--- name: "mod_perl" section: "3pm" platform: "linux" package: "libapache-mod-perl" version: "1.29.0.4-4.1+etch1" release: "Debian 4.0 (Etch)" platforms: ["linux"] url: "https://new.carta.tech/mod_perl" --- # mod\_perl(3pm) mod\_perl - Embed a Perl interpreter in the Apache HTTP server 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 modules entirely in Perl. In addition, the persistent interpreter 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 translate, authentication, authorization, access, type check, fixup and logger stages of a request. The mod\_perl FAQ is maintained by Frank Cringle \: http://perl.apache.org/faq/ See 'perldoc Apache' for info on how to use the Perl-Apache API. See the lib/ directory for example modules and apache-modlist.html for a comprehensive list. See the eg/ directory for example scripts. For using mod\_perl as a CGI replacement see the cgi\_to\_mod\_perl document. You may load modules at server startup via: ``` PerlModule Apache::SSI SomeOther::Module ``` Optionally: ``` PerlRequire perl-scripts/script_to_load_at_startup.pl ``` A **PerlRequire** file is commonly used for intialization during 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 \ 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 configuration directives take one argument, which is the name of the subroutine to call. If the value is not a subroutine name, mod\_perl assumes it is a package name which implements a 'handler' subroutine. ``` PerlChildInitHandler (requires apache_1.3.0 or higher) 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 handlers 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. 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 ``` 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"`. 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 normally setup the common environment variables before spawning a CGI process. Therefore, mod\_perl must feed these variables to `%ENV` directly. Normally, this does not happen until the response stage of a request when `"PerlHandler"` is called. If you wish to set variables that will be available before then, such as for a `"PerlAuthenHandler"`, 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 ``` The `"PerlSetVar"` and `"PerlAddVar"` directives provide a simple mechanism for passing information from configuration files to Perl modules or Registry scripts. The `"PerlSetVar"` directive allows you to set a key/value pair. ``` PerlSetVar SomeKey SomeValue ``` Perl modules or scripts retrieve configuration values using the `"$r->dir_config"` method. ``` $SomeValue = $r->dir_config('SomeKey'); ``` The `"PerlAddVar"` directive allows you to emulate Perl arrays: ``` PerlAddVar SomeKey FirstValue PerlAddVar SomeKey SecondValue ... ... ... PerlAddVar SomeKey Nth-Value ``` In the Perl modules the values are extracted using the `"$r->dir_config->get"` method. ``` @array = $r->dir_config->get('SomeKey'); ``` Alternatively in your code you can extend the setting with: ``` $r->dir_config->add(SomeKey => 'Bar'); ``` `"PerlSetVar"` and `"PerlAddVar"` handle keys case-insensitively. The standard CGI environment variable **GATEWAY\_INTERFACE** is set to `"CGI-Perl/1.1"` when running under 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 } ``` 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 perlmod explains, once a `"BEGIN"` has run, it is immediately undefined. In the mod\_perl environment, this means `"BEGIN"` blocks will not be run 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 module 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 PerlFreshRestart is On As perlmod explains, an `"END"` subroutine is executed as late as possible, that is, when the interpreter 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 during main server startup, i.e. those pulled in by the **PerlRequire** 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 invocations when the script is cached in memory. All other `"END"` blocks encountered during other Perl\*Handler callbacks, 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 embedded 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 mod\_perl\_tuning 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 Makefile.PL DYNAMIC=1'). This may save you some memory, however, 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 mod\_perl\_tuning document for details.\ **MEMORY TIPS** 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. 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_OPTIMIZE"`. With these options, my httpd shrinks down ~150K. 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 children will be able to share this space. 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! It's always a good idea to stay away from global variables 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 instead of **use vars**. Example: ``` package MyPackage; use strict; @MyPackage::ISA = qw(...); $MyPackage::VERSION = "1.00"; ``` vs. ``` package MyPackage; use strict; use vars qw(@ISA $VERSION); @ISA = qw(...); $VERSION = "1.00"; ``` In case I forgot to mention, read Vivek Khera's mod\_perl\_tuning document for more tips on improving Apache/mod\_perl performance. Normally when you run perl from the command line or have the shell invoke it with \`#!', you may choose to pass perl switch arguments such as `"-w"` or `"-T"`. Since the command line is only parsed once, when the server starts, these switches are unavailable to mod\_perl scripts. However, most command line arguments have a perl special variable equivilant. For example, the `$^W` variable coresponds to the `"-w"` switch. Consult perlvar 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 special 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 additional perl startup flags such as **-d** and **-D**. See perlrun. 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: ``` #Apache::Registry script 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 connection in the parent process (via PerlRequire or PerlModule). 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. With the mod\_perl stacked handlers mechanism, it is possible 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 subroutines, 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.: ``` Apache->push_handlers("PerlLogHandler", \&first_one); ``` ``` $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 considered 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 without slowing down response time to the client. PerlTransHandlers may decide, based or uri or other condition, whether or not to handle a request, e.g. Apache::MsqlProxy. Without stacked handlers, users must configure: ``` PerlTransHandler Apache::MsqlProxy::translate 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 document, 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 SetHandler "perl-script" PerlHandler My::header My::body My::footer ``` Parsing the output of another PerlHandler? this is a little more tricky, but consider: ``` SetHandler "perl-script" PerlHandler OutputParser SomeApp SetHandler "perl-script" PerlHandler OutputParser AnotherApp ``` Now, OutputParser goes first, but it untie's \*STDOUT and re-tie's to it's own package like so: ``` package OutputParser; ``` ``` sub handler { 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\_HANDLERS=1, FALSE otherwise. See mod\_perl\_method\_handlers. With \\ sections, it is possible to configure your server entirely in 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 configurations directives can be represented as `$Scalars` or `@Lists`. A `@List` inside these sections is simply converted into a single-space delimited string for you inside. Here's an example: ``` #httpd.conf @PerlModule = qw(Mail::Send Devel::Peek); ``` ``` #run the server as whoever starts it $User = getpwuid($>) || $>; $Group = getgrgid($)) || $); ``` ``` $ServerAdmin = $User; ``` ``` ``` Block sections such as \\ are represented 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\_sections.txt for some examples. A tip for syntax checking outside of httpd: ``` #!perl ``` ``` #... code here ... ``` ``` __END__ ``` Now you may run `"perl -cx httpd.conf"`. It may be the case that \ 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 modperl mailing list. To configure this feature build with \ 'perl Makefile.PL PERL\_SECTIONS=1' 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::handler), Class-\>method call or anonymous sub {} Example: ``` Child accessed times.
``` ``` ``` ``` #don't forget to escape double quotes! Perl is fun to use! ``` The **Apache::Include** module makes it simple to include **Apache::Registry** scripts with the mod\_include perl directive. Example: ``` ``` You can also use 'virtual include' to include Apache::Registry 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 necessary 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. 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 ``` 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 ``` 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 `"PerlChildExitHandler"` 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** How much faster is mod\_perl that CGI? There are many ways to benchmark the two, see the `"benchmark/"` directory for some examples. See also: **Apache::Timeit** See mod\_perl\_traps. See the SUPPORT file. See INSTALL.win32 for building from sources. Info about win32 binary distributions of mod\_perl are available from: ``` http://perl.apache.org/distributions/ ``` $Id: mod\_perl.pod,v 1.22 2002/01/02 09:41:23 stas Exp $ Doug MacEachern