Config::Model::AutoReaUser Contributed Perl DocumentConfig::Model::AutoRead(3)
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 => 'augeas'" or "backend => 'custom'".
You can force to use all backend to write the files by specifying
"backend => 'all'".
"write_back" will croak if no write call-back are known for this node.
NAMEConfig::Model::AutoRead - Load configuration node on demand
VERSION
version 1.235
SYNOPSIS
# Use AutoRead to write data in perl data file
use Config::Model;
use Log::Log4perl qw(:easy);
Log::Log4perl->easy_init($WARN);
# 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::AutoRead
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->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 );
$inst->write_back;
# now look at file /tmp/my_class.pl
DESCRIPTION
This class provides a way to specify how to load or store configuration
data within the model (instead of writing dedicated perl code).
With these specifications, all the configuration information is read
during creation of a node.
This load/store can be done with different "backend":
cds_file
Config dump string (cds) in a file. I.e. a string that describes
the content of a configuration tree is loaded from or saved in a
text file. See Config::Model::Dumper.
ini_file
INI files (written with Config::Model::Backend::IniFile. See
limitations in "Limitations depending on storage".
perl_file
Perl data structure (perl) in a file. See Config::Model::DumpAsData
for details on the data structure.
custom
Any format when the user provides a dedicated class and function to
read and load the configuration tree.
augeas
Data can be loaded or stored using RedHat's Augeas library. See
Config::Model::Backend::Augeas for details.
After loading the data, the object registers itself to the instance.
Then the user can call the "write_back" method on the instance (See
Config::Model::Instance) to store all configuration information back.
Built-in backend
"cds_file", "ini_file" and "perl_file" backend must be specified with
mandatory "config_dir" parameter. For instance:
read_config => { backend => 'cds_file' ,
config_dir => '/etc/cfg_dir',
file => 'cfg_file.cds', #optional
},
If "file" is not specified, a file name will be constructed with
"<config_class_name>.<suffix>" where suffix is "pl" or "ini" or "cds".
Plugin backend classes
A plugin backend class can also be specified with:
read_config => [ { backend => 'foo' ,
config_dir => '/etc/cfg_dir'
file => 'foo.conf', # optional
}
]
In this case, this class will try to load
"Config::Model::Backend::Foo". (The class name is constructed with
"ucfirst($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 => $io_file # IO::File object
check => [ yes|no|skip]
Must return 1 if the read was successful, 0 otherwise.
Following the "my_param" example above, %custom_parameters will
contain " ( 'my_param' , 'my_value' ) ", so "read()" will also be
called with "root", "config_dir", "file_path", "io_handle" and
"my_param => 'my_value'".
write
with parameters:
%$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,
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. If you want to completely handle file
creation in your backend class, set to "undef" or and empty string.
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, 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 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, 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
# 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.
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".
AUTHOR
Dominique Dumont, (ddumont at cpan dot org)
SEE ALSO
Config::Model, Config::Model::Instance, Config::Model::Node,
Config::Model::Dumper, Config::Augeas
perl v5.14.1 2011-07-22 Config::Model::AutoRead(3)
