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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 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


       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

       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::Requests both to ftp and gopher servers, as well as to the
       local file system.

       The main attributes of the request objects are:

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

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

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

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

       o  headers contains additional information about the response and
          describe the content.

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

       o  agent specifies the name that your application uses when it presents
          itself on the network.

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

       o  proxy and no_proxy specify if and when to go through a proxy server.

       o  credentials provides 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 => '');

         # 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
       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

   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


         $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 articles 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-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 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::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-download, lwp-dump 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 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.

           If set to a TRUE value, then the LWP::UserAgent will by default
           call "env_proxy" during initialization.  This makes LWP honor the
           proxy variables described above.

           The default "verify_hostname" setting for LWP::UserAgent.  If not
           set the default will be 1.  Set it as 0 to disable hostname
           verification (the default prior to libwww-perl 5.840.

           The file and/or directory where the trusted Certificate Authority
           certificates is located.  See LWP::UserAgent for details.

           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 KA9|nig, 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 KrA1/4ger, 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 Guenther, Daniel 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 SkyttAx, 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 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.


       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 v5.26.2                      2018-10-10                            LWP(3)

libwww-perl 6.360.0 - Generated Fri Oct 12 06:17:27 CDT 2018
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