///

/// info

To declare headers, you need to use `Header`, because otherwise the parameters would be interpreted as query parameters.

///

## Automatic conversion

`Header` has a little extra functionality on top of what `Path`, `Query` and `Cookie` provide.

Most of the standard headers are separated by a "hyphen" character, also known as the "minus symbol" (`-`).

```Python hl_lines="6"
{!../../docs_src/path_operation_advanced_configuration/tutorial005.py!}
```

If you open the automatic API docs, your extension will show up at the bottom of the specific *path operation*.

<img src="/img/tutorial/path-operation-advanced-configuration/image01.png">

```

</div>

That would work for most of the cases. 😎

You could use that command for example to start your **FastAPI** app in a container, in a server, etc.

## ASGI Servers

Let's go a little deeper into the details.

FastAPI uses a standard for building Python web frameworks and servers called <abbr title="Asynchronous Server Gateway Interface">ASGI</abbr>. FastAPI is an ASGI web framework.

        Mac mac = Mac.getInstance("HmacMD5");
        MessageDigest md = MessageDigest.getInstance("MD5");
        mac.init(key);
        byte[] dk = mac.doFinal(MD5_CONSTANT);
        try {
            // little endian
            md.update((byte) ( ms_usage & 0xFF ));
            md.update((byte) ( ( ms_usage >> 8 ) & 0xFF ));
            md.update((byte) ( ( ms_usage >> 16 ) & 0xFF ));

</pre>
```

</div>

It is **HIGHLY encouraged** that you write or copy the code, edit it and run it locally.

Using it in your editor is what really shows you the benefits of FastAPI, seeing how little code you have to write, all the type checks, autocompletion, etc.

---

## Install FastAPI

The first step is to install FastAPI.

                </mxCell>
                <mxCell id="32" value="" style="pointerEvents=1;shadow=0;dashed=0;html=1;fillColor=#505050;labelPosition=center;verticalLabelPosition=bottom;verticalAlign=top;outlineConnect=0;align=center;shape=mxgraph.office.devices.laptop;strokeColor=none;" parent="33" vertex="1">
                    <mxGeometry width="500" height="350" as="geometry"/>
                </mxCell>

                        RC4 rc4 = new RC4(ntlm2SessionKey);
                        rc4.update(masterKey, 0, 16, exchangedKey, 0);
/* RC4 was not added to Java until 1.5u7 so let's use our own for a little while longer ...
                        try {
                            Cipher rc4 = Cipher.getInstance("RC4");
                            rc4.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(ntlm2SessionKey, "RC4"));

                </mxCell>
                <mxCell id="32" value="" style="pointerEvents=1;shadow=0;dashed=0;html=1;fillColor=#505050;labelPosition=center;verticalLabelPosition=bottom;verticalAlign=top;outlineConnect=0;align=center;shape=mxgraph.office.devices.laptop;strokeColor=none;" parent="33" vertex="1">
                    <mxGeometry width="500" height="350" as="geometry"/>
                </mxCell>

	// OpMerged is several operations merged into one.
	OpMerged
)

const (
	// FlagCRCxxh3 indicates that, the lower 32 bits of xxhash3 of the serialized
	// message will be sent after the serialized message as little endian.
	FlagCRCxxh3 Flags = 1 << iota

	// FlagEOF the stream (either direction) is at EOF.
	FlagEOF

	// FlagStateless indicates the message is stateless.
	// This will retain clients across reconnections or

/*

- test projects for each of these
- how to categorize the problems so that the id of the problem can be match to a page with descriptive help and the test
  project
- nice little sample projects that could be run in the core as well as integration tests

All Possible Errors
- invalid lifecycle phase (maybe same as bad CLI param, though you were talking about embedder too)
- <module> specified is not found