In answer to such a request, the server typically issues an HTTP response, the first line of which is often referred to as the status line. In that line the server echoes the HTTP version and gives a response status code (which is a three-digit integer) and a short message known as a reason phrase. Here’s an example HTTP response:

HTTP/1.0 200 OK

The response status code and reason phrase are essentially intended as machineand human-readable versions of the same message, though the reason phrase may actually vary a little from server to server. Table 1.1 lists some examples of common status codes and reason phrases. The first digit of the status code usually gives some clue about the nature of the message:

• 1**—Information
• 2**—Success
• 3**—Redirected
• 4**—Client error
• 5**—Server error

A detailed list of status codes is maintained by the World Wide Web Consortium, W3C, and is available at http://www.w3.org/Protocols/rfc2616/ rfc2616-sec10.html.

The response may also contain header lines each containing a header and value pair similar to those of the HTTP request but generally containing information about the server and/or the resource being returned:

Server: Apache/1.3.22
Last-Modified: Fri, 24 Dec 1999 13:33:59 GMT