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|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<html>
<head>
<title>SWISH-Enhanced: SWISH::Filter - Perl extension for filtering documents with Swish-e </title>
<link href="./style.css" rel=stylesheet type="text/css" title="refstyle">
</head>
<body>
<h1 class="banner">
<a href="http://swish-e.org"><img border=0 src="images/swish.gif" alt="Swish-E Logo"></a><br>
<img src="images/swishbanner1.gif"><br>
<img src="images/dotrule1.gif"><br>
SWISH::Filter - Perl extension for filtering documents with Swish-e
</h1>
<hr>
<p>
<div class="navbar">
<a href="./spider.html">Prev</a> |
<a href="./index.html">Contents</a> |
</div>
<p>
<div class="toc">
<A NAME="toc"></A>
<P><B>Table of Contents:</B></P>
<UL>
<LI><A HREF="#SYNOPSIS">SYNOPSIS</A>
<LI><A HREF="#DESCRIPTION">DESCRIPTION</A>
<LI><A HREF="#METHODS">METHODS</A>
<UL>
<LI><A HREF="#SWISH_Filter_new_Options">SWISH::Filter->new Options</A>
</UL>
<LI><A HREF="#WRITING_FILTERS">WRITING FILTERS</A>
<LI><A HREF="#SWISH_Filter_document_Methods">SWISH::Filter::document Methods</A>
<UL>
<LI><A HREF="#Methods_used_by_end_users_and_filter_authors">Methods used by end-users and filter authors</A>
<LI><A HREF="#Methods_used_by_filter_authors">Methods used by filter authors</A>
</UL>
<LI><A HREF="#SWISH_Filters_BASE">SWISH::Filters::_BASE</A>
<LI><A HREF="#TESTING">TESTING</A>
<LI><A HREF="#SUPPORT">SUPPORT</A>
<LI><A HREF="#Bugs_todo_items_and_other_notes">Bugs, todo items, and other notes</A>
<LI><A HREF="#AUTHOR">AUTHOR</A>
<LI><A HREF="#COPYRIGHT">COPYRIGHT</A>
</UL>
</div>
[ <B><FONT SIZE=-1><A HREF="#toc">TOC</A></FONT></B> ]
<HR>
<P>
<H1><A NAME="SYNOPSIS">SYNOPSIS</A></H1>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> use SWISH::Filter;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # load available filters into memory
my $filter = SWISH::Filter->new;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # convert a document</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> my $doc = $filter->convert(
document => \$scalar_ref, # path or ref to a doc
content_type => $content_type, # content type if doc reference
name => $real_path, # optional name for this file (useful for debugging)
user_data => $whatever, # optional data to make available to filters
);</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> return unless $doc; # empty doc, zero size, or no filters installed</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # Was the document converted by a filter?
my $was_filtered = $doc->was_filtered;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # Skip if the file is not text
return if $doc->is_binary;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # Print out the doc
my $doc_ref = $doc->fetch_doc;
print $$doc_ref;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # Fetch the final content type of the document
my $content_type = $doc->content_type;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # Fetch Swish-e parser type (TXT*, XML*, HTML*, or undefined)
my $doc_type = $doc->swish_parser_type;</pre>
</td>
</tr>
</table>
<P>
[ <B><FONT SIZE=-1><A HREF="#toc">TOC</A></FONT></B> ]
<HR>
<H1><A NAME="DESCRIPTION">DESCRIPTION</A></H1>
<P>
SWISH::Filter provides a unified way to convert documents into a type that
Swish-e can index. Individual filters are installed as separate perl
modules. For example, there might be a filter that converts from PDF format
to HTML format.
<P>
Note that this is just a framework for filtering documents. Additional
helper programs or Perl module may need to be installed to use
SWISH::Filter to filter documents. For example, to filter PDF documents you
must install the Xpdf package.
<P>
The filters are automatically loaded when <CODE>SWISH::Filters->new()</CODE> is called. Filters define a type and priority that determines the
processing order of the filter. Filters are processed in this sort order
until a filter accepts the document for filtering. The filter uses the
document's content type to determine if the filter should handle the
current document. The content-type is determined by the files suffix if not
supplied by the calling program.
<P>
The individual filters are not designed to be used as separate modules. All
access to the filters is through this SWISH::Filter module.
<P>
Normally, once a document is filtered processing stops. Filters can filter
the document and then set a flag saying that filtering should continue (for
example a filter that uncompresses a MS Word document before passing on to
the filter that converts from MS Word to text). All this should be
transparent to the end user. So, filters can be pipe-lined.
<P>
The idea of SWISH::Filter is that new filters can be created, and then
downloaded and installed to provide new filtering capabilities. For
example, if you needed to index MS Excel documents you might be able to
download a filter from the Swish-e site and magically next time you run
indexing MS Excel docs would be indexed.
<P>
The SWISH::Filter setup can be used with -S prog or -S http. It works best
with the -S prog method because the filter modules only need to be loaded
and compiled one time. The -S prog program <EM>spider.pl</EM> will automatically use SWISH::Filter when spidering with default settings
(using "default" as the first parameter to spider.pl).
<P>
The -S http indexing method uses a Perl helper script called <EM>swishspider</EM>.
<EM>swishspider</EM> has been updated to work with SWISH::Filter, but (unlike spider.pl) does
not contain a "use lib" line to point to the location of
SWISH::Filter. This means that by default <EM>swishspider</EM> will <STRONG>not</STRONG> use SWISH::Filter for filtering. The reason for this is because <EM>swishspider</EM>
runs for every URL fetched, and loading the Filters for each document can
be slow. The recommended way of spidering is using -S prog with spider.pl,
but if -S http is desired the way to enable SWISH::Filter is to set
PERL5LIB before running swish so that <EM>swishspider</EM> will be able to locate the SWISH::Filter module. Here's one way to set the
PERL5LIB with the bash shell:
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> $ export PERL5LIB=`swish-filter-test -path`</pre>
</td>
</tr>
</table>
<P>
[ <B><FONT SIZE=-1><A HREF="#toc">TOC</A></FONT></B> ]
<HR>
<H1><A NAME="METHODS">METHODS</A></H1>
<DL>
<P><DT><STRONG><A NAME="item__filter">$filter = SWISH::Filter->new()</A></STRONG><DD>
<P>
This creates a SWISH::Filter object. You may pass in options as a list or a
hash reference.
</DL>
<P>
[ <B><FONT SIZE=-1><A HREF="#toc">TOC</A></FONT></B> ]
<HR>
<H2><A NAME="SWISH_Filter_new_Options">SWISH::Filter->new Options</A></H2>
<P>
There is currently only one option that can be passed in to
<CODE>new():</CODE>
<DL>
<P><DT><STRONG><A NAME="item_ignore_filters">ignore_filters</A></STRONG><DD>
<P>
Pass in a reference to a list of filter names to ignore. For example, if
you have two filters installed "Pdf2HTML" and "Pdf2XML"
and want to avoid using "Pdf2XML":
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> my $filter = SWISH::Filter->new( ignore_filters => ['Pdf2XML'];</pre>
</td>
</tr>
</table>
<P><DT><STRONG><A NAME="item__doc_object">$doc_object = $filter->convert();</A></STRONG><DD>
<P>
This method filters a document. Returns an object of the class
SWISH::Filter::document or undefined if passed in an empty document, a
filename that cannot be read off disk, or if no filters have been loaded.
<P>
SWISH::Filter::document methods listed below can be called on the object
to, for example, check if the document was filtered and to fetch the
document content (filtered or not).
<P>
You must pass in a hash (or hash reference) of parameters to the
<CODE>convert()</CODE> method. The possible parameters are:
<DL>
<P><DT><STRONG><A NAME="item_document">document</A></STRONG><DD>
<P>
This can be either a path to a file, or a scalar reference to a document in
memory. This is required.
<P><DT><STRONG><A NAME="item_content_type">content_type</A></STRONG><DD>
<P>
The MIME type of the document. This is only required when passing in a
scalar reference to a document. The content type string is what the filters
use to match a document type.
<P>
When passing in a file name and <A HREF="#item_content_type">content_type</A> is not set, then the content type will be determined from the file's
extension by using the MIME::Types Perl module (available on CPAN).
<P><DT><STRONG><A NAME="item_name">name</A></STRONG><DD>
<P>
Optional name to pass in to filters that will be used in error and warning
messages.
<P><DT><STRONG><A NAME="item_user_data">user_data</A></STRONG><DD>
<P>
Optional data structure that all filters may access. This can be fetched in
a filter by:
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> my $user_data = $doc_object->user_data;</pre>
</td>
</tr>
</table>
<P>
And used in the filter as:
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> if ( ref $user_data && $user_data->{pdf2html}{title} ) {
...
}</pre>
</td>
</tr>
</table>
<P>
It's up to the filter author to use a unique first-level hash key for a
given filter.
</DL>
<P>
Example of using the <CODE>convert()</CODE> method:
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> $doc_object = $filter->convert(
document => $doc_ref,
content-type => 'application/pdf',
);</pre>
</td>
</tr>
</table>
<P><DT><STRONG><A NAME="item__filter_mywarn_">$filter->mywarn()</A></STRONG><DD>
<P>
Internal function used for writing warning messages to STDERR if
$ENV{FILTER_DEBUG} is set. Set the environment variable FILTER_DEBUG before
running to see extra messages while processing.
<P><DT><STRONG><A NAME="item__filters">@filters = $filter->filter_list;</A></STRONG><DD>
<P>
Returns a list of filter objects installed.
<P><DT><STRONG><A NAME="item__filter">@filter = $filter->can_filter( $content_type );</A></STRONG><DD>
<P>
This is useful for testing to see if a mimetype might be handled by
SWISH::Filter wihtout having to pass in a document. Helpful if doing HEAD
requests.
<P>
Returns an array of filters that can handle this type of document
<H1><A NAME="WRITING_FILTERS">WRITING FILTERS</A></H1>
<P>
Filters are standard perl modules that are installed into the
SWISH::Filters name space. Filters are not complicated -- see the existing
filters for examples.
<P>
Each filter defines the content-types (or mimetypes) that it can handle.
These are specified as a list of regular expressions to match against the
document's content-type. If one of the mimetypes of a filter match the
incoming document's content-type the filter is called. The filter can then
either filter the content or return undefined indicating that it decided
not to filter the document for some reason. If the document is converted
the filter returns either a reference to a scalar of the content or a file
name where the content is stored. The filter also must change the
content-type of the document to reflect the new document.
<P>
Filters typically use external programs or modules to do that actual work
of converting a document from one type to another. For example, programs in
the Xpdf packages are used for converting PDF files. The filter can (and
should) test for those programs in its <CODE>new()</CODE> method.
<P>
Filters also can define a type and priority. These attributes are used to
set the order filters are tested for a content-type match. This allows you
to have more than one filter that can work on the same content-type.
<P>
If a filter calls <CODE>die()</CODE> then the filter is removed from the
chain and will not be called again <EM>during the same run</EM>. Calling die when running with -S http or -S fs has no effect since the
program is run once per document.
<P>
Once a filter returns something other than undef no more filters will be
called. If the filter calls $filter->set_continue then processing will
continue as if the file was not filtered. For example, a filter can
uncompress data and then set $filter->set_continue and let other filters
process the document.
<P>
This is the list of methods the filter should or may define (as
specificed):
<DL>
<P><DT><STRONG><A NAME="item_new">new() * required *</A></STRONG><DD>
<P>
This method returns either an object which provides access to the filter,
or undefined if the filter is not to be used.
<P>
The <CODE>new()</CODE> method is a good place to check for required modules
or helper programs. Returning undefined prevents the filter from being
included in the filter chain.
<P>
The new method must return a blessed hash reference. The only required
attribute is <STRONG>mimetypes</STRONG>. This attribute must contain a reference to an array of regular
expressions used for matching the content-type of the document passed in.
<P>
Example:
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> sub new {
my ( $class ) = @_;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # List of regular expressions
my @mimetypes = (
qr[application/(x-)?msword],
qr[application/worddoc],
);</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> my %settings = (
mimetypes => \@mimetypes,</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # Optional settings
priority => 20,
type => 2,
);</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> return bless \%settings, $class;
}</pre>
</td>
</tr>
</table>
<P>
The attribute "mimetypes" returns an array reference to a list of
regular expressions. Those patterns are matched against each document's
content type.
<P><DT><STRONG><A NAME="item_filter">filter() * required *</A></STRONG><DD>
<P>
This is the function that does the work of converting a document from one
content type to another. The function is passed the document object. See
document object methods listed below for what methods may be called on a
document.
<P>
The function can return undefined (or any false value) to indicate that the
filter did not want to process the document. Other filters will then be
tested for a content type match.
<P>
If the document is filtered then the filter must set the new document's
content type (if it changed) and return either a file name where the
document can be found or a reference to a scalar containing the document.
<P><DT><STRONG><A NAME="item_type">type()</A></STRONG><DD>
<P>
Returns a number. Filters are sorted (for processing in a specific order)
and this number is simply the primary key used in sorting. If not specified
the filter's type used for sorting is 2.
<P>
This is an optional method. You can also set the type in your
<CODE>new()</CODE> constructor as shown above.
<P><DT><STRONG><A NAME="item_priority">priority()</A></STRONG><DD>
<P>
Returns a number. Filters are sorted (for processing in a specific order)
and this number is simply the secondary key used in sorting. If not
specified the filter's priority is 50.
<P>
This is an optional method. You can also set the priority in your
<CODE>new()</CODE> constructor as shown above.
</DL>
<P>
Again, the point of the <CODE>type()</CODE> and <CODE>priority()</CODE>
methods is to allow setting the sort order of the filters. Useful if you
have two filters for filtering the same content-type, but prefer to use one
over the other. Neither are required.
<P>
Here's a module to convert MS Word documents using the program
"catdoc":
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> package SWISH::Filters::Doc2txt;
use vars qw/ $VERSION /;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> $VERSION = '0.02';</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> sub new {
my ( $class ) = @_;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> my $self = bless {
mimetypes => [ qr!application/(x-)?msword! ],
priority => 50,
}, $class;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # check for helpers
return $self->set_programs( 'catdoc' );</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> }</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> sub filter {
my ( $self, $doc ) = @_;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> my $content = $self->run_catdoc( $doc->fetch_filename ) || return;</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # update the document's content type
$filter->set_content_type( 'text/plain' );</pre>
</td>
</tr>
</table>
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> # return the document
return \$content;
}
1;</pre>
</td>
</tr>
</table>
<P>
The <CODE>new()</CODE> constructor creates a blessed hash which contains an
array reference of mimetypes patterns that this filter accepts. The
priority sets this filter to run after any other filters that might handle
the same type of content. The <EM>set_programs()</EM> function says that we need to call a program called "catdoc". The
function either returns <CODE>$self</CODE> or undefined if catdoc could not
be found. The <EM>set_programs()</EM> function creates a new method for running catdoc.
<P>
The filter function runs catdoc passing in the name of the file (if the
file is in memory a temporary file is created). That <EM>run_catdoc()</EM> function was created by the
<EM>set_programs()</EM> call above.
<H1><A NAME="SWISH_Filter_document_Methods">SWISH::Filter::document Methods</A></H1>
<P>
These methods are available to Filter authors, and also provide access to
the document after calling the <CODE>convert()</CODE> method to end-users
of SWISH::Filter.
<P>
End users of SWISH::Filter will use a subset of these methods. Mostly:
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> $doc_object->fetch_doc # and alias for fetch_document_reference()
$doc_object->was_filtered # true the document was filtered
$doc_object->content_type # document's current content type (mime type)
$doc_object->swish_parser_type # returns a parser type to use with Swish-e -S prog method
$doc_object->is_binary # returns $content_type !~ m[^text/];</pre>
</td>
</tr>
</table>
<P>
These methods are also available to the individual filter modules. The
filter's "filter" function is also passed a
SWISH::Filter::document object. Method calls may be made on this object to
check the document's current content type, or to fetch the document as
either a file name or a reference to a scalar containing the document
content.
<H2><A NAME="Methods_used_by_end_users_and_filter_authors">Methods used by end-users and filter authors</A></H2>
<DL>
<P><DT><STRONG><A NAME="item__doc_ref">$doc_ref = $doc_object->fetch_doc_reference;</A></STRONG><DD>
<P>
Returns a scalar reference to the document. This can be used when the
filter can operate on the document in memory (or if an external program
expects the input to be from standard input).
<P>
If the file is currently on disk then it will be read into memory. If the
file was stored in a temporary file on disk the file will be deleted once
read into memory. The file will be read in binmode if $doc->is_binary is
true.
<P>
Note that $doc_object->fetch_doc is an alias.
<P><DT><STRONG><A NAME="item__was_filtered">$was_filtered = $doc_object->was_filtered</A></STRONG><DD>
<P>
Returns true if some filter processed the document
<P><DT><STRONG><A NAME="item__content_type">$content_type = $doc_object->content_type;</A></STRONG><DD>
<P>
Fetches the current content type for the document.
<P>
Example:
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> return unless $filter->content_type =~ m!application/pdf!;</pre>
</td>
</tr>
</table>
<P><DT><STRONG><A NAME="item__type">$type = $doc_object->swish_parser_type</A></STRONG><DD>
<P>
Returns a parser type based on the content type
<P><DT><STRONG><A NAME="item__doc_object_is_binary">$doc_object->is_binary</A></STRONG><DD>
<P>
Returns true if the document's content-type does not match
"text/".
</DL>
<H2><A NAME="Methods_used_by_filter_authors">Methods used by filter authors</A></H2>
<DL>
<P><DT><STRONG><A NAME="item__file_name">$file_name = $doc_object->fetch_filename;</A></STRONG><DD>
<P>
Returns a path to the document as stored on disk. This name can be passed
to external programs (e.g. catdoc) that expect input as a file name.
<P>
If the document is currently in memory then a temporary file will be
created. Do not expect the file name passed to be the real path of the
document.
<P>
The file will be written in binmode if $doc->is_binary is true.
<P>
This method is not normally used by end-users of SWISH::Filter.
<P><DT><STRONG><A NAME="item__doc_object_set_continue_">$doc_object->set_continue;</A></STRONG><DD>
<P>
Processing will continue to the next filter if this is set to a true value.
This should be set for filters that change encodings or uncompress
documents.
<P><DT><STRONG><A NAME="item__doc_object_set_content_type_">$doc_object->set_content_type( $type );</A></STRONG><DD>
<P>
Sets the content type for a document.
<P><DT><STRONG><A NAME="item__doc_object_name">$doc_object->name</A></STRONG><DD>
<P>
Fetches the name of the current file. This is useful for printing out the
name of the file in an error message. This is the name passed in to the
SWISH::Filter->convert method. It is optional and thus may not always be
set.
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> my $name = $doc_object->name || 'Unknown name';
warn "File '$name': failed to convert -- file may be corrupt\n";</pre>
</td>
</tr>
</table>
<P><DT><STRONG><A NAME="item__doc_object_user_data">$doc_object->user_data</A></STRONG><DD>
<P>
Fetches the the user_data passed in to the filter. This can be any data or
data structure passed into SWISH::Filter->new.
<P>
This is an easy way to pass special parameters into your filters.
<P>
Example:
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> my $data = $doc_object->user_data;
# see if a choice for the <title> was passed in
if ( ref $data eq 'HASH' && $data->{pdf2html}{title_field} {
...
...
}</pre>
</td>
</tr>
</table>
<H1><A NAME="SWISH_Filters_BASE">SWISH::Filters::_BASE</A></H1>
<P>
Each filter is a subclass of SWISH::Filters::_BASE. A number of methods are
available by default (and some can be overridden). Others are useful when
writing your <CODE>new()</CODE> constructor.
<DL>
<P><DT><STRONG><A NAME="item__self_type">$self->type</A></STRONG><DD>
<P>
This method fetches the type of the filter. The value returned sets the
primary sort key for sorting the filters. You can override this in your
filter, or just set it as an attribute in your object. The default is 2.
<P>
The idea of the "type" is to create groups of filters, if needed.
For example, you might have a set of filters that are used for
uncompressing some documents before passing on to another group for
filtering.
<P><DT><STRONG><A NAME="item__self_priority">$self->priority</A></STRONG><DD>
<P>
This method fetches the priority of the filter. The value returned sets the
secondary sort key for sorting the filters. You can override this in your
filter, or just set it as an attribute in your object. The default method
returns 50.
<P>
The priority is useful if you have multiple filters for the same content
type that use different methods for filtering (say one uses wvWare and
another uses catdoc for filtering MS Word files). You might give the wvWare
filter a lower priority number so it runs before the catdoc filter if both
wvWare AND catdoc happen to be installed at the same time.
<P><DT><STRONG><A NAME="item__types">@types = $self->mimetypes</A></STRONG><DD>
<P>
Returns the list of mimetypes (as regular expressions) set for the filter.
<P><DT><STRONG><A NAME="item__pattern">$pattern = $self->can_filter_mimetype( $content_type )</A></STRONG><DD>
<P>
Returns true if passed in content type matches one of the filter's
mimetypes Returns the pattern that matched.
<P><DT><STRONG><A NAME="item_mywarn">mywarn( $message )</A></STRONG><DD>
<P>
method for printing out message if debugging is available
<P><DT><STRONG><A NAME="item__boolean">$boolean = $self->set_programs( @program_list );</A></STRONG><DD>
<P>
Returns true if all the programs listed in <CODE>@program_list</CODE> are
found and can be executed as the current user. Creates a method for each
program with the "run_" prefix. Returns false is ANY program
cannot be found.
<P>
Actually, it returns $self, so you can make it the last statement in your
constructor.
<P>
So in your constructor you might do:
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> return $self->set_programs( qw/ pdftotext pdfinfo / );</pre>
</td>
</tr>
</table>
<P>
Then in your <CODE>filter()</CODE> method:
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> my $content = $self->run_pdfinfo( $doc->fetch_filename, [options] );</pre>
</td>
</tr>
</table>
<P><DT><STRONG><A NAME="item__path">$path = $self->find_binary( $prog );</A></STRONG><DD>
<P>
Use in a filter's <CODE>new()</CODE> method to test for a necesary program
located in $PATH. Returns the path to the program or undefined if not found
or does not pass the -x file test.
<P><DT><STRONG><A NAME="item__bool">$bool = $self->use_modules( @module_list );</A></STRONG><DD>
<P>
Attempts to load each of the module listed and calls its
<CODE>import()</CODE> method.
<P>
Use to test and load required modules within a filter without aborting.
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> return unless $self->use_modules( qw/ Spreadsheet::ParseExcel HTML::Entities / );</pre>
</td>
</tr>
</table>
<P>
A warning message is displayed if the FILTER_DEBUG environment variable is
true. Returns <CODE>$self</CODE> if no error.
</DL>
<P><DT><STRONG>$doc_ref = $self->run_program( $program, @args );</STRONG><DD>
<P>
Runs <CODE>$program</CODE> with @args. Must pass in @args.
<P>
Under Windows calls IPC::Open2, which may pass data through the shell.
Double-quotes are escaped (backslashed) and each parameter is wrapped in
double-quotes.
<P>
On other platforms a fork and exec is used to avoid passing any data
through the shell. Returns a reference to a scalar containing the output
from your program, or dies.
<P>
This method is intended to read output from a program that converts one
format into text. The output is read back in text mode -- on systems like
Windows this means \r\n (CRLF) will be convertet to \n.
</DL>
<H1><A NAME="TESTING">TESTING</A></H1>
<P>
Filters can be tested with the <EM>swish-filter-test</EM> program. Run:
<P>
<table>
<tr>
<td bgcolor="#eeeeee" width="1">
</td>
<td>
<pre> swish-filter-test -man</pre>
</td>
</tr>
</table>
<P>
for documentation.
<H1><A NAME="SUPPORT">SUPPORT</A></H1>
<P>
Please contact the Swish-e discussion list. <A
HREF="http://swish-e.org">http://swish-e.org</A>
<H1><A NAME="Bugs_todo_items_and_other_notes">Bugs, todo items, and other notes</A></H1>
<P>
TBD
<H1><A NAME="AUTHOR">AUTHOR</A></H1>
<P>
Bill Moseley
<H1><A NAME="COPYRIGHT">COPYRIGHT</A></H1>
<P>
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
</DL>
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<BR>SWISH-E is distributed with <B>no warranty</B> under the terms of the
<A HREF="http://www.fsf.org/copyleft/gpl.html">GNU Public License</A>,<BR>
Free Software Foundation, Inc.,
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