SYNOPSIS
use Log::Contextual qw( :log :dlog set_logger with_logger );
use Log::Contextual::SimpleLogger;
use Log::Log4perl ':easy';
Log::Log4perl->easy_init($DEBUG);
my $logger = Log::Log4perl->get_logger;
set_logger $logger;
log_debug { 'program started' };
sub foo {
my $minilogger = Log::Contextual::SimpleLogger->new({
levels => [qw( trace debug )]
});
my @args = @_;
with_logger $minilogger => sub {
log_trace { 'foo entered' };
my ($foo, $bar) = Dlog_trace { "params for foo: $_" } @args;
# ...
log_trace { 'foo left' };
};
}
foo();
Beginning with version 1.008 Log::Dispatchouli also works out of the
box with Log::Contextual:
use Log::Contextual qw( :log :dlog set_logger );
use Log::Dispatchouli;
my $ld = Log::Dispatchouli->new({
ident => 'slrtbrfst',
to_stderr => 1,
debug => 1,
});
set_logger $ld;
log_debug { 'program started' };
DESCRIPTION
Major benefits:
* Efficient
The logging functions take blocks, so if a log level is disabled, the
block will not run:
# the following won't run if debug is off
log_debug { "the new count in the database is " . $rs->count };
Similarly, the D prefixed methods only Dumper the input if the level
is enabled.
* Handy
The logging functions return their arguments, so you can stick them
in the middle of expressions:
for (log_debug { "downloading:\n" . join qq(\n), @_ } @urls) { ... }
* Generic
Log::Contextual is an interface for all major loggers. If you log
through Log::Contextual you will be able to swap underlying loggers
later.
* Powerful
Log::Contextual chooses which logger to use based on user defined
CodeRefs. Normally you don't need to know this, but you can take
advantage of it when you need to later.
* Scalable
If you just want to add logging to your basic application, start with
Log::Contextual::SimpleLogger and then as your needs grow you can
switch to Log::Dispatchouli or Log::Dispatch or Log::Log4perl or
whatever else.
This module is a simple interface to extensible logging. It exists to
abstract your logging interface so that logging is as painless as
possible, while still allowing you to switch from one logger to
another.
It is bundled with a really basic logger,
Log::Contextual::SimpleLogger, but in general you should use a real
logger instead. For something more serious but not overly complicated,
try Log::Dispatchouli (see "SYNOPSIS" for example.)
A WORK IN PROGRESS
This module is certainly not complete, but we will not break the
interface lightly, so I would say it's safe to use in production code.
The main result from that at this point is that doing:
use Log::Contextual;
will die as we do not yet know what the defaults should be. If it turns
out that nearly everyone uses the :log tag and :dlog is really rare,
we'll probably make :log the default. But only time and usage will
tell.
IMPORT OPTIONS
See "SETTING DEFAULT IMPORT OPTIONS" for information on setting these
project wide.
-logger
When you import this module you may use -logger as a shortcut for
"set_logger", for example:
use Log::Contextual::SimpleLogger;
use Log::Contextual qw( :dlog ),
-logger => Log::Contextual::SimpleLogger->new({ levels => [qw( debug )] });
sometimes you might want to have the logger handy for other stuff, in
which case you might try something like the following:
my $var_log;
BEGIN { $var_log = VarLogger->new }
use Log::Contextual qw( :dlog ), -logger => $var_log;
-levels
The -levels import option allows you to define exactly which levels
your logger supports. So the default, [qw(debug trace warn info error
fatal)], works great for Log::Log4perl, but it doesn't support the
levels for Log::Dispatch. But supporting those levels is as easy as
doing
use Log::Contextual
-levels => [qw( debug info notice warning error critical alert emergency )];
-package_logger
The -package_logger import option is similar to the -logger import
option except -package_logger sets the logger for the current package.
Unlike "-default_logger", -package_logger cannot be overridden with
"set_logger" or "with_logger".
package My::Package;
use Log::Contextual::SimpleLogger;
use Log::Contextual qw( :log ),
-package_logger => Log::Contextual::WarnLogger->new({
env_prefix => 'MY_PACKAGE'
});
If you are interested in using this package for a module you are
putting on CPAN we recommend Log::Contextual::WarnLogger for your
package logger.
-default_logger
The -default_logger import option is similar to the -logger import
option except -default_logger sets the default logger for the current
package.
Basically it sets the logger to be used if set_logger is never called;
so
package My::Package;
use Log::Contextual::SimpleLogger;
use Log::Contextual qw( :log ),
-default_logger => Log::Contextual::WarnLogger->new({
env_prefix => 'MY_PACKAGE'
});
SETTING DEFAULT IMPORT OPTIONS
Eventually you will get tired of writing the following in every single
one of your packages:
use Log::Log4perl;
use Log::Log4perl ':easy';
BEGIN { Log::Log4perl->easy_init($DEBUG) }
use Log::Contextual -logger => Log::Log4perl->get_logger;
You can set any of the import options for your whole project if you
define your own Log::Contextual subclass as follows:
package MyApp::Log::Contextual;
use base 'Log::Contextual';
use Log::Log4perl ':easy';
Log::Log4perl->easy_init($DEBUG)
sub arg_default_logger { $_[1] || Log::Log4perl->get_logger }
sub arg_levels { [qw(debug trace warn info error fatal custom_level)] }
sub default_import { ':log' }
# or maybe instead of default_logger
sub arg_package_logger { $_[1] }
# and almost definitely not this, which is only here for completeness
sub arg_logger { $_[1] }
Note the $_[1] || in arg_default_logger. All of these methods are
passed the values passed in from the arguments to the subclass, so you
can either throw them away, honor them, die on usage, etc. To be clear,
if you define your subclass, and someone uses it as follows:
use MyApp::Log::Contextual -default_logger => $foo,
-levels => [qw(bar baz biff)];
Your arg_default_logger method will get $foo and your arg_levels will
get [qw(bar baz biff)];
Additionally, the default_import method is what happens if a user tries
to use your subclass with no arguments. The default just dies, but if
you'd like to change the default to import a tag merely return the tags
you'd like to import. So the following will all work:
sub default_import { ':log' }
sub default_import { ':dlog' }
sub default_import { qw(:dlog :log ) }
See Log::Contextual::Easy::Default for an example of a subclass of
Log::Contextual that makes use of default import options.
FUNCTIONS
set_logger
my $logger = WarnLogger->new;
set_logger $logger;
Arguments: "LOGGER CODEREF"
set_logger will just set the current logger to whatever you pass it. It
expects a CodeRef, but if you pass it something else it will wrap it in
a CodeRef for you. set_logger is really meant only to be called from a
top-level script. To avoid foot-shooting the function will warn if you
call it more than once.
with_logger
my $logger = WarnLogger->new;
with_logger $logger => sub {
if (1 == 0) {
log_fatal { 'Non Logical Universe Detected' };
} else {
log_info { 'All is good' };
}
};
Arguments: "LOGGER CODEREF", CodeRef $to_execute
with_logger sets the logger for the scope of the CodeRef $to_execute.
As with "set_logger", with_logger will wrap $returning_logger with a
CodeRef if needed.
log_$level
Import Tag: :log
Arguments: CodeRef $returning_message, @args
log_$level functions all work the same except that a different method
is called on the underlying $logger object. The basic pattern is:
sub log_$level (&@) {
if ($logger->is_$level) {
$logger->$level(shift->(@_));
}
@_
}
Note that the function returns it's arguments. This can be used in a
number of ways, but often it's convenient just for partial inspection
of passthrough data
my @friends = log_trace {
'friends list being generated, data from first friend: ' .
Dumper($_[0]->TO_JSON)
} generate_friend_list();
If you want complete inspection of passthrough data, take a look at the
"Dlog_$level" functions.
Which functions are exported depends on what was passed to "-levels".
The default (no -levels option passed) would export:
log_trace
log_debug
log_info
log_warn
log_error
log_fatal
logS_$level
Import Tag: :log
Arguments: CodeRef $returning_message, Item $arg
This is really just a special case of the "log_$level" functions. It
forces scalar context when that is what you need. Other than that it
works exactly same:
my $friend = logS_trace {
'I only have one friend: ' . Dumper($_[0]->TO_JSON)
} friend();
See also: "DlogS_$level".
Dlog_$level
Import Tag: :dlog
Arguments: CodeRef $returning_message, @args
All of the following six functions work the same as their "log_$level"
brethren, except they return what is passed into them and put the
stringified (with Data::Dumper::Concise) version of their args into $_.
This means you can do cool things like the following:
my @nicks = Dlog_debug { "names: $_" } map $_->value, $frew->names->all;
and the output might look something like:
names: "fREW"
"fRIOUX"
"fROOH"
"fRUE"
"fiSMBoC"
Which functions are exported depends on what was passed to "-levels".
The default (no -levels option passed) would export:
Dlog_trace
Dlog_debug
Dlog_info
Dlog_warn
Dlog_error
Dlog_fatal
DlogS_$level
Import Tag: :dlog
Arguments: CodeRef $returning_message, Item $arg
Like "logS_$level", these functions are a special case of
"Dlog_$level". They only take a single scalar after the
$returning_message instead of slurping up (and also setting wantarray)
all the @args
my $pals_rs = DlogS_debug { "pals resultset: $_" }
$schema->resultset('Pals')->search({ perlers => 1 });
LOGGER CODEREF
Anywhere a logger object can be passed, a coderef is accepted. This is
so that the user can use different logger objects based on runtime
information. The logger coderef is passed the package of the caller,
and the caller level the coderef needs to use if it wants more caller
information. The latter is in a hashref to allow for more options in
the future.
Here is a basic example of a logger that exploits caller to reproduce
the output of warn with a logger:
my @caller_info;
my $var_log = Log::Contextual::SimpleLogger->new({
levels => [qw(trace debug info warn error fatal)],
coderef => sub { chomp($_[0]); warn "$_[0] at $caller_info[1] line $caller_info[2].\n" }
});
my $warn_faker = sub {
my ($package, $args) = @_;
@caller_info = caller($args->{caller_level});
$var_log
};
set_logger($warn_faker);
log_debug { 'test' };
The following is an example that uses the information passed to the
logger coderef. It sets the global logger to $l3, the logger for the A1
package to $l1, except the lol method in A1 which uses the $l2 logger
and lastly the logger for the A2 package to $l2.
Note that it increases the caller level as it dispatches based on where
the caller of the log function, not the log function itself.
my $complex_dispatcher = do {
my $l1 = ...;
my $l2 = ...;
my $l3 = ...;
my %registry = (
-logger => $l3,
A1 => {
-logger => $l1,
lol => $l2,
},
A2 => { -logger => $l2 },
);
sub {
my ( $package, $info ) = @_;
my $logger = $registry{'-logger'};
if (my $r = $registry{$package}) {
$logger = $r->{'-logger'} if $r->{'-logger'};
my (undef, undef, undef, $sub) = caller($info->{caller_level} + 1);
$sub =~ s/^\Q$package\E:://g;
$logger = $r->{$sub} if $r->{$sub};
}
return $logger;
}
};
set_logger $complex_dispatcher;
LOGGER INTERFACE
Because this module is ultimately pretty looking glue (glittery?) with
the awesome benefit of the Contextual part, users will often want to
make their favorite logger work with it. The following are the methods
that should be implemented in the logger:
is_trace
is_debug
is_info
is_warn
is_error
is_fatal
trace
debug
info
warn
error
fatal
The first six merely need to return true if that level is enabled. The
latter six take the results of whatever the user returned from their
coderef and log them. For a basic example see
Log::Contextual::SimpleLogger.
LOG ROUTING
In between the loggers and the log functions is a log router that is
responsible for finding a logger to handle the log event and passing
the log information to the logger. This relationship is described in
the documentation for Log::Contextual::Role::Router.
Log::Contextual and packages that extend it will by default share a
router singleton that implements the with_logger() and set_logger()
functions and also respects the -logger, -package_logger, and
-default_logger import options with their associated default value
functions. The router singleton is available as the return value of the
router() function. Users of Log::Contextual may overload router() to
return instances of custom log routers that could for example work with
loggers that use a different interface.
CONTRIBUTORS
triddle - Tyler Riddle <t.riddle@shadowcat.co.uk>
voj - Jakob Voß <voss@gbv.de>
DESIGNER
mst - Matt S. Trout <mst@shadowcat.co.uk>