LWP - The World-Wide Web library for Perl


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


       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 sep-
          arately 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 procedur-
          al 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 construct-
          ing 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


       The libwww-perl library is based on HTTP style communication. This sec-
       tion tries to describe what that means.

       Let us start with this quote from the HTTP specification document

       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 pre-
       vious 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 parame-
       ters 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 key-
          word/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:

          The request was was successfully received, understood or accepted.

          The request failed.  The server or the resource might not be avail-
          able, 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 actu-
       ally 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 com-
       munication 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 time-
          out 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 head-
          ers 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:>

       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;
         $ua = LWP::UserAgent->new;
         $ua->agent("MyApp/0.1 ");

         # Create a request
         my $req = HTTP::Request->new(POST => '');

         # 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.


       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 inter-
       nal 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

       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 reg-
       ular 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 mecha-
       nisms (add an "Accept: text/html" header in the request if you want

       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


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

       News Requests

       Access to the USENET News system is implemented through the NNTP proto-
       col.  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 (sur-
       prise!) the POST method.

       GET on newsgroups is not implemented yet.


         $req = HTTP::Request->new(GET => '');

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

       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.


         $req = HTTP::Request->new(GET => 'gopher://');

       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.


         $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.


         $req = HTTP::Request->new(POST => '');
         $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, 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");


       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

        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::Debug         -- Debug logging module
        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


       All modules contain detailed information on the interfaces they pro-
       vide.  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


       The following environment variables are used by LWP:

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

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

           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.

           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.


       LWP was made possible by contributions from Adam Newby, Albert Dvornik,
       Alexandre Duret-Lutz, Andreas Gustafsson, Andreas Knig, 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 MacEach-
       ern, 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 Till-
       man, 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 Krger, 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 Skytt, 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 Nier-
       strasz, 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 1995-2005, 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.


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

       The best place to discuss this code is on the <> mailing

perl v5.8.8                       2004-04-06                            LWP(3)
See also Bundle::LWP(3)
See also LWP::Authen::Ntlm(3)
See also LWP::ConnCache(3)
See also LWP::Debug(3)
See also LWP::DebugFile(3)
See also LWP::MediaTypes(3)
See also LWP::MemberMixin(3)
See also LWP::Protocol(3)
See also LWP::RobotUA(3)
See also LWP::Simple(3)
See also LWP::UserAgent(3)

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