### [Fast Fallback](https://square.github.io/okhttp/4.x/okhttp/okhttp3/-ok-http-client/-builder/fast-fallback/)

Since version 5.0, `OkHttpClient` supports fast fallback, which is our implementation of Happy Eyeballs [RFC 6555](https://datatracker.ietf.org/doc/html/rfc6555).

<span style="color: green;">INFO</span>:     Waiting for application startup.
<span style="color: green;">INFO</span>:     Application startup complete.
```

</div>

!!! note
    La commande `uvicorn main:app` fait référence à :

    * `main` : le fichier `main.py` (le module Python).
    * `app` : l'objet créé dans `main.py` via la ligne `app = FastAPI()`.

# FORMAT NOT DOCUMENTED YET (parser is urltestparser.js)

# Based on http://trac.webkit.org/browser/trunk/LayoutTests/fast/url/script-tests/segments.js
http://example\t.\norg http://example.org/foo/bar s:http h:example.org p:/
http://user:pass@foo:21/bar;par?b#c  s:http u:user pass:pass h:foo port:21 p:/bar;par q:?b f:#c
http:foo.com  s:http h:example.org p:/foo/foo.com
\t\s\s\s:foo.com\s\s\s\n  s:http h:example.org p:/foo/:foo.com

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šaipus
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# Conjunctions
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tikko
turpretī
arī
kaut
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tādēļ
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tikvien
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kamēr
# Particles
ar
diezin
droši
diemžēl
nebūt
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taču
nu
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tiklab
iekšpus
nedz
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nevis

ASM: a very small and fast Java bytecode manipulation framework
Copyright (c) 2000-2011 INRIA, France Telecom
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
  notice, this list of conditions and the following disclaimer.

 */
package okhttp3

import okio.IOException

/**
 * Listener for connection events. Extend this class to monitor the new connections and closes.
 *
 * All event methods must execute fast, without external locking, cannot throw exceptions,
 * attempt to mutate the event parameters, or be reentrant back into the client.
 * Any IO - writing to files or network should be done asynchronously.
 */
@ExperimentalOkHttpApi

```Python hl_lines="20-37 39-40"
{!../../../docs_src/path_operation_advanced_configuration/tutorial006.py !}
```

/**
 * Modern reflection based SocketAdapter for Conscrypt class SSLSockets.
 *
 * This is used directly for providers where class name is known e.g. the Google Play Provider
 * but we can't compile directly against it, or in fact reliably know if it is registered and
 * on classpath.
 */
open class AndroidSocketAdapter(private val sslSocketClass: Class<in SSLSocket>) : SocketAdapter {
  private val setUseSessionTickets: Method =

---

FastAPI is a modern, fast (high-performance), web framework for building APIs with Python based on standard Python type hints.

The key features are:

* **Fast**: Very high performance, on par with **NodeJS** and **Go** (thanks to Starlette and Pydantic). [One of the fastest Python frameworks available](#performance).
* **Fast to code**: Increase the speed to develop features by about 200% to 300%. *

But you can return a `JSONResponse` directly from your *path operations*.

It might be useful, for example, to return custom headers or cookies.

## Return a `Response`

In fact, you can return any `Response` or any sub-class of it.

!!! tip
    `JSONResponse` itself is a sub-class of `Response`.

And when you return a `Response`, **FastAPI** will pass it directly.