src::mod_perl::docs::api::Apache2::Log(3)

NAME
Apache2::Log - Perl API for Apache Logging Methods

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";

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().

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);

  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:

"Apache2::Const::LOG_EMERG"

"Apache2::Const::LOG_ALERT"

"Apache2::Const::LOG_CRIT"

"Apache2::Const::LOG_ERR"

"Apache2::Const::LOG_WARNING"

"Apache2::Const::LOG_NOTICE"

"Apache2::Const::LOG_INFO"

"Apache2::Const::LOG_DEBUG"

  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:

"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;

"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.

"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

Server Logging Methods

  "$s->log"
get a log handle which can be used to log messages of different levels.

  my $slog = $s->log;

obj: $s ( "Apache2::ServerRec object" )
ret: $slog ( "Apache2::Log::Server" object )
    "Apache2::Log::Server" object to be used with LogLevel methods.

since: 2.0.00

  "$s->log_error"
just logs the supplied message to error_log

  $s->log_error(@message);

obj: $s ( "Apache2::ServerRec object" )
arg1: @message ( strings ARRAY )
    what to log

ret: no return value
since: 2.0.00

For example:

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

  "$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);

obj: $s ( "Apache2::ServerRec object" )
arg1: $file ( string )
    The file in which this function is called

arg2: $line ( number )
    The line number on which this function is called

arg3: $level ( "Apache2::LOG_* constant" )
    The level of this error message

arg4: $status ( "APR::Const status constant" )
    The status code from the last command (similar to $! in perl), usually "APR::Const constant" or coming from an exception object.

arg5: @message ( strings ARRAY )
    The log message(s)

ret: no return value
since: 2.0.00

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");

  "$s->warn"
  $s->warn(@warnings);

is the same as:

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

obj: $s ( "Apache2::ServerRec object" )
arg1: @warnings ( strings ARRAY )
    array of warning strings

ret: no return value
since: 2.0.00

For example:

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

Request Logging Methods

  "$r->log"
get a log handle which can be used to log messages of different levels.

  $rlog = $r->log;

obj: $r ( "Apache2::RequestRec object" )
ret: $rlog ( "Apache2::Log::Request" object )
    "Apache2::Log::Request" object to be used with LogLevel methods.

since: 2.0.00

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

  $r->log_error(@message);

obj: $r ( "Apache2::RequestRec object" )
arg1: @message ( strings ARRAY )
    what to log

ret: no return value
since: 2.0.00

For example:

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

  "$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);

obj: $r ( "Apache2::RequestRec object" )
arg1: $message ( string )
    the message to log

opt arg2: $filename ( string )
    where to report the error as coming from (e.g. "__FILE__")

ret: no return value
since: 2.0.00

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.

  "$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".

since: 2.0.00

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");

  "$r->warn"
  $r->warn(@warnings);

is the same as:

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

obj: $r ( "Apache2::RequestRec object" )
arg1: @warnings ( strings ARRAY )
    array of warning strings

ret: no return value
since: 2.0.00

For example:

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

Other Logging Methods

  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);

obj: $slog ( server or request log handle )
arg1: @message ( strings ARRAY )
ret: no return value
since: 2.0.00

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.

  "alert"
See LogLevel Methods.

  "crit"
See LogLevel Methods.

  "debug"
See LogLevel Methods.

  "emerg"
See LogLevel Methods.

  "error"
See LogLevel Methods.

  "info"
See LogLevel Methods.

  "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.)

  "warn"
See LogLevel Methods.

General Functions

  "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();

ret1: $file ( string )
ret2: $line ( number )
since: 2.0.00

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" ).

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.

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.

  "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);

obj: $p ( "APR::Pool object" )
    The pool to use for logging

arg1: $fname ( file path )
    The name of the file to log to

ret: no return value
since: subject to change

See Also
mod_perl 2.0 documentation.

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

Authors
The mod_perl development team and numerous contributors.