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Config-Model-2.113
River stage two • 11 direct dependents • 11 total dependents
3 ++
/ Config::Model::Backend::Any

NAME

Config::Model::Backend::Any - Virtual class for other backends

VERSION

version 2.113

SYNOPSIS

 package Config::Model::Backend::Foo ;
 use Mouse ;

 extends 'Config::Model::Backend::Any';

 # optional
 sub suffix {
   return '.conf';
 }

 # mandatory
 sub read {
    my $self = shift ;
    my %args = @_ ;

    # args are:
    # root       => './my_test',  # fake root directory, used for tests
    # config_dir => /etc/foo',    # absolute path
    # file       => 'foo.conf',   # file name
    # file_path  => './my_test/etc/foo/foo.conf'
    # io_handle  => $io           # IO::File object opened for read
    # check      => yes|no|skip

    return 0 unless defined $args{io_handle} ; # or die, your choice

    # read the file line by line
    # we assume the file contain lines like 'key=value'
    foreach ($args{io_handle}->getlines) {
        chomp ;   # remove trailing \n
        s/#.*// ; # remove any comment
        next unless /\S/; # skip blank line

        # $data is 'foo=bar' which is compatible with load 
        $self->node->load(steps => $_, check => $args{check} ) ;
    }
    return 1 ;
 }

 # mandatory
 sub write {
    my $self = shift ;
    my %args = @_ ;

    # args are:
    # root       => './my_test',  # fake root directory, used for tests
    # config_dir => /etc/foo',    # absolute path 
    # file       => 'foo.conf',   # file name
    # file_path  => './my_test/etc/foo/foo.conf'
    # io_handle  => $io           # IO::File object opened for write
    # check      => yes|no|skip

    my $ioh = $args{io_handle} ;

    # read the content of the configuration tree
    foreach my $elt ($self->node->children) {
        # read the value from element $elt
        my $v = $self->node->grab_value($elt) ;

        # write value in file
        $ioh->print(qq!$elt="$v"\n!) if defined $v ;
    }

    return 1;
 }

DESCRIPTION

Some application have configuration files with a syntax which is not supported by existing Config::Model::Backend::* classes.

In this case a new backend must be written. Config::Model::Backend::Any was created to facilitate this task.

The new backend class must use Mouse and must extends (inherit) Config::Model::Backend::Any.

How to write your own backend

Declare the new backend in a node of the model

As explained in "Backend specification" in Config::Model::BackendMgr, the new backend must be declared as an attribute of a Config::Model::Node specification.

Let's say your new backend is Config::Model::Backend::Foo. This new backend can be specified with:

 rw_config  => {
    backend    => 'Foo' , # can also be 'foo'
    config_dir => '/etc/cfg_dir'
    file       => 'foo.conf', # optional
 }

(The backend class name is constructed with ucfirst($backend_name))

rw_config can also have custom parameters that are passed verbatim to Config::Model::Backend::Foo methods:

 rw_config  => {
    backend    => 'Foo' , # can also be 'foo'
    config_dir => '/etc/cfg_dir'
    file       => 'foo.conf', # optional
    my_param   => 'my_value',
 }

Config::Model::Backend::Foo class must inherit (extend) Config::Model::Backend::Any and is expected to provide the following methods:

read

read() is called with the following parameters:

 %custom_parameters,       # e.g. my_param   => 'my_value' in the example above
 object     => $obj,         # Config::Model::Node object
 root       => $root_dir,  # fake root directory, used for tests
 backend    => $backend,   # backend name
 config_dir => $read_dir,  # path below root
 file       => 'foo.conf',   # file name
 file_path  => $full_name, # full file name (root+path+file)
 io_handle  => $io_file    # IO::File object opened for read
 check      => [yes|no|skip]

The IO::File object is undef if the file cannot be read.

This method must return 1 if the read was successful, 0 otherwise.

Following the my_param example above, %custom_parameters contains ( 'my_param' , 'my_value' ) , so read() is called with root, config_dir, file_path, io_handle and my_param => 'my_value'.

write

write() is called with the following parameters:

 %$custom_parameters,         # e.g. my_param   => 'my_value' in the example above
 object      => $obj,         # Config::Model::Node object
 root        => $root_dir,    # fake root directory, used for tests
 auto_create => $auto_create, # boolean specified in backend declaration
 auto_delete => $auto_delete, # boolean specified in backend declaration
 backend     => $backend,     # backend name
 config_dir  => $write_dir,   # override from instance
 file        => 'foo.conf',   # file name
 file_path   => $full_name, # full file name (root+path+file)
 io_handle   => $fh,          # IO::File object
 write       => 1,            # always
 check       => [ yes|no|skip] ,
 backup      => [ undef || '' || suffix ] # backup strategy required by user

The IO::File object is undef if the file cannot be written to.

This method must return 1 if the write was successful, 0 otherwise

If io_handle is defined, the backup has already been done before opening the config file. If io_handle is not defined, there's not enough information in the model to read the configuration file and create the backup. Your write() method will have to do the backup requested by user.

When both config_dir and file are specified, the backend manager opens the configuration file for write (and thus clobbers it) before calling the write call-back with the file handle with io_handle parameter. write should use this handle to write data in the target configuration file.

If this behavior causes problem, the solution is to override skip_open method in your backend to return 1.

How to test your new backend

Using Config::Model::Tester, you can test your model with your backend following the instructions given in Config::Model::Tester.

You can also test your backend with a minimal model (and Config::Model::Tester). In this case, you need to specify a small model to test in a *-test-conf.pl file. See the IniFile backend test for an example and its examples files.

CONSTRUCTOR

new ( node => $node_obj, name => backend_name )

The constructor should be used only by Config::Model::Node.

Methods to override

annotation

Whether the backend supports reading and writing annotation (a.k.a comments). Default is 0. Override this method to return 1 if your backend supports annotations.

suffix

Suffix of the configuration file. This method returns undef by default.

read

Read the configuration file. This method must be overridden.

write

Write the configuration file. This method must be overridden.

Methods

node

Return the node (a Config::Model::Node) holding this backend.

instance

Return the instance (a Config::Model::Instance) holding this configuration.

show_message( string )

Show a message to STDOUT (unless overridden). Delegated to "show_message( string )" in Config::Model::Instance.

read_global_comments

Parameters:

  • array ref of string containing the lines to be parsed

  • A string to specify how a comment is started. Each character is recognized as a comment starter (e.g '#;' allow a comment to begin with '#' or ';')

Read the global comments (i.e. the first block of comments until the first blank or non comment line) and store them as root node annotation.

Example:

 $self->read_global_comments( \@lines, ';');
 $self->read_global_comments( \@lines, '#;');

associates_comments_with_data

Parameters:

  • array ref of string containing the lines to be parsed

  • A string to specify how a comment is started. Each character is recognized as a comment starter (e.g '#;' allow a comment to begin with '#' or ';')

This method extracts comments from the passed lines and associate them with actual data found in the file lines. Data is associated with comments preceding or on the same line as the data. Returns a list of [ data, comment ].

Example:

  my @lines = (
    '# Foo comments',
    'foo= 1',
    'Baz = 0 # Baz comments'
  );
  my @res = $self->associates_comments_with_data( \@lines, '#')
  # @res is:
  # ( [ 'foo= 1', 'Foo comments' ] , [ 'Baz = 0' , 'Baz comments' ] )

write_global_comments( io_handle , comment_char)

Write global comments from configuration root annotation into the io_handle (if defined). Returns the string written to the io_handle.

write_data_and_comments( io_handle , comment_char , data1, comment1, data2, comment2 ...)

Write data and comments in the io_handle (if defined). Comments are written before the data. Returns the string written to the io_handle. If a data is undef, the comment is written on its own line.

Replacing a custom backend

Custom backend are now deprecated and must be replaced with a class inheriting this module.

Please:

  • Rename your class to begin with Config::Model::Backend::

  • Add use Mouse ; and extends 'Config::Model::Backend::Any'; in the header of your custom class.

  • Add my $self = shift; as the beginning of read and write functions... well... methods.

Here's an example of such a change.

AUTHOR

Dominique Dumont, (ddumont at cpan dot org)

SEE ALSO

Config::Model, Config::Model::BackendMgr, Config::Model::Node, Config::Model::Backend::Yaml,

AUTHOR

Dominique Dumont

COPYRIGHT AND LICENSE

This software is Copyright (c) 2005-2017 by Dominique Dumont.

This is free software, licensed under:

  The GNU Lesser General Public License, Version 2.1, February 1999