## $Id: LWP.pm,v 1.1 1997/11/18 00:32:38 neeri Exp $package LWP;$VERSION = "5.13";sub Version { $VERSION; }require 5.004;require LWP::UserAgent;  # this should load everything you need1;__END__=head1 NAMELWP - Library for WWW access in Perl=head1 SYNOPSIS  use LWP;  print "This is libwww-perl-$LWP::VERSION\n";=head1 DESCRIPTIONLibwww-perl is a collection of Perl modules which provides a simpleand consistent 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, thus libwww-perl said to be a WWWclient library. The library also contain modules that are of moregeneral use.The main architecture of the library is object oriented.  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 should be easy to extendand customize for your needs.The main features of the library are:=over 3=item *Contains various reusable components (modules) that can beused separately or together.=item *Provides an object oriented model of HTTP-style communication.  Withinthis framework we currently support access to http, gopher, ftp, news,file, and mailto resources.=item *The library be used through the full object oriented interface orthrough a very simple procedural interface.=item *Support the basic and digest authorization schemes.=item *Transparent redirect handling.=item *Supports access through proxy servers.=item *URL handling (both absolute and relative URLs are supported).=item *A parser for F<robots.txt> files and a framework for constructing robots.=item *An experimental HTML parser and formatters (for PostScript and plaintext).=item *The library can cooperate with Tk.  A simple Tk-based GUI browsercalled 'tkweb' is distributed with the Tk extension for perl.=item *An implementation of the HTTP content negotiation algorithm that canbe used both in protocol modules and in server scripts (like CGIscripts).=item *A simple command line client application called C<lwp-request>.=back=head1 HTTP STYLE COMMUNICATIONThe libwww-perl library is based on HTTP style communication. Thissection try to describe what that means.Let us start with this quote from the HTTP specification document<URL:http://www.w3.org/pub/WWW/Protocols/>:=over 3=item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.=backWhat this means to libwww-perl is that communication always take placethrough these steps: First a I<request> object is created andconfigured. This object is then passed to a server and we get aI<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!=head2 The Request ObjectThe request object has the class name C<HTTP::Request> inlibwww-perl. The fact that the class name use C<HTTP::> as a name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 I<request>to.  For instance, we will send C<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:=over 3=item *The B<method> is a short string that tells what kind ofrequest this is.  The most used methods are B<GET>, B<PUT>,B<POST> and B<HEAD>.=item *The B<url> is a string denoting the protocol, server andthe name of the "document" we want to access.  The B<url> mightalso encode various other parameters.=item *The B<headers> contain additional information about therequest and can also used to describe the content.  The headersis a set of keyword/value pairs.=item *The B<content> is an arbitrary amount of data.=back=head2 The Response ObjectThe request object has the class name C<HTTP::Response> inlibwww-perl.  The main attributes of objects of this class are:=over 3=item *The B<code> is a numerical value that encode the overalloutcome of the request.=item *The B<message> is a short (human readable) string thatcorresponds to the I<code>.=item *The B<headers> contain additional information about theresponse and they also describe the content.=item *The B<content> is an arbitrary amount of data.=backSince we don't want to handle all possible I<code> values directly inour programs, the libwww-perl response object have methods that can beused to query what kind of response this is.  The most commonly usedresponse classification methods are:=over 3=item is_success()The request was was successfully received, understood or accepted.=item 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.=back=head2 The User AgentLet us assume that we have created a I<request> object. What do weactually do with it in order to receive a I<response>?The answer is that you pass it on to a I<user agent> object and thisobject will take care of all the things that need to be done(low-level communication and error handling). The user agent will giveyou back a I<response> object. The user agent represents yourapplication on the network and it provides you with an interface thatcan accept I<requests> and will return I<responses>.You should think about the user agent as 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 libwww-perl class name for the user agent isC<LWP::UserAgent>. Every libwww-perl application that wants tocommunicate should create at least one object of this kind. The mainmethod provided by this object is request(). This method takes anC<HTTP::Request> object as argument and will (eventually) return aC<HTTP::Response> object.The user agent has many other attributes that lets youconfigure how it will interact with the network and with yourapplication code.=over 3=item *The B<timeout> specify how much time we give remote servers increating responses before the library disconnect and creates aninternal I<timeout> response.=item *The B<agent> specify the name that your application should use when itpresents itself on the network.=item *The B<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.=item *The B<use_alarm> specify if it is OK for the user agent to use thealarm(2) system to implement timeouts.=item *The B<use_eval> specify if the agent should raise anexception (C<die> in perl) if an error condition occur.=item *The B<parse_head> specify whether we should initialize responseheaders from the E<lt>head> section of HTML documents.=item *The B<proxy> and B<no_proxy> specify if and when communication shouldgo through a proxy server. <URL:http://www.w3.org/pub/WWW/Proxies/>=item *The B<credentials> provide a way to set up user names andpasswords that is needed to access certain services.=backMany applications would want even more control over how they interactwith the network and they get this by specializing theC<LWP::UserAgent> by sub-classing.  The library provide aspecialization called C<LWP::RobotUA> that is used by robotapplications.=head2 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 = new LWP::UserAgent;  $ua->agent("AgentName/0.1 " . $ua->agent);  # Create a request  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');  # 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 "Bad luck this time\n";  }The $ua is created once when the application starts up.  New requestobjects are normally created for each request sent.=head1 NETWORK SUPPORTThis section goes through the various protocol schemes and describethe HTTP style methods that are supported and the headers that mighthave any effect.For all requests, a "User-Agent" header is added and initialized fromthe $ua->agent value before the request is handed to the networklayer.  In the same way, a "From" header is initialized from the$ua->from value.For all responses, the library will add a header called "Client-Date".This header will encode the time when the response was received byyour application.  This format and semantics of the header is justlike the server created "Date" header.=head2 HTTP RequestsHTTP request are really just handed off to an HTTP server and it willdecide what happens.  Few servers implement methods beside the usual"GET", "HEAD", "POST" and "PUT" but CGI-scripts can really 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 GET request you might want to add the "If-Modified-Since" headerto make the request conditional.For POST request you should add the "Content-Type" header.  When youtry to emulate HTML E<lt>FORM> handling you should usually let the valueof the "Content-Type" header be "application/x-www-form-urlencoded".See L<lwpcook> for examples of this.The libwww-perl HTTP implementation currently support the HTTP/1.0protocol.  HTTP/0.9 servers are also handled correctly.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 L<LWP::UserAgent> fordocumentation of this.=head2 FTP RequestsThe library currently support GET, HEAD and PUT requests.  GET willretrieve a file or a directory listing from an FTP server.  PUT willstore a file on a ftp server.You can specify a ftp account for servers that want this in additionuser name and password.  This is specified by passing an "Account"header in the request.User name/password can be specified using basic authorization or beencoded in the URL.  Bad logins return an UNAUTHORIZED response with"WWW-Authenticate: Basic" and can be treated as basic authorizationfor HTTP.The library support ftp ASCII transfer mode by specifying the "type=a"parameter in the URL.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 C<File::Listing> module provide functionality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).The normal file retrievals, the "Content-Type" is guessed based on thefile name suffix. See L<LWP::MediaTypes>.The "If-Modified-Since" header is not honored yet.Example:  $req = HTTP::Request->new(GET => 'ftp://me:passwd@ftp.some.where.com/');  $req->header(Accept => "text/html, */*;q=0.1");=head2 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 the news:-URLs.The library support 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:abc1234@a.sn.no');  $req = HTTP::Request->new(POST => 'news:comp.lang.perl.test');  $req->header(Subject => 'This is a test',               From    => 'me@some.where.org');  $req->content(<<EOT);  This is the content of the message that we are sending to  the world.  EOT=head2 Gopher RequestThe library supports the GET and HEAD method for gopher request.  Allrequest header values are ignored.  HEAD cheats and will return 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/');=head2 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 I<host> component of the file URL must be empty or setto "localhost".  Any other I<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');=head2 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:libwww-perl-request@ics.uci.edu');  $req->header("Subject", "subscribe");  $req->content("Please subscribe me to the libwww-perl mailing list!\n");=head1 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::Socket        -- Socket creation and IO 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 URI::URL           -- Uniform Resource Locators WWW::RobotRules    -- Parse robots.txt files   WWW::RobotRules::AnyDBM_File -- Persistent RobotRules HTML::Parser       -- Parse HTML documents   HTML::TreeBuilder-- Build a HTML syntax tree   HTML::HeadParser -- Parse the <HEAD> section of a HTML document   HTML::LinkExtor  -- Extract links from a HTML document HTML::Element      -- Building block for the HTML::TreeBuilder HTML::Formatter    -- Convert HTML syntax trees to readable formats   HTML::FormatText -- Output is plain text   HTML::FormatPS   -- Output is PostScript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 HTML::Entities     -- Expand or unexpand entities in HTML text File::Listing      -- Parse directory listingsHTTP use the Base64 encoding at some places.  The QuotedPrint moduleis just included to make the MIME:: collection more complete. MIME::Base64       -- Base64 encoding/decoding routines MIME::QuotedPrint  -- Quoted Printable encoding/decoding routinesThe following modules does not have much to do with the World WideWeb, but are included just because I am lazy and did not bother tomake separate distributions for them.  Regard them as bonus, providedfree for your pleasure. Font::AFM          -- Parse Adobe Font Metric files File::CounterFile  -- Persistent counter class=head1 MORE DOCUMENTATIONAll modules contain detailed information on the interfaces theyprovide.  The L<lwpcook> 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 C<lwp-request>, C<lwp-rget> and C<lwp-mirror>are implemented.=head1 BUGSThe library can not handle multiple simultaneous requests yet.  TheHTML:: modules are still experimental.  Also, check out what's left inthe TODO file.=head1 ACKNOWLEDGEMENTSThis package owes a lot in motivation, design, and code, to thelibwww-perl library for Perl 4, maintained by Roy FieldingE<lt>fielding@ics.uci.edu>.That package used 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.The primary architect for this Perl 5 library is Martijn Koster andGisle Aas, with lots of help from Graham Barr, Tim Bunce, AndreasKoenig, Jared Rhine, and Jack Shirazi.=head1 COPYRIGHT  Copyright 1995-1997, 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.=head1 AVAILABILITYThe latest version of this library is likely to be available from: http://www.sn.no/libwww-perl/The best place to discuss this code is on the<libwww-perl@ics.uci.edu> mailing list.=cut