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Simulating an HTTP request

A good way to understand the mechanics of HTTP is to simulate a request and observe the response using the program telnet. From a command prompt, the telnet program is run with the domain name component of the URL and the port number 80. This instructs the telnet program to connect to the host machine on port 80, the port that the web server usually listens on. Then an HTTP request is sent by typing in a request line followed by a blank line (pressing the Enter key twice).

Example B-1 shows the request line:

HEAD / HTTP/1.0

followed by the server response. The HEAD keyword asks the server to respond with only the HTTP response header fields and not the whole requested document, which is useful if the requested page is large, or the request is for an image. The HEAD keyword is followed by the resource component of the URL and the version of HTTP that the client supports. To see a full response, the request line:

GET / HTTP/1.1

is entered followed by a blank line.

Example B-1. A simulated HTTP request using telnet
% telnet www.w3.org 80
Trying 18.29.1.35...
Connected to www.w3.org.
Escape character is '^]'.
HEAD / HTTP/1.1
HTTP/1.1 200 OK
Date: Wed, 26 Sep 2001 03:42:32 GMT
Server: Apache/1.3.6 (Unix) PHP/3.0.11
P3P: policyref="http://www.w3.org/2001/05/P3P/p3p.xml"
Cache-Control: max-age=600
Expires: Wed, 26 Sep 2001 03:52:32 GMT
Last-Modified: Tue, 25 Sep 2001 21:08:00 GMT
ETag: "5b42a7-4b06-3bb0f230"
Accept-Ranges: bytes
Content-Length: 19206
Connection: close
Content-Type: text/html; charset=us-ascii
Connection closed by foreign host.
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