On Apache
Under GNU General Public License
2012-05-25 08:33 @38.107.179.239 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)
WWW::Search(3) User Contributed Perl Documentation WWW::Search(3)
NAME
WWW::Search - Virtual base class for WWW searches
SYNOPSIS
require WWW::Search;
$sEngine = "AltaVista";
$oSearch = new WWW::Search($sEngine);
DESCRIPTION
This class is the parent for all access methods supported by the "WWW::Search" library.
This library implements a Perl API to web-based search engines.
See README for a list of search engines currently supported, and for a lot of interesting
high-level information about this distribution.
Search results can be limited, and there is a pause between each request to avoid over-
loading either the client or the server.
Sample program
Here is a sample program:
my $sQuery = 'Columbus Ohio sushi restaurant';
my $oSearch = new WWW::Search('AltaVista');
$oSearch->native_query(WWW::Search::escape_query($sQuery));
$oSearch->login($sUser, $sPassword);
while (my $oResult = $oSearch->next_result())
{
print $oResult->url, "\n";
} # while
$oSearch->logout;
Results are objects of type "WWW::Search::Result" (see WWW::Search::Result for details).
Note that different backends support different result fields. All backends are required
to support title and url.
SEE ALSO
For specific search engines, see WWW::Search::TheEngineName (replacing TheEngineName with
a particular search engine).
For details about the results of a search, see WWW::Search::Result.
METHODS AND FUNCTIONS
Methods and functions marked as PRIVATE are, in general, only useful to backend program-
mers.
new
To create a new WWW::Search, call
$oSearch = new WWW::Search('SearchEngineName');
where SearchEngineName is replaced with a particular search engine. For example:
$oSearch = new WWW::Search('Yahoo');
If no search engine is specified, a default (currently 'Null::Empty') will be chosen for
you. The next step is usually:
$oSearch->native_query('search-engine-specific+query+string');
version
Returns the value of the $VERSION variable of the backend engine, or $WWW::Search::VERSION
if the backend does not contain $VERSION.
maintainer
Returns the value of the $MAINTAINER variable of the backend engine, or
$WWW::Search::MAINTAINER if the backend does not contain $MAINTAINER.
installed_engines
Returns a list of the names of all installed backends. We can not tell if they are up-to-
date or working, though.
use WWW::Search;
my @asEngines = sort &WWW::Search::installed_engines();
local $" = ', ';
print (" + These WWW::Search backends are installed: @asEngines\n");
# Choose a backend at random:
my $oSearch = WWW::Search->new($asEngines[rand(scalar(@asEngines))]);
native_query
Specify a query (and optional options) to the current search object. Previous query (if
any) and its cached results (if any) will be thrown away. The option values and the query
must be escaped; call WWW::Search::escape_query() to escape a string. The search process
is not actually begun until "results()" or "next_result()" is called (lazy!), so
native_query does not return anything.
Example:
$oSearch->native_query('search-engine-specific+escaped+query+string',
{ option1 => 'able', option2 => 'baker' } );
The hash of options following the query string is optional. The query string is back-
end-specific. There are two kinds of options: options specific to the backend, and
generic options applicable to multiple backends.
Generic options all begin with 'search_'. Currently a few are supported:
search_url
Specifies the base URL for the search engine.
search_debug
Enables backend debugging. The default is 0 (no debugging).
search_parse_debug
Enables backend parser debugging. The default is 0 (no debugging).
search_to_file FILE
Causes the search results to be saved in a set of files prefixed by FILE. (Used
internally by the test-suite, not intended for general use.)
search_from_file FILE
Reads a search from a set of files prefixed by FILE. (Used internally by the
test-suite, not intended for general use.)
Some backends may not implement these generic options, but any which do implement them
must provide these semantics.
Backend-specific options are described in the documentation for each backend. In most
cases the options and their values are packed together to create the query portion of the
final URL.
Details about how the search string and option hash are interpreted might be found in the
search-engine-specific manual pages (WWW::Search::SearchEngineName).
After "native_query()", the next step is usually:
while ($oResult = $oSearch->next_result())
{
# do_something($oResult);
}
gui_query
Specify a query to the current search object; the query will be performed with the
engine's default options, as if it were typed by a user in a browser window.
Same arguments as "native_query()" above.
Currently, this feature is supported by only a few backends; consult the documentation for
each backend to see if it is implemented.
cookie_jar
Call this method (anytime before asking for results) if you want to communicate cookie
data with the search engine. Takes one argument, either a filename or an HTTP::Cookies
object. If you give a filename, WWW::Search will attempt to read/store cookies there (by
in turn passing the filename to HTTP::Cookies::new).
$oSearch->cookie_jar('/tmp/my_cookies');
If you give an HTTP::Cookies object, it is up to you to save the cookies if/when you wish.
use HTTP::Cookies;
my $oJar = HTTP::Cookies->new(...);
$oSearch->cookie_jar($oJar);
If you pass in no arguments, the cookie jar (if any) is returned.
my $oJar = $oSearch->cookie_jar;
unless (ref $oJar) { print "No jar" };
date_from
Set/get the start date for limiting the query by a date range. See the documentation for
each backend to find out if date ranges are supported for each search engine.
date_to
Set/get the end date for limiting the query by a date range. See the documentation for
each backend to find out if date ranges are supported for each search engine.
env_proxy
Enable loading proxy settings from *_proxy environment variables. The proxy URL will be
read from $ENV{http_proxy}. The username for authentication will be read from
$ENV{http_proxy_user}. The password for authentication will be read from
$ENV{http_proxy_pwd}.
If you don't want to put passwords in the environment, then subclass LWP::UserAgent and
use $ENV{WWW_SEARCH_USERAGENT} instead (see user_agent below).
env_proxy() must be called before the first retrieval is attempted.
Example:
$ENV{http_proxy } = 'http://my.proxy.com:80';
$ENV{http_proxy_user} = 'bugsbun';
$ENV{http_proxy_pwd } = 'c4rr0t5';
$oSearch->env_proxy('yes'); # Turn on with any true value
...
$oSearch->env_proxy(0); # Turn off with zero or undef
...
if ($oSearch->env_proxy) # Test
http_proxy
Set-up an HTTP proxy (for connections from behind a firewall).
Takes the same arguments as LWP::UserAgent::proxy().
This routine should be called before calling any of the result functions (next_result or
results).
Example:
# Turn on and set address:
$oSearch->http_proxy(['http','ftp'] => 'http://proxy:8080');
# Turn off:
$oSearch->http_proxy('');
http_proxy_user, http_proxy_pwd
Set/get HTTP proxy authentication data.
These routines set/get username and password used in proxy authentication. Authentication
is attempted only if all three items (proxy URL, username and password) have been set.
Example:
$oSearch->http_proxy_user("myuser");
$oSearch->http_proxy_pwd("mypassword");
$oSearch->http_proxy_user(undef); # Example for no authentication
$username = $oSearch->http_proxy_user();
is_http_proxy_auth_data (PRIVATE)
Returns true if all authentication data (proxy URL, username, and password) are available.
maximum_to_retrieve
Set the maximum number of hits to return. Queries resulting in more than this many hits
will return the first hits, up to this limit. Although this specifies a maximum limit,
search engines might return less than this number.
Defaults to 500.
Example:
$max = $oSearch->maximum_to_retrieve(100);
You can also spell this method "maximum_to_return".
timeout
The maximum length of time any portion of the query should take, in seconds.
Defaults to 60.
Example:
$oSearch->timeout(120);
approximate_result_count
Some backends indicate how many hits they have found. Typically this is an approximate
value.
results
Return all the results of a query as an array of WWW::Search::Result objects.
Example:
@results = $oSearch->results();
foreach $oResult (@results) {
print $oResult->url(), "\n";
};
On error, results() will return undef and set "response()" to the HTTP response code.
next_result
Call this method repeatedly to return each result of a query as a WWW::Search::Result
object. Example:
while ($oResult = $oSearch->next_result())
{
print $oResult->url(), "\n";
} # while
On error, next_result() will return undef and set "response()" to an HTTP response object.
login
Backends which need to login to the search engine should implement this function. Takes
two arguments, user and password. Return nonzero if login was successful. Return 0 if
login failed.
logout
Backends which need to logout from the search engine should implement this function.
response
Returns the an HTTP::Response object which resulted from the most-recently-sent query (see
HTTP::Response). If the query returns no results (i.e. $oSearch->results is "undef"),
errors can be reported like this:
my $response = $oSearch->response();
if ($response->is_success) {
print "normal end of result list\n";
} else {
print "error: " . $response->as_string() . "\n";
}
Note to backend authors: even if the backend does not involve the web, it should return an
HTTP::Response object.
seek_result($offset)
Set which result should be returned next time "next_result()" is called. Results are
zero-indexed.
The only guaranteed valid offset is 0, which will replay the results from the beginning.
In particular, seeking past the end of the current cached results probably will not do
what you might think it should.
Results are cached, so this does not re-issue the query or cause IO (unless you go off the
end of the results). To re-do the query, create a new search object.
Example:
$oSearch->seek_result(0);
reset_search (PRIVATE)
Resets internal data structures to start over with a new search (on the same engine).
submit
This method can be used to submit URLs to the search engines for indexing. Consult the
documentation for each backend to find out if it is implemented there, and if so what the
arguments are.
Returns an HTTP::Response object describing the result of the submission request. Consult
the documentation for each backend to find out the meaning of the response.
opaque
This function provides an application a place to store one opaque data element (or many,
via a Perl reference). This facility is useful to (for example), maintain client-specific
information in each active query when you have multiple concurrent queries.
escape_query
Escape a query. Before queries are sent to the internet, special characters must be
escaped so that a proper URL can be formed. This is like escaping a URL, but all non-
alphanumeric characters are escaped and and spaces are converted to "+"s.
Example:
$escaped = WWW::Search::escape_query('+hi +mom');
(Returns "%2Bhi+%2Bmom").
See also "unescape_query()". NOTE that this is not a method, it is a plain function.
unescape_query
Unescape a query. See "escape_query()" for details.
Example:
$unescaped = WWW::Search::unescape_query('%22hi+mom%22');
(Returns '"hi mom"').
NOTE that this is not a method, it is a plain function.
strip_tags
Given a string, returns a copy of that string with HTML tags removed. This should be used
by each backend as they insert the title and description values into the search results
objects.
NOTE that this is not a method, it is a plain function.
hash_to_cgi_string (PRIVATE) (DEPRECATED)
Deprecated.
Given a reference to a hash of string => string, constructs a CGI parameter string that
looks like 'key1=value1&key2=value2'.
If the value is undef, the key will not be added to the string.
At one time, for testing purposes, we asked backends to use this function rather than
piecing the URL together by hand, to ensure that URLs are identical across platforms and
software versions. But this is no longer necessary.
Example:
$self->{_options} = {
'opt3' => 'val3',
'search_url' => 'http://www.deja.com/dnquery.xp',
'opt1' => 'val1',
'QRY' => $native_query,
'opt2' => 'val2',
};
$self->{_next_url} = $self->{_options}{'search_url'} .'?'.
$self->hash_to_cgi_string($self->{_options});
user_agent($NON_ROBOT) (PRIVATE)
This internal routine creates a user-agent for derived classes that query the web. If any
non-false argument is given, a normal LWP::UserAgent (rather than a LWP::RobotUA) is used.
Returns the user-agent object.
If a backend needs the low-level LWP::UserAgent or LWP::RobotUA to have a particular name,
$oSearch->{'agent_name'} (and possibly $oSearch->{'agent_e_mail'}) should be set to the
desired values *before* calling $oSearch->user_agent():
If the environment variable WWW_SEARCH_USERAGENT has a value, it will be used as the class
for a new user agent object. This class should be a subclass of LWP::UserAgent. For
example,
$ENV{WWW_SEARCH_USERAGENT} = 'My::Own::UserAgent';
# If this env.var. has no value,
# LWP::UserAgent or LWP::RobotUA will be used.
$oSearch = new WWW::Search('MyBackend');
$oSearch->{'agent_e_mail'} = $oSearch->{'agent_name'};
$oSearch->{'agent_name'} = 'Mozilla/MSIE 5.5';
$oSearch->user_agent('non-robot');
Backends should use robot-style user-agents whenever possible.
http_referer (PRIVATE)
Get / set the value of the HTTP_REFERER variable for this search object. Some search
engines might only accept requests that originated at some specific previous page. This
method lets backend authors "fake" the previous page. Call this method before calling
http_request.
$oSearch->http_referer('http://prev.engine.com/wherever/setup.html');
$oResponse = $oSearch->http_request('GET', $url);
http_method (PRIVATE)
Get / set the method to be used for the HTTP request. Must be either 'GET' or 'POST'.
Call this method before calling http_request. (Normally you would set this during
native_setup_search().) The default is 'GET'.
$oSearch->http_method('POST');
http_request($method, $url)
Return the response from an http request. Similar to LWP::UserAgent::request. Handles
cookies, follows redirects, etc. Requires that http_referer already be set up, if needed.
next_url (PRIVATE)
Get or set the URL for the next backend request. This can be used to save the WWW::Search
state between sessions (e.g. if you are showing pages of results to the user in a web
browser). Before closing down a session, save the value of next_url:
...
$oSearch->maximum_to_return(10);
while ($oSearch->next_result) { ... }
my $urlSave = $oSearch->next_url;
Then, when you start up the next session (e.g. after the user clicks your "next" button),
restore this value before calling for the results:
$oSearch->native_query(...);
$oSearch->next_url($urlSave);
$oSearch->maximum_to_return(20);
while ($oSearch->next_result) { ... }
WARNING: It is entirely up to you to keep your interface in sync with the number of hits
per page being returned from the backend. And, we make no guarantees whether this method
will work for any given backend. (Their caching scheme might not enable you to jump into
the middle of a list of search results, for example.)
split_lines (PRIVATE)
This internal routine splits data (typically the result of the web page retrieval) into
lines in a way that is OS independent. If the first argument is a reference to an array,
that array is taken to be a list of possible delimiters for this split. For example,
Yahoo.pm uses <p> and <dd><li> as "line" delimiters for convenience.
generic_option (PRIVATE)
This internal routine checks if an option is generic or backend specific. Currently all
generic options begin with 'search_'. This routine is not a method.
setup_search (PRIVATE)
This internal routine does generic Search setup. It calls "native_setup_search()" to do
backend-specific setup.
user_agent_delay (PRIVATE)
Derived classes should call this between requests to remote servers to avoid overloading
them with many, fast back-to-back requests.
absurl (PRIVATE)
An internal routine to convert a relative URL into a absolute URL. It takes two argu-
ments, the 'base' url (usually the search engine CGI URL) and the URL to be converted.
Returns a URI object.
retrieve_some (PRIVATE)
An internal routine to interface with "native_retrieve_some()". Checks for overflow.
native_retrieve_some (PRIVATE)
Fetch the next page of results from the web engine, parse the results, and prepare for the
next page of results.
If a backend defines this method, it is in total control of the WWW fetch, parsing, and
preparing for the next page of results. See the WWW::Search::AltaVista module for example
usage of the native_retrieve_some method.
An easier way to achieve this is to inherit native_retrieve_some from WWW::Search, and do
only the parsing in the backend code. Simply define a method parse_tree which takes one
argument, an HTML::TreeBuilder object, and returns an integer, the number of results found
on this page. See the WWW::Search::Yahoo module for example usage of the parse_tree
method.
A backend should, in general, define either parse_tree() or native_retrieve_some(), but
not both.
Additional features of the default native_retrieve_some method:
Sets $self->{_prev_url} to the URL of the page just retrieved.
Calls $self->preprocess_results_page() on the raw HTML of the page.
Then, parses the page with an HTML::TreeBuilder object and passes that populated object to
$self->parse_tree().
Additional notes on using the parse_tree method:
The built-in HTML::TreeBuilder object used to parse the page has store_comments turned ON.
If a backend needs to use a subclassed or modified HTML::TreeBuilder object, the backend
should set $self->{'_treebuilder'} to that object before any results are retrieved. The
best place to do this is at the end of native_setup_search.
my $oTree = new myTreeBuilder;
$oTree->store_pis(1); # for example
$self->{'_treebuilder'} = $oTree;
When parse_tree() is called, the $self->next_url is cleared. During parsing, the backend
should set $self->next_url to the appropriate URL for the next page of results. (If
parse_tree() does not set the value, the search will end after parsing this page of
results.)
When parse_tree() is called, the URL for the page being parsed can be found in
$self->{_prev_url}.
preprocess_results_page (PRIVATE)
A filter on the raw HTML of the results page. This allows the backend to alter the HTML
before it is parsed, such as to correct for known problems, HTML that can not be parsed
correctly, etc.
Takes one argument, a string (the HTML webpage); returns one string (the same HTML, modi-
fied).
This method is called from within native_retrieve_some (above) before the HTML of the page
is parsed.
See the WWW::Search::Ebay distribution 2.07 or higher for example usage.
test_cases (deprecated)
Deprecated.
Returns the value of the $TEST_CASES variable of the backend engine.
IMPLEMENTING NEW BACKENDS
"WWW::Search" supports backends to separate search engines. Each backend is implemented
as a subclass of "WWW::Search". WWW::Search::Yahoo provides a good sample backend.
A backend must have the routine "native_setup_search()". A backend must have the routine
"native_retrieve_some()" or "parse_tree()".
"native_setup_search()" is invoked before the search. It is passed a single argument: the
escaped, native version of the query.
"native_retrieve_some()" is the core of a backend. It will be called periodically to
fetch URLs. It should retrieve several hits from the search service and add them to the
cache. It should return the number of hits found, or undef when there are no more hits.
Internally, "native_retrieve_some()" typically sends an HTTP request to the search ser-
vice, parses the HTML, extracts the links and descriptions, then saves the URL for the
next page of results. See the code for the "WWW::Search::AltaVista" module for an exam-
ple.
Alternatively, a backend can define the method "parse_tree()" instead of
"native_retrieve_some()". See the "WWW::Search::Ebay" module for a good example.
If you implement a new backend, please let the authors know.
BUGS AND DESIRED FEATURES
The bugs are there for you to find (some people call them Easter Eggs).
Desired features:
A portable query language.
A portable language would easily allow you to move queries easily between different
search engines. A query abstraction is non-trivial and unfortunately will not be done
anytime soon by the current maintainers. If you want to take a shot at it, please let
me know.
AUTHOR
"WWW::Search" was written by John Heidemann, "johnh AT isi.edu". "WWW::Search" is currently
maintained by Martin Thurn, "mthurn AT cpan.org".
backends and applications for WWW::Search were originally written by John Heidemann, Wm.
L. Scheding, Cesare Feroldi de Rosa, and GLen Pringle.
COPYRIGHT
Copyright (c) 1996 University of Southern California. All rights reserved.
Redistribution and use in source and binary forms are permitted provided that the above
copyright notice and this paragraph are duplicated in all such forms and that any documen-
tation, advertising materials, and other materials related to such distribution and use
acknowledge that the software was developed by the University of Southern California,
Information Sciences Institute. The name of the University may not be used to endorse or
promote products derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUD-
ING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PAR-
TICULAR PURPOSE.
perl v5.8.1 2003-11-25 WWW::Search(3)
Generated by $Id: phpMan.php,v 4.49 2006/02/26 13:18:18 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2012-05-25 08:33 @38.107.179.239 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)