Template::Provider - Provider module for loading/compiling templates

    $provider = Template::Provider->new(\%options);

    ($template, $error) = $provider->fetch($name);

The Template::Provider is used to load, parse, compile and cache template documents. This object may be sub-classed to provide more specific facilities for loading, or otherwise providing access to templates.

The Template::Context objects maintain a list of Template::Provider objects which are polled in turn (via fetch()) to return a requested template. Each may return a compiled template, raise an error, or decline to serve the reqest, giving subsequent providers a chance to do so.

This is the Chain of Responsiblity pattern. See 'Design Patterns' for further information.

This documentation needs work.

Constructor method which instantiates and returns a new Template::Provider object. The optional parameter may be a hash reference containing any of the following items:

INCLUDE_PATH

The INCLUDE_PATH is used to specify one or more directories in which template files are located. When a template is requested that isn't defined locally as a BLOCK, each of the INCLUDE_PATH directories is searched in turn to locate the template file. Multiple directories can be specified as a reference to a list or as a single string where each directory is delimited by ':'.

    my $provider = Template::Provider->new({
        INCLUDE_PATH => '/usr/local/templates',
    });

    my $provider = Template::Provider->new({
        INCLUDE_PATH => '/usr/local/templates:/tmp/my/templates',
    });

    my $provider = Template::Provider->new({
        INCLUDE_PATH => [ '/usr/local/templates', 
                          '/tmp/my/templates' ],
    });

On Win32 systems, a little extra magic is invoked, ignoring delimiters that have ':' followed by a '/' or '\'. This avoids confusion when using directory names like 'C:\Blah Blah'. When specified as a list, the INCLUDE_PATH path can contain elements which dynamically generate a list of INCLUDE_PATH directories. These generator elements can be specified as a reference to a subroutine or an object which implements a paths() method.

    my $provider = Template::Provider->new({
        INCLUDE_PATH => [ '/usr/local/templates', 
                          \&incpath_generator, 
                          My::IncPath::Generator->new( ... ) ],
    });

Each time a template is requested and the INCLUDE_PATH examined, the subroutine or object method will be called. A reference to a list of directories should be returned. Generator subroutines should report errors using die(). Generator objects should return undef and make an error available via its error() method. For example:

    sub incpath_generator {

        # ...some code...

        if ($all_is_well) {
            return \@list_of_directories;
        }
        else {
            die "cannot generate INCLUDE_PATH...\n";
        }
    }

or:

    package My::IncPath::Generator;

    # Template::Base (or Class::Base) provides error() method
    use Template::Base;
    use base qw( Template::Base );

    sub paths {
        my $self = shift;

        # ...some code...

        if ($all_is_well) {
            return \@list_of_directories;
        }
        else {
            return $self->error("cannot generate INCLUDE_PATH...\n");
        }
    }

    1;

DELIMITER

Used to provide an alternative delimiter character sequence for separating paths specified in the INCLUDE_PATH. The default value for DELIMITER is ':'.

    # tolerate Silly Billy's file system conventions
    my $provider = Template::Provider->new({
        DELIMITER    => '; ',
        INCLUDE_PATH => 'C:/HERE/NOW; D:/THERE/THEN',
    });

    # better solution: install Linux!  :-)

On Win32 systems, the default delimiter is a little more intelligent, splitting paths only on ':' characters that aren't followed by a '/'. This means that the following should work as planned, splitting the INCLUDE_PATH into 2 separate directories, C:/foo and C:/bar.

    # on Win32 only
    my $provider = Template::Provider->new({
        INCLUDE_PATH => 'C:/Foo:C:/Bar'
    });

However, if you're using Win32 then it's recommended that you explicitly set the DELIMITER character to something else (e.g. ';') rather than rely on this subtle magic.

ABSOLUTE

The ABSOLUTE flag is used to indicate if templates specified with absolute filenames (e.g. '/foo/bar') should be processed. It is disabled by default and any attempt to load a template by such a name will cause a 'file' exception to be raised.

    my $provider = Template::Provider->new({
        ABSOLUTE => 1,
    });

    # this is why it's disabled by default
    [% INSERT /etc/passwd %]

On Win32 systems, the regular expression for matching absolute pathnames is tweaked slightly to also detect filenames that start with a driver letter and colon, such as:

    C:/Foo/Bar

RELATIVE

The RELATIVE flag is used to indicate if templates specified with filenames relative to the current directory (e.g. './foo/bar' or '../../some/where/else') should be loaded. It is also disabled by default, and will raise a 'file' error if such template names are encountered.

    my $provider = Template::Provider->new({
        RELATIVE => 1,
    });

    [% INCLUDE ../logs/error.log %]

DEFAULT

The DEFAULT option can be used to specify a default template which should be used whenever a specified template can't be found in the INCLUDE_PATH.

    my $provider = Template::Provider->new({
        DEFAULT => 'notfound.html',
    });

If a non-existant template is requested through the Template process() method, or by an INCLUDE, PROCESS or WRAPPER directive, then the DEFAULT template will instead be processed, if defined. Note that the DEFAULT template is not used when templates are specified with absolute or relative filenames, or as a reference to a input file handle or text string.

CACHE_SIZE

The Template::Provider module caches compiled templates to avoid the need to re-parse template files or blocks each time they are used. The CACHE_SIZE option is used to limit the number of compiled templates that the module should cache. By default, the CACHE_SIZE is undefined and all compiled templates are cached. When set to any positive value, the cache will be limited to storing no more than that number of compiled templates. When a new template is loaded and compiled and the cache is full (i.e. the number of entries == CACHE_SIZE), the least recently used compiled template is discarded to make room for the new one. The CACHE_SIZE can be set to 0 to disable caching altogether.

    my $provider = Template::Provider->new({
        CACHE_SIZE => 64,   # only cache 64 compiled templates
    });

    my $provider = Template::Provider->new({
        CACHE_SIZE => 0,   # don't cache any compiled templates
    });

COMPILE_EXT

From version 2 onwards, the Template Toolkit has the ability to compile templates to Perl code and save them to disk for subsequent use (i.e. cache persistence). The COMPILE_EXT option may be provided to specify a filename extension for compiled template files. It is undefined by default and no attempt will be made to read or write any compiled template files.

    my $provider = Template::Provider->new({
        COMPILE_EXT => '.ttc',
    });

If COMPILE_EXT is defined (and COMPILE_DIR isn't, see below) then compiled template files with the COMPILE_EXT extension will be written to the same directory from which the source template files were loaded. Compiling and subsequent reuse of templates happens automatically whenever the COMPILE_EXT or COMPILE_DIR options are set. The Template Toolkit will automatically reload and reuse compiled files when it finds them on disk. If the corresponding source file has been modified since the compiled version as written, then it will load and re-compile the source and write a new compiled version to disk. This form of cache persistence offers significant benefits in terms of time and resources required to reload templates. Compiled templates can be reloaded by a simple call to Perl's require(), leaving Perl to handle all the parsing and compilation. This is a Good Thing.

COMPILE_DIR

The COMPILE_DIR option is used to specify an alternate directory root under which compiled template files should be saved.

    my $provider = Template::Provider->new({
        COMPILE_DIR => '/tmp/ttc',
    });

The COMPILE_EXT option may also be specified to have a consistent file extension added to these files.

    my $provider1 = Template::Provider->new({
        COMPILE_DIR => '/tmp/ttc',
        COMPILE_EXT => '.ttc1',
    });

    my $provider2 = Template::Provider->new({
        COMPILE_DIR => '/tmp/ttc',
        COMPILE_EXT => '.ttc2',
    });

When COMPILE_EXT is undefined, the compiled template files have the same name as the original template files, but reside in a different directory tree. Each directory in the INCLUDE_PATH is replicated in full beneath the COMPILE_DIR directory. This example:

    my $provider = Template::Provider->new({
        COMPILE_DIR  => '/tmp/ttc',
        INCLUDE_PATH => '/home/abw/templates:/usr/share/templates',
    });

would create the following directory structure:

    /tmp/ttc/home/abw/templates/
    /tmp/ttc/usr/share/templates/

Files loaded from different INCLUDE_PATH directories will have their compiled forms save in the relevant COMPILE_DIR directory. On Win32 platforms a filename may by prefixed by a drive letter and colon. e.g.

    C:/My Templates/header

The colon will be silently stripped from the filename when it is added to the COMPILE_DIR value(s) to prevent illegal filename being generated. Any colon in COMPILE_DIR elements will be left intact. For example:

    # Win32 only
    my $provider = Template::Provider->new({
        DELIMITER    => ';',
        COMPILE_DIR  => 'C:/TT2/Cache',
        INCLUDE_PATH => 'C:/TT2/Templates;D:/My Templates',
    });

This would create the following cache directories:

    C:/TT2/Cache/C/TT2/Templates
    C:/TT2/Cache/D/My Templates

TOLERANT

The TOLERANT flag is used by the various Template Toolkit provider modules (Template::Provider, Template::Plugins, Template::Filters) to control their behaviour when errors are encountered. By default, any errors are reported as such, with the request for the particular resource (template, plugin, filter) being denied and an exception raised. When the TOLERANT flag is set to any true values, errors will be silently ignored and the provider will instead return STATUS_DECLINED. This allows a subsequent provider to take responsibility for providing the resource, rather than failing the request outright. If all providers decline to service the request, either through tolerated failure or a genuine disinclination to comply, then a '<resource> not found' exception is raised.

PARSER

The Template::Parser module implements a parser object for compiling templates into Perl code which can then be executed. A default object of this class is created automatically and then used by the Template::Provider whenever a template is loaded and requires compilation. The PARSER option can be used to provide a reference to an alternate parser object.

    my $provider = Template::Provider->new({
        PARSER => MyOrg::Template::Parser->new({ ... }),
    });

DEBUG

The DEBUG option can be used to enable debugging messages from the Template::Provider module by setting it to include the DEBUG_PROVIDER value.

    use Template::Constants qw( :debug );

    my $template = Template->new({
        DEBUG => DEBUG_PROVIDER,
    });

Returns a compiled template for the name specified. If the template cannot be found then (undef, STATUS_DECLINED) is returned. If an error occurs (e.g. read error, parse error) then ($error, STATUS_ERROR) is returned, where CW$error is the error message generated. If the TOLERANT flag is set the the method returns (undef, STATUS_DECLINED) instead of returning an error. Stores the compiled template, CW$template, in the cache under the name, CW$name. Susbequent calls to fetch($name) will return this template in preference to any disk-based file.

Accessor method for the INCLUDE_PATH setting. If called with an argument, this method will replace the existing INCLUDE_PATH with the new value.

This method generates a copy of the INCLUDE_PATH list. Any elements in the list which are dynamic generators (e.g. references to subroutines or objects implementing a paths() method) will be called and the list of directories returned merged into the output list.

It is possible to provide a generator which returns itself, thus sending this method into an infinite loop. To detect and prevent this from happening, the CW$MAX_DIRS package variable, set to 64 by default, limits the maximum number of paths that can be added to, or generated for the output list. If this number is exceeded then the method will immediately return an error reporting as much.

Andy Wardley <abw@andywardley.com>

<http://www.andywardley.com/|http://www.andywardley.com/>

2.81, distributed as part of the Template Toolkit version 2.14, released on 04 October 2004.

  Copyright (C) 1996-2004 Andy Wardley.  All Rights Reserved.
  Copyright (C) 1998-2002 Canon Research Centre Europe Ltd.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

Template, Template::Parser, Template::Context