Agent::Tag(3p)

NAME
Log::Agent::Tag - formats caller information

SYNOPSIS
 Intended to be inherited from

DESCRIPTION
This class is meant to be inherited by all the classes implementing a log message tag.

A message tag is a little string that is either appended or prepended to all log messages.

For instance, and oversimplifying a bit, a tag meant to be prepended will be inserted in front of the current log message, separated by separator, which defaults to a single space:

   +------------+-----------+---------------------------------+
   | tag string | separator |      current log message        |
   +------------+-----------+---------------------------------+

This operation is called tag insertion. The whole string then becomes the current log message, and can be the target of another tag insertion.

The reality is a little bit more complex, to allow successive tags to be prepended or appended in the order they are specified, and not in reverse order as they would be if naively implemented. See Log::Agent::Message for the exact semantics of append() and prepend() operations.

FEATURES
This section documents the interface provided to heirs, in case you wish to implement your own tag class.

_init(name, postfix, separator)
    Initialization routine that should be called by all heirs during creation to initialize the common attributes.

postfix
    When true, the tag is meant to be appended to the log message. Otherwise, it is prepended.

name
    The name of this tag. It is meant to provide by-name access to tags, check whether a given tag is recorded, etc... The names "caller" and "priority" are architecturally defined to refer to "Log::Agent::Tag::Caller" and "Log::Agent::Tag::Priority" objects.

    NOTE: Currently unused by any client code.

separator
    The sperating string inserted between the tag and the log message. It defaults to " " if not specified, i.e. left to "undef" when calling _init().

string()
    A deferred routine, to be implemented by heirs.

    Returns the tag string only, without the separator, since its exact placement depends on the value of the "postfix" attribute.

insert(message)
    Insert this tag withing the "Log::Agent::Message" message, according to the tag specifications (placement, separator). Calls string() to produce the tag string.

    This routine is frozen and should not be redefined by heirs.

STANDARD TAGGING CLASSES
Tagging classes define via their string() routine what is the string to be used as a tag. The insertion of the tag within the log message is done via a frozen routine from the "Log::Agent::Tag" ancestor.

The following classes are provided by "Log::Agent":

"Log::Agent::Tag::Callback"
    The string() routine invokes a user-supplied callback, given as a "Callback" object. You need the Callback module from CPAN if you wish to use this class.

"Log::Agent::Tag::Caller"
    Used internally to compute the caller and format it according to user specifications.

"Log::Agent::Tag::Priority"
    Used internally to format message priorities and add them to the log messages.

"Log::Agent::Tag::String"
    Defines a constant tagging string that should be added in all the log messages, e.g. a web session ID.

AUTHOR
Raphael Manfredi <Raphael_Manfredi@pobox.com>

SEE ALSO
Log::Agent::Message(3).