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LWP - The World-Wide Web library for Perl
use LWP; print "This is libwww-perl-$LWP::VERSION\n";
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:
Let us start with this quote from the HTTP specification document <URL:http://www.w3.org/pub/WWW/Protocols/>:
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).
The main attributes of the request objects are:
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 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.
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.
# 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 => '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.
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.
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 this.
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.
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@ftp.some.where.com/'); $req->header(Accept => "text/html, */*;q=0.1");
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@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
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/');
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');
Example:
$req = HTTP::Request->new(POST => 'mailto:libwww@perl.org');
$req->header(Subject => "subscribe");
$req->content("Please subscribe me to the libwww-perl mailing list!\n");
$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");
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::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 HTML::Form -- Processing for <form>s in HTML documents
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 1995-2005, 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.
http://www.linpro.no/lwp/
The best place to discuss this code is on the <libwww@perl.org> mailing list.
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