HTTP Basics (Sun Java System Web Server 6.1 SP11 NSAPI Programmer's Guide)

Sun Java System Web Server 6.1 SP11 NSAPI Programmer's Guide

HTTP Basics

As a quick summary, the HTTP/1.1 protocol works as follows:

The client (usually a browser) opens a connection to the server and sends a request.
The server processes the request, generates a response, and closes the connection if it finds a Connection: Close header.

The request consists of a line indicating a method such as GET or POST, a Uniform Resource Identifier (URI) indicating which resource is being requested, and an HTTP protocol version separated by spaces.

This is normally followed by a number of headers, a blank line indicating the end of the headers, and sometimes body data. Headers may provide various information about the request or the client body data. Headers are typically only sent for POST and PUT methods.

The example request shown below would be sent by a Netscape browser to request the server foo.com to send back the resource in /index.html. In this example, no body data is sent because the method is GET (the point of the request is to get some data, not to send it).

GET /index.html HTTP/1.0
User-agent: Mozilla
Accept: text/html, text/plain, image/jpeg, image/gif, */*
Host: foo.com

The server receives the request and processes it. It handles each request individually, although it may process many requests simultaneously. Each request is broken down into a series of steps that together make up the request-handling process.

The server generates a response that includes the HTTP protocol version, HTTP status code, and a reason phrase separated by spaces. This is normally followed by a number of headers. The end of the headers is indicated by a blank line. The body data of the response follows. A typical HTTP response might look like this:

HTTP/1.0 200 OK
Server: Sun-Java System-Web-Server/6.1
content-type: text/html
Content-length: 83

<HTML>
<HEAD><TITLE>Hello World</Title></HEAD>
<BODY>Hello World</BODY>
</HTML>

The status code and reason phrase tell the client how the server handled the request. Normally the status code 200 is returned, indicating that the request was handled successfully and the body data contains the requested item. Other result codes indicate redirection to another server or the browser’s cache, or various types of HTTP errors such as 404 Not Found.