PC World 2003 March/PCWorld_2003-03_cd.bin/Software/Topware/activeperl/ActivePerl/Perl/site/lib/lwpcook.pod

Text File | 2001-11-14 | 9.2 KB | 308 lines

=head1 NAME

lwpcook - The libwww-perl cookbook

=head1 DESCRIPTION

This document contain some examples that show typical usage of the
libwww-perl library.  You should consult the documentation for the
individual modules for more detail.

All examples should be runnable programs. You can, in most cases, test
the code sections by piping the program text directly to perl.



=head1 GET

It is very easy to use this library to just fetch documents from the
net.  The LWP::Simple module provides the get() function that return
the document specified by its URL argument:

  use LWP::Simple;
  $doc = get 'http://www.linpro.no/lwp/';

or, as a perl one-liner using the getprint() function:

  perl -MLWP::Simple -e 'getprint "http://www.linpro.no/lwp/"'

or, how about fetching the latest perl by running this command:

  perl -MLWP::Simple -e '
    getstore "ftp://ftp.sunet.se/pub/lang/perl/CPAN/src/latest.tar.gz",
             "perl.tar.gz"'

You will probably first want to find a CPAN site closer to you by
running something like the following command:

  perl -MLWP::Simple -e 'getprint "http://www.perl.com/perl/CPAN/CPAN.html"'

Enough of this simple stuff!  The LWP object oriented interface gives
you more control over the request sent to the server.  Using this
interface you have full control over headers sent and how you want to
handle the response returned.

  use LWP::UserAgent;
  $ua = LWP::UserAgent->new;
  $ua->agent("$0/0.1 " . $ua->agent);
  # $ua->agent("Mozilla/8.0") # pretend we are very capable browser

  $req = HTTP::Request->new(GET => 'http://www.linpro.no/lwp');
  $req->header('Accept' => 'text/html');

  # send request
  $res = $ua->request($req);

  # check the outcome
  if ($res->is_success) {
     print $res->content;
  } else {
     print "Error: " . $res->status_line . "\n";
  }

The lwp-request program (alias GET) that is distributed with the
library can also be used to fetch documents from WWW servers.



=head1 HEAD

If you just want to check if a document is present (i.e. the URL is
valid) try to run code that looks like this:

  use LWP::Simple;

  if (head($url)) {
     # ok document exists
  }

The head() function really returns a list of meta-information about
the document.  The first three values of the list returned are the
document type, the size of the document, and the age of the document.

More control over the request or access to all header values returned
require that you use the object oriented interface described for GET
above.  Just s/GET/HEAD/g.


=head1 POST

There is no simple procedural interface for posting data to a WWW server.  You
must use the object oriented interface for this. The most common POST
operation is to access a WWW form application:

  use LWP::UserAgent;
  $ua = LWP::UserAgent->new;

  my $req = HTTP::Request->new(POST => 'http://www.perl.com/cgi-bin/BugGlimpse');
  $req->content_type('application/x-www-form-urlencoded');
  $req->content('match=www&errors=0');

  my $res = $ua->request($req);
  print $res->as_string;

Lazy people use the HTTP::Request::Common module to set up a suitable
POST request message (it handles all the escaping issues) and has a
suitable default for the content_type:

  use HTTP::Request::Common qw(POST);
  use LWP::UserAgent;
  $ua = LWP::UserAgent->new;

  my $req = POST 'http://www.perl.com/cgi-bin/BugGlimpse',
                [ search => 'www', errors => 0 ];

  print $ua->request($req)->as_string;

The lwp-request program (alias POST) that is distributed with the
library can also be used for posting data.



=head1 PROXIES

Some sites use proxies to go through fire wall machines, or just as
cache in order to improve performance.  Proxies can also be used for
accessing resources through protocols not supported directly (or
supported badly :-) by the libwww-perl library.

You should initialize your proxy setting before you start sending
requests:

  use LWP::UserAgent;
  $ua = LWP::UserAgent->new;
  $ua->env_proxy; # initialize from environment variables
  # or
  $ua->proxy(ftp  => 'http://proxy.myorg.com');
  $ua->proxy(wais => 'http://proxy.myorg.com');
  $ua->no_proxy(qw(no se fi));

  my $req = HTTP::Request->new(GET => 'wais://xxx.com/');
  print $ua->request($req)->as_string;

The LWP::Simple interface will call env_proxy() for you automatically.
Applications that use the $ua->env_proxy() method will normally not
use the $ua->proxy() and $ua->no_proxy() methods.

Some proxies also require that you send it a username/password in
order to let requests through.  You should be able to add the
required header, with something like this:

 use LWP::UserAgent;

 $ua = LWP::UserAgent->new;
 $ua->proxy(['http', 'ftp'] => 'http://username:[e-mail]');

 $req = HTTP::Request->new('GET',"http://www.perl.com");

 $res = $ua->request($req);
 print $res->content if $res->is_success;

Replace C<proxy.myorg.com>, C<username> and
C<password> with something suitable for your site.


=head1 ACCESS TO PROTECTED DOCUMENTS

Documents protected by basic authorization can easily be accessed
like this:

  use LWP::UserAgent;
  $ua = LWP::UserAgent->new;
  $req = HTTP::Request->new(GET => 'http://www.linpro.no/secret/');
  $req->authorization_basic('aas', 'mypassword');
  print $ua->request($req)->as_string;

The other alternative is to provide a subclass of I<LWP::UserAgent> that
overrides the get_basic_credentials() method. Study the I<lwp-request>
program for an example of this.


=head1 COOKIES

Some sites like to play games with cookies.  By default LWP ignores
cookies provided by the servers it visits.  LWP will collect cookies
and respond to cookie requests if you set up a cookie jar.

  use LWP::UserAgent;
  use HTTP::Cookies;

  $ua = LWP::UserAgent->new;
  $ua->cookie_jar(HTTP::Cookies->new(file => "lwpcookies.txt",
                     autosave => 1));

  # and then send requests just as you used to do
  $res = $ua->request(HTTP::Request->new(GET => "http://www.yahoo.no"));
  print $res->status_line, "\n";

As you visit sites that send you cookies to keep, then the file
F<lwpcookies.txt"> will grow.

=head1 HTTPS

URLs with https scheme are accessed in exactly the same way as with
http scheme, provided that an SSL interface module for LWP has been
properly installed (see the F<README.SSL> file found in the
libwww-perl distribution for more details).  If no SSL interface is
installed for LWP to use, then you will get "501 Protocol scheme
'https' is not supported" errors when accessing such URLs.

Here's an example of fetching and printing a WWW page using SSL:

  use LWP::UserAgent;

  my $ua = LWP::UserAgent->new;
  my $req = HTTP::Request->new(GET => 'https://www.helsinki.fi/');
  my $res = $ua->request($req);
  if ($res->is_success) {
      print $res->as_string;
  } else {
      print "Failed: ", $res->status_line, "\n";
  }

=head1 MIRRORING

If you want to mirror documents from a WWW server, then try to run
code similar to this at regular intervals:

  use LWP::Simple;

  %mirrors = (
     'http://www.sn.no/'             => 'sn.html',
     'http://www.perl.com/'          => 'perl.html',
     'http://www.sn.no/libwww-perl/' => 'lwp.html',
     'gopher://gopher.sn.no/'        => 'gopher.html',
  );

  while (($url, $localfile) = each(%mirrors)) {
     mirror($url, $localfile);
  }

Or, as a perl one-liner:

  perl -MLWP::Simple -e 'mirror("http://www.perl.com/", "perl.html")';

The document will not be transfered unless it has been updated.



=head1 LARGE DOCUMENTS

If the document you want to fetch is too large to be kept in memory,
then you have two alternatives.  You can instruct the library to write
the document content to a file (second $ua->request() argument is a file
name):

  use LWP::UserAgent;
  $ua = LWP::UserAgent->new;

  my $req = HTTP::Request->new(GET =>
                'http://www.linpro.no/lwp/libwww-perl-5.46.tar.gz');
  $res = $ua->request($req, "libwww-perl.tar.gz");
  if ($res->is_success) {
     print "ok\n";
  }
  else {
     print $res->status_line, "\n";
  }


Or you can process the document as it arrives (second $ua->request()
argument is a code reference):

  use LWP::UserAgent;
  $ua = LWP::UserAgent->new;
  $URL = 'ftp://ftp.unit.no/pub/rfc/rfc-index.txt';

  my $expected_length;
  my $bytes_received = 0;
  my $res =
     $ua->request(HTTP::Request->new(GET => $URL),
               sub {
                   my($chunk, $res) = @_;
                   $bytes_received += length($chunk);
               unless (defined $expected_length) {
                  $expected_length = $res->content_length || 0;
                   }
           if ($expected_length) {
                printf STDERR "%d%% - ",
                              100 * $bytes_received / $expected_length;
                   }
               print STDERR "$bytes_received bytes received\n";

                   # XXX Should really do something with the chunk itself
               # print $chunk;
               });
   print $res->status_line, "\n";



=head1 COPYRIGHT

Copyright 1996-2001, Gisle Aas

This library is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.