Charon API

Charon is the relay backend of the Veil project. It lets clients running different messenger apps exchange messages with each other by acting as a neutral, anonymous relay: the server routes messages between addresses, but it never has access to their plaintext content.

What it does

• Registration — a client connects over WebTransport and registers with an address (token) and a device_id. The server keeps a live session (Client) for that pair for as long as the connection is open.
• Message relaying — a client sends a message addressed to a destination address (src → dst). Charon looks up all currently connected sessions for that destination and forwards the message to them directly.
• Offline storage — if the destination has no active session, the message is queued in in-memory storage and delivered once that address reconnects.

Privacy model

Message payloads are treated as opaque bytes (Vec<u8>) end to end — Charon never parses or inspects their content, it only reads the src/dst addresses needed to route them.

Architecture

• Transport: WebTransport, via the internal wt-server / wt-client crates.
• Routes (src/routes):
  • register — client registration (AuthorizationRoute).
  • message — message send/relay (MessageRoute).
• Services (src/services):
  • authorization — registers a client's wt-client session under a CId { token, device_id }.
  • clients_manager — in-memory registry of live client sessions, keyed by CId, looked up by destination address.
  • message — decides whether to forward a message to a live session or queue it in storage.
  • message_storage — in-memory store of undelivered messages per destination address.
  • veil_client — the outbound side, used to push a message over an existing session and get back a response.