1LWP(3)                User Contributed Perl Documentation               LWP(3)
2
3
4

NAME

6       LWP - The World-Wide Web library for Perl
7

SYNOPSIS

9         use LWP;
10         print "This is libwww-perl-$LWP::VERSION\n";
11

DESCRIPTION

13       The libwww-perl collection is a set of Perl modules which provides a
14       simple and consistent application programming interface (API) to the
15       World-Wide Web.  The main focus of the library is to provide classes
16       and functions that allow you to write WWW clients. The library also
17       contain modules that are of more general use and even classes that help
18       you implement simple HTTP servers.
19
20       Most modules in this library provide an object oriented API.  The user
21       agent, requests sent and responses received from the WWW server are all
22       represented by objects.  This makes a simple and powerful interface to
23       these services.  The interface is easy to extend and customize for your
24       own needs.
25
26       The main features of the library are:
27
28       •  Contains various reusable components (modules) that can be used
29          separately or together.
30
31       •  Provides an object oriented model of HTTP-style communication.
32          Within this framework we currently support access to "http",
33          "https", "gopher", "ftp", "news", "file", and "mailto" resources.
34
35       •  Provides a full object oriented interface or a very simple
36          procedural interface.
37
38       •  Supports the basic and digest authorization schemes.
39
40       •  Supports transparent redirect handling.
41
42       •  Supports access through proxy servers.
43
44       •  Provides parser for robots.txt files and a framework for
45          constructing robots.
46
47       •  Supports parsing of HTML forms.
48
49       •  Implements HTTP content negotiation algorithm that can be used both
50          in protocol modules and in server scripts (like CGI scripts).
51
52       •  Supports HTTP cookies.
53
54       •  Some simple command line clients, for instance "lwp-request" and
55          "lwp-download".
56

HTTP STYLE COMMUNICATION

58       The libwww-perl library is based on HTTP style communication. This
59       section tries to describe what that means.
60
61       Let us start with this quote from the HTTP specification document
62       <URL:http://www.w3.org/Protocols/>:
63
64       •  The HTTP protocol is based on a request/response paradigm. A client
65          establishes a connection with a server and sends a request to the
66          server in the form of a request method, URI, and protocol version,
67          followed by a MIME-like message containing request modifiers, client
68          information, and possible body content. The server responds with a
69          status line, including the message's protocol version and a success
70          or error code, followed by a MIME-like message containing server
71          information, entity meta-information, and possible body content.
72
73       What this means to libwww-perl is that communication always take place
74       through these steps: First a request object is created and configured.
75       This object is then passed to a server and we get a response object in
76       return that we can examine. A request is always independent of any
77       previous requests, i.e. the service is stateless.  The same simple
78       model is used for any kind of service we want to access.
79
80       For example, if we want to fetch a document from a remote file server,
81       then we send it a request that contains a name for that document and
82       the response will contain the document itself.  If we access a search
83       engine, then the content of the request will contain the query
84       parameters and the response will contain the query result.  If we want
85       to send a mail message to somebody then we send a request object which
86       contains our message to the mail server and the response object will
87       contain an acknowledgment that tells us that the message has been
88       accepted and will be forwarded to the recipient(s).
89
90       It is as simple as that!
91
92   The Request Object
93       The libwww-perl request object has the class name HTTP::Request.  The
94       fact that the class name uses "HTTP::" as a prefix only implies that we
95       use the HTTP model of communication.  It does not limit the kind of
96       services we can try to pass this request to.  For instance, we will
97       send HTTP::Requests both to ftp and gopher servers, as well as to the
98       local file system.
99
100       The main attributes of the request objects are:
101
102method is a short string that tells what kind of request this is.
103          The most common methods are GET, PUT, POST and HEAD.
104
105uri is a string denoting the protocol, server and the name of the
106          "document" we want to access.  The uri might also encode various
107          other parameters.
108
109headers contains additional information about the request and can
110          also used to describe the content.  The headers are a set of
111          keyword/value pairs.
112
113content is an arbitrary amount of data.
114
115   The Response Object
116       The libwww-perl response object has the class name HTTP::Response.  The
117       main attributes of objects of this class are:
118
119code is a numerical value that indicates the overall outcome of the
120          request.
121
122message is a short, human readable string that corresponds to the
123          code.
124
125headers contains additional information about the response and
126          describe the content.
127
128content is an arbitrary amount of data.
129
130       Since we don't want to handle all possible code values directly in our
131       programs, a libwww-perl response object has methods that can be used to
132       query what kind of response this is.  The most commonly used response
133       classification methods are:
134
135       is_success()
136          The request was successfully received, understood or accepted.
137
138       is_error()
139          The request failed.  The server or the resource might not be
140          available, access to the resource might be denied or other things
141          might have failed for some reason.
142
143   The User Agent
144       Let us assume that we have created a request object. What do we
145       actually do with it in order to receive a response?
146
147       The answer is that you pass it to a user agent object and this object
148       takes care of all the things that need to be done (like low-level
149       communication and error handling) and returns a response object. The
150       user agent represents your application on the network and provides you
151       with an interface that can accept requests and return responses.
152
153       The user agent is an interface layer between your application code and
154       the network.  Through this interface you are able to access the various
155       servers on the network.
156
157       The class name for the user agent is LWP::UserAgent.  Every libwww-perl
158       application that wants to communicate should create at least one object
159       of this class. The main method provided by this object is request().
160       This method takes an HTTP::Request object as argument and (eventually)
161       returns a HTTP::Response object.
162
163       The user agent has many other attributes that let you configure how it
164       will interact with the network and with your application.
165
166timeout specifies how much time we give remote servers to respond
167          before the library disconnects and creates an internal timeout
168          response.
169
170agent specifies the name that your application uses when it presents
171          itself on the network.
172
173from can be set to the e-mail address of the person responsible for
174          running the application.  If this is set, then the address will be
175          sent to the servers with every request.
176
177parse_head specifies whether we should initialize response headers
178          from the <head> section of HTML documents.
179
180proxy and no_proxy specify if and when to go through a proxy server.
181          <URL:http://www.w3.org/History/1994/WWW/Proxies/>
182
183credentials provides a way to set up user names and passwords needed
184          to access certain services.
185
186       Many applications want even more control over how they interact with
187       the network and they get this by sub-classing LWP::UserAgent.  The
188       library includes a sub-class, LWP::RobotUA, for robot applications.
189
190   An Example
191       This example shows how the user agent, a request and a response are
192       represented in actual perl code:
193
194         # Create a user agent object
195         use LWP::UserAgent;
196         my $ua = LWP::UserAgent->new;
197         $ua->agent("MyApp/0.1 ");
198
199         # Create a request
200         my $req = HTTP::Request->new(POST => 'http://search.cpan.org/search');
201         $req->content_type('application/x-www-form-urlencoded');
202         $req->content('query=libwww-perl&mode=dist');
203
204         # Pass request to the user agent and get a response back
205         my $res = $ua->request($req);
206
207         # Check the outcome of the response
208         if ($res->is_success) {
209             print $res->content;
210         }
211         else {
212             print $res->status_line, "\n";
213         }
214
215       The $ua is created once when the application starts up.  New request
216       objects should normally created for each request sent.
217

NETWORK SUPPORT

219       This section discusses the various protocol schemes and the HTTP style
220       methods that headers may be used for each.
221
222       For all requests, a "User-Agent" header is added and initialized from
223       the $ua->agent attribute before the request is handed to the network
224       layer.  In the same way, a "From" header is initialized from the
225       $ua->from attribute.
226
227       For all responses, the library adds a header called "Client-Date".
228       This header holds the time when the response was received by your
229       application.  The format and semantics of the header are the same as
230       the server created "Date" header.  You may also encounter other
231       "Client-XXX" headers.  They are all generated by the library internally
232       and are not received from the servers.
233
234   HTTP Requests
235       HTTP requests are just handed off to an HTTP server and it decides what
236       happens.  Few servers implement methods beside the usual "GET", "HEAD",
237       "POST" and "PUT", but CGI-scripts may implement any method they like.
238
239       If the server is not available then the library will generate an
240       internal error response.
241
242       The library automatically adds a "Host" and a "Content-Length" header
243       to the HTTP request before it is sent over the network.
244
245       For a GET request you might want to add a "If-Modified-Since" or "If-
246       None-Match" header to make the request conditional.
247
248       For a POST request you should add the "Content-Type" header.  When you
249       try to emulate HTML <FORM> handling you should usually let the value of
250       the "Content-Type" header be "application/x-www-form-urlencoded".  See
251       lwpcook for examples of this.
252
253       The libwww-perl HTTP implementation currently support the HTTP/1.1 and
254       HTTP/1.0 protocol.
255
256       The library allows you to access proxy server through HTTP.  This means
257       that you can set up the library to forward all types of request through
258       the HTTP protocol module.  See LWP::UserAgent for documentation of
259       this.
260
261   HTTPS Requests
262       HTTPS requests are HTTP requests over an encrypted network connection
263       using the SSL protocol developed by Netscape.  Everything about HTTP
264       requests above also apply to HTTPS requests.  In addition the library
265       will add the headers "Client-SSL-Cipher", "Client-SSL-Cert-Subject" and
266       "Client-SSL-Cert-Issuer" to the response.  These headers denote the
267       encryption method used and the name of the server owner.
268
269       The request can contain the header "If-SSL-Cert-Subject" in order to
270       make the request conditional on the content of the server certificate.
271       If the certificate subject does not match, no request is sent to the
272       server and an internally generated error response is returned.  The
273       value of the "If-SSL-Cert-Subject" header is interpreted as a Perl
274       regular expression.
275
276   FTP Requests
277       The library currently supports GET, HEAD and PUT requests.  GET
278       retrieves a file or a directory listing from an FTP server.  PUT stores
279       a file on a ftp server.
280
281       You can specify a ftp account for servers that want this in addition to
282       user name and password.  This is specified by including an "Account"
283       header in the request.
284
285       User name/password can be specified using basic authorization or be
286       encoded in the URL.  Failed logins return an UNAUTHORIZED response with
287       "WWW-Authenticate: Basic" and can be treated like basic authorization
288       for HTTP.
289
290       The library supports ftp ASCII transfer mode by specifying the "type=a"
291       parameter in the URL. It also supports transfer of ranges for FTP
292       transfers using the "Range" header.
293
294       Directory listings are by default returned unprocessed (as returned
295       from the ftp server) with the content media type reported to be
296       "text/ftp-dir-listing". The File::Listing module provides methods for
297       parsing of these directory listing.
298
299       The ftp module is also able to convert directory listings to HTML and
300       this can be requested via the standard HTTP content negotiation
301       mechanisms (add an "Accept: text/html" header in the request if you
302       want this).
303
304       For normal file retrievals, the "Content-Type" is guessed based on the
305       file name suffix. See LWP::MediaTypes.
306
307       The "If-Modified-Since" request header works for servers that implement
308       the "MDTM" command.  It will probably not work for directory listings
309       though.
310
311       Example:
312
313         $req = HTTP::Request->new(GET => 'ftp://me:passwd@ftp.some.where.com/');
314         $req->header(Accept => "text/html, */*;q=0.1");
315
316   News Requests
317       Access to the USENET News system is implemented through the NNTP
318       protocol.  The name of the news server is obtained from the NNTP_SERVER
319       environment variable and defaults to "news".  It is not possible to
320       specify the hostname of the NNTP server in news: URLs.
321
322       The library supports GET and HEAD to retrieve news articles through the
323       NNTP protocol.  You can also post articles to newsgroups by using
324       (surprise!) the POST method.
325
326       GET on newsgroups is not implemented yet.
327
328       Examples:
329
330         $req = HTTP::Request->new(GET => 'news:abc1234@a.sn.no');
331
332         $req = HTTP::Request->new(POST => 'news:comp.lang.perl.test');
333         $req->header(Subject => 'This is a test',
334                      From    => 'me@some.where.org');
335         $req->content(<<EOT);
336         This is the content of the message that we are sending to
337         the world.
338         EOT
339
340   Gopher Request
341       The library supports the GET and HEAD methods for gopher requests.  All
342       request header values are ignored.  HEAD cheats and returns a response
343       without even talking to server.
344
345       Gopher menus are always converted to HTML.
346
347       The response "Content-Type" is generated from the document type encoded
348       (as the first letter) in the request URL path itself.
349
350       Example:
351
352         $req = HTTP::Request->new(GET => 'gopher://gopher.sn.no/');
353
354   File Request
355       The library supports GET and HEAD methods for file requests.  The "If-
356       Modified-Since" header is supported.  All other headers are ignored.
357       The host component of the file URL must be empty or set to "localhost".
358       Any other host value will be treated as an error.
359
360       Directories are always converted to an HTML document.  For normal
361       files, the "Content-Type" and "Content-Encoding" in the response are
362       guessed based on the file suffix.
363
364       Example:
365
366         $req = HTTP::Request->new(GET => 'file:/etc/passwd');
367
368   Mailto Request
369       You can send (aka "POST") mail messages using the library.  All headers
370       specified for the request are passed on to the mail system.  The "To"
371       header is initialized from the mail address in the URL.
372
373       Example:
374
375         $req = HTTP::Request->new(POST => 'mailto:libwww@perl.org');
376         $req->header(Subject => "subscribe");
377         $req->content("Please subscribe me to the libwww-perl mailing list!\n");
378
379   CPAN Requests
380       URLs with scheme "cpan:" are redirected to a suitable CPAN mirror.  If
381       you have your own local mirror of CPAN you might tell LWP to use it for
382       "cpan:" URLs by an assignment like this:
383
384         $LWP::Protocol::cpan::CPAN = "file:/local/CPAN/";
385
386       Suitable CPAN mirrors are also picked up from the configuration for the
387       CPAN.pm, so if you have used that module a suitable mirror should be
388       picked automatically.  If neither of these apply, then a redirect to
389       the generic CPAN http location is issued.
390
391       Example request to download the newest perl:
392
393         $req = HTTP::Request->new(GET => "cpan:src/latest.tar.gz");
394

OVERVIEW OF CLASSES AND PACKAGES

396       This table should give you a quick overview of the classes provided by
397       the library. Indentation shows class inheritance.
398
399        LWP::MemberMixin   -- Access to member variables of Perl5 classes
400          LWP::UserAgent   -- WWW user agent class
401            LWP::RobotUA   -- When developing a robot applications
402          LWP::Protocol          -- Interface to various protocol schemes
403            LWP::Protocol::http  -- http:// access
404            LWP::Protocol::file  -- file:// access
405            LWP::Protocol::ftp   -- ftp:// access
406            ...
407
408        LWP::Authen::Basic -- Handle 401 and 407 responses
409        LWP::Authen::Digest
410
411        HTTP::Headers      -- MIME/RFC822 style header (used by HTTP::Message)
412        HTTP::Message      -- HTTP style message
413          HTTP::Request    -- HTTP request
414          HTTP::Response   -- HTTP response
415        HTTP::Daemon       -- A HTTP server class
416
417        WWW::RobotRules    -- Parse robots.txt files
418          WWW::RobotRules::AnyDBM_File -- Persistent RobotRules
419
420        Net::HTTP          -- Low level HTTP client
421
422       The following modules provide various functions and definitions.
423
424        LWP                -- This file.  Library version number and documentation.
425        LWP::MediaTypes    -- MIME types configuration (text/html etc.)
426        LWP::Simple        -- Simplified procedural interface for common functions
427        HTTP::Status       -- HTTP status code (200 OK etc)
428        HTTP::Date         -- Date parsing module for HTTP date formats
429        HTTP::Negotiate    -- HTTP content negotiation calculation
430        File::Listing      -- Parse directory listings
431        HTML::Form         -- Processing for <form>s in HTML documents
432

MORE DOCUMENTATION

434       All modules contain detailed information on the interfaces they
435       provide.  The lwpcook manpage is the libwww-perl cookbook that contain
436       examples of typical usage of the library.  You might want to take a
437       look at how the scripts lwp-request, lwp-download, lwp-dump and lwp-
438       mirror are implemented.
439

ENVIRONMENT

441       The following environment variables are used by LWP:
442
443       HOME
444           The LWP::MediaTypes functions will look for the .media.types and
445           .mime.types files relative to you home directory.
446
447       http_proxy
448       ftp_proxy
449       xxx_proxy
450       no_proxy
451           These environment variables can be set to enable communication
452           through a proxy server.  See the description of the "env_proxy"
453           method in LWP::UserAgent.
454
455       PERL_LWP_ENV_PROXY
456           If set to a TRUE value, then the LWP::UserAgent will by default
457           call "env_proxy" during initialization.  This makes LWP honor the
458           proxy variables described above.
459
460       PERL_LWP_SSL_VERIFY_HOSTNAME
461           The default "verify_hostname" setting for LWP::UserAgent.  If not
462           set the default will be 1.  Set it as 0 to disable hostname
463           verification (the default prior to libwww-perl 5.840.
464
465       PERL_LWP_SSL_CA_FILE
466       PERL_LWP_SSL_CA_PATH
467           The file and/or directory where the trusted Certificate Authority
468           certificates is located.  See LWP::UserAgent for details.
469
470       PERL_HTTP_URI_CLASS
471           Used to decide what URI objects to instantiate.  The default is
472           URI.  You might want to set it to URI::URL for compatibility with
473           old times.
474

AUTHORS

476       LWP was made possible by contributions from Adam Newby, Albert Dvornik,
477       Alexandre Duret-Lutz, Andreas Gustafsson, Andreas König, Andrew
478       Pimlott, Andy Lester, Ben Coleman, Benjamin Low, Ben Low, Ben Tilly,
479       Blair Zajac, Bob Dalgleish, BooK, Brad Hughes, Brian J. Murrell, Brian
480       McCauley, Charles C. Fu, Charles Lane, Chris Nandor, Christian Gilmore,
481       Chris W. Unger, Craig Macdonald, Dale Couch, Dan Kubb, Dave Dunkin,
482       Dave W. Smith, David Coppit, David Dick, David D. Kilzer, Doug
483       MacEachern, Edward Avis, erik, Gary Shea, Gisle Aas, Graham Barr,
484       Gurusamy Sarathy, Hans de Graaff, Harald Joerg, Harry Bochner, Hugo,
485       Ilya Zakharevich, INOUE Yoshinari, Ivan Panchenko, Jack Shirazi, James
486       Tillman, Jan Dubois, Jared Rhine, Jim Stern, Joao Lopes, John Klar,
487       Johnny Lee, Josh Kronengold, Josh Rai, Joshua Chamas, Joshua Hoblitt,
488       Kartik Subbarao, Keiichiro Nagano, Ken Williams, KONISHI Katsuhiro, Lee
489       T Lindley, Liam Quinn, Marc Hedlund, Marc Langheinrich, Mark D.
490       Anderson, Marko Asplund, Mark Stosberg, Markus B Krüger, Markus Laker,
491       Martijn Koster, Martin Thurn, Matthew Eldridge, Matthew.van.Eerde, Matt
492       Sergeant, Michael A. Chase, Michael Quaranta, Michael Thompson, Mike
493       Schilli, Moshe Kaminsky, Nathan Torkington, Nicolai Langfeldt, Norton
494       Allen, Olly Betts, Paul J. Schinder, peterm, Philip Guenther, Daniel
495       Buenzli, Pon Hwa Lin, Radoslaw Zielinski, Radu Greab, Randal L.
496       Schwartz, Richard Chen, Robin Barker, Roy Fielding, Sander van Zoest,
497       Sean M. Burke, shildreth, Slaven Rezic, Steve A Fink, Steve Hay, Steven
498       Butler, Steve_Kilbane, Takanori Ugai, Thomas Lotterer, Tim Bunce, Tom
499       Hughes, Tony Finch, Ville Skyttä, Ward Vandewege, William York, Yale
500       Huang, and Yitzchak Scott-Thoennes.
501
502       LWP owes a lot in motivation, design, and code, to the libwww-perl
503       library for Perl4 by Roy Fielding, which included work from Alberto
504       Accomazzi, James Casey, Brooks Cutter, Martijn Koster, Oscar
505       Nierstrasz, Mel Melchner, Gertjan van Oosten, Jared Rhine, Jack
506       Shirazi, Gene Spafford, Marc VanHeyningen, Steven E. Brenner, Marion
507       Hakanson, Waldemar Kebsch, Tony Sanders, and Larry Wall; see the
508       libwww-perl-0.40 library for details.
509
511         Copyright 1995-2009, Gisle Aas
512         Copyright 1995, Martijn Koster
513
514       This library is free software; you can redistribute it and/or modify it
515       under the same terms as Perl itself.
516

AVAILABILITY

518       The latest version of this library is likely to be available from CPAN
519       as well as:
520
521         http://github.com/libwww-perl/libwww-perl
522
523       The best place to discuss this code is on the <libwww@perl.org> mailing
524       list.
525
526
527
528perl v5.34.0                      2021-09-21                            LWP(3)
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