Template::Provider(3)

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

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

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

DESCRIPTION
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 request, giving subsequent providers a chance to do so.

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

The Template::Provider can also be subclassed to provide templates from a different source, e.g. a database. See SUBCLASSING below.

This documentation needs work.

PUBLIC METHODS

  new(\%options)
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
        });

    As well as caching templates as they are found, the Template::Provider also implements negative caching to keep track of templates that are not found. This allows the provider to quickly decline a request for a template that it has previously failed to locate, saving the effort of going to look for it again. This is useful when an INCLUDE_PATH includes multiple providers, ensuring that the request is passed down through the providers as quickly as possible.

STAT_TTL
    This value can be set to control how long the Template::Provider will keep a template cached in memory before checking to see if the source template has changed.

        my $provider = Template::Provider->new({
            STAT_TTL => 60,  # one minute
        });

    The default value is 1 (second). You'll probably want to set this to a higher value if you're running the Template Toolkit inside a persistent web server application (e.g. mod_perl). For example, set it to 60 and the provider will only look for changes to templates once a minute at most. However, during development (or any time you're making frequent changes to templates) you'll probably want to keep it set to a low value so that you don't have to wait for the provider to notice that your templates have changed.

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,
        });

  fetch($name)
Returns a compiled template for the name specified. If the template cannot be found then (undef, STATUS_DECLINED) is returned. If an error occurs (e.g. read error, parse error) then ($error, STATUS_ERROR) is returned, where $error is the error message generated. If the TOLERANT flag is set the the method returns (undef, STATUS_DECLINED) instead of returning an error.

  store($name, $template)
Stores the compiled template, $template, in the cache under the name, $name. Susbequent calls to fetch($name) will return this template in preference to any disk-based file.

  include_path(\@newpath))
Accessor method for the INCLUDE_PATH setting. If called with an argument, this method will replace the existing INCLUDE_PATH with the new value.

  paths()
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 $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.

SUBCLASSING
The Template::Provider module can be subclassed to provide templates from a different source (e.g. a database). In most cases you'll just need to provide custom implementations of the "_template_modified()" and "_template_content()" methods. If your provider requires and custom initialisation then you'll also need to implement a new "_init()" method.

Caching in memory and on disk will still be applied (if enabled) when overriding these methods.

_template_modified($path)
    Returns a timestamp of the $path passed in by calling stat(). This can be overridden, for example, to return a last modified value from a database. The value returned should be a timestamp value (as returned by "time()", although a sequence number should work as well.

_template_content($path)
    This method returns the content of the template for all INCLUDE, PROCESS, and INSERT directives.

    When called in scalar context, the method returns the content of the template located at $path, or undef if $path is not found.

    When called in list context it returns "($content, $error, $mtime)", where $content is the template content, $error is an error string (e.g. "$path: File not found"), and $mtime is the template modification time.

AUTHOR
Andy Wardley <abw@wardley.org>

<http://wardley.org/|http://wardley.org/>

VERSION
2.93, distributed as part of the Template Toolkit version 2.19, released on 27 April 2007.

COPYRIGHT
  Copyright (C) 1996-2007 Andy Wardley.  All Rights Reserved.

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

SEE ALSO
Template, Template::Parser, Template::Context