Provided by: libconfig-model-perl_2.082-1_all 
NAME
Config::Model::BackendMgr - Load configuration node on demand
VERSION
version 2.082
SYNOPSIS
# Use BackendMgr to write data in perl data file
use Config::Model;
# define configuration tree object
my $model = Config::Model->new;
$model->create_config_class(
name => "Foo",
element => [
[qw/foo bar/] => {
type => 'leaf',
value_type => 'string'
},
]
);
$model->create_config_class(
name => "MyClass",
# read_config spec is used by Config::Model::BackendMgr
read_config => [
{
backend => 'perl_file',
config_dir => '/tmp/',
file => 'my_class.pl',
auto_create => 1,
},
],
element => [
[qw/foo bar/] => {
type => 'leaf',
value_type => 'string'
},
hash_of_nodes => {
type => 'hash', # hash id
index_type => 'string',
cargo => {
type => 'node',
config_class_name => 'Foo'
},
},
],
);
my $inst = $model->node->instance( root_class_name => 'MyClass' );
my $root = $inst->config_root;
# put data
my $step = 'foo=FOO hash_of_nodes:fr foo=bonjour -
hash_of_nodes:en foo=hello ';
$root->load( step => $step );
$inst->write_back;
# now look at file /tmp/my_class.pl
DESCRIPTION
This class provides a way to specify how to load or store configuration data within the
model (instead of writing dedicated perl code).
With these specifications, all the configuration information is read during creation of a
node.
This load/store can be done with different "backend":
cds_file
Config dump string (cds) in a file. I.e. a string that describes the content of a
configuration tree is loaded from or saved in a text file. See Config::Model::Dumper.
IniFile
INI files (written with Config::Model::Backend::IniFile. See limitations in
"Limitations depending on storage".
perl_file
Perl data structure (perl) in a file. See Config::Model::DumpAsData for details on the
data structure.
custom
Any format when the user provides a dedicated class and function to read and load the
configuration tree.
After loading the data, the object registers itself to the instance. Then the user can
call the "write_back" method on the instance (See Config::Model::Instance) to store all
configuration information back.
Built-in backend
"cds_file", "IniFile" and "perl_file" backend must be specified with mandatory
"config_dir" parameter. For instance:
read_config => { backend => 'cds_file' ,
config_dir => '/etc/cfg_dir',
file => 'cfg_file.cds', #optional
},
If "file" is not specified, a file name will be constructed with
"<config_class_name>.<suffix>" where suffix is "pl" or "ini" or "cds".
Plugin backend classes
A plugin backend class can also be specified with:
read_config => [ { backend => 'foo' ,
config_dir => '/etc/cfg_dir'
file => 'foo.conf', # optional
}
]
In this case, this class will try to load "Config::Model::Backend::Foo". (The class name
is constructed with "ucfirst($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 must inherit Config::Model::Backend::Any and is
expected to provide the following methods:
new Mandatory 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 => $io_file # IO::File object
check => [ yes|no|skip]
Must return 1 if the read was successful, 0 otherwise.
Following the "my_param" example above, %custom_parameters will contain " ( 'my_param'
, 'my_value' ) ", so "read()" will also be called with "root", "config_dir",
"file_path", "io_handle" and "my_param => 'my_value'".
write
with parameters:
%$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
check => [ yes|no|skip] ,
root => $root_dir,
backup => [ undef || '' || suffix ] # backup strategy required by user
Must return 1 if the write was successful, 0 otherwise
If "io_handle" is defined, the backup has already been done while 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.
Custom backend
Custom backend is provided to be backward compatible but should not be used for new
project. Using a plugin backend as described above is preferred.
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. "config_dir" beginning with '"~"' will be munged so "~"
is replaced by "File::HomeDir->my_data". See File::HomeDir for details.
os_config_dir
Specify alternate location of a configuration directory depending on the OS (as
returned by $^O, see "PLATFORMS" in perlport). For instance:
config_dir => '/etc/ssh',
os_config_dir => { darwin => '/etc' }
file
optional. Configuration file. This parameter may not apply if the configuration is
stored in several files. By default, the instance name is used as configuration file
name.
default_layer
Optional. Specifies where to find a global configuration file that specifies default
values. For instance, this is used by OpenSSH to specify a global configuration file
("/etc/ssh/ssh_config") that is overridden by user's file:
'default_layer' => {
os_config_dir => { 'darwin' => '/etc' },
config_dir => '/etc/ssh',
file => 'ssh_config'
}
Only the 3 above parameters can be specified in "default_layer".
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 successful. 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 with "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, 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 with binmode :utf8
check => [yes|no|skip]
The IO::File object is undef if the file cannot be read.
The callback must return 0 on failure and 1 on successful read.
write callback
Write callback function will be called with these parameters:
object => $obj, # Config::Model::Node object
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 in write mode
# with binmode :utf8
auto_create => 1 # create dir as needed
check => [yes|no|skip]
The IO::File object is undef if the file cannot be written to.
The callback must return 0 on failure and 1 on successful write.
Configuration file will be deleted if callback returns 2.
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 either to:
• Set "file" to undef or an empty string 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".
Methods
write_back ( ... )
Try to run all subroutines registered by auto_write_init write the configuration
information until one succeeds (returns true).
You can specify here a pseudo root directory or another config directory to write
configuration data back with "root" and "config_dir" parameters. This will override the
model specifications.
You can force to use a backend by specifying "backend => xxx". For instance, "backend =>
'perl_file'" or "backend => 'custom'".
You can force to use all backend to write the files by specifying "backend => 'all'".
You can force a specific config file to write with "config_file => 'foo/bar.conf'"
"write_back" will croak if no write call-back are known for this node.
support_annotation
Returns 1 if at least one of the backends support to read and write annotations (aka
comments) in the configuration file.
AUTHOR
Dominique Dumont, (ddumont at cpan dot org)
SEE ALSO
Config::Model, Config::Model::Instance, Config::Model::Node, Config::Model::Dumper
AUTHOR
Dominique Dumont
COPYRIGHT AND LICENSE
This software is Copyright (c) 2005-2016 by Dominique Dumont.
This is free software, licensed under:
The GNU Lesser General Public License, Version 2.1, February 1999