Overview

Miso.WebSocket provides a full-duplex WebSocket client that integrates directly into the MVU loop. Every operation — connecting, sending, and closing — returns an Effect, making WebSocket communication a first-class citizen of the update function.

Quick start

import Miso
import Miso.WebSocket

data Action
  = Connect
  | Connected  WebSocket
  | Received   MisoString
  | Disconnected Closed
  | WsError    MisoString
  | Send       MisoString
  | Disconnect

-- Hold the socket handle in the model so we can send later
data Model = Model { ws :: WebSocket }

update :: Action -> Effect p props Model Action
update Connect =
  connectText "wss://echo.websocket.org"
    Connected Disconnected Received WsError
update (Connected sock) =
  modify (\m -> m { ws = sock })
update (Received msg) =
  io_ (consoleLog msg)
update (Send txt) = do
  sock <- gets ws
  sendText sock txt
update Disconnect = do
  sock <- gets ws
  close sock
update _ = pure ()

Connection variants

Five connect functions cover every wire format. They all share the same callback signature — onOpen, onClosed, onMessage, onError — but differ in how the message payload is decoded:

connectText

MisoString — plain UTF-8 text

connectJSON

json (FromJSON json) — auto-decoded from JSON

connectBLOB

Blob — raw binary Blob

connectArrayBuffer

ArrayBuffer — raw binary buffer

connect

Payload json — mixed; caller pattern-matches the payload ADT

Sending messages

The WebSocket handle delivered to onOpen must be stored in the model and passed to each send call:

sendText        :: WebSocket -> MisoString -> Effect p props model action
sendJSON        :: ToJSON json => WebSocket -> json -> Effect p props model action
sendBLOB        :: WebSocket -> Blob -> Effect p props model action
sendArrayBuffer :: WebSocket -> ArrayBuffer -> Effect p props model action

Lifecycle

• Always call close when the connection is no longer needed to avoid resource leaks. It is safe to call close multiple times — subsequent calls are no-ops.
• socketState lets you query the current SocketState (CONNECTING, OPEN, CLOSING, CLOSED) asynchronously.
• emptyWebSocket (= -1) is a null sentinel you can store in the model before a connection has been established.

Types

• WebSocket — an opaque integer file descriptor returned by onOpen.
• URL — alias for MisoString.
• SocketState — four-state enum mirroring the JS readyState property.
• Closed — close event data: closedCode, wasClean, reason.
• CloseCode — typed close codes from RFC 6455.
• Payload — JSON value | BLOB Blob | TEXT MisoString | BUFFER ArrayBuffer.
• Blob / ArrayBuffer — re-exported from Miso.FFI.Internal.

See also

• Miso.EventSource — Server-Sent Events (SSE), a unidirectional alternative
• Miso.Fetch — one-shot HTTP requests
• Miso.Effect — Effect, io_