Log::ger::Manual::Tutorial::490_WritingAnOutputPlugin - Writing an output plugin


version 0.033.000


A lot of output plugins have been written. Search CPAN for Log::ger::Output::* modules. If none suits your needs, there's still Log::ger::Output::LogDispatchOutput which can use a Log::Dispatch output module (of which there are many), or Log::ger::Output::Callback which lets you supply just a coderef to do the logging.

If you really want to write your own Log::ger output plugin, the following will show you how. Let's say we want to log to some logging server using a client library called Lancard. Create Log::ger::Output::Lancard as follows:

 # in lib/Log/ger/Output/
 package Log::ger::Output::Lancard;

 use 5.010;
 use strict;
 use warnings;

 sub get_hooks {
     require Lancard::Client;
     my %plugin_conf = @_;

     $plugin_conf{host} or die "Please specify host";

     my $lancard = Lancard::Client->connect(
         host => $plugin_conf{host},
         port => $plugin_conf{port} // 12345,

     return {
         create_outputter => [
             __PACKAGE__, # key
             50,          # priority
             sub {        # hook
                 my %hook_args = @_;
                 my $outputter = sub {
                     my ($ctx, $msg) = @_;


The only subroutine you have to provide is get_hooks to return the hooks that this plugin wants to add. For output plugin, usually this is hook in the create_outputter. Our get_hooks should return a hashref with phase names as keys and hook records as values. Hook record is [$key, $priority, $hook] where $key is usually __PACKAGE__, and $priority is usually 50 unless you want to do something tricky or advanced.

At this point, it will really help if you understand how hooks work by reading Log::ger::Manual::Internals. But, without reading the said documentation, it's still possible to write an output plugin so let's continue right away if you want to skip reading the internals documentation.

The actual hook coderef ($hook) should return an outputter routine, which is another coderef ($outputter in the above code). Outputter will receive ($per_target_conf, $msg, $per_msg_conf) as argument where $msg is the already-formatted message. You typically just need to send $msg (which is almost always a string) to some output. In our example, we send the log message string to the logging server via the client object $lancard.

Note that a separate logger routine will be created for each logging level (and for each target package that uses logging!), so you'd want to keep $outputter small, like avoid instantiating your Lancard client $lancard inside $outputter as there will be multiple clients instantiated.

To use your newly written output plugin, do the usual:

 use Log::ger::Output Lancard => (host => '');


 use Log::ger::Output;
 Log::ger::Output->set(Lancard => (host => ''));



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