virtual MAC, and datagram budget
- welcome/reject handling with assigned peer id and effective TAP MTU
- QUIC DATAGRAM support and negotiated datagram budget diagnostics
- reliable relay control-event reads for peer lifecycle messages
- Ethernet frame send/receive helpers over QUIC DATAGRAM
- client tunnel statistics for frame/datagram rx/tx and drops
- reliable client stats snapshot sends for relay diagnostics
- best-effort graceful disconnect messages before QUIC close

### `lanparty-client-route`

Windows route-table boundary:

- read-only best-route lookup for a relay destination IP
- selected source address, next hop, interface index/LUID, prefix, and metric
- interface index/LUID lookup from Windows network adapter GUIDs
- scoped IP interface MTU overrides with restore-on-drop behavior
- scoped IP interface metric overrides with restore-on-drop behavior
- scoped default-route suppression with restore-on-drop behavior
- unicast IP address snapshots for TAP diagnostics
- scoped host-route pinning for the relay IP on the pre-TAP interface
- non-Windows builds return a clear unsupported-platform error

### `lanparty-client-tap`

Windows TAP adapter boundary:

- TAP-Windows6 adapter discovery from the Windows network adapter registry
- TAP `NetworkAddress` registry configuration for the tunnel MAC identity
- `\\.\Global\{NetCfgInstanceId}.tap` device path construction
- blocking Ethernet frame reads/writes through the TAP device handle
- TAP driver IOCTL helpers for media status, adapter MAC, and MTU

### `lanparty-relay`

Public relay binary and relay-owned room state:

- QUIC endpoint binding and first-stream hello/welcome admission
- room admission for clients and gateways
- one gateway per room, duplicate client MAC rejection, and room limits
- stable effective room MTU chosen before Ethernet datagrams flow
- live Ethernet datagram forwarding with no ingress reflection
- reliable `PeerJoined`/`PeerLeft` notifications to existing room peers
- L2 safety filters for jumbo, switch-control, DHCP-server, and IPv6-RA frames
- client broadcast/multicast, unknown-unicast, and total bandwidth limiting
- malformed peer datagram disconnect threshold
- peer stats control events retained for relay diagnostics
- graceful disconnect control events propagated as peer-leave reasons
- per-peer last-seen timestamps in relay room snapshots
- peer leave cleanup for room membership and MAC indexes

## Build

```bash
cargo check --workspace
```

## Relay

```bash
cargo run -p lanparty-relay -- --listen 443/udp --dev-cert-der-out relay-cert.der
```

`--listen` accepts either a socket address or a UDP port shorthand such as
`443/udp`. The relay binds a QUIC endpoint, accepts a control-stream `hello`,
replies with `welcome` or `reject`, and forwards live Ethernet QUIC datagrams
between accepted peers in the same room. It currently uses a generated
self-signed development certificate; `--dev-cert-der-out` writes that
certificate so the gateway and client can pin it in development. Production
certificate handling remains future work. Ethernet forwarding decisions are
logged with room, peer, MAC, ethertype, action, drop reason, and target count.
Unknown unicast from a client is forwarded only to the gateway port; unknown
unicast from the gateway is dropped instead of flooded to every remote client.
When a peer joins or leaves, the relay sends a reliable lifecycle control event
to peers that are still present in the room. Newly joined peers also receive
`PeerJoined` events for peers that were already present.

### MVP Trust Model

The MVP relay terminates QUIC for every client and gateway connection. QUIC
protects traffic on the public network path, but the relay process sees
plaintext Ethernet frames while forwarding them between peers in a room. That is
acceptable for the first LAN-party proof, where the relay is an operator-trusted
component, but it is not end-to-end encrypted.

Future room-key payload encryption should keep the relay-visible routing header
small and leave only Ethernet payload bytes encrypted end-to-end between clients
and the LAN gateway.

## Gateway

```bash
cargo run -p lanparty-gateway -- \
  --relay lanparty-relay.local \
  --server-name lanparty-relay.local \
  --relay-ca-cert relay-cert.der \
  --room ROOM1 \
  --iface eth0
```

The gateway connects to the relay as `role = gateway`, completes the
control-stream hello/welcome handshake, opens an AF_PACKET socket on the LAN
interface with promiscuous packet membership, and bridges Ethernet frames
between the relay and wired LAN until shutdown. `--relay` accepts a DNS name or
socket address; bare hosts default to UDP/443. It tracks remote-client source
MACs seen from relay traffic and periodically emits small CAM refresh frames so
the physical switch keeps those MACs associated with the gateway port. Gateway
frame logs include direction, peer id when present, MACs, ethertype/length,
frame length, action, and drop reason. The gateway also tracks frame/datagram
counters and periodically sends stats snapshots to the relay. Relay lifecycle
events seed and retire remote-client MACs for CAM refresh even before that
client sends traffic. On shutdown, the gateway sends a best-effort disconnect
control message before closing QUIC so the relay can report the intended reason.

## Windows Client

```bash
cargo run -p lanparty-client-win -- \
  --relay lanparty-relay.local \
  --server-name lanparty-relay.local \
  --relay-ca-cert relay-cert.der \
  --room ROOM1
```

The Windows client binary currently connects to the relay as `role = client`
with a generated locally administered virtual MAC persisted in
`lanparty-client-identity.json`, resolves the relay DNS name before TAP
activation, completes the control-stream hello/welcome handshake, pins a host
route for the resolved relay IP on the current pre-TAP interface, verifies that
the relay route still uses that pinned host route after TAP activation, and then
bridges Ethernet frames between the relay and the first TAP-Windows6 adapter
until shutdown. `--relay` accepts a DNS name or socket address; bare hosts
default to UDP/443. Before opening the adapter, it writes the
generated tunnel MAC to the TAP driver's `NetworkAddress` registry setting.
The startup status reports whether the relay already has a LAN gateway for the
room.
`--virtual-mac` can still override the stored identity for manual testing. On
Windows it sets the TAP IP interface MTU to the relay-selected MTU, marks the
TAP media connected, and reports the driver MAC/MTU before forwarding frames,
along with the TAP interface index/LUID. The client applies a scoped TAP
interface metric and disables TAP default routes while it runs, periodically
rechecks that the relay route remains pinned, then restores the previous route
policy on exit. Startup still fails before bridging if the driver-reported MAC
does not match the tunnel identity, because an already-initialized Windows TAP
adapter may need to be disabled/enabled or reinstalled before it reloads the
configured `NetworkAddress`.
It prints and reports client diagnostics snapshots with relay reachability,
route-pinning, QUIC datagram budget, TAP status/IP, frame/datagram counters,
and drops. The periodic diagnostics refresh the TAP unicast IP so DHCP results
that arrive after bridging starts become visible in later status lines.
Relay lifecycle events are logged as they arrive, including gateway joins and
peer leaves. The client remembers peer identities from join and catch-up events
so later leave logs can identify a disconnected LAN gateway or client MAC when
that peer was known.