NAME

Connector - a generic connection to a hierarchical-structured data set

DESCRIPTION

The Connector is generic connection to a data set, typically configuration data in a hierarchical structure. Each connector object accepts the get(KEY) method, which, when given a key, returns the associated value from the connector's data source.

Typically, a connector acts as a proxy to a simple data source like YAML, Config::Std, Config::Versioned, or to a more complex data source like an LDAP server or Proc::SafeExec. The standard calling convention via get(KEY) makes the connectors interchangeable.

In addition, a set of meta-connectors may be used to combine multiple connectors into more complex chains. The Connector::Multi, for example, allows for redirection to delegate connectors via symbolic links. If you have a list of connectors and want to use them in a load-balancing, round-robin fashion or have the list iterated until a value is found, use Connector::List and choose the algorithm to perform.

SYNOPSIS

    use Connector::MODULENAME;

    my $conn = Connector::MODULENAME->new( {
        LOCATION => $path_to_config_for_module,
    });

    my $val = $conn->get('full.name.of.key');

Connector Class

This is the base class for all Connector implementations. It provides common helper methods and performs common sanity checking.

Usually this class should not be instantiated directly.

CONFIGURATION

die_on_undef

Set to true if you want the connector to die when a query reaches a non-exisiting node. This will affect calls to get/get_list/get_hash and will not affect values that are explicitly set to undef (if supported by the connector!).

Accessor Methods

Each accessor method is valid only on special types of nodes. If you call them on a wrong type of node, the connector may retunr unexpected result or simply die.

exists

get

Basic method to obtain a scalar value at the leaf of the config tree.

  my $value = $connector->get('smartcard.owners.tokenid.bob');

Each implementation must also accept an arrayref as path. The path is contructed from the elements. The default behaviour allows strings using the delimiter character inside an array element. If you want each array element to be parsed, you need to pass "RECURSEPATH => 1" to the constructor.

  my $value = $connector->get( [ 'smartcard','owners','tokenid','bob.builder' ] );

Some implementations accept control parameters, which can be passed by params, which is a hash ref of key => value pairs.

  my $value = $connector->get( 'smartcard.owners.tokenid.bob' , { version => 1 } );

get_list

This method is only valid if it is called on a "n-1" depth node representing an ordered list of items (array). The return value is an array with all values present below the node.

  my @items = $connector->get_list( 'smartcard.owners.tokenid'  );

get_size

This method is only valid if it is called on a "n-1" depth node representing an ordered list of items (array). The return value is the number of elements in this array (including undef elements if they are explicitly given).

  my $count = $connector->get_size( 'smartcard.owners.tokens.bob' );

If the node does not exist, 0 is returned.

get_hash

This method is only valid if it is called on a "n-1" depth node representing a key => value list (hash). The return value is a hash ref.

  my %data = %{$connector->get_hash( 'smartcard.owners.tokens.bob' )};

get_keys

This method is only valid if it is called on a "n-1" depth node representing a key => value list (hash). The return value is an array holding the values of all keys (including undef elements if they are explicitly given).

  my @keys = $connector->get_keys( 'smartcard.owners.tokens.bob' );

If the node does not exist, an empty list is returned.

get_reference

Rarely used, returns the value of a reference node. Currently used by Connector::Multi in combination with Connector::Proxy::Config::Versioned to create internal links and cascaded connectors. See Connector::Multi for details.

set

The set method is a "all in one" implementation, that is used for either type of value. If the value is not a scalar, it must be passed by reference.

  $connector->set('smartcard.owners.tokenid.bob', $value, $params);

The value parameter holds a scalar or ref to an array/hash with the data to be written. params is a hash ref which holds additional parameters for the operation and can be undef if not needed.

STRUCTURAL METHODS

get_meta

This method returns some structural information about the current node as hash ref. At minimum it must return the type of node at the current path.

Valid values are scalar, list, hash, reference. The types match the accessor methods given above (use "get" for scalar).

    my $meta = $connector->get_meta( 'smartcard.owners' );
    my $type = $meta->{TYPE};

When you call a proxy connector without sufficient arguments to perform the query, you will receive a value of connector for type. Running a get_* method against such a node will cause the connector to die!

cleanup

Advise connectors to close, release or flush any open handle or sessions. Should be called directly before the program terminates. Connectors might be stale and not respond any longer after this was called.

IMPLEMENTATION GUIDELINES

You SHOULD use the _node_not_exists method if the requested path does not exist or has an undefined value. This will internally take care of the die_on_undef setting and throw an exception or return undef. So you can just write:

    if (path not exists || not defined val) {
        return $self->_node_not_exists( pathspec );
    }

As connectors are often used in eval constructs where the error messages are swallowed you SHOULD log a verbose error before aborting with die/confess. You can use the _log_and_die method for this purpose. It will send a message to the logger on error level before calling "die $message".

path building

You should always pass the first parameter to the private "_build_path" method. This method converts any valid path spec representation to a valid path. It takes care of the RECURSEPATH setting and returns the path elements as list.

Supported methods

The methods get, get_list, get_size, get_hash, get_keys, set, get_meta are routed to the appropriate connector.

You MUST implement at minimum one of the three data getters, if get_list/get_keys is omited, the base class will do a get_list/get_keys call and return the info which will be a correct result but might be expensive, so you can provide your own implementiation if required.

You MUST also implement the get_meta method. If you have a connector with a fixed type, you MAY check if the particular path exists and return the result of _node_not_exists.

cleanup

Connectors that keep locks or use long-lived sessions that are not bound to the lifetime of the perl process should implement this method and cleanup their mess. While it would be nice, that connectors can be revived after cleanup was called, this is not a strict requirement.

AUTHORS

Scott Hardin <mrscotty@cpan.org>

Martin Bartosch

Oliver Welter

COPYRIGHT

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