thin_ws

tiye/thin_ws is a thin WebSocket FFI package for MoonBit with typed JSON messaging.

• Node.js server: starts a ws-based WebSocket server with UUID-keyed client registry.
• Browser client: wraps the native WebSocket API, auto-builds the backend URL for dev/prod.

Both sides speak typed MoonBit values. JSON serialization/deserialization is handled internally — callers never touch raw text.

Server usage

let send = @thin_ws.run_json_server(
  5022,           // port — nothing hardcoded
  "/ws",          // path
  fn(sid) { log("connect \{sid}") },
  fn(sid, op : MyClientOp) { handle(sid, op) },
  fn(sid) { log("disconnect \{sid}") },
)
// send a typed message to a client
send(sid, my_server_event)

Browser client usage

let url = @thin_ws.make_ws_url("5173,5174", 5022, "/ws")
let (socket, send) = @thin_ws.connect_json(
  url,
  fn() { log("opened") },
  fn(payload : MyServerEvent) { apply_delta(payload) },
  fn() { log("closed") },
)
// send a typed op to the server (no-op until the connection opens)
send(my_client_op)

Key design choices

• Generic over message types — In : @json.FromJson / Out : ToJson
• No hardcoded ports or paths — all caller-supplied
• Ready guard on browser side — send is safe to call before the socket opens; messages are dropped silently
• Log helpers — server_log, ws_log, ws_warn, ws_error write to runtime monitor and console

Import

In your moon.pkg (or moon.pkg.json):

import {
  "tiye/thin_ws" @thin_ws,
}

node_server.mbt compiles only for ["js"] target (Node.js). browser_client.mbt compiles only for ["js"] target (browser).