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Previous: C.1 A Simple ClientAppendix C
Networking Clients
Next: C.3 An Interactive Client

C.2 A Webget Client

Here's a simple client that contacts a remote server and fetches a list of documents from it. This is a more interesting client than the previous one because it sends a line of data to the server before fetching that server's response.

#!/usr/bin/perl -w
use IO::Socket;
unless (@ARGV > 1) { die "usage: $0 host document ..." }
$host = shift(@ARGV);
foreach $document ( @ARGV ) {
    $remote = IO::Socket::INET->new( Proto => "tcp",
    PeerAddr => $host,
    PeerPort => "http(80)",
    unless ($remote) { die "cannot connect to http daemon on $host" }
    print $remote "GET $document HTTP/1.0\n\n";
    while ( <$remote> ) { print }
    -close $remote;

The web server handling the http service is assumed to be at its standard port, number 80. If the server you're trying to connect to is at a different port (say, 8080), you should give PeerPort => 8080 as the third argument to new( ). The autoflush method is used on the socket because otherwise the system would buffer up the output we sent it. (If you're on a Mac, you'll need to change every \n in your code that sends data over the network to be \015\012 instead.)

Connecting to the server is only the first part of the process: once you have the connection, you have to use the server's language. Each server on the network has its own little command language that it expects as input. The string that we send to the server starting with "GET" is in HTTP syntax. In this case, we simply request each specified document. Yes, we really are making a new connection for each document, even though it's the same host. That's the way it works with HTTP. (Recent versions of web browsers may request that the remote server leave the connection open a little while, but the server doesn't have to honor such a request.)

We'll call our program webget. Here's how it might execute:

shell_prompt$ webget www.perl.com /guanaco.html
HTTP/1.1 404 File Not Found
Date: Thu, 08 May 1997 18:02:32 GMT
Server: Apache/1.2b6
Connection: close
Content-type: text/html
<HEAD><TITLE>404 File Not Found</TITLE></HEAD>
<BODY><H1>File Not Found</H1>
The requested URL /guanaco.html was not found on this server.<P>

OK, so that's not very interesting, because it didn't find that particular document. But a long response wouldn't have fit on this page.

For a more fully-featured version of this program, you should look for the lwp-request program included with the LWP modules from CPAN. (LWP is discussed a bit at the end of Chapter 19.)

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