Xynq Daemon

Backend daemon for Xynq.

The daemon manages peer discovery, secure networking, and communication between devices. Native applications communicate with the daemon over IPC, while daemons communicate over QUIC.

Serialization

Channel	Format
Native App ↔ Daemon	Protocol Buffers
Daemon ↔ Daemon	Postcard (Serde binary format)

Protocol definitions are available in xynq-proto.

Status

• ✅ IPC service
• ✅ QUIC networking
• ✅ LAN discovery
• ✅ Relay discovery
• ✅ Mutual authentication
• 🚧 Native applications

Architecture

                 Native Application
                         │
                    IPC (Protobuf)
                         │
                  ┌──────────────┐
                  │ Xynq Daemon  │
                  ├──────────────┤
                  │ IPC Service  │
                  │ Network Svc  │
                  └──────┬───────┘
                         │
            ┌────────────┴────────────┐
            │                         │
     LAN Transport             Relay Transport
      ┌──────────┐             ┌──────────┐
      │   mDNS   │             │  Relay   │
      │   QUIC   │             │   QUIC   │
      └────┬─────┘             └────┬─────┘
           │                        │
           └──────────┬─────────────┘
                      │
               Remote Daemon

The daemon consists of two services:

• IPC Service — Receives commands and streams events to native applications.
• Network Service — Discovers peers, establishes QUIC sessions, authenticates devices, and transports daemon messages.

Cluster

Each synchronization group is called a cluster.

A cluster consists of:

• Cluster ID (UUID v4)
• Device ID (UUID v7)
• Shared cluster secret

These values are generated by the native application and provisioned to the daemon through IPC.

A new device joins using:

• QR code
• Human-readable pairing code

Discovery

Xynq supports both LAN and Relay discovery.

LAN

LAN discovery uses mDNS.

Every daemon continuously advertises its presence.

When another daemon is discovered:

• Cluster IDs must match.
• Device IDs must differ.

The daemon with the smaller UUID v7 initiates the QUIC connection. The other daemon accepts it. This prevents duplicate simultaneous connections.

Relay

Each daemon establishes a persistent QUIC connection to the relay server.

The relay organizes connected daemons into cluster groups.

• If a cluster does not exist, the relay creates it.
• Otherwise, the daemon joins the existing cluster group.

Daemons in the same relay group can discover each other regardless of their network.

Authentication

Authentication is completely mutual.

Once a QUIC connection is established, both peers simultaneously send:

• nonce
• timestamp
• HMAC-SHA256 signature

signature =
HMAC_SHA256(
    shared_cluster_secret,
    nonce || timestamp
)

Both peers verify:

• HMAC signature
• Timestamp validity
• Nonce freshness

The connection is accepted only if every check succeeds.

Since QUIC provides independent bidirectional streams, authentication happens concurrently without client/server roles.

Transport

All daemon-to-daemon communication uses QUIC bidirectional streams.

Payloads are serialized using Postcard.

Typical messages include:

• Authentication
• Peer metadata
• Cluster events
• Control messages
• Heartbeats

Each logical operation uses its own QUIC stream, allowing multiple concurrent operations over a single connection.

Repository Structure

src/
├── ipc/
│   ├── command.rs          # IPC request definitions
│   └── event.rs            # IPC event definitions
│
├── network/
│   ├── lan/
│   │   ├── crypto.rs       # QUIC TLS certificates & credentials
│   │   └── discovery.rs    # mDNS discovery
│   │
│   ├── relay/
│   │   └── crypto.rs       # QUIC TLS certificates & credentials
│   │
│   ├── session/
│   │   ├── message.rs      # Daemon protocol messages
│   │   └── sign.rs         # HMAC authentication
│   │
│   ├── lan.rs              # LAN transport
│   ├── relay.rs            # Relay transport
│   └── session.rs          # QUIC session management
│
├── config.rs               # Configuration
├── id.rs                   # Cluster & device identifiers
├── ipc.rs                  # IPC service
├── logging.rs              # Logging initialization
├── network.rs              # Network service
├── service.rs              # Shared service abstractions
├── transport.rs            # Common transport interface
└── main.rs                 # Entry point