HTTP can run in two modes:

• Non-Persistent - each response/request is sent over separate TCP connection
• Persistent - re-using same TCP connection for all request/responses

There are two HTTP message types:

• Request
• Response

Both have a start line, headers, an empty line and optional body.

First line in the Request Message is called a request line. The subsequent lines are called headers line.

Request line has three fields:

1. Method
2. URL
3. HTTP version

First line in Response Message is called a status line. Then we have six header lines and then entity body.

Status line has three fields:

1. Protocol version
2. Status code
3. Corresponding status message

HTTP is a Stateless protocol. Cookie is the primary mechanism for maintaining state. Cookies allows a web server to know:

• Whether you've visited before
• Whether you're logged in
• What's in your shopping cart
• What language you selected