## Create a `websocket` { #create-a-websocket }

In your **FastAPI** application, create a `websocket`:

{* ../../docs_src/websockets/tutorial001.py hl[1,46:47] *}

/// note | Technical Details

You could also use `from starlette.websockets import WebSocket`.

**FastAPI** provides the same `WebSocket` directly just as a convenience for you, the developer. But it comes directly from Starlette.

///

        .Builder()
        .webSocketUpgrade(serverListener)
        .build(),
    )
    val webSocket: WebSocket = newWebSocket()
    clientListener.assertOpen()
    val server = serverListener.assertOpen()
    webSocket.send("Hello, WebSockets!")
    serverListener.assertTextMessage("Hello, WebSockets!")
    closeWebSockets(webSocket, server)
  }

  @Test
  fun binaryMessage() {
    webServer.enqueue(

# 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>.

          text: String,
        ) {
          webSocket.send(text)
        }

        override fun onClosing(
          webSocket: WebSocket,
          code: Int,
          reason: String,
        ) {
          webSocket.close(1000, null)
          latch.countDown()
        }

        override fun onFailure(
          webSocket: WebSocket,
          t: Throwable,
          response: Response?,

    taskFaker.runTasks()
    server.webSocket!!.tearDown()
    client.webSocket!!.tearDown()
    taskFaker.close()
  }

  @Test
  fun close() {
    client.webSocket!!.close(1000, "Hello!")
    // This will trigger a close response.
    assertThat(server.processNextFrame()).isFalse()
    server.listener.assertClosing(1000, "Hello!")
    server.webSocket!!.finishReader()
    server.webSocket!!.close(1000, "Goodbye!")

    webSocket: WebSocket,
    code: Int,
    reason: String,
  ) {
    Platform.get().log("[WS $name] onClosed $code", Platform.INFO, null)
    val delegate = delegate
    if (delegate != null) {
      this.delegate = null
      delegate.onClosed(webSocket, code, reason)
    } else {
      events.add(Closed(code, reason))
    }
  }

  override fun onFailure(
    webSocket: WebSocket,
    t: Throwable,

 * Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits=15
 * Sec-WebSocket-Extensions: permessage-deflate; client_no_context_takeover
 * Sec-WebSocket-Extensions: permessage-deflate; server_max_window_bits="15"
 * Sec-WebSocket-Extensions: permessage-deflate; server_max_window_bits=15
 * Sec-WebSocket-Extensions: permessage-deflate; server_no_context_takeover
 * Sec-WebSocket-Extensions: permessage-deflate; server_no_context_takeover;

      object : WebSocketListener() {
        override fun onOpen(
          webSocket: WebSocket,
          response: Response,
        ) = TODO()

        override fun onMessage(
          webSocket: WebSocket,
          text: String,
        ) = TODO()

        override fun onMessage(
          webSocket: WebSocket,
          bytes: ByteString,
        ) = TODO()

            .put("SEC_WEBSOCKET_ACCEPT", "Sec-WebSocket-Accept")
            .put("SEC_WEBSOCKET_EXTENSIONS", "Sec-WebSocket-Extensions")
            .put("SEC_WEBSOCKET_KEY", "Sec-WebSocket-Key")
            .put("SEC_WEBSOCKET_PROTOCOL", "Sec-WebSocket-Protocol")
            .put("SEC_WEBSOCKET_VERSION", "Sec-WebSocket-Version")
            .put("X_WEBKIT_CSP", "X-WebKit-CSP")

func initGlobalGrid(ctx context.Context, eps EndpointServerPools) error {
	hosts, local := eps.GridHosts()
	lookupHost := globalDNSCache.LookupHost
	g, err := grid.NewManager(ctx, grid.ManagerOptions{
		// Pass Dialer for websocket grid, make sure we do not
		// provide any DriveOPTimeout() function, as that is not
		// useful over persistent connections.
		Dialer: grid.ConnectWS(