You can get Headers and Cookies with the Request Object, and how to set it is by using the Response Object.

How to get cookies?

Consider the following HTTP request:

GET /hello HTTP/1.1
Host: localhost:8000
User-Agent: curl/7.74.0
Accept: */*
Cookie: a=123

You can get the Cookie value with:

print(
    server['request'].headers.get(b'cookie')
)

A bytes-like object will be returned:

bytearray(b'a=123')

What if there are two cookies?

Cookie: a=123
Cookie: a=xyz

In this case a list object will be returned:

[bytearray(b'a=123'), bytearray(b'a=xyz')]

There is a better way to get cookies with:

print(
    server['request'].cookies.get('a')
)

It then may return:

['123'] or ['123', 'xyz']

How to set cookies?

There are two ways.

First, using the set_header of the Response Object:

server['response'].set_header('Set-Cookie', 'a=xyz')

And the proper way is by using the set_cookie. It provides a convenient parameter for easily set cookie expiration, etc.

server['response'].set_cookie('a', 'xyz', expires=3600)

Get the values of multiple fields as a list

In HTTP, some fields are allowed to have the same name, such as Cookie, Accept-Encoding, etc.

In such special cases, request.headers.getlist() can be used to retrieve all values at once.

In the request header as follows:

Accept-Encoding: br
Accept-Encoding: gzip, deflate

print(request.headers.getlist(b'accept-encoding')) will return a list with three items:

[b'br', b'gzip', d'deflate']