The Perl Toolchain Summit needs more sponsors. If your company depends on Perl, please support this very important event.
 / 
Config-Model-1.202
River stage two • 11 direct dependents • 11 total dependents
3 ++
/ Config::Model::AutoRead

NAME

Config::Model::AutoRead - Load configuration node on demand

SYNOPSIS

  # top level config file name matches instance name
  $model->create_config_class 
  (
   name => 'OneAutoReadConfigClass',

   read_config  => [ { backend => 'cds_file' , config_dir => '/etc/cfg_dir'},
                     { backend => 'custom' , 
                       class => 'ProcessRead' ,
                       config_dir => '/etc/foo', # optional
                       file  => 'foo.conf',      # optional
                       auto_create => 1,         # optional
                     }
                   ],
   # if omitted, write_config will be written using read_config specifications
   # write_config can be array of hash ref to write several syntaxes
   write_config => { backend => 'cds_file', config_dir => '/etc/cfg_dir' } ,


   element => ...
  ) ;

  # config data will be written in /etc/my_config_dir/foo.cds
  # according to the instance name
  my $instance = $model->instance(instance_name => 'foo') ;

DESCRIPTION

This class provides a way to specify how to load or store configuration data within the model (instead of writing dedicated perl code).

With these specifications, all the configuration information is read during creation of a node.

This load/store can be done with different backend:

cds_file

Config dump string (cds) in a file. I.e. a string that describes the content of a configuration tree is loaded from or saved in a text file. See Config::Model::Dumper.

ini_file

Ini files (written with Config::Tiny. See limitations in "Limitations depending on storage".

perl_file

Perl data structure (perl) in a file. See Config::Model::DumpAsData for details on the data structure.

custom

Any format when the user provides a dedicated class and function to read and load the configuration tree.

augeas

Data can be loaded or stored using RedHat's Augeas library. See Config::Model::Backend::Augeas for details.

After loading the data, the object registers itself to the instance. Then the user can call the write_back method on the instance (See Config::Model::Instance) to store all configuration information back.

Built-in backend

cds_file, ini_file and perl_file backend must be specified with mandatory config_dir parameter. For instance:

   read_config  => { backend    => 'cds_file' , 
                     config_dir => '/etc/cfg_dir',
                     file       => 'cfg_file.cds', #optional
                   },

If file is not specified, a file name will be constructed with <config_class_name>.<suffix> where suffix is pl or ini or cds.

Plugin backend classes

A plugin backend class can also be specified with:

  read_config  => [ { backend    => 'foo' , 
                      config_dir => '/etc/cfg_dir'
                      file       => 'foo.conf', # optional
                    }
                  ]

In this case, this class will try to load Config::Model::Backend::Foo. (The class name is constructed with ucfirst($backend_name))

read_config can also have custom parameters that will passed verbatim to Config::Model::Backend::Foo methods:

  read_config  => [ { backend    => 'foo' , 
                      config_dir => '/etc/cfg_dir',
                      my_param   => 'my_value',
                    } 
                  ]

This Config::Model::Backend::Foo class is expected to provide the following methods:

new

with parameters:

 node => ref_to_config_model_node

new() must return the newly created object

read

with parameters:

 %custom_parameters,      # model data
 root => $root_dir,       # mostly used for tests
 config_dir => $read_dir, # path below root
 file_path => $full_name, # full file name (root+path+file)
 io_handle => $io_file    # IO::File object

Must return 1 if the read was successful, 0 otherwise.

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

write

with parameters:

 %$write,                     # model data
 auto_create => $auto_create, # from model
 backend     => $backend,     # backend name
 config_dir  => $write_dir,   # override from instance
 io_handle   => $fh,          # IO::File object
 write       => 1,            # always
 root        => $root_dir,

Must return 1 if the write was successful, 0 otherwise

Custom backend

Custom backend must be specified with a class name that will features the methods used to write and read the configuration files:

  read_config  => [ { backend => 'custom' , 
                      class => 'MyRead',
                      config_dir => '/etc/foo', # optional
                      file => 'foo.conf',       # optional
                    } ]

custom backend parameters are:

class

Specify the class that contain the read method

config_dir

Specify configuration directory. This parameter is optional as the directory can be hardcoded in the custom class.

file

optional. This parameter may not apply if the configuration is stored in several files. By default, the instance name is used as configuration file name.

function

Function name that will be called back to read the file. See "read callback" for details. (default is read)

auto_create

By default, an exception is thrown if no read was successfull. This behavior can be overridden by specifying auto_create => 1 in one of the backend specification. For instance:

    read_config  => [ { backend => 'cds_file', config_dir => '/etc/my_cfg/' } , 
                      { backend => 'custom', class => 'Bar' ,
                        auto_create => 1
                      },
                    ],

This feature is necessary to create a configuration from scratch

When set in write backend, missing directory and files will be created with current umask. Default is false.

Write specification is similar to read_specification. Except that the default value for function is write. Here's an example:

   write_config  => [ { backend => 'cds_file', config_dir => '/etc/my_cfg/' } , 
                      { backend => 'custom', class => 'Bar' ,
                        function => 'my_write',
                      },
                    ],

Limitations depending on storage

Some storage system will limit the structure of the model you can map to the file.

Ini files limitation

Structure of the Config::Model must be very simple. Either:

  • A single class with hash of leaves elements.

  • 2 levels of classes. The top level has nodes elements. All other classes have only leaf elements.

Configuration class with auto read or auto write

read specification

A configuration class will be declared with optional read_config parameter:

  read_config  => [ { backend => 'cds_file', config_dir => '/etc/my_cfg/' } , 
                    { backend => 'custom', class => 'Bar' },
                  ],

The read backends will be tried in the specified order:

  • First the cds file whose name depend on the parameters used in model creation and instance creation: <model_config_dir>/<instance_name>.cds The syntax of the cds file is described in Config::Model::Dumper.

  • A callback to Bar::read. See ""read callback" for details.

When a read operation is successful, the remaining read methods will be skipped.

write specification

A configuration class will be declared with optional write_config parameters (along with read_config parameter):

  write_config => [ { backend => 'cds_file', config_dir => '/etc/my_cfg/',
                      auto_create => 1, },
                    { backend => 'custom', class => 'NewFormat' } ],

By default, the specifications are tried in order, until the first succeeds.

When required by the user, all configuration information is written back using all the write specifications. See "write_back ( ... )" in Config::Model::Instance for details.

The write class declared witn custom backend must provide a call-back. See "write callback" for details.

read write directory

By default, configurations files are read from the directory specified by config_dir parameter specified in the model. You may override the root directory for test.

read callback

Read callback function will be called with these parameters:

  object     => $obj,         # Config::Model::Node object 
  root       => './my_test',  # fake root directory, userd 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

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

The callback must return 0 on failure and 1 on succesfull read.

write callback

Write callback function will be called with these parameters:

  object      => $obj,         # Config::Model::Node object 
  root        => './my_test',  # fake root directory, userd 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 in write mode
  auto_create => 1             # create dir as needed

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

The callback must return 0 on failure and 1 on succesfull write.

CAVEATS

When both config_dir and file are specified, this class will write-open the configuration file (and thus clobber it) before calling the write call-back and pass 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 (e.g. with augeas backend), the solution is to:

  • Skip either file or config_dir parameter in the write_config specification.

  • Create a skip_open function in your backend class that returns 1

EXAMPLES

In the example below, only a cds file is written. But, both custom format and cds file are tried for read. This is also an example of a graceful migration from a customized format to a cds format.

  read_config  => [ { backend => 'cds_file', config_dir => '/etc/my_cfg/' } , 
                    { backend => 'custom', class => 'Bar' },
                  ],
  write_config => [{ backend => 'cds_file', config_dir => '/etc/my_cfg/' }],

You can choose also to read and write only customized files:

  read_config  => [{ backend => 'custom', class => 'Bar'}],

Or to read and write only cds files :

  read_config  => [{ backend => 'cds_file'}] ,

You can also specify more parameters that must be passed to your custom class:

  read_config  => [{ backend => 'custom', class => 'Bar', 
                    config_dir => '/etc/foo'}],

To migrate from an old format to a new format:

  read_config  => [ { backend => 'custom',
                      class => 'OldFormat',
                      function => 'old_read'
                    } ,
                    { backend => 'custom',
                      class => 'NewFormat',
                      function => 'new_read'
                    }
                  ],
  write_config => [ { backend => 'custom',
                      class => 'NewFormat'
                    }
                  ],

If write_config is missing, the data provided by read_config will be used. For instance:

  read_config  => [ { backend => 'custom',
                      class => 'Bar',
                      config_dir => '/etc/foo'
                  } ],

In this case, configuration data will be read by Bar::read in directory /etc/foo and will be written back there by Bar::write.

AUTHOR

Dominique Dumont, (ddumont at cpan dot org)

SEE ALSO

Config::Model, Config::Model::Instance, Config::Model::Node, Config::Model::Dumper, Config::Augeas