---
title: "mix-websocket concepts & security"
description: "How MixWebSocket differs from the browser WebSocket, and what the IPR exit sees."
schemaType: "TechArticle"
section: "Developers"
lastUpdated: "2026-06-05"
---

import { Callout } from 'nextra/components'

# Concepts & security

## Differences from the browser WebSocket

`MixWebSocket` extends `EventTarget` and mirrors the standard WebSocket surface where it makes sense. Differences are intentional and follow from the underlying WASM transport:

| Browser `WebSocket` | `MixWebSocket` | Why |
|---|---|---|
| Synchronous constructor; readiness via the `open` event | Asynchronous constructor; readiness via `await ws.opened()` or the `open` event | The mixnet connect, smoltcp socket open, and TLS handshake all happen in the worker. |
| `binaryType: 'blob' \| 'arraybuffer'` (default Blob) | `binaryType` is fixed to `'arraybuffer'` | Blob construction in a Web Worker requires a transferable; ArrayBuffer is the lowest common denominator. |
| `bufferedAmount` | Not exposed | Writes queue inside the worker; no main-thread byte counter. |
| `send()` returns `void` synchronously | `send()` returns `Promise<void>` | The send hops the worker boundary. |
| `close(code, reason)` returns `void` | `close(code, reason)` returns `Promise<void>` | Same reason. |
| `protocols` argument supports string or string[] | Same | (no difference) |

The standard `open`, `message`, `close`, and `error` events fire as you would expect. `MessageEvent.data` is `string` for text frames and `ArrayBuffer` for binary frames.

## Security model

`mix-websocket` follows the shared [mixnet exit security model](/developers/concepts/exit-security). What that means specifically for WS/WSS:

| At the IPR exit | What's visible |
|---|---|
| Secure (`wss://`) | Destination IP and port. Frames are TLS ciphertext, terminating at the destination. |
| Plain (`ws://`) | Destination IP and port, plus every frame in plaintext. |

<Callout type="warning">
TLS terminates inside the WASM bundle (via [`rustls`](https://docs.rs/rustls) in smolmix-wasm), not in the browser. Mozilla's CA bundle is compiled into the WASM. Use `wss://` for any non-public traffic; `ws://` is visible to the IPR in full.
</Callout>
