Provided by: liblog-report-perl_1.26-1_all 
NAME
Log::Report - report a problem, with exceptions and translation support
INHERITANCE
Log::Report
is a Exporter
SYNOPSIS
# Invocation with 'mode' to get trace and verbose messages
use Log::Report mode => 'DEBUG';
# Usually invoked with a domain, which groups packages for translation
use Log::Report 'my-domain', %options;
# Interpolation syntax via String::Print
# First step to translations, once you need it.
print __x"my name is {name}", name => $n; # print, so no exception
print __"Hello World\n"; # no interpolation, optional translation
print __x'Hello World'; # SYNTAX ERROR!! ' is alternative for ::
# Functions replacing die/warn/carp, casting exceptions.
error "oops"; # exception like die(), no translation
-f $config or panic "Help!"; # alert/error/fault/info/...more
# Combined exception, interpolation, and optional translation
error __x"Help!"; # __x() creates ::Message object
error __x('gettext msgid', param => $value, ...)
if $condition;
# Also non fatal "exceptions" find their way to dispatchers
info __x"started {pid}", pid => $$; # translatable
debug "$i was here!"; # you probably do not want to translate debug
panic "arrghhh"; # like Carp::Confess
# Many destinations for an exception message (may exist in parallel)
dispatcher PERL => 'default' # see Log::Report::Dispatcher: use die/warn
, reasons => 'NOTICE-'; # this dispatcher is already present at start
dispatcher SYSLOG => 'syslog'# also send to syslog
, charset => 'iso-8859-1' # explicit character conversions
, locale => 'en_US'; # overrule user's locale
dispatcher close => 'default'; # stop default die/warn dispatcher
# Fill-in values, like Locale::TextDomain and gettext
# See Log::Report::Message section DETAILS
fault __x"cannot allocate {size} bytes", size => $size;
fault "cannot allocate $size bytes"; # no translation, ok
fault __x"cannot allocate $size bytes"; # not translatable, wrong
# Translation depending on count
# Leading and trailing whitespace stay magically outside translation
# tables. @files in scalar context. Special parameter with _
print __xn"found one file\n", "found {_count} files", @files;
# Borrow from an other text-domain (see Log::Report::Message)
print __x(+"errors in {line}", _domain => 'global', line => $line);
# catch errors (implements hidden eval/die)
try { error };
if($@) {...} # $@ isa Log::Report::Dispatcher::Try
if(my $exception = $@->wasFatal) # ::Exception object
# Language translations at the output component
# Translation management via Log::Report::Lexicon
use POSIX::1003::Locale qw/setlocale LC_ALL/;
setlocale(LC_ALL, 'nl_NL');
info __"Hello World!"; # in Dutch, if translation table found
# Exception classes, see Log::Report::Exception
try { error __x"something", _class => 'parsing,schema' };
if($@->wasFatal->inClass('parsing')) ...
DESCRIPTION
Get messages to users and logs. "Log::Report" combines three tasks which are closely
related in one:
. logging (like Log::Log4Perl and syslog), and
. exceptions (like error and info), with
. translations (like "gettext" and Locale::TextDomain)
You do not need to use this module for all three reasons: pick what you need now, maybe
extend the usage later. Read more about how and why in the "DETAILS" section, below.
Especially, you should read about the REASON parameter.
Also, you can study this module swiftly via the article published in the German Perl
"$foo-magazine". English version:
http://perl.overmeer.net/log-report/papers/201306-PerlMagazine-article-en.html
FUNCTIONS
Report Production and Configuration
dispatcher( <$type, $name, %options>|<$command, @names> )
The "dispatcher" function controls access to dispatchers: the back-ends which process
messages, do the logging. Dispatchers are global entities, addressed by a symbolic
$name. Please read Log::Report::Dispatcher as well.
The "Log::Report" suite has its own dispatcher @types, but also connects to external
dispatching frameworks. Each need some (minor) conversions, especially with respect
to translation of REASONS of the reports into log-levels as the back-end understands.
[1.10] When you open a dispatcher with a $name which is already in use, that existing
dispatcher gets closed. Except when you have given an 'dispatcher "do-not-reopen"'
earlier, in which case the first object stays alive, and the second attempt ignored.
[1.11] The automatically created default dispatcher will get replaced, even when this
option is given, by another dispatcher which is named 'default'.
The %options are a mixture of parameters needed for the Log::Report dispatcher wrapper
and the settings of the back-end. See Log::Report::Dispatcher, the documentation for
the back-end specific wrappers, and the back-ends for more details.
Implemented COMMANDs are "close", "find", "list", "disable", "enable", "mode",
"filter", "needs", "active-try", and "do-not-reopen".
Most commands are followed by a LIST of dispatcher @names to be addressed. For "mode"
see section "Run modes"; it requires a MODE argument before the LIST of NAMEs. Non-
existing names will be ignored. When "ALL" is specified, then all existing dispatchers
will get addressed. For "filter" see "Filters" in Log::Report::Dispatcher; it
requires a CODE reference before the @names of the dispatchers which will have the it
applied (defaults to all).
With "needs", you only provide a REASON: it will return the list of dispatchers which
need to be called in case of a message with the REASON is triggered. The "active-try"
[1.09] returns the closest surrounding exception catcher, a
Log::Report::Dispatcher::Try object.
For both the creation as COMMANDs version of this method, all objects involved are
returned as LIST, non-existing ones skipped. In SCALAR context with only one name,
the one object is returned.
example: play with dispatchers
dispatcher Log::Dispatcher::File => mylog =>
, accept => 'MISTAKE-' # for wrapper
, locale => 'pt_BR' # other language
, filename => 'logfile'; # for back-end
dispatcher close => 'mylog'; # cleanup
my $obj = dispatcher find => 'mylog';
my @obj = dispatcher 'list';
dispatcher disable => 'syslog';
dispatcher enable => 'mylog', 'syslog'; # more at a time
dispatcher mode => 'DEBUG', 'mylog';
dispatcher mode => 'DEBUG', 'ALL';
my $catcher = dispatcher 'active-try';
dispatcher 'do-not-reopen';
my @need_info = dispatcher needs => 'INFO';
if(dispatcher needs => 'INFO') ... # anyone needs INFO
# Getopt::Long integration: see Log::Report::Dispatcher::mode()
dispatcher PERL => 'default', mode => 'DEBUG', accept => 'ALL'
if $debug;
report( [%options], $reason, $message|<STRING,$params>, )
The "report" function is sending (for some $reason) a $message to be displayed or
logged (by a `dispatcher'). This function is the core for error(), info() etc
functions, which are nicer names for this exception throwing: better use those short
names.
The $reason is a string like 'ERROR' (for function "error()"). The $message is a
Log::Report::Message object (which are created with the special translation syntax
like __x()). The $message may also be a plain string, or an Log::Report::Exception
object. The optional first parameter is a HASH which can be used to influence the
dispatchers.
The optional %options are listed below. Quite differently from other functions and
methods, they have to be passed in a HASH as first parameter.
This function returns the LIST of dispatchers which accepted the $message. When
empty, no back-end has accepted it so the $message was "lost". Even when no back-end
needs the message, the program will still exit when there is a $reason to "die()".
-Option --Default
errno $! or 1
is_fatal <depends on reason>
locale undef
location undef
stack undef
to undef
errno => INTEGER
When the $reason includes the error text (See "Run modes"), you can overrule the
error code kept in $!. In other cases, the return code defaults to 1 (historical
UNIX behavior). When the message $reason (combined with the run-mode) is severe
enough to stop the program, this value as return code of the program. The use of
this option itself will not trigger an "die()".
is_fatal => BOOLEAN
Some logged exceptions are fatal, other aren't. The default usually is correct.
However, you may want an error to be caught (usually with try()), redispatch it to
syslog, but without it killing the main program.
locale => LOCALE
Use this specific locale, in stead of the user's preference.
location => STRING
When defined, this location is used in the display. Otherwise, it is determined
automatically if needed. An empty string will disable any attempt to display this
line.
stack => ARRAY
When defined, that data is used to display the call stack. Otherwise, it is
collected via "caller()" if needed.
to => NAME|ARRAY-of-NAMEs
Sent the $message only to the NAMEd dispatchers. Ignore unknown NAMEs. Still, the
dispatcher needs to be enabled and accept the REASONs.
example: for use of report()
# long syntax example
report TRACE => "start processing now";
report INFO => '500: ' . __'Internal Server Error';
# explicit dispatcher, no translation
report {to => 'syslog'}, NOTICE => "started process $$";
notice "started process $$", _to => 'syslog'; # same
# short syntax examples
trace "start processing now";
warning __x'Disk {percent%.2f}% full', percent => $p
if $p > 97;
# error message, overruled to be printed in Brazilian
report {locale => 'pt_BR'}
, WARNING => "do this at home!";
try(CODE, %options)
Execute the CODE while blocking all dispatchers as long as it is running. The
exceptions which occur while running the CODE are caught until it has finished. When
there where no fatal errors, the result of the CODE execution is returned.
After the CODE was tried, the $@ will contain a Log::Report::Dispatcher::Try object,
which contains the collected messages.
Run-time errors from Perl and die's, croak's and confess's within the program (which
shouldn't appear, but you never know) are collected into an Log::Report::Message
object, using Log::Report::Die.
The %options are passed to the constructor of the try-dispatcher, see
Log::Report::Dispatcher::Try::new(). For instance, you may like to add "mode =>
'DEBUG'", or "accept => 'ERROR-'".
Be warned that the parameter to "try" is a CODE reference. This means that you shall
not use a comma after the block when there are %options specified. On the other hand,
you shall use a semi-colon after the block if there are no arguments.
Be warned that the {} are interpreted as subroutine, which means that, for instance,
it has its own @_. The manual-page of Try::Tiny lists a few more side-effects of
this.
example:
my $x = try { 3/$x }; # mind the ';' !!
if($@) { # signals something went wrong
if(try {...}) { # block ended normally, returns bool
try { ... } # no comma!!
mode => 'DEBUG', accept => 'ERROR-';
try sub { ... }, # with comma, also \&function
mode => 'DEBUG', accept => 'ALL';
my $response = try { $ua->request($request) };
if(my $e = $@->wasFatal) ...
Abbreviations for report()
The following functions are all wrappers for calls to report(), and available when "syntax
is SHORT" (by default, see import()). You cannot specify additional options to influence
the behavior of "report()", which are usually not needed anyway.
alert($message)
Short for "report ALERT => $message"
assert($message)
Short for "report ASSERT => $message"
error($message)
Short for "report ERROR => $message"
failure($message)
Short for "report FAILURE => $message"
fault($message)
Short for "report FAULT => $message"
info($message)
Short for "report INFO => $message"
mistake($message)
Short for "report MISTAKE => $message"
notice($message)
Short for "report NOTICE => $message"
panic($message)
Short for "report PANIC => $message"
trace($message)
Short for "report TRACE => $message"
warning($message)
Short for "report WARNING => $message"
Messages (optionally translatable)
Even when you do not support translations (yet) you may want to use message objects to
improve the logging feature. For instance, you get very powerful interpolation from
String::Print.
The language translations are initiate by limited set of functions which contain two
under-scores ("__") in their name. Most of them return a Log::Report::Message object.
Be warned(1) that -in general- its considered very bad practice to combine multiple
translations into one message: translating may also affect the order of the translated
components. Besides, when the person which translates only sees smaller parts of the text,
his (or her) job becomes more complex. So:
print __"Hello" . ', ' . __"World!"; # works, but to be avoided
print __"Hello, World!"; # preferred, complete sentence
The the former case, tricks with overloading used by the Log::Report::Message objects will
still make delayed translations work.
In normal situations, it is not a problem to translate interpolated values:
print __"the color is {c}", c => __"red";
Be warned(2) that using "__'Hello'" will produce a syntax error like "String found where
operator expected at .... Can't find string terminator "'" anywhere before EOF". The
first quote is the cause of the complaint, but the second generates the error. In the
early days of Perl, the single quote was used to separate package name from function name,
a role which was later replaced by a double-colon. So "__'Hello'" gets interpreted as
"__::Hello '". Then, there is a trailing single quote which has no counterpart.
N__($msgid)
Label to indicate that the string is a text which will be translated later. The
function itself does nothing. See also N__w().
This no-op function is used as label to the xgettext program to build the translation
tables.
example: how to use N__()
# add three msgids to the translation table
my @colors = (N__"red", N__"green", N__"blue");
my @colors = N__w "red green blue"; # same
print __ $colors[1]; # translate green
# using __(), would work as well
my @colors = (__"red", __"green", __"blue");
print $colors[1];
# however: this will always create all Log::Report::Message objects,
# where maybe only one is used.
N__n($single_msgid, $plural_msgid)
Label to indicate that the two MSGIDs are related, the first as single, the seconds as
its plural. Only used to find the text fragments to be translated. The function
itself does nothing.
example: how to use N__n()
my @save = N__n "save file", "save files";
my @save = (N__n "save file", "save files");
my @save = N__n("save file", "save files");
# be warned about SCALARs in prototype!
print __n @save, $nr_files; # wrong!
print __n $save[0], $save[1], @files, %vars;
N__w(STRING)
This extension to the Locale::TextDomain syntax, is a combined "qw" (list of quoted
words) and N__() into a list of translatable words.
example: of N__w()
my @colors = (N__"red", N__"green", N__"blue");
my @colors = N__w"red green blue"; # same
print __ $colors[1];
__($msgid)
This function (name is two under-score characters) will cause the $msgid to be
replaced by the translations when doing the actual output. Returned is a
Log::Report::Message object, which will be used in translation later. Translating is
invoked when the object gets stringified. When you have no translation tables, the
$msgid will be shown untranslated.
If you need options for Log::Report::Message::new() then use __x(); the prototype of
this function does not permit parameters: it is a prefix operator!
example: how to use __()
print __"Hello World"; # translated into user's language
print __'Hello World'; # syntax error!
print __('Hello World'); # ok, translated
print __"Hello", " World"; # World not translated
my $s = __"Hello World"; # creates object, not yet translated
print ref $s; # Log::Report::Message
print $s; # ok, translated
print $s->toString('fr'); # ok, forced into French
__n($msgid, $plural_msgid, $count, PAIRS)
It depends on the value of $count (and the selected language) which text will be
displayed. When translations can not be performed, then $msgid will be used when
$count is 1, and PLURAL_MSGSID in other cases. However, some languages have more
complex schemes than English.
The PAIRS are options for Log::Report::Message::new() and variables to be filled in.
example: how to use __n()
print __n "one", "more", $a;
print __n("one", "more", $a), "\n";
print +(__n "one", "more", $a), "\n";
# new-lines are ignore at lookup, but printed.
print __n "one\n", "more\n", $a;
# count is in scalar context
# the value is also available as _count
print __n "found one\n", "found {_count}\n", @r;
# ARRAYs and HASHes are counted
print __n "one", "more", \@r;
__nx($msgid, $plural_msgid, $count, PAIRS)
It depends on the value of $count (and the selected language) which text will be
displayed. See details in __n(). After translation, the VARIABLES will be filled-in.
The PAIRS are options for Log::Report::Message::new() and variables to be filled in.
example: how to use __nx()
print __nx "one file", "{_count} files", $nr_files;
print __nx "one file", "{_count} files", @files;
local $" = ', ';
print __nx "one file: {f}", "{_count} files: {f}", @files, f => \@files;
__x($msgid, PAIRS)
Translate the $msgid and then interpolate the VARIABLES in that string. Of course,
translation and interpolation is delayed as long as possible. Both OPTIONS and
VARIABLES are key-value pairs.
The PAIRS are options for Log::Report::Message::new() and variables to be filled in.
__xn($single_msgid, $plural_msgid, $count, $paurs)
Same as __nx(), because we have no preferred order for 'x' and 'n'.
Messages with msgctxt
In Log::Report, the message context (mgsctxt in the PO-files --in the translation tables)
can be used in a very powerful way. Read all about it in Log::Report::Translator::Context
The msgctxt versions of the tranditional gettext infrastructure are far less useful for
Log::Report, because we can easily work with different text domains within the same
program. That should avoid most of the accidental translation conflicts between
components of the code.
Just for compatibility with Locale::TextDomain and completeness, the 'p' versions of above
methods are supported. See examples for these functions in Locale::TextDomain.
Warnings: Functions "N__p()" and "N__np()" seem not to be usable in reality, hence not
implemented. The script xgettext-perl and Log::Report::Extract::PerlPPI (both in the
Log::Report::Lexicon distribution) do not yet support these functions.
__np($msgctxt, $msgid, $plural, count)
__npx($msgctxt, $msgid, $plural, count, PAIRS)
__p($msgctxt, $msgid)
__px($msgctxt, $msgid, PAIRS)
Configuration
$obj->import( [$level,][$domain,] %options )
The import is automatically called when the package is compiled. For all packages but
one in your distribution, it will only contain the name of the $domain.
For one package, the import list may additionally contain textdomain configuration
%options. These %options are used for all packages which use the same $domain. These
are alternatives:
# Do not use variables in the %*config! They are not yet initialized
# when Log::Report->import is run!!!
use Log::Report 'my-domain', %config, %domain_config;
use Log::Report 'my-domain', %config;
textdomain 'my-domain', %domain_config; # vars allowed
The latter syntax has major advantages, when the configuration of the domain is
determined at run-time. It is probably also easier to understand.
See Log::Report::Domain::configure(), for the list of %options for the domain
configuration. Here, we only list the options which are related to the normal import
behavior.
The export $level is a plus (+) followed by a number, for instance +1, to indicate to
on which caller level we need to work. This is used in Log::Report::Optional. It
defaults to '0': my direct caller.
-Option --Default
import undef
message_class Log::Report::Message
mode 'NORMAL'
syntax 'SHORT'
import => FUNCTION|ARRAY
[0.998] When not specified, the "syntax" option determines the list of functions
which are being exported. With this option, the "syntax" option is ignored and only
the specified FUNCTION(s) are imported.
message_class => CLASS
[1.08] Use a more powerful message object class, for instance because your messages
need extra attributes. The provided CLASS must extend Log::Report::Message
mode => LEVEL
This sets the default mode for all created dispatchers. You can also selectively
change the output mode, like
dispatcher PERL => 'default', mode => 3
syntax => 'REPORT'|'SHORT'|'LONG'
The SHORT syntax will add the report abbreviations (like function error()) to your
name-space. Otherwise, each message must be produced with report(). "LONG" is an
alternative to "REPORT": both do not pollute your namespace with the useful abbrev
functions.
example: of import
use Log::Report mode => 3; # '3' or 'DEBUG'
use Log::Report 'my-domain'; # in each package producing messages
use Log::Report 'my-domain' # in one package, top of distr
, mode => 'VERBOSE'
, syntax => 'REPORT' # report ERROR, not error()
, translator => Log::Report::Translator::POT->new
( lexicon => '/home/mine/locale' # translation tables
)
, native_language => 'nl_NL'; # untranslated msgs are Dutch
use Log::Report import => 'try'; # or ARRAY of functions
textdomain( <[$name],$config>|<$name, 'DELETE'|'EXISTS'>|$domain )
[1.00] Without CONFIGuration, this returns the Log::Report::Domain object which
administers the $domain, by default the domain effective in the scope of the package.
A very special case is "DELETE", which will remove the domain configuration. [1.20]
"EXISTS" will check for existence: when it exists, it will be returned, but a domain
will not be automagically created.
[1.20] You may also pass a pre-configured domain.
Reasons
Log::Report->needs( $reason, [$reasons] )
Returns true when the reporter needs any of the $reasons, when any of the active
dispatchers is collecting messages in the specified level. This is useful when the
processing of data for the message is relatively expensive, but for instance only
required in debug mode.
example:
if(Log::Report->needs('TRACE'))
{ my @args = ...expensive calculation...;
trace "your options are: @args";
}
DETAILS
Introduction
Getting messages to users and logs. The distincting concept of this module, is that three
tasks which are strongly related are merged into one simple syntax. The three tasks:
produce some text on a certain condition,
translate it to the proper language, and
deliver it in some way to a user.
Text messages in Perl are produced by commands like "print", "die", "warn", "carp", or
"croak". But where is that output directed to? Translations is hard. There is no clean
exception mechanism.
Besides, the "print"/"warn"/"die" together produce only three different output "levels"
with a message. Think of the variation syslog offers: more than 7 levels. Many people
manually implement their own tricks to get additional levels, like verbose and debug
flags. Log::Report offers that variety.
The (optional) translations use the beautiful syntax defined by Locale::TextDomain, with
some own extensions (of course). A very important difference is that translations are
delayed till the delivery step: until a dispatcher actually writes your message into a
file, sends it to syslog, or shows it on the screen. This means that the pop-up in the
graphical interface of the user may show the text in the language of the user --say
Chinese in utf8--, but at the same time syslog may write the latin1 English version of the
same message.
Background ideas
The following ideas are the base of this implementation:
. simplification
Handling errors and warnings is probably the most labor-intensive task for a
programmer: when programs are written correctly, up-to three-quarters of the code is
related to testing, reporting, and handling (problem) conditions. Simplifying the way
to create reports, simplifies programming and maintenance.
. multiple dispatchers
It is not the location where the (for instance) error occurs which determines what
will happen with the text, but the main application which uses the the complaining
module has control. Messages have a reason. Based on the `reason' classification,
they can get ignored, send to one or multiple dispatchers, like Log::Dispatch,
Log::Log4perl, or UNIX syslog.
. delayed translations
The background ideas are that of Locale::TextDomain, based on "gettext()". However,
in the "Log::Report" infrastructure, translations are postponed until the text is
dispatched to a screen or log-file; the same report can be sent to syslog in (for
instance) English and to the user interface in Dutch.
. context sensitive
Using contexts, you can set-up how to translate or rewrite messages, to improve
messages. A typical problem is whether to use gender in text (use 'his' or 'her'):
you can set a gender in a context, and the use translation tables to pick the right
one.
Error handling models
There are two approaches to handling errors and warnings. In the first approach, as
produced by "die", "warn" and the "carp" family of commands, the program handles the
problem immediately on the location where the problem appears. In the second approach, an
exception is thrown on the spot where the problem is created, and then somewhere else in
the program the condition is handled.
The implementation of exceptions in Perl5 is done with a eval-die pair: on the spot where
the problem occurs, "die" is called. But, because of the execution of that routine is
placed within an "eval", the program as a whole will not die, just the execution of a part
of the program will seize. However, what if the condition which caused the routine to die
is solvable on a higher level? Or what if the user of the code doesn't bother that a part
fails, because it has implemented alternatives for that situation? Exception handling is
quite clumsy in Perl5.
The "Log::Report" set of distributions let modules concentrate on the program flow, and
let the main program decide on the report handling model. The infrastructure to translate
messages into multiple languages, whether to create exceptions or carp/die, to collect
longer explanations with the messages, to log to mail or syslog, and so on, is decided in
pluggable back-ends.
The Reason for the report
Traditionally, perl has a very simple view on error reports: you either have a warning or
an error. However, it would be much clearer for user's and module-using applications,
when a distinction is made between various causes. For instance, a configuration error is
quite different from a disk-full situation. In "Log::Report", the produced reports in the
code tell what is wrong. The main application defines loggers, which interpret the cause
into (syslog) levels.
Defined by "Log::Report" are
. trace (debug, program)
The message will be used when some logger has debugging enabled. The messages show
steps taken by the program, which are of interest by the developers and maintainers of
the code, but not for end-users.
. assert (program)
Shows an unexpected condition, but continues to run. When you want the program to
abort in such situation, that use "panic".
. info (verbose, program)
These messages show larger steps in the execution of the program. Experienced users
of the program usually do not want to see all these intermediate steps. Most programs
will display info messages (and higher) when some "verbose" flag is given on the
command-line.
. notice (program)
An user may need to be aware of the program's accidental smart behavior, for instance,
that it initializes a lasting "Desktop" directory in your home directory. Notices
should be sparse.
. warning (program)
The program encountered some problems, but was able to work around it by smart
behavior. For instance, the program does not understand a line from a log-file, but
simply skips the line.
. mistake (user)
When a user does something wrong, but what is correctable by smart behavior of the
program. For instance, in some configuration file, you can fill-in "yes" or "no", but
the user wrote "yeah". The program interprets this as "yes", producing a mistake
message as warning.
It is much nicer to tell someone that he/she made a mistake, than to call that an
error.
. error (user)
The user did something wrong, which is not automatically correctable or the program is
not willing to correct it automatically for reasons of code quality. For instance, an
unknown option flag is given on the command-line. These are configuration issues, and
have no useful value in $!. The program will be stopped, usually before taken off.
. fault (system)
The program encountered a situation where it has no work-around. For instance, a file
cannot be opened to be written. The cause of that problem can be some user error
(i.e. wrong filename), or external (you accidentally removed a directory yesterday).
In any case, the $! ($ERRNO) variable is set here.
. alert (system)
Some external cause disturbs the execution of the program, but the program stays alive
and will try to continue operation. For instance, the connection to the database is
lost. After a few attempts, the database can be reached and the program continues as
if nothing happened. The cause is external, so $! is set. Usually, a system
administrator needs to be informed about the problem.
. failure (system)
Some external cause makes it impossible for this program to continue. $! is set, and
usually the system administrator wants to be informed. The program will die.
The difference with "fault" is subtile and not always clear. A fault reports an error
returned by an operating system call, where the failure would report an operational
problem, like a failing mount.
. panic (program)
All above report classes are expected: some predictable situation is encountered, and
therefore a message is produced. However, programs often do some internal checking.
Of course, these conditions should never be triggered, but if they do... then we can
only stop.
For instance, in an OO perl module, the base class requires all sub-classes to
implement a certain method. The base class will produce a stub method with triggers a
panic when called. The non-dieing version of this test "assert".
Debugging or being "verbose" are run-time behaviors, and have nothing directly to do with
the type of message which is produced. These two are modes which can be set on the
dispatchers: one dispatcher may be more verbose that some other.
On purpose, we do not use the terms "die" or "fatal", because the dispatcher can be
configured what to do in cause of which condition. For instance, it may decide to stop
execution on warnings as well.
The terms "carp" and "croak" are avoided, because the program cause versus user cause
distinction (warn vs carp) is reflected in the use of different reasons. There is no need
for "confess" and "croak" either, because the dispatcher can be configured to produce
stack-trace information (for a limited sub-set of dispatchers)
Report levels
Various frameworks used with perl programs define different labels to indicate the reason
for the message to be produced.
Perl5 Log::Dispatch Syslog Log4Perl Log::Report
print 0,debug debug debug trace
print 0,debug debug debug assert
print 1,info info info info
warn\n 2,notice notice info notice
warn 3,warning warn warn mistake
carp 3,warning warn warn warning
die\n 4,error err error error
die 5,critical crit fatal fault
croak 6,alert alert fatal alert
croak 7,emergency emerg fatal failure
confess 7,emergency emerg fatal panic
Run modes
The run-mode change which messages are passed to a dispatcher, but from a different angle
than the dispatch filters; the mode changes behavioral aspects of the messages, which are
described in detail in "Processing the message" in Log::Report::Dispatcher. However, it
should behave as you expect: the DEBUG mode shows more than the VERBOSE mode, and both
show more than the NORMAL mode.
. Example: extract run mode from Getopt::Long
The "GetOptions()" function will count the number of "v" options on the command-line when
a "+" is after the option name.
use Log::Report;
use Getopt::Long qw(:config no_ignore_case bundling);
my $mode; # defaults to NORMAL
GetOptions 'v+' => \$mode
, 'verbose=i' => \$mode
, 'mode=s' => \$mode
or exit 1;
dispatcher 'PERL', 'default', mode => $mode;
Now, "-vv" will set $mode to 2, as will "--verbose 2" and "--verbose=2" and
"--mode=ASSERT". Of course, you do not need to provide all these options to the user:
make a choice.
. Example: the mode of a dispatcher
my $mode = dispatcher(find => 'myname')->mode;
. Example: run-time change mode of a dispatcher
To change the running mode of the dispatcher, you can do
dispatcher mode => DEBUG => 'myname';
However, be warned that this does not change the types of messages accepted by the
dispatcher! So: probably you will not receive the trace, assert, and info messages after
all. So, probably you need to replace the dispatcher with a new one with the same name:
dispatcher FILE => 'myname', to => ..., mode => 'DEBUG';
This may reopen connections (depends on the actual dispatcher), which might be not what
you wish to happened. In that case, you must take the following approach:
# at the start of your program
dispatcher FILE => 'myname', to => ...
, accept => 'ALL'; # overrule the default 'NOTICE-' !!
# now it works
dispatcher mode => DEBUG => 'myname'; # debugging on
...
dispatcher mode => NORMAL => 'myname'; # debugging off
Of course, this comes with a small overall performance penalty.
Exceptions
The simple view on live says: you 're dead when you die. However, more complex situations
try to revive the dead. Typically, the "die" is considered a terminating exception, but
not terminating the whole program, but only some logical block. Of course, a wrapper
round that block must decide what to do with these emerging problems.
Java-like languages do not "die" but throw exceptions which contain the information about
what went wrong. Perl modules like "Exception::Class" simulate this. It's a hassle to
create exception class objects for each emerging problem, and the same amount of work to
walk through all the options.
Log::Report follows a simpler scheme. Fatal messages will "die", which is caught with
"eval", just the Perl way (used invisible to you). However, the wrapper gets its hands on
the message as the user has specified it: untranslated, with all unprocessed parameters
still at hand.
try { fault __x "cannot open file {file}", file => $fn };
if($@) # is Log::Report::Dispatcher::Try
{ my $cause = $@->wasFatal; # is Log::Report::Exception
$cause->throw if $cause->message->msgid =~ m/ open /;
# all other problems ignored
}
See Log::Report::Dispatcher::Try and Log::Report::Exception.
Comparison
Some notes on differences between the Log::Report approach and other Perl concepts.
die/warn/Carp
Perl's built-in exception system is very primitive: "die" and "warn". Most programming
languages provide a much more detailed exception mechanism.
A typical perl program can look like this:
my $dir = '/etc';
File::Spec->file_name is_absolute($dir)
or die "ERROR: directory name must be absolute.\n";
-d $dir
or die "ERROR: what platform are you on?";
until(opendir DIR, $dir)
{ warn "ERROR: cannot read system directory $dir: $!";
sleep 60;
}
print "Processing directory $dir\n"
if $verbose;
while(defined(my $file = readdir DIR))
{ if($file =~ m/\.bak$/)
{ warn "WARNING: found backup file $dir/$f\n";
next;
}
die "ERROR: file $dir/$file is binary"
if $debug && -B "$dir/$file";
print "DEBUG: processing file $dir/$file\n"
if $debug;
open FILE, "<", "$dir/$file"
or die "ERROR: cannot read from $dir/$f: $!";
close FILE
or croak "ERROR: read errors in $dir/$file: $!";
}
Where "die", "warn", and "print" are used for various tasks. With "Log::Report", you
would write
use Log::Report;
# can be left-out when there is no debug/verbose
dispatcher PERL => 'default', mode => 'DEBUG';
my $dir = '/etc';
File::Spec->file_name is_absolute($dir)
or mistake "directory name must be absolute";
-d $dir
or panic "what platform are you on?";
until(opendir DIR, $dir)
{ alert "cannot read system directory $dir";
sleep 60;
}
info "Processing directory $dir";
while(defined(my $file = readdir DIR))
{ if($file =~ m/\.bak$/)
{ notice "found backup file $dir/$f";
next;
}
assert "file $dir/$file is binary"
if -B "$dir/$file";
trace "processing file $dir/$file";
unless(open FILE, "<", "$dir/$file")
{ error "no permission to read from $dir/$f"
if $!==ENOPERM;
fault "unable to read from $dir/$f";
}
close FILE
or failure "read errors in $dir/$file";
}
A lot of things are quite visibly different, and there are a few smaller changes. There
is no need for a new-line after the text of the message. When applicable (error about
system problem), then the $! is added automatically.
Log::Dispatch and Log::Log4perl
The two major logging frameworks for Perl are Log::Dispatch and Log::Log4perl; both
provide a pluggable logging interface.
Both frameworks do not have (gettext or maketext) language translation support, which has
various consequences. When you wish for to report in some other language, it must be
translated before the logging function is called. This may mean that an error message is
produced in Chinese, and therefore also ends-up in the syslog file in Chinese. When this
is not your language, you have a problem.
Log::Report translates only in the back-end, which means that the user may get the message
in Chinese, but you get your report in your beloved Dutch. When no dispatcher needs to
report the message, then no time is lost in translating.
With both logging frameworks, you use terminology comparable to syslog: the module
programmer determines the seriousness of the error message, not the application which
integrates multiple modules. This is the way perl programs usually work, but often the
cause for inconsequent user interaction.
Locale::gettext and Locate::TextDomain
Both on GNU gettext based implementations can be used as translation frameworks.
Locale::TextDomain syntax is supported, with quite some extensions. Read the excellent
documentation of Locale::Textdomain. Only the tried access via "$__" and "%__" are not
supported.
The main difference with these modules is the moment when the translation takes place. In
Locale::TextDomain, an "__x()" will result in an immediate translation request via
"gettext()". "Log::Report"'s version of "__x()" will only capture what needs to be
translated in an object. When the object is used in a print statement, only then the
translation will take place. This is needed to offer ways to send different translations
of the message to different destinations.
To be able to postpone translation, objects are returned which stringify into the
translated text.
DIAGNOSTICS
Error: in SCALAR context, only one dispatcher name accepted
The dispatcher() method returns the Log::Report::Dispatcher objects which it has
accessed. When multiple names where given, it wishes to return a LIST of objects, not
the count of them.
SEE ALSO
This module is part of Log-Report distribution version 1.26, built on January 23, 2018.
Website: http://perl.overmeer.net/CPAN/
LICENSE
Copyrights 2007-2018 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 http://dev.perl.org/licenses/