LWP - phpMan

NAME
    LWP - The World-Wide Web library for Perl

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

DESCRIPTION
    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:

    *  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".

HTTP STYLE COMMUNICATION
    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
    <http://www.w3.org/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 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:

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

    *  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.

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

    *  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:

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

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

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

    *  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:

    is_success()
       The request 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 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.

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

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

    *  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.

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

    *  proxy and no_proxy specify if and when to go through a proxy server.
       <http://www.w3.org/History/1994/WWW/Proxies/>

    *  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 => 'http://search.cpan.org/search');
      $req->content_type('application/x-www-form-urlencoded');
      $req->content('query=libwww-perl&mode=dist');

      # 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.

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 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 an "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 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 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
    though.

    Example:

      $req = HTTP::Request->new(GET => 'ftp://me:passwd AT ftp.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 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 AT a.no');

      $req = HTTP::Request->new(POST => 'news:comp.lang.perl.test');
      $req->header(Subject => 'This is a test',
                   From    => 'me AT some.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 = HTTP::Request->new(POST => 'mailto:libwww AT perl.org');
      $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
    CPAN.pm, 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");

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::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

     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

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-download, lwp-dump and lwp-mirror are
    implemented.

ENVIRONMENT
    The following environment variables are used by LWP:

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

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

    PERL_LWP_ENV_PROXY
        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.

    PERL_LWP_SSL_VERIFY_HOSTNAME
        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.

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

    PERL_HTTP_URI_CLASS
        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.

AUTHORS
    LWP was made possible by contributions from Adam Newby, Albert Dvornik,
    Alexandre Duret-Lutz, Andreas Gustafsson, Andreas König, 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 Krüger, 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 Skyttä, 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
      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.

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

      http://github.com/libwww-perl/libwww-perl

    The best place to discuss this code is on the <libwww AT perl.org> mailing
    list.