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

       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 program-
       ming 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:

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

       ?  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.

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

       ?  Supports the basic and digest authorization schemes.

       ?  Supports transparent redirect handling.

       ?  Supports access through proxy servers.

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

       ?  Supports parsing of HTML forms.

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

       ?  Supports HTTP cookies.

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

       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:>;:

       ?  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:

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

       ?  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.

       ?  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.

       ?  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:

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

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

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

       ?  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 classifi-
       cation methods are:

          The request was was successfully received, understood or accepted.

          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

       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 repre-
       sents your application on the network and provides you with an interface that can accept requests and return

       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.

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

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

       ?  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.

       ?  The parse_head specifies whether we should initialize response headers from the <head> section of HTML docu-

       ?  The proxy and no_proxy attributes specify if and when to go through a proxy server.

       ?  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

       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

       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

       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 for-
       ward 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 con-
       tent 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 speci-
       fied 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.


         $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 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 arti-
       cles to newsgroups by using (surprise!) 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-Encod-
       ing" 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

        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::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 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.

       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

           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 Gustafs-
       son, Andreas Konig, 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, KON-
       ISHI Katsuhiro, Lee T Lindley, Liam Quinn, Marc Hedlund, Marc Langheinrich, Mark D. Anderson, Marko Asplund,
       Mark Stosberg, Markus B Kruger, 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, 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 Melch-
       ner, 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 1995-2008, 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 list.

perl v5.8.8                       2008-12-05                            LWP(3)