mod_perl - Embed a Perl interpreter in the Apache HTTP
server
DESCRIPTION
The Apache/Perl integration project brings together the
full power of the Perl programming language and the Apache
HTTP server. This is achieved by linking the Perl runtime
library into the server and providing an object oriented
Perl interface to the server's C language API. These
pieces are seamlessly glued together by the `mod_perl'
server plugin, making it is possible to write Apache mod
ules entirely in Perl. In addition, the persistent inter
preter embedded in the server avoids the overhead of
starting an external interpreter and the penalty of Perl
start-up (compile) time.
Without question, the most popular Apache/Perl module is
Apache::Registry module. This module emulates the CGI
environment, allowing programmers to write scripts that
run under CGI or mod_perl without change. Existing CGI
scripts may require some changes, simply because a CGI
script has a very short lifetime of one HTTP request,
allowing you to get away with "quick and dirty" scripting.
Using mod_perl and Apache::Registry requires you to be
more careful, but it also gives new meaning to the work
"quick"! Apache::Registry maintains a cache of compiled
scripts, which happens the first time a script is accessed
by a child server or once again if the file is updated on
disk.
Although it may be all you need, a speedy CGI replacement
is only a small part of this project. Callback hooks are
in place for each stage of a request. Apache-Perl modules
may step in during the handler, header parser, uri trans
late, authentication, authorization, access, type check,
fixup and logger stages of a request.
FAQ
The mod_perl FAQ is maintained by Frank Cringle
<fdc@cliwe.ping.de>: http://perl.apache.org/faq/
Apache/Perl API
See 'perldoc Apache' for info on how to use the Perl-
Apache API.
See the lib/ directory for example modules and the apache-
modlist.html manpage for a comprehensive list.
See the eg/ directory for example scripts.
mod_perl
For using mod_perl as a CGI replacement see the the
cgi_to_mod_perl manpage document.
PerlModule Apache::SSI SomeOther::Module
Optionally:
PerlRequire perl-scripts/script_to_load_at_startup.pl
A PerlRequire file is commonly used for intialization dur
ing server startup time. A PerlRequire file name can be
absolute or relative to ServerRoot or a path in `@INC'.
A PerlRequire'd file must return a true value, i.e., the
end of this file should have a:
1; #return true value
See eg/startup.pl for an example to start with.
In an httpd.conf <Location /foo> or .htaccess you need:
PerlHandler sub_routine_name
This is the name of the subroutine to call to handle each
request. e.g. in the PerlModule Apache::Registry this is
"Apache::Registry::handler".
If PerlHandler is not a defined subroutine, mod_perl
assumes it is a package name which defines a subroutine
named "handler".
PerlHandler Apache::Registry
Would load Registry.pm (if it is not already) and call
it's subroutine "handler".
There are several stages of a request where the Apache API
allows a module to step in and do something. The Apache
documentation will tell you all about those stages and
what your modules can do. By default, these hooks are
disabled at compile time, see the INSTALL document for
information on enabling these hooks. The following con
figuration directives take one argument, which is the name
of the subroutine to call. If the value is not a subrou
tine name, mod_perl assumes it is a package name which
implements a 'handler' subroutine.
PerlPostReadRequestHandler (requires apache_1.3.0 or higher)
PerlInitHandler
PerlTransHandler
PerlHeaderParserHandler
PerlAccessHandler
PerlAuthenHandler
PerlAuthzHandler
PerlTypeHandler
PerlFixupHandler
PerlHandler
PerlLogHandler
PerlCleanupHandler
PerlChildExitHandler (requires apache_1.3.0 or higher)
Only ChildInit, ChildExit, PostReadRequest and Trans han
dlers are not allowed in .htaccess files.
Modules can check if the code is being run in the parent
server during startup by checking the
$Apache::Server::Starting variable.
RESTARTING
PerlFreshRestart
By default, if a server is restarted (ala kill -USR1
`cat logs/httpd.pid`), Perl scripts and modules are
not reloaded. To reload PerlRequire's, PerlModule's,
other use()'d modules and flush the Apache::Registry
cache, enable with this command:
PerlFreshRestart On
PERL_DESTRUCT_LEVEL
With Apache versions 1.3.0 and higher, mod_perl will
call the perl_destruct() Perl API function during the
child exit phase. This will cause proper execution of
END blocks found during server startup along with
invoking the DESTROY method on global objects who are
still alive. It is possible that this operation may
take a long time to finish, causing problems during a
restart. If your code does not contain and END blocks
or DESTROY methods which need to be run during child
server shutdown, this destruction can be avoided by
setting the PERL_DESTRUCT_LEVEL environment variable
to `-1'.
ENVIRONMENT
Under CGI the Perl hash `%ENV' is magical in that it
inherits environment variables from the parent process and
will set them should a process spawn a child. However,
with mod_perl we're in the parent process that would nor
mally setup the common environment variables before spawn
ing a CGI process. Therefore, mod_perl must feed these
happen until the response stage of a request when `Perl
Handler' is called. If you wish to set variables that
will be available before then, such as for a `PerlAuthen
Handler', you may use the `PerlSetEnv' configuration
directive:
PerlSetEnv SomeKey SomeValue
You may also use the `PerlPassEnv' directive to pass an
already existing environment variable to Perl's `%ENV':
PerlPassEnv SomeKey
CONFIGURATION
The `PerlSetVar' directive provides a simple mechanism
for passing information from configuration files to
Perl modules or Registry scripts:
PerlSetVar SomeKey SomeValue
Perl modules or scripts retrieve configuration values
using the `$r->dir_config' method (see 'perldoc
Apache').
`PerlSetVar' handles keys case-insensitively.
GATEWAY_INTERFACE
The standard CGI environment variable GATEWAY_INTER
FACE is set to `CGI-Perl/1.1' when running under
mod_perl.
MOD_PERL
The environment variable `MOD_PERL' is set so scripts
can say:
if(exists $ENV{MOD_PERL}) {
#we're running under mod_perl
...
}
else {
#we're NOT running under mod_perl
}
BEGIN blocks
Perl executes `BEGIN' blocks during the compile time of
code as soon as possible. The same is true under
mod_perl. However, since mod_perl normally only compiles
scripts and modules once, in the parent server or once
per-child, `BEGIN' blocks in that code will only be run
once. As the perlmod manpage explains, once a `BEGIN' has
run, it is immediately undefined. In the mod_perl
during each incoming request unless that request happens
to be one that is compiling the code.
Modules and files pulled in via require/use which contain
`BEGIN' blocks will be executed:
- only once, if pulled in by the parent process
- once per-child process if not pulled in by the parent
process
- an additional time, once per-child process if the mod
ule is pulled in off of disk again via Apache::StatINC
- an additional time, in the parent process on each
restart if PerlFreshRestart is On
- unpredictable if you fiddle with `%INC' yourself
Apache::Registry scripts which contain `BEGIN' blocks will
be executed:
- only once, if pulled in by the parent process via
Apache::RegistryLoader
- once per-child process if not pulled in by the parent
process
- an additional time, once per-child process if the
script file has changed on disk
- an additional time, in the parent process on each
restart if pulled in by the
parent process via Apache::RegistryLoader and Perl
FreshRestart is On
END blocks
As the perlmod manpage explains, an `END' subroutine is
executed as late as possible, that is, when the inter
preter is being exited. In the mod_perl environment, the
interpreter does not exit until the server is shutdown.
However, mod_perl does make a special case for
Apache::Registry scripts.
Normally, `END' blocks are executed by Perl during it's
`perl_run()' function, which is called once each time the
Perl program is executed, e.g. once per (mod_cgi) CGI
scripts. However, mod_perl only calls `perl_run()' once,
during server startup. Any `END' blocks encountered dur
ing main server startup, i.e. those pulled in by the Perl
Require or by any PerlModule are suspended and run at
server shutdown, aka `child_exit' (requires apache
1.3.0+). Any `END' blocks that are encountered during
compilation of Apache::Registry scripts are called after
the script done is running, including subsequent invoca
tions when the script is cached in memory. All other
`END' blocks encountered during other Perl*Handler call
backs, e.g. PerlChildInitHandler, will be suspended while
the process is running and called during `child_exit' when
the process is shutting down. Module authors may be wish
to use `$r->register_cleanup' as an alternative to `END'
blocks if this behavior is not desirable.
Don't be alarmed by the size of your httpd after you've
linked with mod_perl. No matter what, your httpd will be
larger than normal to start, simply because you've linked
with perl's runtime.
Here's I'm just running
% /usr/bin/perl -e '1 while 1'
PID USERNAME PRI NICE SIZE RES STATE TIME WCPU CPU COMMAND
10214 dougm 67 0 668K 212K run 0:04 71.55% 21.13% perl
Now with a few random modules:
% /usr/bin/perl -MDBI -MDBD::mSQL -MLWP::UserAgent -MFileHandle -MIO -MPOSIX -e '1 while 1'
10545 dougm 49 0 3732K 3340K run 0:05 54.59% 21.48% perl
Here's my httpd linked with libperl.a, not having served a
single request:
10386 dougm 5 0 1032K 324K sleep 0:00 0.12% 0.11% httpd-a
You can reduce this if you configure perl 5.004+ with
-Duseshrplib. Here's my httpd linked with libperl.sl, not
having served a single request:
10393 dougm 5 0 476K 368K sleep 0:00 0.12% 0.10% httpd-s
Now, once the server starts receiving requests, the embed
ded interpreter will compile code for each 'require' file
it has not seen yet, each new Apache::Registry subroutine
that's compiled, along with whatever modules it's use'ing
or require'ing. Not to mention AUTOLOADing. (Modules
that you 'use' will be compiled when the server starts
unless they are inside an eval block.) httpd will grow
just as big as our /usr/bin/perl would, or a CGI process
for that matter, it all depends on your setup. The the
mod_perl_tuning manpage document gives advice on how to
best setup your mod_perl server environment.
The mod_perl INSTALL document explains how to build the
Apache:: extensions as shared libraries (with 'perl Make
file.PL DYNAMIC=1'). This may save you some memory, how
ever, it doesn't work on a few systems such as aix and
unixware.
However, on most systems, this strategy will only make the
httpd look smaller. When in fact, an httpd with Perl
linked static with take up less real memory and preform
faster than shared libraries at the same time. See the
the mod_perl_tuning manpage document for details.
Leaks
If you are using a module that leaks or have code of
their own that leaks, in any case using the apache
configuration directive 'MaxRequestsPerChild' is your
best bet to keep the size down.
Perl Options
Newer Perl versions also have other options to reduce
runtime memory consumption. See Perl's INSTALL file
for details on `-DPACK_MALLOC' and `-DTWO_POT_OPTI
MIZE'. With these options, my httpd shrinks down
~150K.
Server Startup
Use the PerlRequire and PerlModule directives to load
commonly used modules such as CGI.pm, DBI, etc., when
the server is started. On most systems, server chil
dren will be able to share this space.
Importing Functions
When possible, avoid importing of a module functions
into your namespace. The aliases which are created
can take up quite a bit of space. Try to use method
interfaces and fully qualified Package::function names
instead. Here's a freshly started httpd who's served
one request for a script using the CGI.pm method
interface:
TTY PID USERNAME PRI NI SIZE RES STATE TIME %WCPU %CPU COMMAND
p4 5016 dougm 154 20 3808K 2636K sleep 0:01 9.62 4.07 httpd
Here's a freshly started httpd who's served one
request for the same script using the CGI.pm function
interface:
TTY PID USERNAME PRI NI SIZE RES STATE TIME %WCPU %CPU COMMAND
p4 5036 dougm 154 20 3900K 2708K sleep 0:01 3.19 2.18 httpd
Now do the math: take that difference, figure in how
many other scripts import the same functions and how
many children you have running. It adds up!
Global Variables
It's always a good idea to stay away from global vari
ables when possible. Some variables must be global so
Perl can see them, such as a module's @ISA or $VERSION
variables. In common practice, a combination of `use
strict' and `use vars' keeps modules clean and reduces
a bit of noise. However, use vars also creates
aliases as the Exporter does, which eat up more space.
When possible, try to use fully qualified names
package MyPackage;
use strict;
@MyPackage::ISA = qw(...);
$MyPackage::VERSION = "1.00";
vs.
package MyPackage;
use strict;
use vars qw(@ISA $VERSION);
@ISA = qw(...);
$VERSION = "1.00";
Further Reading
In case I forgot to mention, read Vivek Khera's the
mod_perl_tuning manpage document for more tips on
improving Apache/mod_perl performance.
SWITCHES
Normally when you run perl from the command line or have
the shell invoke it with `#!', you may choose to pass perl
switch arguments such as `-w' or `-T'. Since the command
line is only parsed once, when the server starts, these
switches are unavailable to mod_perl scripts. However,
most command line arguments have a perl special variable
equivilant. For example, the `$^W' variable coresponds to
the `-w' switch. Consult the perlvar manpage for more
details. With mod_perl it is also possible to turn on
warnings globaly via the PerlWarn directive:
PerlWarn On
The switch which enables taint checks does not have a spe
cial variable, so mod_perl provides the PerlTaintCheck
directive to turn on taint checks. In httpd.conf, enable
with:
PerlTaintCheck On
Now, any and all code compiled inside httpd will be
checked.
The environment variable PERL5OPT can be used to set addi
tional perl startup flags such as -d and -D. See the
perlrun manpage.
PERSISTENT DATABASE CONNECTIONS
Another popular use of mod_perl is to take advantage of
it's persistance to maintain open database connections.
The basic idea goes like so:
use strict;
use vars qw($dbh);
$dbh ||= SomeDbPackage->connect(...);
Since `$dbh' is a global variable, it will not go out of
scope, keeping the connection open for the lifetime of a
server process, establishing it during the script's first
request for that process.
It's recommended that you use one of the Apache::*
database connection wrappers. Currently for DBI users
there is `Apache::DBI' and for Sybase users
`Apache::Sybase::DBlib'. These modules hide the peculiar
code example above. In addition, different scripts may
share a connection, minimizing resource consumption.
Example:
#httpd.conf has
# PerlModule Apache::DBI
#DBI scripts look exactly as they do under CGI
use strict;
my $dbh = DBI->connect(...);
Although $dbh shown here will go out of scope when the
script ends, the Apache::DBI module's reference to it does
not, keep the connection open.
WARNING: Do not attempt to open a persistent database con
nection in the parent process (via PerlRequire or PerlMod
ule). If you do, children will get a copy of this handle,
causing clashes when the handle is used by two processes
at the same time. Each child must have it's own unique
connection handle.
STACKED HANDLERS
With the mod_perl stacked handlers mechanism, it is possi
ble for more than one Perl*Handler to be defined and run
during each stage of a request.
Perl*Handler directives can define any number of subrou
tines, e.g. (in config files)
PerlTransHandler OneTrans TwoTrans RedTrans BlueTrans
With the method, Apache->push_handlers, callbacks can be
added to the stack by scripts at runtime by mod_perl
scripts.
Apache->push_handlers takes the callback hook name as it's
first argument and a subroutine name or reference as it's
second. e.g.:
$r->push_handlers("PerlLogHandler", sub {
print STDERR "__ANON__ called\n";
return 0;
});
After each request, this stack is cleared out.
All handlers will be called unless a handler returns a
status other than OK or DECLINED, this needs to be consid
ered more. Post apache-1.2 will have a DONE return code
to signal termiation of a stage, which Rob and I came up
with while back when first discussing the idea of stacked
handlers. 2.0 won't come for quite sometime, so mod_perl
will most likely handle this before then.
example uses:
CGI.pm maintains a global object for it's plain function
interface. Since the object is global, it does not go out
of scope, DESTROY is never called. CGI->new can call:
Apache->push_handlers("PerlCleanupHandler", \&CGI::_reset_globals);
This function will be called during the final stage of a
request, refreshing CGI.pm's globals before the next
request comes in.
Apache::DCELogin establishes a DCE login context which
must exist for the lifetime of a request, so the
DCE::Login object is stored in a global variable. Without
stacked handlers, users must set
PerlCleanupHandler Apache::DCELogin::purge
in the configuration files to destroy the context. This
is not "user-friendly". Now, Apache::DCELogin::handler
can call:
Apache->push_handlers("PerlCleanupHandler", \&purge);
Persistent database connection modules such as Apache::DBI
could push a PerlCleanupHandler handler that iterates over
%Connected, refreshing connections or just checking that
ones have not gone stale. Remember, by the time we get to
PerlCleanupHandler, the client has what it wants and has
gone away, we can spend as much time as we want here with
out slowing down response time to the client.
PerlTransHandlers may decide, based or uri or other condi
tion, whether or not to handle a request, e.g.
Apache::MsqlProxy. Without stacked handlers, users must
configure:
PerlHandler Apache::MsqlProxy
PerlHandler is never actually invoked unless translate()
sees the request is a proxy request ($r->proxyreq), if it
is a proxy request, translate() set $r->handler("perl-
script"), only then will PerlHandler handle the request.
Now, users do not have to specify 'PerlHandler
Apache::MsqlProxy', the translate() function can set it
with push_handlers().
Includes, footers, headers, etc., piecing together a docu
ment, imagine (no need for SSI parsing!):
PerlHandler My::Header Some::Body A::Footer
This was my first test:
#My.pm
package My;
sub header {
my $r = shift;
$r->content_type("text/plain");
$r->send_http_header;
$r->print("header text\n");
}
sub body { shift->print("body text\n") }
sub footer { shift->print("footer text\n") }
1;
__END__
#in config
<Location /foo>
SetHandler "perl-script"
PerlHandler My::header My::body My::footer
</Location>
Parsing the output of another PerlHandler? this is a lit
tle more tricky, but consider:
<Location /foo>
SetHandler "perl-script"
PerlHandler OutputParser SomeApp
</Location>
<Location /bar>
SetHandler "perl-script"
PerlHandler OutputParser AnotherApp
</Location>
Now, OutputParser goes first, but it untie's *STDOUT and
re-tie's to it's own package like so:
package OutputParser;
my $r = shift;
untie *STDOUT;
tie *STDOUT => 'OutputParser', $r;
}
sub TIEHANDLE {
my($class, $r) = @_;
bless { r => $r}, $class;
}
sub PRINT {
my $self = shift;
for (@_) {
#do whatever you want to $_
$self->{r}->print($_ . "[insert stuff]");
}
}
1;
__END__
To build in this feature, configure with:
% perl Makefile.PL PERL_STACKED_HANDLERS=1 [PERL_FOO_HOOK=1,etc]
Another method 'Apache->can_stack_handlers' will return
TRUE if mod_perl was configured with PERL_STACKED_HAN
DLERS=1, FALSE otherwise.
PERL METHOD HANDLERS
See the mod_perl_method_handlers manpage.
PERL SECTIONS
With <Perl></Perl> sections, it is possible to configure
your server entirely in Perl.
<Perl> sections can contain *any* and as much Perl code as
you wish. These sections are compiled into a special
package who's symbol table mod_perl can then walk and
grind the names and values of Perl variables/structures
through the Apache core config gears. Most of the con
figurations directives can be represented as `$Scalars' or
`@Lists'. A `@List' inside these sections is simply con
verted into a single-space delimited string for you
inside. Here's an example:
#httpd.conf
<Perl>
@PerlModule = qw(Mail::Send Devel::Peek);
#run the server as whoever starts it
$User = getpwuid($>) || $>;
$Group = getgrgid($)) || $);
</Perl>
Block sections such as <Location></Location> are repre
sented in a `%Hash', e.g.:
$Location{"/~dougm/"} = {
AuthUserFile => '/tmp/htpasswd',
AuthType => 'Basic',
AuthName => 'test',
DirectoryIndex => [qw(index.html index.htm)],
Limit => {
METHODS => 'GET POST',
require => 'user dougm',
},
};
#If a Directive can take say, two *or* three arguments
#you may push strings and the lowest number of arguments
#will be shifted off the @List
#or use array reference to handle any number greater than
#the minimum for that directive
push @Redirect, "/foo", "http://www.foo.com/";
push @Redirect, "/imdb", "http://www.imdb.com/";
push @Redirect, [qw(temp "/here" "http://www.there.com")];
Other section counterparts include `%VirtualHost',
`%Directory' and `%Files'.
These are somewhat boring examples, but they should give
you the basic idea. You can mix in any Perl code your
heart desires. See eg/httpd.conf.pl and eg/perl_sec
tions.txt for some examples.
A tip for syntax checking outside of httpd:
<Perl>
#!perl
#... code here ...
__END__
</Perl>
Now you may run `perl -cx httpd.conf'.
It may be the case that <Perl> sections are not completed
or an oversight was made in an certain area. If they do
not behave as you expect, please send a report to the mod
perl mailing list.
'perl Makefile.PL PERL_SECTIONS=1'
mod_perl and mod_include integration
As of apache 1.2.0, mod_include can handle Perl callbacks.
A `sub' key value may be anything a Perl*Handler can be:
subroutine name, package name (defaults to package::han
dler), Class->method call or anonymous sub {}
Example:
Child <!--#perl sub="sub {print $$}" --> accessed
<!--#perl sub="sub {print ++$Access::Cnt }" --> times. <br>
<!--#perl sub="Package::handler" arg="one" arg="two" -->
#don't forget to escape double quotes!
Perl is
<!--#perl sub="sub {for (0..10) {print \"very \"}}"-->
fun to use!
The Apache::Include module makes it simple to include
Apache::Registry scripts with the mod_include perl direc
tive.
Example:
<!--#perl sub="Apache::Include" arg="/perl/ssi.pl" -->
You can also use 'virtual include' to include Apache::Reg
istry scripts of course. However, using #perl will save
the overhead of making Apache go through the motions of
creating/destroying a subrequest and making all the neces
sary access checks to see that the request would be
allowed outside of a 'virtual include' context.
To enable perl in mod_include parsed files, when building
apache the following must be present in the Configuration
file:
EXTRA_CFLAGS=-DUSE_PERL_SSI -I. `perl -MExtUtils::Embed -ccopts`
mod_perl's Makefile.PL script can take care of this for
you as well:
perl Makefile.PL PERL_SSI=1
If you're interested in sprinkling Perl code inside your
HTML documents, you'll also want to look at the
Apache::Embperl (http://perl.apache.org/embperl/),
Apache::ePerl and Apache::SSI modules.
MOD_PERL_TRACE
To enable mod_perl debug tracing configure mod_perl
with the PERL_TRACE option:
perl Makefile.PL PERL_TRACE=1
The trace levels can then be enabled via the
MOD_PERL_TRACE environment variable which can contain
any combination of:
d - Trace directive handling during configuration read
s - Trace processing of perl sections
h - Trace Perl*Handler callbacks
g - Trace global variable handling, intepreter construction, END blocks, etc.
all - all of the above
spinning httpds
To see where an httpd is "spinning", try adding this
to your script or a startup file:
use Carp ();
$SIG{'USR1'} = sub {
Carp::confess("caught SIGUSR1!");
};
Then issue the command line:
kill -USR1 <spinning_httpd_pid>
PROFILING
It is possible to profile code run under mod_perl with the
Devel::DProf module available on CPAN. However, you must
have apache version 1.3.0 or higher and the `PerlChildEx
itHandler' enabled. When the server is started,
Devel::DProf installs an `END' block to write the tmon.out
file, which will be run when the server is shutdown.
Here's how to start and stop a server with the profiler
enabled:
% setenv PERL5OPT -d:DProf
% httpd -X -d `pwd` &
... make some requests to the server here ...
% kill `cat logs/httpd.pid`
% unsetenv PERL5OPT
% dprofpp
See also: Apache::DProf
BENCHMARKING
How much faster is mod_perl that CGI? There are many ways
to benchmark the two, see the `benchmark/' directory for
See also: Apache::Timeit
WARNINGS
See the mod_perl_traps manpage.
SUPPORT
See the the SUPPORT manpage file.
Win32
See the INSTALL.win32 manpage for building from sources.
Info about win32 binary distributions of mod_perl are
available from:
http://perl.apache.org/distributions/
REVISION
$Id: mod_perl.pod,v 1.20 2000/03/05 23:46:30 dougm Exp $
AUTHOR
Doug MacEachern
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