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).