Dancer2::Plugin::LogReport(3) logging and exceptions via Log::Report


# Load the plugin into Dancer2
# see Log::Report::import() for %options
use Log::Report (); # load early in main
use Dancer2::Plugin::LogReport %options;
# Stop execution, redirect, and display an error to the user
$name or error "Please enter a name";
# Add debug information to logger
trace "We're here";
# Handling user errors cleanly
if (process( sub {MyApp::Model->create_user} )) {
# Success, redirect user elsewhere
} else {
# Failed, continue as if submit hadn't been made.
# Error message will be in session for display later.
# Send errors to template for display
hook before_template => sub {
my $tokens = shift;
$tokens->{messages} = session 'messages';
session 'messages' => [];


[The Dancer2 plugin was contributed by Andrew Beverley]

This module provides easy access to the extensive logging facilities provided by Log::Report. Along with Dancer2::Logger::LogReport, this brings together all the internal Dancer2 logging, handling for expected and unexpected exceptions, translations and application logging.

Logging is extremely flexible using many of the available dispatchers. Multiple dispatchers can be used, each configured separately to display different messages in different formats. By default, messages are logged to a session variable for display on a webpage, and to STDERR.

Messages within this plugin use the extended Dancer2::Logger::LogReport::Message class rather than the standard Log::Report::Message class.

Read the ``DETAILS'' in below in this manual-page.


"process()" is an eval, but one which expects and handles exceptions generated by Log::Report. Any messages will be logged as normal in accordance with the dispatchers, but any fatal exceptions will be caught and handled gracefully. This allows much simpler error handling, rather than needing to test for lots of different scenarios.

In a module, it is enough to simply use the "error" keyword in the event of a fatal error.

The return value will be 1 for success or 0 if a fatal exception occurred.

See the ``DETAILS'' for an example of how this is expected to be used.

Modules do not need to use this plugin, instead they can "use Log::Report".


All the standard Log::Report functions are available to use. Please see the ``The Reason for the report'' in Log::Report for details of when each one should be used.

Log::Report class functionality to class messages (which can then be tested later):

  notice __x"Class me up", _class => 'label';
  if ($msg->inClass('label')) ...

Dancer2::Plugin::LogReport has a special message class, "no_session", which prevents the message from being saved to the messages session variable. This is useful, for example, if you are writing messages within the session hooks, in which case recursive loops can be experienced.

This is a special additional type, equivalent to "notice". The difference is that messages using this keyword will have the class "success" added, which can be used to color the messages differently to the end user. For example, Dancer2::Plugin::LogReport::Message#bootstrap_color uses this to display the message in green.


This chapter will guide you through the myriad of ways that you can use Log::Report in your Dancer2 application.

We will set up our application to do the following:

Messages to the user
We'll look at an easy way to output messages to the user's web page, whether they be informational messages, warnings or errors.
Debug information
We'll look at an easy way to log debug information, at different levels.
Manage unexpected exceptions
We'll handle unexpected exceptions cleanly, in the unfortunate event that they happen in your production application.
Email alerts of significant errors
If we do get unexpected errors then we want to be notified them.
Log DBIC information and errors
We'll specifically look at nice ways to log SQL queries and errors when using DBIx::Class.

Larger example

In its simplest form, this module can be used for more flexible logging

  get '/route' => sub {
      # Stop execution, redirect, and display an error to the user
      $name or error "Please enter a name";
      # The same but translated
      $name or error __"Please enter a name";
      # The same but translated and with variables
      $name or error __x"{name} is not valid", name => $name;
      # Show the user a warning, but continue execution
      mistake "Not sure that's what you wanted";
      # Add debug information, can be caught in syslog by adding
      # the (for instance) syslog dispatcher
      trace "Hello world";

Setup and Configuration

To make full use of Log::Report, you'll need to use both Dancer2::Logger::LogReport and Dancer2::Plugin::LogReport.


Set up Dancer2::Logger::LogReport by adding it to your Dancer2 application configuration (see Dancer2::Config). By default, all messages will go to STDERR.

To get all message out ``the Perl way'' (using print, warn and die) just use

  logger: "LogReport"

At start, these are handled by a Log::Report::Dispatcher::Perl object, named 'default'. If you open a new dispatcher with the name 'default', the output via the perl mechanisms will be stopped.

To also send messages to your syslog:

  logger: "LogReport"
        log_format: %a%i%m
        app_name: MyApp
          default:              # Name
            type: SYSLOG        # Log::Reporter::dispatcher() options
            identity: myapp
            facility: local0
            flags: "pid ndelay nowait"
            mode: DEBUG

To send messages to a file:

  logger: "LogReport"
        log_format: %a%i%m
        app_name: MyApp
          logfile:              # "default" dispatcher stays open as well
            type: FILE
            to: /var/log/myapp.log
            charset: utf-8
            mode: DEBUG

See Log::Report::Dispatcher for full details of options.

Finally: a Dancer2 script may run many applications. Each application can have its own logger configuration. However, Log::Report dispatchers are global, so will be shared between Dancer2 applications. Any attempt to create a new Log::Report dispatcher by the same name (as will happen when a new Dancer2 application is started with the same configuration) will be ignored.


To use the plugin, you simply use it in your application:

  package MyApp;
  use Log::Report ();  # use early and minimal once
  use Dancer2;
  use Dancer2::Plugin::LogReport %config;

Dancer2::Plugin::LogReport takes the same %config options as Log::Report itself (see Log::Report::import()).

If you want to send messages from your modules/models, there is no need to use this specific plugin. Instead, you should simply "use Log::Report" to negate the need of loading all the Dancer2 specific code.

In use

Logging debug information

In its simplest form, you can now use all the Log::Report logging functions to send messages to your dispatchers (as configured in the Logger configuration):

  trace "I'm here";
  warning "Something dodgy happened";
  panic "I'm bailing out";
  # Additional, special Dancer2 keyword
  success "Settings saved successfully";


Log::Report is a combination of a logger and an exception system. Messages to be logged are thrown to all listening dispatchers to be handled.

This module will also catch any unexpected exceptions:

  # This will be caught, the error will be logged (full stacktrace to STDOUT,
  # short message to the session messages), and the user will be forwarded
  # (default to /). This would also be sent to syslog with the appropriate
  # dispatcher.
  get 'route' => sub {
      my $foo = 1;
      my $bar = $foo->{x}; # whoops

For a production application ("show_errors: 1"), the message saved in the session will be the generic text ``An unexpected error has occurred''. This can be customised in the configuration file, and will be translated.

Sending messages to the user

To make it easier to send messages to your users, messages at the following levels are also stored in the user's session: "notice", "warning", "mistake", "error", "fault", "alert", "failure" and "panic".

You can pass these to your template and display them at each page render:

  hook before_template => sub {
    my $tokens = shift;
    $tokens->{messages} = session 'messages';
    session 'messages' => []; # Clear the message queue

Then in your template (for example the main layout):

  [% FOR message IN messages %]
    <div class="alert alert-[% message.bootstrap_color %]">
      [% message.toString | html_entity %]
  [% END %]

The "bootstrap_color" of the message is compatible with Bootstrap contextual colors: "success", "info", "warning" or "danger".

Now, anywhere in your application that you have used Log::Report, you can

  warning "Hey user, you should now about this";

and the message will be sent to the next page the user sees.

Handling user errors

Sometimes we write a function in a model, and it would be nice to have a nice easy way to return from the function with an error message. One way of doing this is with a separate error message variable, but that can be messy code. An alternative is to use exceptions, but these can be a pain to deal with in terms of catching them. Here's how to do it with Log::Report.

In this example, we do use exceptions, but in a neat, easier to use manner.

First, your module/model:

  package MyApp::CD;
  sub update {
    my ($self, %values) = @_;
    $values{title} or error "Please enter a title";
    $values{description} or warning "No description entered";

Then, in your controller:

  package MyApp;
  use Dancer2;
  post '/cd' => sub {
    my %values = (
      title       => param('title');
      description => param('description');
    if (process sub { MyApp::CD->update(%values) } ) {
      success "CD updated successfully";
      redirect '/cd';
    template 'cd' => { values => \%values };

Now, when update() is called, any exceptions are caught. However, there is no need to worry about any error messages. Both the error and warning messages in the above code will have been stored in the messages session variable, where they can be displayed using the code in the previous section. The "error" will have caused the code to stop running, and process() will have returned false. "warning" will have simply logged the warning and not caused the function to stop running.

Logging DBIC database queries and errors

If you use DBIx::Class in your application, you can easily integrate its logging and exceptions. To log SQL queries:

  # Log all queries and execution time
  $schema->storage->debugobj(new Log::Report::DBIC::Profiler);

By default, exceptions from DBIC are classified at the level ``error''. This is normally a user level error, and thus may be filtered as normal program operation. If you do not expect to receive any DBIC exceptions, then it is better to class them at the level ``panic'':

  # panic() DBIC errors
  $schema->exception_action(sub { panic @_ });
  # Optionally get a stracktrace too

If you are occasionally running queries where you expect to naturally get exceptions (such as not inserting multiple values on a unique constraint), then you can catch these separately:

  try { $self->schema->resultset('Unique')->create() };
  # Log any messages from try block, but only as trace
  $@->reportAll(reason => 'TRACE');

Email alerts of exceptions

If you have an unexpected exception in your production application, then you probably want to be notified about it. One way to do so is configure rsyslog to send emails of messages at the panic level. Use the following configuration to do so:

  # Normal logging from LOCAL0
  local0.*                        -/var/log/myapp.log
  # Load the mail module
  $ModLoad ommail
  # Configure sender, receiver and mail server
  $ActionMailSMTPServer localhost
  $ActionMailFrom root
  $ActionMailTo root
  # Set up an email template
  $template mailSubject,"Critical error on %hostname%"
  $template mailBody,"RSYSLOG Alert\r\nmsg='%msg%'\r\nseverity='%syslogseverity-text%'"
  $ActionMailSubject mailSubject
  # Send an email no more frequently than every minute
  $ActionExecOnlyOnceEveryInterval 60
  # Configure the level of message to notify via email
  if $syslogfacility-text == 'local0' and $syslogseverity < 3 then :ommail:;mailBody
  $ActionExecOnlyOnceEveryInterval 0

With the above configuration, you will only be emailed of severe errors, but can view the full log information in /var/log/myapp.log


All configuration is optional. The example configuration file below shows the configuration options and defaults.

        # Whether to handle Dancer HTTP errors such as 404s. Currently has
        # no effect due to unresolved issues saving messages to the session
        # and accessing the DSL at that time.
        handle_http_errors: 1
        # Where to forward users in the event of an uncaught fatal
        # error within a GET request
        forward_url: /
        # Or you can specify a template instead [1.13]
        forward_template: error_template_file   # Defaults to empty
        # For a production server (show_errors: 0), this is the text that
        # will be displayed instead of unexpected exception errors
        fatal_error_message: An unexpected error has occurred
        # The levels of messages that will be saved to the session, and
        # thus displayed to the end user


Copyrights 2007-2016 by [Mark Overmeer]. For other contributors see ChangeLog.

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