# WebSockets { #websockets }

You can use <a href="https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API" class="external-link" target="_blank">WebSockets</a> with **FastAPI**.

## Install `WebSockets` { #install-websockets }

Make sure you create a [virtual environment](../virtual-environments.md){.internal-link target=_blank}, activate it, and install `websockets`:

<div class="termy">

```console
$ pip install websockets

---> 100%

# Testing WebSockets { #testing-websockets }

You can use the same `TestClient` to test WebSockets.

For this, you use the `TestClient` in a `with` statement, connecting to the WebSocket:

{* ../../docs_src/app_testing/tutorial002.py hl[27:31] *}

/// note

For more details, check Starlette's documentation for <a href="https://www.starlette.io/testclient/#testing-websocket-sessions" class="external-link" target="_blank">testing WebSockets</a>.

            webSockets.add(client.newWebSocket(request, clientListener))
            attempts.countDown()
          }
        }
      }
    clientListener.setNextEventDelegate(reconnectOnFailure)
    webSockets.add(client.newWebSocket(request, clientListener))
    attempts.await()
    synchronized(webSockets) {
      for (webSocket in webSockets) {
        webSocket.cancel()
      }
    }

    - advanced/dataclasses.md
    - advanced/middleware.md
    - advanced/sub-applications.md
    - advanced/behind-a-proxy.md
    - advanced/templates.md
    - advanced/websockets.md
    - advanced/events.md
    - advanced/testing-websockets.md
    - advanced/testing-events.md
    - advanced/testing-dependencies.md
    - advanced/async-tests.md
    - advanced/settings.md
    - advanced/openapi-callbacks.md

* Досконаліші (але однаково прості) техніки для оголошення **глибоко вкладених моделей JSON** (завдяки Pydantic).
* Багато додаткових функцій (завдяки Starlette) як-от:
    * **WebSockets**
    * надзвичайно прості тести на основі HTTPX та `pytest`
    * **CORS**
    * **Cookie Sessions**
    * ...та більше.

## Продуктивність

* HTTP Caching- [RFC 9111](https://datatracker.ietf.org/doc/html/rfc9111)
* HTTP/1.1 - [RFC 9112](https://datatracker.ietf.org/doc/html/rfc9112)
* HTTP/2 - [RFC 9113](https://datatracker.ietf.org/doc/html/rfc9113)
* Websockets - [RFC 6455](https://datatracker.ietf.org/doc/html/rfc6455)
* SSE - [Server-sent events](https://html.spec.whatwg.org/multipage/server-sent-events.html#server-sent-events)

    val e = InterruptedIOException("timeout")
    if (cause != null) e.initCause(cause)
    return e
  }

  /**
   * Stops applying the timeout before the call is entirely complete. This is used for WebSockets
   * and duplex calls where the timeout only applies to the initial setup.
   */
  fun timeoutEarlyExit() {
    check(!timeoutEarlyExit)
    timeoutEarlyExit = true
    timeout.exit()
  }

  /**

* Tích hợp **GraphQL** với <a href="https://strawberry.rocks" class="external-link" target="_blank">Strawberry</a> và các thư viện khác.
* Nhiều tính năng mở rộng (cảm ơn Starlette) như:
    * **WebSockets**
    * kiểm thử vô cùng dễ dàng dựa trên HTTPX và `pytest`
    * **CORS**
    * **Cookie Sessions**
    * ...và nhiều hơn thế.

## Hiệu năng

* **GraphQL** Integration mit <a href="https://strawberry.rocks" class="external-link" target="_blank">Strawberry</a> und anderen Bibliotheken.
* Viele zusätzliche Funktionen (dank Starlette) wie:
    * **WebSockets**
    * extrem einfache Tests auf Basis von `httpx` und `pytest`
    * **CORS**
    * **Cookie Sessions**
    * ... und mehr.

## Performanz

* Tecniche più avanzate (ma ugualmente semplici) per dichiarare **modelli JSON altamente nidificati** (grazie a Pydantic).
* E altre funzionalità (grazie a Starlette) come:
    * **WebSockets**
    * **GraphQL**
    * test molto facili basati su `requests` e `pytest`
    * **CORS**
    * **Cookie Sessions**
    * ...e altro ancora.

## Prestazioni