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Lumberjack::Message::JSON cpan:JSTOWE last updated on 2021-02-06



JSON representation of a Lumberjack::Message

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use Lumberjack;
use Lumberjack::Message::JSON;

my $message = => 'this is a message');
$message does Lumberjack::Message::JSON;

my $str = $;


my $new-message = (Lumberjack::Message but Lumberjack::Message::JSON).from-json($str);

# Alternatively the derived type can be provided as a constant:

constant JSONMessage = (Lumberjack::Message but Lumberjack::Message::JSON);



This is used by Lumberjack::Dispatcher::EventSource, Lumberjack::Dispatcher::Proxy, Lumberjack::Application::PSGI and Lumberjack::Application::WebSocket to serialise and deserialise the Lumberjack::Message to/from JSON for transport over HTTP or websockets.

It is implemented as role that can be mixed at run-time to existing Message objects and to create a derived type to un-marshal to (see the Synopsis.)

Itself it uses JSON::Class to provide to-json and from-json and provides custom marshallers and un-marshallers to ensure that the data is rendered meaningfully in JSON.

The JSON will be something like:

   "backtrace" : [
         "file" : "-e",
         "line" : 1,
         "subname" : "<unit>",
         "code" : {}
   "message" : "this is a test",
   "class" : {
      "log-level" : 2,
      "is-logger" : false,
      "name" : "Any"
   "level" : 2,
   "when" : "2016-04-12T00:18:34.435650+01:00"

Which reflects the Lumberjack::Message fairly closely. There may of course be more backtrace frames.

The 'class' object in the JSON when de-serialised may cause a temporary type to be created with the name provided if the type is not available on the target system, if "is-logger" is true then it will have the Lumberjack::Logger applied and the log-level set. This is done so that the message will appear the same as one created on the local system for a message received from a remote logger.


Assuming you have a working Rakudo installation you should be able to install this with zef:

zef install Lumberjack::Message::JSON


I originally made this as an internal class to Lumberjack::Application but found another use for it, so it may not do everything that your application may need.

Any suggestions/patches/bugs can be reported at

This is free software, please see the LICENCE for further details.

© Jonathan Stowe 2021 -