What does an HTTP header include and what role does it play in data transfer?

An HTTP header is a part of an HTTP request or response that contains metadata about the message. It includes key-value pairs that convey information about content type, encoding, length, cookies, authentication, caching, and other parameters.

The role of HTTP headers is to ensure proper interpretation and processing of data between the client and server. For example, the Content-Type header indicates the format of the data being transmitted (JSON, HTML, image, etc.), and Authorization transmits authentication data.

Example of an HTTP header:

GET /index.html HTTP/1.1
Host: example.com
User-Agent: Mozilla/5.0
Accept: text/html

Here, the headers Host, User-Agent, and Accept help the server understand where the request came from, who sent it, and what data formats the client is willing to accept.