use LWP; print "This is libwww-perl-$LWP::VERSION\n";
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:
lwp-request.
Let us start with this quote from the HTTP specification document <URL:http://www.w3.org/pub/WWW/Protocols/>:
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!
HTTP::Request in libwww-perl. The fact that the class name use 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 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:
HTTP::Response in libwww-perl. The main attributes of objects of this class are:
The answer is that you pass it on to a 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 response object. The user agent represents your application on the network and it provides you with an interface that can accept requests and will return 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
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
HTTP::Request object as argument and will (eventually) return a
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.
alarm(2)
system to implement timeouts.
LWP::UserAgent by sub-classing. The library provide a specialization called LWP::RobotUA that is used by robot applications.
# 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.
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.
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 < FORM> handling you should usually let the value of the ``Content-Type'' header be ``application/x-www-form-urlencoded''. See the lwpcook manpage 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 UserAgent for documentation of this.
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 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 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");
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
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-request@ics.uci.edu');
$req->header("Subject", "subscribe");
$req->content("Please subscribe me to the libwww-perl mailing list!\n");
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
lwp-request, lwp-rget and lwp-mirror
are implemented.
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.
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.
http://www.sn.no/libwww-perl/
The best place to discuss this code is on the