LWP(3)                                         User Contributed Perl Documentation                                        LWP(3)



NAME
       LWP - The World-Wide Web library for Perl

SYNOPSIS
         use LWP;
         print "This is libwww-perl-$LWP::VERSION\n";

DESCRIPTION
       The libwww-perl collection is a set of Perl modules which provides a simple and consistent application programming
       interface (API) to the World-Wide Web.  The main focus of the library is to provide classes and functions that allow you
       to write WWW clients. The library also contain modules that are of more general use and even classes that help you
       implement simple HTTP servers.

       Most modules in this library provide an object oriented API.  The user agent, requests sent and responses received from
       the WWW server are all represented by objects.  This makes a simple and powerful interface to these services.  The
       interface is easy to extend and customize for your own needs.

       The main features of the library are:

       o  Contains various reusable components (modules) that can be used separately or together.

       o  Provides an object oriented model of HTTP-style communication.  Within this framework we currently support access to
          http, https, gopher, ftp, news, file, and mailto resources.

       o  Provides a full object oriented interface or a very simple procedural interface.

       o  Supports the basic and digest authorization schemes.

       o  Supports transparent redirect handling.

       o  Supports access through proxy servers.

       o  Provides parser for robots.txt files and a framework for constructing robots.

       o  Supports parsing of HTML forms.

       o  Implements HTTP content negotiation algorithm that can be used both in protocol modules and in server scripts (like
          CGI scripts).

       o  Supports HTTP cookies.

       o  Some simple command line clients, for instance "lwp-request" and "lwp-download".

HTTP STYLE COMMUNICATION
       The libwww-perl library is based on HTTP style communication. This section tries to describe what that means.

       Let us start with this quote from the HTTP specification document <URL:http://www.w3.org/pub/WWW/Protocols/>;:

       o  The HTTP protocol is based on a request/response paradigm. A client establishes a connection with a server and sends a
          request to the server in the form of a request method, URI, and protocol version, followed by a MIME-like message
          containing request modifiers, client information, and possible body content. The server responds with a status line,
          including the message's protocol version and a success or error code, followed by a MIME-like message containing
          server information, entity meta-information, and possible body content.

       What this means to libwww-perl is that communication always take place through these steps: First a request object is
       created and configured. This object is then passed to a server and we get a response object in return that we can
       examine. A request is always independent of any previous requests, i.e. the service is stateless.  The same simple model
       is used for any kind of service we want to access.

       For example, if we want to fetch a document from a remote file server, then we send it a request that contains a name for
       that document and the response will contain the document itself.  If we access a search engine, then the content of the
       request will contain the query parameters and the response will contain the query result.  If we want to send a mail
       message to somebody then we send a request object which contains our message to the mail server and the response object
       will contain an acknowledgment that tells us that the message has been accepted and will be forwarded to the
       recipient(s).

       It is as simple as that!

   The Request Object
       The libwww-perl request object has the class name "HTTP::Request".  The fact that the class name uses "HTTP::" as a
       prefix only implies that we use the HTTP model of communication.  It does not limit the kind of services we can try to
       pass this request to.  For instance, we will send "HTTP::Request"s both to ftp and gopher servers, as well as to the
       local file system.

       The main attributes of the request objects are:

       o  The method is a short string that tells what kind of request this is.  The most common methods are GET, PUT, POST and
          HEAD.

       o  The uri is a string denoting the protocol, server and the name of the "document" we want to access.  The uri might
          also encode various other parameters.

       o  The headers contain additional information about the request and can also used to describe the content.  The headers
          are a set of keyword/value pairs.

       o  The content is an arbitrary amount of data.

   The Response Object
       The libwww-perl response object has the class name "HTTP::Response".  The main attributes of objects of this class are:

       o  The code is a numerical value that indicates the overall outcome of the request.

       o  The message is a short, human readable string that corresponds to the code.

       o  The headers contain additional information about the response and describe the content.

       o  The content is an arbitrary amount of data.

       Since we don't want to handle all possible code values directly in our programs, a libwww-perl response object has
       methods that can be used to query what kind of response this is.  The most commonly used response classification methods
       are:

       is_success()
          The request was was successfully received, understood or accepted.

       is_error()
          The request failed.  The server or the resource might not be available, access to the resource might be denied or
          other things might have failed for some reason.

   The User Agent
       Let us assume that we have created a request object. What do we actually do with it in order to receive a response?

       The answer is that you pass it to a user agent object and this object takes care of all the things that need to be done
       (like low-level communication and error handling) and returns a response object. The user agent represents your
       application on the network and provides you with an interface that can accept requests and return responses.

       The user agent is an interface layer between your application code and the network.  Through this interface you are able
       to access the various servers on the network.

       The class name for the user agent is "LWP::UserAgent".  Every libwww-perl application that wants to communicate should
       create at least one object of this class. The main method provided by this object is request(). This method takes an
       "HTTP::Request" object as argument and (eventually) returns a "HTTP::Response" object.

       The user agent has many other attributes that let you configure how it will interact with the network and with your
       application.

       o  The timeout specifies how much time we give remote servers to respond before the library disconnects and creates an
          internal timeout response.

       o  The agent specifies the name that your application should use when it presents itself on the network.

       o  The from attribute can be set to the e-mail address of the person responsible for running the application.  If this is
          set, then the address will be sent to the servers with every request.

       o  The parse_head specifies whether we should initialize response headers from the <head> section of HTML documents.

       o  The proxy and no_proxy attributes specify if and when to go through a proxy server.
          <URL:http://www.w3.org/pub/WWW/Proxies/>;

       o  The credentials provide a way to set up user names and passwords needed to access certain services.

       Many applications want even more control over how they interact with the network and they get this by sub-classing
       "LWP::UserAgent".  The library includes a sub-class, "LWP::RobotUA", for robot applications.

   An Example
       This example shows how the user agent, a request and a response are represented in actual perl code:

         # Create a user agent object
         use LWP::UserAgent;
         my $ua = LWP::UserAgent->new;
         $ua->agent("MyApp/0.1 ");

         # Create a request
         my $req = HTTP::Request->new(POST => 'http://search.cpan.org/search');
         $req->content_type('application/x-www-form-urlencoded');
         $req->content('query=libwww-perl&mode=dist');

         # Pass request to the user agent and get a response back
         my $res = $ua->request($req);

         # Check the outcome of the response
         if ($res->is_success) {
             print $res->content;
         }
         else {
             print $res->status_line, "\n";
         }

       The $ua is created once when the application starts up.  New request objects should normally created for each request
       sent.

NETWORK SUPPORT
       This section discusses the various protocol schemes and the HTTP style methods that headers may be used for each.

       For all requests, a "User-Agent" header is added and initialized from the $ua->agent attribute before the request is
       handed to the network layer.  In the same way, a "From" header is initialized from the $ua->from attribute.

       For all responses, the library adds a header called "Client-Date".  This header holds the time when the response was
       received by your application.  The format and semantics of the header are the same as the server created "Date" header.
       You may also encounter other "Client-XXX" headers.  They are all generated by the library internally and are not received
       from the servers.

   HTTP Requests
       HTTP requests are just handed off to an HTTP server and it decides what happens.  Few servers implement methods beside
       the usual "GET", "HEAD", "POST" and "PUT", but CGI-scripts may implement any method they like.

       If the server is not available then the library will generate an internal error response.

       The library automatically adds a "Host" and a "Content-Length" header to the HTTP request before it is sent over the
       network.

       For a GET request you might want to add a "If-Modified-Since" or "If-None-Match" header to make the request conditional.

       For a POST request you should add the "Content-Type" header.  When you try to emulate HTML <FORM> handling you should
       usually let the value of the "Content-Type" header be "application/x-www-form-urlencoded".  See lwpcook for examples of
       this.

       The libwww-perl HTTP implementation currently support the HTTP/1.1 and HTTP/1.0 protocol.

       The library allows you to access proxy server through HTTP.  This means that you can set up the library to forward all
       types of request through the HTTP protocol module.  See LWP::UserAgent for documentation of this.

   HTTPS Requests
       HTTPS requests are HTTP requests over an encrypted network connection using the SSL protocol developed by Netscape.
       Everything about HTTP requests above also apply to HTTPS requests.  In addition the library will add the headers "Client-
       SSL-Cipher", "Client-SSL-Cert-Subject" and "Client-SSL-Cert-Issuer" to the response.  These headers denote the encryption
       method used and the name of the server owner.

       The request can contain the header "If-SSL-Cert-Subject" in order to make the request conditional on the content of the
       server certificate.  If the certificate subject does not match, no request is sent to the server and an internally
       generated error response is returned.  The value of the "If-SSL-Cert-Subject" header is interpreted as a Perl regular
       expression.

   FTP Requests
       The library currently supports GET, HEAD and PUT requests.  GET retrieves a file or a directory listing from an FTP
       server.  PUT stores a file on a ftp server.

       You can specify a ftp account for servers that want this in addition to user name and password.  This is specified by
       including an "Account" header in the request.

       User name/password can be specified using basic authorization or be encoded in the URL.  Failed logins return an
       UNAUTHORIZED response with "WWW-Authenticate: Basic" and can be treated like basic authorization for HTTP.

       The library supports ftp ASCII transfer mode by specifying the "type=a" parameter in the URL. It also supports transfer
       of ranges for FTP transfers using the "Range" header.

       Directory listings are by default returned unprocessed (as returned from the ftp server) with the content media type
       reported to be "text/ftp-dir-listing". The "File::Listing" module provides methods for parsing of these directory
       listing.

       The ftp module is also able to convert directory listings to HTML and this can be requested via the standard HTTP content
       negotiation mechanisms (add an "Accept: text/html" header in the request if you want this).

       For normal file retrievals, the "Content-Type" is guessed based on the file name suffix. See LWP::MediaTypes.

       The "If-Modified-Since" request header works for servers that implement the MDTM command.  It will probably not work for
       directory listings though.

       Example:

         $req = HTTP::Request->new(GET => 'ftp://me:passwdATftp.com/');
         $req->header(Accept => "text/html, */*;q=0.1");

   News Requests
       Access to the USENET News system is implemented through the NNTP protocol.  The name of the news server is obtained from
       the NNTP_SERVER environment variable and defaults to "news".  It is not possible to specify the hostname of the NNTP
       server in news: URLs.

       The library supports GET and HEAD to retrieve news articles through the NNTP protocol.  You can also post articles to
       newsgroups by using (surprise!) the POST method.

       GET on newsgroups is not implemented yet.

       Examples:

         $req = HTTP::Request->new(GET => 'news:abc1234ATa.no');

         $req = HTTP::Request->new(POST => 'news:comp.lang.perl.test');
         $req->header(Subject => 'This is a test',
                      From    => 'meATsome.org');
         $req->content(<<EOT);
         This is the content of the message that we are sending to
         the world.
         EOT

   Gopher Request
       The library supports the GET and HEAD methods for gopher requests.  All request header values are ignored.  HEAD cheats
       and returns a response without even talking to server.

       Gopher menus are always converted to HTML.

       The response "Content-Type" is generated from the document type encoded (as the first letter) in the request URL path
       itself.

       Example:

         $req = HTTP::Request->new(GET => 'gopher://gopher.sn.no/');

   File Request
       The library supports GET and HEAD methods for file requests.  The "If-Modified-Since" header is supported.  All other
       headers are ignored.  The host component of the file URL must be empty or set to "localhost".  Any other host value will
       be treated as an error.

       Directories are always converted to an HTML document.  For normal files, the "Content-Type" and "Content-Encoding" in the
       response are guessed based on the file suffix.

       Example:

         $req = HTTP::Request->new(GET => 'file:/etc/passwd');

   Mailto Request
       You can send (aka "POST") mail messages using the library.  All headers specified for the request are passed on to the
       mail system.  The "To" header is initialized from the mail address in the URL.

       Example:

         $req = HTTP::Request->new(POST => 'mailto:libwwwATperl.org');
         $req->header(Subject => "subscribe");
         $req->content("Please subscribe me to the libwww-perl mailing list!\n");

   CPAN Requests
       URLs with scheme "cpan:" are redirected to the a suitable CPAN mirror.  If you have your own local mirror of CPAN you
       might tell LWP to use it for "cpan:" URLs by an assignment like this:

         $LWP::Protocol::cpan::CPAN = "file:/local/CPAN/";

       Suitable CPAN mirrors are also picked up from the configuration for the CPAN.pm, so if you have used that module a
       suitable mirror should be picked automatically.  If neither of these apply, then a redirect to the generic CPAN http
       location is issued.

       Example request to download the newest perl:

         $req = HTTP::Request->new(GET => "cpan:src/latest.tar.gz");

OVERVIEW OF CLASSES AND PACKAGES
       This table should give you a quick overview of the classes provided by the library. Indentation shows class inheritance.

        LWP::MemberMixin   -- Access to member variables of Perl5 classes
          LWP::UserAgent   -- WWW user agent class
            LWP::RobotUA   -- When developing a robot applications
          LWP::Protocol          -- Interface to various protocol schemes
            LWP::Protocol::http  -- http:// access
            LWP::Protocol::file  -- file:// access
            LWP::Protocol::ftp   -- ftp:// access
            ...

        LWP::Authen::Basic -- Handle 401 and 407 responses
        LWP::Authen::Digest

        HTTP::Headers      -- MIME/RFC822 style header (used by HTTP::Message)
        HTTP::Message      -- HTTP style message
          HTTP::Request    -- HTTP request
          HTTP::Response   -- HTTP response
        HTTP::Daemon       -- A HTTP server class

        WWW::RobotRules    -- Parse robots.txt files
          WWW::RobotRules::AnyDBM_File -- Persistent RobotRules

        Net::HTTP          -- Low level HTTP client

       The following modules provide various functions and definitions.

        LWP                -- This file.  Library version number and documentation.
        LWP::MediaTypes    -- MIME types configuration (text/html etc.)
        LWP::Simple        -- Simplified procedural interface for common functions
        HTTP::Status       -- HTTP status code (200 OK etc)
        HTTP::Date         -- Date parsing module for HTTP date formats
        HTTP::Negotiate    -- HTTP content negotiation calculation
        File::Listing      -- Parse directory listings
        HTML::Form         -- Processing for <form>s in HTML documents

MORE DOCUMENTATION
       All modules contain detailed information on the interfaces they provide.  The lwpcook manpage is the libwww-perl cookbook
       that contain examples of typical usage of the library.  You might want to take a look at how the scripts lwp-request,
       lwp-rget and lwp-mirror are implemented.

ENVIRONMENT
       The following environment variables are used by LWP:

       HOME
           The "LWP::MediaTypes" functions will look for the .media.types and .mime.types files relative to you home directory.

       http_proxy
       ftp_proxy
       xxx_proxy
       no_proxy
           These environment variables can be set to enable communication through a proxy server.  See the description of the
           "env_proxy" method in LWP::UserAgent.

       PERL_LWP_USE_HTTP_10
           Enable the old HTTP/1.0 protocol driver instead of the new HTTP/1.1 driver.  You might want to set this to a TRUE
           value if you discover that your old LWP applications fails after you installed LWP-5.60 or better.

       PERL_HTTP_URI_CLASS
           Used to decide what URI objects to instantiate.  The default is "URI".  You might want to set it to "URI::URL" for
           compatibility with old times.

AUTHORS
       LWP was made possible by contributions from Adam Newby, Albert Dvornik, Alexandre Duret-Lutz, Andreas Gustafsson, Andreas
       KA~Xnig, Andrew Pimlott, Andy Lester, Ben Coleman, Benjamin Low, Ben Low, Ben Tilly, Blair Zajac, Bob Dalgleish, BooK,
       Brad Hughes, Brian J. Murrell, Brian McCauley, Charles C. Fu, Charles Lane, Chris Nandor, Christian Gilmore, Chris W.
       Unger, Craig Macdonald, Dale Couch, Dan Kubb, Dave Dunkin, Dave W. Smith, David Coppit, David Dick, David D. Kilzer, Doug
       MacEachern, Edward Avis, erik, Gary Shea, Gisle Aas, Graham Barr, Gurusamy Sarathy, Hans de Graaff, Harald Joerg, Harry
       Bochner, Hugo, Ilya Zakharevich, INOUE Yoshinari, Ivan Panchenko, Jack Shirazi, James Tillman, Jan Dubois, Jared Rhine,
       Jim Stern, Joao Lopes, John Klar, Johnny Lee, Josh Kronengold, Josh Rai, Joshua Chamas, Joshua Hoblitt, Kartik Subbarao,
       Keiichiro Nagano, Ken Williams, KONISHI Katsuhiro, Lee T Lindley, Liam Quinn, Marc Hedlund, Marc Langheinrich, Mark D.
       Anderson, Marko Asplund, Mark Stosberg, Markus B KrA~Xger, Markus Laker, Martijn Koster, Martin Thurn, Matthew Eldridge,
       Matthew.van.Eerde, Matt Sergeant, Michael A. Chase, Michael Quaranta, Michael Thompson, Mike Schilli, Moshe Kaminsky,
       Nathan Torkington, Nicolai Langfeldt, Norton Allen, Olly Betts, Paul J. Schinder, peterm, Philip GuentherDaniel Buenzli,
       Pon Hwa Lin, Radoslaw Zielinski, Radu Greab, Randal L. Schwartz, Richard Chen, Robin Barker, Roy Fielding, Sander van
       Zoest, Sean M. Burke, shildreth, Slaven Rezic, Steve A Fink, Steve Hay, Steven Butler, Steve_Kilbane, Takanori Ugai,
       Thomas Lotterer, Tim Bunce, Tom Hughes, Tony Finch, Ville SkyttA~X, Ward Vandewege, William York, Yale Huang, and
       Yitzchak Scott-Thoennes.

       LWP owes a lot in motivation, design, and code, to the libwww-perl library for Perl4 by Roy Fielding, which included work
       from Alberto Accomazzi, James Casey, Brooks Cutter, Martijn Koster, Oscar Nierstrasz, Mel Melchner, Gertjan van Oosten,
       Jared Rhine, Jack Shirazi, Gene Spafford, Marc VanHeyningen, Steven E. Brenner, Marion Hakanson, Waldemar Kebsch, Tony
       Sanders, and Larry Wall; see the libwww-perl-0.40 library for details.

COPYRIGHT
         Copyright 1995-2009, Gisle Aas
         Copyright 1995, Martijn Koster

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

AVAILABILITY
       The latest version of this library is likely to be available from CPAN as well as:

         http://github.com/gisle/libwww-perl

       The best place to discuss this code is on the <libwwwATperl.org> mailing list.



perl v5.12.4                                               2010-09-20                                                     LWP(3)