lwpcook - libwww-perl cookbook


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.


GET

       It is very easy to use this library to just fetch docu­
       ments 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.sn.no/libwww-perl/';

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

         perl -MLWP::Simple -e 'getprint "http://www.sn.no/libwww-perl/"'

       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);

         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.


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-informa­
       tion about the document.  The first three values of the
       list returned are the document type, the size of the docu­
       ment, and the age of the document.

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


POST

       There is no simple procedural interface for posting data
       to a WWW server.  You must use the object oriented inter­
       face 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 escap­
       ing issues) and has a suitable default for the con­
       tent_type:

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

                       [ 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.


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 lib­
       www-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 user­
       name/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://proxy.myorg.com');

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

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

       Replace `proxy.myorg.com', `proxy_user' and `proxy_pass­
       word' with something suitable for your site.

       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
       LWP::UserAgent that overrides the get_basic_credentials()
       method. Study the lwp-request program for an example of
       this.


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 lwpcookies.txt" will grow.


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
       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 $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";
         }


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.


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


         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";


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.


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