mod_perl logo perl icon
previous page: Apache2::HookRun - Perl API for Invoking Apache HTTP phasespage up: mod_perl 2.0 APInext page: Apache2::MPM - Perl API for accessing Apache MPM information

Apache2::Log - Perl API for Apache Logging Methods






Writing Apache Modules with Perl and C

Writing Apache Modules with Perl and C

By Lincoln Stein, Doug MacEachern
Embedding Perl in HTML with Mason

Embedding Perl in HTML with Mason

By Dave Rolsky, Ken Williams
mod_perl2 User's Guide

mod_perl2 User's Guide

By Stas Bekman, Jim Brandt
Practical mod_perl

Practical mod_perl

By Stas Bekman, Eric Cholet
The mod_perl Developer's Cookbook

The mod_perl Developer's Cookbook

By Geoffrey Young, Paul Lindner, Randy Kobes
mod_perl Pocket Reference

mod_perl Pocket Reference

By Andrew Ford


Table of Contents

Synopsis

  # in startup.pl
  #--------------
  use Apache2::Log;
  
  use Apache2::Const -compile => qw(OK :log);
  use APR::Const    -compile => qw(:error SUCCESS);
  
  my $s = Apache2::ServerUtil->server;
  
  $s->log_error("server: log_error");
  $s->log_serror(__FILE__, __LINE__, Apache2::Const::LOG_ERR,
                 APR::Const::SUCCESS, "log_serror logging at err level");
  $s->log_serror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_DEBUG,
                 APR::Const::ENOTIME, "debug print");
  Apache2::ServerRec->log_error("routine warning");
  
  Apache2::ServerRec::warn("routine warning");

  # in a handler
  #-------------
  package Foo;
  
  use strict;
  use warnings FATAL => 'all';
  
  use Apache2::Log;
  
  use Apache2::Const -compile => qw(OK :log);
  use APR::Const    -compile => qw(:error SUCCESS);
  
  sub handler {
      my $r = shift;
      $r->log_error("request: log_error");
  
      my $rlog = $r->log;
      for my $level qw(emerg alert crit error warn notice info debug) {
          no strict 'refs';
          $rlog->$level($package, "request: $level log level");
      }
  
      # can use server methods as well
      my $s = $r->server;
      $s->log_error("server: log_error");
  
      $r->log_rerror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_DEBUG,
                     APR::Const::ENOTIME, "in debug");
  
      $s->log_serror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_INFO,
                     APR::Const::SUCCESS, "server info");
  
      $s->log_serror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_ERR,
                     APR::Const::ENOTIME, "fatal error");
  
      $r->log_reason("fatal error");
      $r->warn('routine request warning');
      $s->warn('routine server warning');
  
      return Apache2::Const::OK;
  }
  1;

  # in a registry script
  # httpd.conf: PerlOptions +GlobalRequest
  use Apache2::ServerRec qw(warn); # override warn locally
  print "Content-type: text/plain\n\n";
  warn "my warning";


TOP

Description

Apache2::Log provides the Perl API for Apache logging methods.

Depending on the the current LogLevel setting, only logging with the same log level or higher will be loaded. For example if the current LogLevel is set to warning, only messages with log level of the level warning or higher (err, crit, elert and emerg) will be logged. Therefore this:

  $r->log_rerror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_WARNING,
                 APR::Const::ENOTIME, "warning!");

will log the message, but this one won't:

  $r->log_rerror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_INFO,
                 APR::Const::ENOTIME, "just an info");

It will be logged only if the server log level is set to info or debug. LogLevel is set in the configuration file, but can be changed using the $s->loglevel() method.

The filename and the line number of the caller are logged only if Apache2::Const::LOG_DEBUG is used (because that's how Apache 2.0 logging mechanism works).

Note: On Win32 Apache attempts to lock all writes to a file whenever it's opened for append (which is the case with logging functions), as Unix has this behavior built-in, while Win32 does not. Therefore Apache2::Log functions could be slower than Perl's print()/warn().



TOP

Constants

Log level constants can be compiled all at once:

  use Apache2::Const -compile => qw(:log);

or individually:

  use Apache2::Const -compile => qw(LOG_DEBUG LOG_INFO);


TOP

LogLevel Constants

The following constants (sorted from the most severe level to the least severe) are used in logging methods to specify the log level at which the message should be logged:



TOP

Apache2::Const::LOG_EMERG



TOP

Apache2::Const::LOG_ALERT



TOP

Apache2::Const::LOG_CRIT



TOP

Apache2::Const::LOG_ERR



TOP

Apache2::Const::LOG_WARNING



TOP

Apache2::Const::LOG_NOTICE



TOP

Apache2::Const::LOG_INFO



TOP

Apache2::Const::LOG_DEBUG



TOP

Other Constants

Make sure to compile the APR status constants before using them. For example to compile APR::Const::SUCCESS and all the APR error status constants do:

  use APR::Const    -compile => qw(:error SUCCESS);

Here is the rest of the logging related constants:



TOP

Apache2::Const::LOG_LEVELMASK

used to mask off the level value, to make sure that the log level's value is within the proper bits range. e.g.:

  $loglevel &= LOG_LEVELMASK;


TOP

Apache2::Const::LOG_TOCLIENT

used to give content handlers the option of including the error text in the ErrorDocument sent back to the client. When Apache2::Const::LOG_TOCLIENT is passed to log_rerror() the error message will be saved in the $r's notes table, keyed to the string "error-notes", if and only if the severity level of the message is Apache2::Const::LOG_WARNING or greater and there are no other "error-notes" entry already set in the request record's notes table. Once the "error-notes" entry is set, it is up to the error handler to determine whether this text should be sent back to the client. For example:

  use Apache2::Const -compile => qw(:log);
  use APR::Const    -compile => qw(ENOTIME);
  $r->log_rerror(Apache2::Log::LOG_MARK,
                 Apache2::Const::LOG_ERR|Apache2::Const::LOG_TOCLIENT,
                 APR::Const::ENOTIME,
                 "request log_rerror");

now the log message can be retrieved via:

  $r->notes->get("error-notes");

Remember that client-generated text streams sent back to the client MUST be escaped to prevent CSS attacks.



TOP

Apache2::Const::LOG_STARTUP

is useful for startup message where no timestamps, logging level is wanted. For example:

  use Apache2::Const -compile => qw(:log);
  use APR::Const    -compile => qw(SUCCESS);
  $s->log_serror(Apache2::Log::LOG_MARK,
                 Apache2::Const::LOG_INFO,
                 APR::Const::SUCCESS,
                 "This log message comes with a header");

will print:

  [Wed May 14 16:47:09 2003] [info] This log message comes with a header

whereas, when Apache2::Const::LOG_STARTUP is binary ORed as in:

  use Apache2::Const -compile => qw(:log);
  use APR::Const    -compile => qw(SUCCESS);
  $s->log_serror(Apache2::Log::LOG_MARK,
                 Apache2::Const::LOG_INFO|Apache2::Const::LOG_STARTUP,
                 APR::Const::SUCCESS,
                 "This log message comes with no header");

then the logging will be:

  This log message comes with no header


TOP

Server Logging Methods



TOP

$s->log

get a log handle which can be used to log messages of different levels.

  my $slog = $s->log;


TOP

$s->log_error

just logs the supplied message to error_log

  $s->log_error(@message);

For example:

  $s->log_error("running low on memory");


TOP

$s->log_serror

This function provides a fine control of when the message is logged, gives an access to built-in status codes.

  $s->log_serror($file, $line, $level, $status, @message);

For example:

  use Apache2::Const -compile => qw(:log);
  use APR::Const    -compile => qw(ENOTIME SUCCESS);
  $s->log_serror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_ERR,
                 APR::Const::SUCCESS, "log_serror logging at err level");
  
  $s->log_serror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_DEBUG,
                 APR::Const::ENOTIME, "debug print");


TOP

$s->warn

  $s->warn(@warnings);

is the same as:

  $s->log_serror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_WARNING,
                 APR::Const::SUCCESS, @warnings)

For example:

  $s->warn('routine server warning');


TOP

Request Logging Methods



TOP

$r->log

get a log handle which can be used to log messages of different levels.

  $rlog = $r->log;


TOP

$r->log_error

just logs the supplied message (similar to $s->log_error ).

  $r->log_error(@message);

For example:

  $r->log_error("the request is about to end");


TOP

$r->log_reason

This function provides a convenient way to log errors in a preformatted way:

  $r->log_reason($message);
  $r->log_reason($message, $filename);

For example:

  $r->log_reason("There is no enough data");

will generate a log entry similar to the following:

  [Fri Sep 24 11:58:36 2004] [error] access to /someuri
  failed for 127.0.0.1, reason: There is no enough data.


TOP

$r->log_rerror

This function provides a fine control of when the message is logged, gives an access to built-in status codes.

  $r->log_rerror($file, $line, $level, $status, @message);

arguments are identical to $s->log_serror.

For example:

  use Apache2::Const -compile => qw(:log);
  use APR::Const    -compile => qw(ENOTIME SUCCESS);
  $r->log_rerror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_ERR,
                 APR::Const::SUCCESS, "log_rerror logging at err level");
  
  $r->log_rerror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_DEBUG,
                 APR::Const::ENOTIME, "debug print");


TOP

$r->warn

  $r->warn(@warnings);

is the same as:

  $r->log_rerror(Apache2::Log::LOG_MARK, Apache2::Const::LOG_WARNING,
                 APR::Const::SUCCESS, @warnings)

For example:

  $r->warn('routine server warning');


TOP

Other Logging Methods



TOP

LogLevel Methods

after getting the log handle with $s->log or $r->log, use one of the following methods (corresponding to the LogLevel levels):

  emerg(), alert(), crit(), error(), warn(), notice(), info(), debug()

to control when messages should be logged:

  $s->log->emerg(@message);
  $r->log->emerg(@message);

For example if the LogLevel is error and the following code is executed:

  my $slog = $s->log;
  $slog->debug("just ", "some debug info");
  $slog->warn(@warnings);
  $slog->crit("dying");

only the last command's logging will be performed. This is because warn, debug and other logging command which are listed right to error will be disabled.



TOP

alert

See LogLevel Methods.



TOP

crit

See LogLevel Methods.



TOP

debug

See LogLevel Methods.



TOP

emerg

See LogLevel Methods.



TOP

error

See LogLevel Methods.



TOP

info

See LogLevel Methods.



TOP

notice

See LogLevel Methods.

Though Apache treats notice() calls as special. The message is always logged regardless the value of ErrorLog, unless the error log is set to use syslog. (For details see httpd-2.0/server/log.c.)



TOP

warn

See LogLevel Methods.



TOP

General Functions



TOP

LOG_MARK

Though looking like a constant, this is a function, which returns a list of two items: (__FILE__, __LINE__), i.e. the file and the line where the function was called from.

  my ($file, $line) = Apache2::Log::LOG_MARK();

It's mostly useful to be passed as the first argument to those logging methods, expecting the filename and the line number as the first arguments (e.g., $s->log_serror and $r->log_rerror ).



TOP

Virtual Hosts

Code running from within a virtual host needs to be able to log into its ErrorLog file, if different from the main log. Calling any of the logging methods on the $r and $s objects will do the logging correctly.

If the core warn() is called, it'll be always logged to the main log file. Here is how to make it log into the vhost error_log file. Let's say that we start with the following code:

  warn "the code is smoking";
  1. First, we need to use mod_perl's logging function, instead of CORE::warn

    Either replace warn with Apache2::ServerRec::warn:

      use Apache2::Log ();
      Apache2::ServerRec::warn("the code is smoking");

    or import it into your code:

      use Apache2::ServerRec qw(warn); # override warn locally
      warn "the code is smoking";

    or override CORE::warn:

      use Apache2::Log ();
      *CORE::GLOBAL::warn = \&Apache2::ServerRec::warn;
      warn "the code is smoking";

    Avoid using the latter suggestion, since it'll affect all the code running on the server, which may break things. Of course you can localize that as well:

      use Apache2::Log ();
      local *CORE::GLOBAL::warn = \&Apache2::ServerRec::warn;
      warn "the code is smoking";

    Chances are that you need to make the internal Perl warnings go into the vhost's error_log file as well. Here is how to do that:

      use Apache2::Log ();
      local $SIG{__WARN__} = \&Apache2::ServerRec::warn;
      eval q[my $x = "aaa" + 1;]; # this issues a warning

    Notice that it'll override any previous setting you may have had, disabling modules like CGI::Carp which also use $SIG{__WARN__}

  2. Next we need to figure out how to get hold of the vhost's server object.

    Inside HTTP request handlers this is possible via Apache2->request. Which requires either PerlOptions +GlobalRequest setting or can be also done at runtime if $r is available:

      use Apache2::RequestUtil ();
      sub handler {
          my $r = shift;
          Apache2::RequestUtil->request($r);
          ...

    Outside HTTP handlers at the moment it is not possible, to get hold of the vhost's error_log file. This shouldn't be a problem for the code that runs only under mod_perl, since the always available $s object can invoke a plethora of methods supplied by Apache2::Log. This is only a problem for modules, which are supposed to run outside mod_perl as well.

    META: To solve this we think to introduce 'PerlOptions +GlobalServer', a big brother for 'PerlOptions +GlobalRequest', which will be set in modperl_hook_pre_connection.



TOP

Unsupported API

Apache2::Log also provides auto-generated Perl interface for a few other methods which aren't tested at the moment and therefore their API is a subject to change. These methods will be finalized later as a need arises. If you want to rely on any of the following methods please contact the the mod_perl development mailing list so we can help each other take the steps necessary to shift the method to an officially supported API.



TOP

log_pid

META: what is this method good for? it just calls getpid and logs it. In any case it has nothing to do with the logging API. And it uses static variables, it probably shouldn't be in the Apache public API.

Log the current pid

  Apache2::Log::log_pid($pool, $fname);


TOP

See Also

mod_perl 2.0 documentation.



TOP

Copyright

mod_perl 2.0 and its core modules are copyrighted under The Apache Software License, Version 2.0.



TOP

Authors

The mod_perl development team and numerous contributors.






TOP
previous page: Apache2::HookRun - Perl API for Invoking Apache HTTP phasespage up: mod_perl 2.0 APInext page: Apache2::MPM - Perl API for accessing Apache MPM information