HTTP Header

An HTTP header is a component of the header section in an HTTP request and response messages, used to convey additional information about the request or response between the client and server. HTTP headers are essential for defining parameters of the HTTP transaction, and they facilitate the proper handling and transfer of data.

Types

1. Request Headers. Set by the client, these include information about the client browser, the requested resource, credentials, and more.
2. Response Headers. Sent by the server, these provide information about the server, the data being sent, how to handle the data, and more.
3. General Headers. Apply to both requests and responses, dealing with caching, connection management, and other general data.
4. Entity Headers. Describe the length, type, and other characteristics of the body of the request or response.

Functions

1. Content-Type. Specifies the media type of the resource.
2. Authorization. Contains credentials for authenticating the client to the server.
3. User-Agent. Identifies the client software making the request to the server.
4. Accept. Specifies the media types that the client is willing to receive.
5. Cookies. Sends stored cookies from the client to the server.
6. Extensibility. Custom headers can be used for additional functionality not covered by standard headers.

HTTP headers are integral to HTTP, providing flexibility and configurability in HTTP requests and responses, and are critical for security, caching, authentication, and more in web interactions.