LWP - Library for WWW access in Perl


SYNOPSIS

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


DESCRIPTION

       Libwww-perl is a collection 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, thus libwww-perl is a WWW client
       library. The library also contain modules that are of more
       general use.

       Most modules in this library are 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:

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

       ·  Provides an object oriented model of HTTP-style commu­
          nication.  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.

       ·  Cooperates with Tk.  A simple Tk-based GUI browser
          called 'tkweb' is distributed with the Tk extension for
          perl.

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


       ·  A simple command line client application called
          `lwp-request'.


HTTP STYLE COMMUNICATION

       The libwww-perl library is based on HTTP style communica­
       tion. 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/>:

          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 mes­
          sage'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 acknowledg­
       ment 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

       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 used methods are GET, PUT,
          POST and HEAD.

       ·  The url is a string denoting the protocol, server and
          the name of the "document" we want to access.  The url
          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 over­
          all outcome of the request.

       ·  The message is a short, human readable string that cor­
          responds 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 classi­
       fication 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 rea­
          son.


       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 inter­
       face that can accept requests and return responses.

       The user agent is an interface layer between your applica­
       tion 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
       `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 con­
       figure 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
          ments.

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

       ·  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-class­
       ing `LWP::UserAgent'.  The library includes a sub-class,


       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 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 ini­
       tialized 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.

       erate 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 <FORM> handling you should
       usually let the value of the "Content-Type" header be
       "application/x-www-form-urlencoded".  See the lwpcook man­
       page for examples of this.

       The libwww-perl HTTP implementation currently support the
       HTTP/1.0 protocol.  HTTP/0.9 servers are also handled cor­
       rectly.

       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 mod­
       ule.  See the LWP::UserAgent manpage 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 inter­
       nally 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.

       tion 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.

       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 the LWP::MediaTypes
       manpage.

       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:passwd@ftp.some.where.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 arti­
       cles 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.

       Examples:

         $req = HTTP::Request->new(GET => 'news:abc1234@a.sn.no');

         $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

       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->header(Subject => "subscribe");
         $req->content("Please subscribe me to the libwww-perl mailing list!\n");


OVERVIEW OF CLASSES AND PACKAGES

       This table should give you a quick overview of the classes
       provided by the library. Indentation shows class inheri­
       tance.

        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

       The following modules provide various functions and defi­
       nitions.

        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


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 imple­
       mented.


BUGS

       The library can not handle multiple simultaneous requests



ACKNOWLEDGEMENTS

       This package owes a lot in motivation, design, and code,
       to the libwww-perl library for Perl 4, maintained by Roy
       Fielding <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 Shi­
       razi, 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.


COPYRIGHT

         Copyright 1995-2001, 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 avail­
       able from CPAN as well as:

        http://www.linpro.no/lwp/

       The best place to discuss this code is on the <lib­
       www@perl.org> mailing list.


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