<img src="/img/tutorial/websockets/image01.png">

You can type messages in the input box, and send them:

<img src="/img/tutorial/websockets/image02.png">

And your **FastAPI** application with WebSockets will respond back:

<img src="/img/tutorial/websockets/image03.png">

You can send (and receive) many messages:

<img src="/img/tutorial/websockets/image04.png">

And all of them will use the same WebSocket connection.

# If you're looking at this file in a different repo and want to make a change, please go to the
# common-files repo, make the change there and check it in. Then come back to this repo and run
# "make update-common".

# Copyright Istio Authors
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.

* It should not be client-specific.
  * In Istio sidecars, historically we had a lot of client-specific xDS. For example, putting the xDS-client's IP back into the xDS response. This makes efficient control plane implementation (most notably, caching), extremely challenging.

By default, OkHttp will attempt a `MODERN_TLS` connection.  However by configuring the client connectionSpecs you can allow a fall back to `COMPATIBLE_TLS` connection if the modern configuration fails.

```java
OkHttpClient client = new OkHttpClient.Builder()
    .connectionSpecs(Arrays.asList(ConnectionSpec.MODERN_TLS, ConnectionSpec.COMPATIBLE_TLS))

      var low = 0
      var high = size
      var match: String? = null
      while (low < high) {
        var mid = (low + high) / 2
        // Search for a '\n' that marks the start of a value. Don't go back past the start of the
        // array.
        while (mid > -1 && this[mid] != '\n'.code.toByte()) {
          mid--
        }
        mid++

        // Now look for the ending '\n'.
        var end = 1

      private val source: BufferedSource = source.buffer()

      // Visible for testing.
      @JvmField var dynamicTable = arrayOfNulls<Header>(8)

      // Array is populated back to front, so new entries always have lowest index.
      private var nextHeaderIndex = dynamicTable.size - 1

      @JvmField var headerCount = 0

      @JvmField var dynamicTableByteCount = 0

    client.processNextFrame()
    taskFaker.runTasks()
    server.webSocket!!.pong("pong 3".encodeUtf8())
    client.processNextFrame()

    // After 500ms the client automatically pings and the server pongs back.
    taskFaker.advanceUntil(ns(500L))
    server.processNextFrame() // Ping.
    client.processNextFrame() // Pong.

    // After 1000ms the client will attempt a ping 2, but we don't process it. That'll cause the

<div class="termy">

```console
$ pip install pytest

---> 100%
```

</div>

It will detect the files and tests automatically, execute them, and report the results back to you.

Run the tests with:

<div class="termy">

```console
$ pytest

================ test session starts ================
platform linux -- Python 3.6.9, pytest-5.3.5, py-1.8.1, pluggy-0.13.1

der stattfindet, wenn Ihre API-Anwendung die *externe API* aufruft, wird als „Callback“ („Rückruf“) bezeichnet. Denn die Software, die der externe Entwickler geschrieben hat, sendet einen Request an Ihre API und dann *ruft Ihre API zurück* (*calls back*) und sendet einen Request an eine *externe API* (die wahrscheinlich vom selben Entwickler erstellt wurde).

In diesem Fall möchten Sie möglicherweise dokumentieren, wie diese externe API aussehen *sollte*. Welche *Pfadoperation* sie haben sollte,...

Each section gradually builds on the previous ones, but it's structured to separate topics, so that you can go directly to any specific one to solve your specific API needs.

It is also built to work as a future reference.

So you can come back and see exactly what you need.

## Run the code

All the code blocks can be copied and used directly (they are actually tested Python files).