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

      $req = new HTTP::Request 'GET' => 'http://www.sn.no/libwww-perl';
      $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.

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.

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 = new LWP::UserAgent;

      my $req = new HTTP::Request '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 = new LWP::UserAgent;

      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.

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 = new LWP::UserAgent;
      $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 = new HTTP::Request '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 = new LWP::UserAgent;
     $ua->proxy(['http', 'ftp'] => 'http://proxy.myorg.com');

     $req = new HTTP::Request '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_password' with
    something suitable for your site.

ACCESS TO PROTECTED DOCUMENTS
    Documents protected by basic authorization can easily be accessed like
    this:

      use LWP::UserAgent;
      $ua = new LWP::UserAgent;
      $req = new HTTP::Request GET => 'http://www.sn.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.

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 = new LWP::UserAgent;

      my $req = new HTTP::Request 'GET',
                    'http://www.sn.no/~aas/perl/www/libwww-perl-5.00.tar.gz';
      $res = $ua->request($req, "libwww-perl.tar.gz");
      if ($res->is_success) {
         print "ok\n";
      }

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

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

      my $expected_length;
      my $bytes_received = 0;
      $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;
                   });

HTML FORMATTING
    It is easy to convert HTML code to "readable" text.

      use LWP::Simple;
      use HTML::Parse;
      print parse_html(get 'http://www.sn.no/libwww-perl/')->format;

PARSE URLS
    To access individual elements of a URL, try this:

      use URI::URL;
      $host = url("http://www.sn.no/")->host;

    or

      use URI::URL;
      $u = url("ftp://ftp.sn.no/test/aas;type=i");
      print "Protocol scheme is ", $u->scheme, "\n";
      print "Host is ", $u->host, " at port ", $u->port, "\n";

    or even

      use URI::URL;
      my($host,$port) = (url("ftp://ftp.sn.no/test/aas;type=i")->crack)[3,4];

EXPAND RELATIVE URLS
    This code reads URLs and print expanded version.

      use URI::URL;
      $BASE = "http://www.sn.no/some/place?query";
      while (<>) {
         print url($_, $BASE)->abs->as_string, "\n";
      }

    We can expand URLs in an HTML document by using the parser to build a
    tree that we then traverse:

      %link_elements =
      (
       'a'    => 'href',
       'img'  => 'src',
       'form' => 'action',
       'link' => 'href',
      );

      use HTML::Parse;
      use URI::URL;

      $BASE = "http://somewhere/root/";
      $h = parse_htmlfile("xxx.html");
      $h->traverse(\&expand_urls, 1);

      print $h->as_HTML;

      sub expand_urls
      {
         my($e, $start) = @_;
         return 1 unless $start;
         my $attr = $link_elements{$e->tag};
         return 1 unless defined $attr;
         my $url = $e->attr($attr);
         return 1 unless defined $url;
         $e->attr($attr, url($url, $BASE)->abs->as_string);
      }

BASE URL
    If you want to resolve relative links in a page you will have to
    determine which base URL to use. The HTTP::Response objects now has a
    base() method.

      $BASE = $res->base;

COPYRIGHT
    Copyright 1996-1997, Gisle Aas

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