1WWW::Search(3)        User Contributed Perl Documentation       WWW::Search(3)
2
3
4

NAME

6       WWW::Search - Virtual base class for WWW searches
7

SYNOPSIS

9         use WWW::Search;
10         my $sEngine = 'AltaVista';
11         my $oSearch = new WWW::Search($sEngine);
12

DESCRIPTION

14       This class is the parent for all access methods supported by the
15       "WWW::Search" library.  This library implements a Perl API to web-based
16       search engines.
17
18       See README for a list of search engines currently supported, and for a
19       lot of interesting high-level information about this distribution.
20
21       Search results can be limited, and there is a pause between each
22       request to avoid overloading either the client or the server.
23
24   Sample program
25       Here is a sample program:
26
27         my $sQuery = 'Columbus Ohio sushi restaurant';
28         my $oSearch = new WWW::Search('AltaVista');
29         $oSearch->native_query(WWW::Search::escape_query($sQuery));
30         $oSearch->login($sUser, $sPassword);
31         while (my $oResult = $oSearch->next_result())
32           {
33           print $oResult->url, "\n";
34           } # while
35         $oSearch->logout;
36
37       Results are objects of type "WWW::SearchResult" (see WWW::SearchResult
38       for details).  Note that different backends support different result
39       fields.  All backends are required to support title and url.
40

SEE ALSO

42       For specific search engines, see WWW::Search::TheEngineName (replacing
43       TheEngineName with a particular search engine).
44
45       For details about the results of a search, see WWW::SearchResult.
46

METHODS AND FUNCTIONS FOR SEARCHERS

48       new To create a new WWW::Search, call
49
50               $oSearch = new WWW::Search('SearchEngineName');
51
52           where SearchEngineName is replaced with a particular search engine.
53           For example:
54
55               $oSearch = new WWW::Search('Yahoo');
56
57           If no search engine is specified, a default (currently
58           'Null::Empty') will be chosen for you.
59
60       version
61           Returns the value of the $VERSION variable of the backend engine,
62           or $WWW::Search::VERSION if the backend does not contain $VERSION.
63
64       maintainer
65           Returns the value of the $MAINTAINER variable of the backend
66           engine, or $WWW::Search::MAINTAINER if the backend does not contain
67           $MAINTAINER.
68
69       installed_engines
70           Returns a list of the names of all installed backends.  We can not
71           tell if they are up-to-date or working, though.
72
73             use WWW::Search;
74             my @asEngines = sort &WWW::Search::installed_engines();
75             local $" = ', ';
76             print (" + These WWW::Search backends are installed: @asEngines\n");
77             # Choose a backend at random (yes, this is rather silly):
78             my $oSearch = WWW::Search->new($asEngines[rand(scalar(@asEngines))]);
79
80       native_query
81           Specify a query (and optional options) to the current search
82           object.  Previous query (if any) and its cached results (if any)
83           will be thrown away.  The option values and the query must be
84           escaped; call WWW::Search::escape_query() to escape a string.  The
85           search process is not actually begun until "results()" or
86           "next_result()" is called (lazy!), so native_query does not return
87           anything.
88
89           Example:
90
91             $oSearch->native_query('search-engine-specific+escaped+query+string',
92                                   { option1 => 'able', option2 => 'baker' } );
93
94           The hash of options following the query string is optional.  The
95           query string is backend-specific.  There are two kinds of options:
96           options specific to the backend, and generic options applicable to
97           multiple backends.
98
99           Generic options all begin with 'search_'.  Currently a few are
100           supported:
101
102           search_url
103               Specifies the base URL for the search engine.
104
105           search_debug
106               Enables backend debugging.  The default is 0 (no debugging).
107
108           search_parse_debug
109               Enables backend parser debugging.  The default is 0 (no
110               debugging).
111
112           search_to_file FILE
113               Causes the search results to be saved in a set of files
114               prefixed by FILE.  (Used internally by the test-suite, not
115               intended for general use.)
116
117           search_from_file FILE
118               Reads a search from a set of files prefixed by FILE.  (Used
119               internally by the test-suite, not intended for general use.)
120
121           Some backends may not implement these generic options, but any
122           which do implement them must provide these semantics.
123
124           Backend-specific options are described in the documentation for
125           each backend.  In most cases the options and their values are
126           packed together to create the query portion of the final URL.
127
128           Details about how the search string and option hash are interpreted
129           might be found in the search-engine-specific manual pages
130           (WWW::Search::SearchEngineName).
131
132       gui_query
133           Specify a query to the current search object; the query will be
134           performed with the engine's default options, as if it were typed by
135           a user in a browser window.
136
137           Same arguments as "native_query()" above.
138
139           Currently, this feature is supported by only a few backends;
140           consult the documentation for each backend to see if it is
141           implemented.
142
143       cookie_jar
144           Call this method (anytime before asking for results) if you want to
145           communicate cookie data with the search engine.  Takes one
146           argument, either a filename or an HTTP::Cookies object.  If you
147           give a filename, WWW::Search will attempt to read/store cookies
148           there (by passing the filename to HTTP::Cookies::new).
149
150             $oSearch->cookie_jar('/tmp/my_cookies');
151
152           If you give an HTTP::Cookies object, it is up to you to save the
153           cookies if/when you wish.
154
155             use HTTP::Cookies;
156             my $oJar = HTTP::Cookies->new(...);
157             $oSearch->cookie_jar($oJar);
158
159           If you pass in no arguments, the cookie jar (if any) is returned.
160
161             my $oJar = $oSearch->cookie_jar;
162             unless (ref $oJar) { print "No jar" };
163
164       date_from
165           Set/get the start date for limiting the query by a date range.  See
166           the documentation for each backend to find out if date ranges are
167           supported.
168
169       date_to
170           Set/get the end date for limiting the query by a date range.  See
171           the documentation for each backend to find out if date ranges are
172           supported.
173
174       env_proxy
175           Enable loading proxy settings from environment variables.  The
176           proxy URL will be read from $ENV{http_proxy}.  The username for
177           authentication will be read from $ENV{http_proxy_user}.  The
178           password for authentication will be read from $ENV{http_proxy_pwd}.
179
180           If you don't want to put passwords in the environment, one solution
181           would be to subclass LWP::UserAgent and use
182           $ENV{WWW_SEARCH_USERAGENT} instead (see user_agent below).
183
184           env_proxy() must be called before the first retrieval is attempted.
185
186           Example:
187
188             $ENV{http_proxy     } = 'http://my.proxy.com:80';
189             $ENV{http_proxy_user} = 'bugsbun';
190             $ENV{http_proxy_pwd } = 'c4rr0t5';
191             $oSearch->env_proxy('yes');  # Turn on with any true value
192             ...
193             $oSearch->env_proxy(0);  # Turn off with zero
194             ...
195             if ($oSearch->env_proxy)  # Test
196
197       http_proxy
198           Set up an HTTP proxy (for connections from behind a firewall).
199
200           Takes the same arguments as LWP::UserAgent::proxy().
201
202           This routine should be called before calling any of the result
203           functions (any method with "result" in its name).
204
205           Example:
206
207             # Turn on and set address:
208             $oSearch->http_proxy(['http','ftp'] => 'http://proxy:8080');
209             # Turn off:
210             $oSearch->http_proxy('');
211
212       http_proxy_user, http_proxy_pwd
213           Set/get HTTP proxy authentication data.
214
215           These routines set/get username and password used in proxy
216           authentication.  Authentication is attempted only if all three
217           items (proxy URL, username and password) have been set.
218
219           Example:
220
221               $oSearch->http_proxy_user("myuser");
222               $oSearch->http_proxy_pwd("mypassword");
223               $oSearch->http_proxy_user(undef);   # Example for no authentication
224
225               $username = $oSearch->http_proxy_user();
226
227       maximum_to_retrieve
228           Set the maximum number of hits to return.  Queries resulting in
229           more than this many hits will return the first hits, up to this
230           limit.  Although this specifies a maximum limit, search engines
231           might return less than this number.
232
233           Defaults to 500.
234
235           Example:
236               $max = $oSearch->maximum_to_retrieve(100);
237
238           You can also spell this method "maximum_to_return".
239
240       maximum_to_return
241           Synonym for maximum_to_retrieve
242
243       timeout
244           The maximum length of time any portion of the query should take, in
245           seconds.
246
247           Defaults to 60.
248
249           Example:
250               $oSearch->timeout(120);
251
252       login
253           Backends which need to login to the search engine should implement
254           this function.  Takes two arguments, user and password.  Return
255           nonzero if login was successful.  Return undef or 0 if login
256           failed.
257
258       logout
259           Backends which need to logout from the search engine should
260           implement this function.
261
262       approximate_result_count
263           Some backends indicate how many results they have found, e.g. with
264           a number shown at the top of the search results page.  Note that
265           there is no corresponding method that returns the actual count of
266           results; that's because results are normally retrieved in batches
267           (i.e. pages) and at any given time there's no way to know how big
268           the final list of results will be.  NEW: if request has not been
269           made to the search provider, this method will return undef (used to
270           return zero).  NEW: if the results page does not explicitly
271           indicate the result count, this method will return undef (used to
272           return zero).
273
274       approximate_hit_count
275           This is an alias for approximate_result_count().
276
277       results
278           Return all the results of a query as an array of WWW::SearchResult
279           objects.
280
281           Note: This might take a while, because a web backend will keep
282           asking the search engine for "next page of results" over and over
283           until there are no more next pages, and THEN return from this
284           function.
285
286           If an error occurs at any time during query processing, it will be
287           indicated in the response().
288
289           Example:
290
291               @results = $oSearch->results();
292               # Go have a cup of coffee while the previous line executes...
293               foreach $oResult (@results)
294                 {
295                 print $oResult->url(), "\n";
296                 } # foreach
297
298       next_result
299           Call this method repeatedly to return each result of a query as a
300           WWW::SearchResult object.  Example:
301
302               while ($oResult = $oSearch->next_result())
303                 {
304                 print $oResult->url(), "\n";
305                 } # while
306
307           When there are no more results, or if an error occurs,
308           next_result() will return undef.
309
310           If an error occurs at any time during query processing, it will be
311           indicated in the response().
312
313       seek_result($offset)
314           Set which result should be returned next time "next_result()" is
315           called.  Results are zero-indexed.
316
317           The only guaranteed valid offset is 0, which will replay the
318           results from the beginning.  In particular, seeking past the end of
319           the current cached results probably will not do what you might
320           think it should.
321
322           Results are cached, so this does not re-issue the query or cause IO
323           (unless you go off the end of the results).  To re-do the query,
324           create a new search object.
325
326           Example:
327
328               $oSearch->seek_result(0);
329
330       response
331           Returns an HTTP::Response object which resulted from the most-
332           recently-sent query.  Errors can be detected like this:
333
334               if (! $oSearch->response->is_success)
335                 {
336                 print STDERR "Error:  " . $oSearch->response->as_string() . "\n";
337                 } # if
338
339           Note to backend authors: even if the backend does not involve the
340           web, it should return an HTTP::Response object.
341
342       submit
343           This method can be used to submit URLs to the search engines for
344           indexing.  Consult the documentation for each backend to find out
345           if it is implemented there, and if so what the arguments are.
346
347           Returns an HTTP::Response object describing the result of the
348           submission request.  Consult the documentation for each backend to
349           find out the meaning of the response.
350
351       opaque
352           This function provides an application a place to store one opaque
353           data element (or many, via a Perl reference).  This facility is
354           useful to (for example), maintain client-specific information in
355           each active query when you have multiple concurrent queries.
356
357       escape_query
358           Escape a query.  Before queries are sent to the internet, special
359           characters must be escaped so that a proper URL can be formed.
360           This is like escaping a URL, but all non-alphanumeric characters
361           are escaped and and spaces are converted to "+"s.
362
363           Example:
364
365               $escaped = WWW::Search::escape_query('+hi +mom');
366               # $escaped is now '%2Bhi+%2Bmom'
367
368           See also "unescape_query()".  NOTE that this is not a method, it is
369           a plain function.
370
371       unescape_query
372           Unescape a query.  See "escape_query()" for details.
373
374           Example:
375
376               $unescaped = WWW::Search::unescape_query('%22hi+mom%22');
377               # $unescaped eq q{"hi mom"}
378
379           NOTE that this is not a method, it is a plain function.
380
381       strip_tags
382           Given a string, returns a copy of that string with HTML tags
383           removed.  This should be used by each backend as they insert the
384           title and description values into the search results objects.
385
386           NOTE that this is not a method, it is a plain function.
387
388       is_http_proxy
389           Returns true if proxy information is available.
390

METHODS AND FUNCTIONS FOR BACKEND PROGRAMMERS

392       reset_search
393           Resets internal data structures to start over with a new search (on
394           the same engine).
395
396       is_http_proxy_auth_data
397           Returns true if all authentication data (proxy URL, username, and
398           password) are available.
399
400       agent_name($sName)
401           If your search engine rejects certain browser, you can trick it
402           into thinking you're any browser type you want.  See below under
403           user_agent().
404
405       agent_email($sName)
406       user_agent($NON_ROBOT)
407           This internal routine creates a user-agent for derived classes that
408           query the web.  If any non-false argument is given, a normal
409           LWP::UserAgent (rather than a LWP::RobotUA) is used.
410
411           Returns the user-agent object.
412
413           If a backend needs the low-level LWP::UserAgent or LWP::RobotUA to
414           have a particular name, $oSearch->agent_name() and possibly
415           $oSearch->agent_email() should be called to set the desired values
416           *before* calling $oSearch->user_agent().
417
418           If the environment variable WWW_SEARCH_USERAGENT has a value, it
419           will be used as the class for a new user agent object.  This class
420           should be a subclass of LWP::UserAgent.  For example,
421
422             $ENV{WWW_SEARCH_USERAGENT} = 'My::Own::UserAgent';
423             # If this env.var. has no value,
424             # LWP::UserAgent or LWP::RobotUA will be used.
425             $oSearch = new WWW::Search('MyBackend');
426             $oSearch->agent_name('MySpider');
427             if ($iBackendWebsiteRequiresNonRobot)
428               {
429               $oSearch->user_agent('non-robot');
430               }
431             else
432               {
433               $oSearch->agent_email('me@here.com');
434               $oSearch->user_agent();
435               }
436
437           Backends should use robot-style user-agents whenever possible.
438
439       http_referer
440           Get / set the value of the HTTP_REFERER variable for this search
441           object.  Some search engines might only accept requests that
442           originated at some specific previous page.  This method lets
443           backend authors "fake" the previous page.  Call this method before
444           calling http_request.
445
446             $oSearch->http_referer('http://prev.engine.com/wherever/setup.html');
447             $oResponse = $oSearch->http_request('GET', $url);
448
449       http_method
450           Get / set the method to be used for the HTTP request.  Must be
451           either 'GET' or 'POST'.  Call this method before calling
452           http_request.  (Normally you would set this during
453           _native_setup_search().)  The default is 'GET'.
454
455             $oSearch->http_method('POST');
456
457       http_request($method, $url)
458           Submit the HTTP request to the world, and return the response.
459           Similar to LWP::UserAgent::request.  Handles cookies, follows
460           redirects, etc.  Requires that http_referer already be set up, if
461           needed.
462
463       next_url
464           Get or set the URL for the next backend request.  This can be used
465           to save the WWW::Search state between sessions (e.g. if you are
466           showing pages of results to the user in a web browser).  Before
467           closing down a session, save the value of next_url:
468
469             ...
470             $oSearch->maximum_to_return(10);
471             while ($oSearch->next_result) { ... }
472             my $urlSave = $oSearch->next_url;
473
474           Then, when you start up the next session (e.g. after the user
475           clicks your "next" button), restore this value before calling for
476           the results:
477
478             $oSearch->native_query(...);
479             $oSearch->next_url($urlSave);
480             $oSearch->maximum_to_return(20);
481             while ($oSearch->next_result) { ... }
482
483           WARNING: It is entirely up to you to keep your interface in sync
484           with the number of hits per page being returned from the backend.
485           And, we make no guarantees whether this method will work for any
486           given backend.  (Their caching scheme might not enable you to jump
487           into the middle of a list of search results, for example.)
488
489       split_lines
490           This internal routine splits data (typically the result of the web
491           page retrieval) into lines in a way that is OS independent.  If the
492           first argument is a reference to an array, that array is taken to
493           be a list of possible delimiters for this split.  For example,
494           Yahoo.pm uses <p> and <dd><li> as "line" delimiters for
495           convenience.
496
497       generic_option
498           This internal routine checks if an option is generic or backend
499           specific.  Currently all generic options begin with 'search_'.
500           This routine is not a method.
501
502       _native_setup_search
503           Do some backend-specific initialization.  It will be called with
504           the same arguments as native_query().
505
506       setup_search
507           This internal routine does generic Search setup.  It calls
508           "_native_setup_search()" to do backend-specific setup.
509
510       need_to_delay
511           A backend should override this method in order to dictate whether
512           user_agent_delay() needs to be called before the next HTTP request
513           is sent.  Return any perlish true or zero value.
514
515       user_agent_delay
516           According to what need_to_delay() returns, user_agent_delay() will
517           be called between requests to remote servers to avoid overloading
518           them with many back-to-back requests.
519
520       absurl
521           An internal routine to convert a relative URL into a absolute URL.
522           It takes two arguments, the 'base' url (usually the search engine
523           CGI URL) and the URL to be converted.  Returns a URI object.
524
525       retrieve_some
526           An internal routine to interface with "_native_retrieve_some()".
527           Checks for overflow.
528
529       _native_retrieve_some
530           Fetch the next page of results from the web engine, parse the
531           results, and prepare for the next page of results.
532
533           If a backend defines this method, it is in total control of the WWW
534           fetch, parsing, and preparing for the next page of results.  See
535           the WWW::Search::AltaVista module for example usage of the
536           _native_retrieve_some method.
537
538           An easier way to achieve this in a backend is to inherit
539           _native_retrieve_some from WWW::Search, and do only the HTML
540           parsing.  Simply define a method _parse_tree which takes one
541           argument, an HTML::TreeBuilder object, and returns an integer, the
542           number of results found on this page.  See the WWW::Search::Yahoo
543           module for example usage of the _parse_tree method.
544
545           A backend should, in general, define either _parse_tree() or
546           _native_retrieve_some(), but not both.
547
548           Additional features of the default _native_retrieve_some method:
549
550           Sets $self->{_prev_url} to the URL of the page just retrieved.
551
552           Calls $self->preprocess_results_page() on the raw HTML of the page.
553
554           Then, parses the page with an HTML::TreeBuilder object and passes
555           that populated object to $self->_parse_tree().
556
557           Additional notes on using the _parse_tree method:
558
559           The built-in HTML::TreeBuilder object used to parse the page has
560           store_comments turned ON.  If a backend needs to use a subclassed
561           or modified HTML::TreeBuilder object, the backend should set
562           $self->{'_treebuilder'} to that object before any results are
563           retrieved.  The best place to do this is at the end of
564           _native_setup_search.
565
566             my $oTree = new myTreeBuilder;
567             $oTree->store_pis(1);  # for example
568             $self->{'_treebuilder'} = $oTree;
569
570           When _parse_tree() is called, the $self->next_url is cleared.
571           During parsing, the backend should set $self->next_url to the
572           appropriate URL for the next page of results.  (If _parse_tree()
573           does not set the value, the search will end after parsing this page
574           of results.)
575
576           When _parse_tree() is called, the URL for the page being parsed can
577           be found in $self->{_prev_url}.
578
579       result_as_HTML
580           Given a WWW::SearchResult object, formats it human-readable with
581           HTML.
582
583       preprocess_results_page
584           A filter on the raw HTML of the results page.  This allows the
585           backend to alter the HTML before it is parsed, such as to correct
586           for known problems, HTML that can not be parsed correctly, etc.
587
588           Takes one argument, a string (the HTML webpage); returns one string
589           (the same HTML, modified).
590
591           This method is called from within _native_retrieve_some (above)
592           before the HTML of the page is parsed.
593
594           See the WWW::Search::Ebay distribution 2.07 or higher for example
595           usage.
596
597       test_cases (DEPRECATED)
598           Deprecated.
599
600           Returns the value of the $TEST_CASES variable of the backend
601           engine.
602
603       hash_to_cgi_string (DEPRECATED)
604           Given a reference to a hash of string => string, constructs a CGI
605           parameter string that looks like 'key1=value1&key2=value2'.
606
607           If the value is undef, the key will not be added to the string.
608
609           At one time, for testing purposes, we asked backends to use this
610           function rather than piecing the URL together by hand, to ensure
611           that URLs are identical across platforms and software versions.
612           But this is no longer necessary.
613
614           Example:
615
616               $self->{_options} = {
617                                    'opt3' => 'val3',
618                                    'search_url' => 'http://www.deja.com/dnquery.xp',
619                                    'opt1' => 'val1',
620                                    'QRY' => $native_query,
621                                    'opt2' => 'val2',
622                                   };
623               $self->{_next_url} = $self->{_options}{'search_url'} .'?'.
624                                    $self->hash_to_cgi_string($self->{_options});
625

IMPLEMENTING NEW BACKENDS

627       "WWW::Search" supports backends to separate search engines.  Each
628       backend is implemented as a subclass of "WWW::Search".
629       WWW::Search::Yahoo provides a good sample backend.
630
631       A backend must have the routine "_native_setup_search()".  A backend
632       must have the routine "_native_retrieve_some()" or "_parse_tree()".
633
634       "_native_setup_search()" is invoked before the search.  It is passed a
635       single argument: the escaped, native version of the query.
636
637       "_native_retrieve_some()" is the core of a backend.  It will be called
638       periodically to fetch URLs.  It should retrieve several hits from the
639       search service and add them to the cache.  It should return the number
640       of hits found, or undef when there are no more hits.
641
642       Internally, "_native_retrieve_some()" typically sends an HTTP request
643       to the search service, parses the HTML, extracts the links and
644       descriptions, then saves the URL for the next page of results.  See the
645       code for the "WWW::Search::AltaVista" module for an example.
646
647       Alternatively, a backend can define the method "_parse_tree()" instead
648       of "_native_retrieve_some()".  See the "WWW::Search::Ebay" module for a
649       good example.
650
651       If you implement a new backend, please let the authors know.
652

BUGS AND DESIRED FEATURES

654       The bugs are there for you to find (some people call them Easter Eggs).
655
656       Desired features:
657
658       A portable query language.
659           A portable language would easily allow you to move queries easily
660           between different search engines.  A query abstraction is non-
661           trivial and unfortunately will not be done any time soon by the
662           current maintainer.  If you want to take a shot at it, please let
663           me know.
664

AUTHOR

666       John Heidemann <johnh@isi.edu> Maintained by Martin Thurn,
667       "mthurn@cpan.org", <http://www.sandcrawler.com/SWB/cpan-modules.html>.
668
670       Copyright (c) 1996 University of Southern California.  All rights
671       reserved.
672
673       Redistribution and use in source and binary forms are permitted
674       provided that the above copyright notice and this paragraph are
675       duplicated in all such forms and that any documentation, advertising
676       materials, and other materials related to such distribution and use
677       acknowledge that the software was developed by the University of
678       Southern California, Information Sciences Institute.  The name of the
679       University may not be used to endorse or promote products derived from
680       this software without specific prior written permission.
681
682       THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
683       WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
684       MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
685
686
687
688perl v5.32.1                      2021-01-27                    WWW::Search(3)
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