Dancer2/Plugin/LogReport.pod

=encoding utf8

=head1 NAME

Dancer2::Plugin::LogReport - logging and exceptions via Log::Report

=head1 INHERITANCE

 Dancer2::Plugin::LogReport
   is a Dancer2::Plugin

=head1 SYNOPSIS

  # Load the plugin into Dancer2
  # see Log::Report::import() for %options
  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' => [];
  }

=head1 DESCRIPTION

[The Dancer2 plugin was contributed by Andrew Beverley]

This module provides easy access to the extensive logging facilities
provided by L<Log::Report|Log::Report>. Along with L<Dancer2::Logger::LogReport|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
L<dispatchers|Log::Report::Dispatcher/DETAILS>.  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
L<Dancer2::Logger::LogReport::Message> class rather than the standard
L<Log::Report::Message> class.

Note that it is currently recommended to use the plugin in all apps within
a Dancer2 program, not only some. Therefore, wherever you C<use Dancer2>
you should also C<use Dancer2::Plugin::LogReport>. This does not apply if
using the same app name (C<use Dancer2 appname, 'Already::Exists'>). In
all other modules, you can just C<use Log::Report>.

Read the L</DETAILS> in below in this manual-page.

=head1 METHODS

=over 4

=item $obj-E<gt>B<fatal_handler>()

C<fatal_handler()> allows alternative handlers to be defined in place of (or in
addition to) the default redirect handler that is called on a fatal error.

Calls should be made with 1 parameter: the subroutine to call in the case of a
fatal error. The subroutine is passed 3 parameters: the DSL, the message in
question, and the reason. The subroutine should return true or false depending
on whether it handled the error. If it returns false, the next fatal handler is
called, and if there are no others then the default redirect fatal handler is
called.

example: Error handler based on URL (e.g. API)

  fatal_handler sub {
    my ($dsl, $msg, $reason) = @_;
    return if $dsl->app->request->uri !~ m!^/api/!;
    status $reason eq 'PANIC' ? 'Internal Server Error' : 'Bad Request';
    $dsl->send_as(JSON => {
        error             => 1,
        error_description => $msg->toString,
    }, {
        content_type => 'application/json; charset=UTF-8',
    });
  };

example: Return JSON responses for requests with content-type of application/json

fatal_handler sub {
    my ($dsl, $msg, $reason, $default) = @_;

    (my $ctype = $dsl->request->header('content-type')) =~ s/;.*//;
    return if $ctype ne 'application/json';
    status $reason eq 'PANIC' ? 'Internal Server Error' : 'Bad Request';
    $dsl->send_as(JSON => {
        error       => 1,
        description => $msg->toString,
    }, {
        content_type => 'application/json; charset=UTF-8',
    });
  };

=item $obj-E<gt>B<process>()

C<process()> is an eval, but one which expects and understands exceptions
generated by L<Log::Report|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 C<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 L</DETAILS> for an example of how this is expected to be used.

This module is configured only once in your application. The other modules
which make your website do not need to require this plugin, instead they
can C<use Log::Report> to get useful functions like error and fault.

=back

=head2 Handlers

All the standard L<Log::Report|Log::Report> functions are available to use. Please see the
L<Log::Report/"The Reason for the report"> for details
of when each one should be used.

L<Log::Report class functionality|Log::Report::Message.pod#class-STRING-ARRAY>
to class messages (which can then be tested later):

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

L<Dancer2::Plugin::LogReport|Dancer2::Plugin::LogReport> has a special message class, C<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.

=over 4

=item $obj-E<gt>B<alert>()

=item $obj-E<gt>B<assert>()

=item $obj-E<gt>B<error>()

=item $obj-E<gt>B<failure>()

=item $obj-E<gt>B<fault>()

=item $obj-E<gt>B<info>()

=item $obj-E<gt>B<mistake>()

=item $obj-E<gt>B<notice>()

=item $obj-E<gt>B<panic>()

=item $obj-E<gt>B<success>()

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

=item $obj-E<gt>B<trace>()

=item $obj-E<gt>B<warning>()

=back

=head1 DETAILS

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

We will set up our application to do the following:

=over 4

=item 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.

=item Debug information

We'll look at an easy way to log debug information, at different levels.

=item Manage unexpected exceptions

We'll handle unexpected exceptions cleanly, in the unfortunate event that
they happen in your production application.

=item Email alerts of significant errors

If we do get unexpected errors then we want to be notified them.

=item Log DBIC information and errors

We'll specifically look at nice ways to log SQL queries and errors when
using DBIx::Class.

=back

=head2 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";
   };

=head2 Setup and Configuration

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

=head3 Dancer2::Logger::LogReport

Set up L<Dancer2::Logger::LogReport> by adding it to your Dancer2
application configuration (see L<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 L<Log::Report::Dispatcher::Perl|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"

  engines:
    logger:
      LogReport:
        log_format: %a%i%m      # See Dancer2::Logger::LogReport
        app_name: MyApp
        dispatchers:
          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"

  engines:
    logger:
      LogReport:
        log_format: %a%i%m      # See Dancer2::Logger::LogReport
        app_name: MyApp
        dispatchers:
          logfile:              # "default" dispatcher stays open as well
            type: FILE
            to: /var/log/myapp.log
            charset: utf-8
            mode: DEBUG

See L<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.

=head3 Dancer2::Plugin::LogReport

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 C<%config> options as
L<Log::Report> itself (see L<Log::Report::import()|Log::Report/"Configuration">).

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

=head2 In use

=head3 Logging debug information

In its simplest form, you can now use all the
L<Log::Report logging functions|Log::Report#The-Reason-for-the-report>
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";

=head3 Exceptions

Log::Report is a combination of a logger and an exception system.  Messages
to be logged are I<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 (C<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.

=head3 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: C<notice>, C<warning>, C<mistake>,
C<error>, C<fault>, C<alert>, C<failure> and C<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 %]
    </div>
  [% END %]

The C<bootstrap_color> of the message is compatible with Bootstrap contextual
colors: C<success>, C<info>, C<warning> or C<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.

=head3 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 C<error> will have caused the code to stop running, and process()
will have returned false. C<warning> will have simply logged the warning
and not caused the function to stop running.

=head3 Logging DBIC database queries and errors

If you use L<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);
  $schema->storage->debug(1);

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
  $schema->stacktrace(1);

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');

=head3 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

=head1 CONFIGURATION

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

    plugins:
      LogReport:
        # 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
        session_messages: [ NOTICE, WARNING, MISTAKE, ERROR, FAULT, ALERT, FAILURE, PANIC ]

=head1 SEE ALSO

This module is part of Log-Report distribution version 1.33,
built on July 17, 2021. Website: F<http://perl.overmeer.net/CPAN/>

=head1 LICENSE

Copyrights 2007-2021 by [Mark Overmeer <markov@cpan.org>]. 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 F<http://dev.perl.org/licenses/>