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mod_perl Configuration | |
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mod_perl Configuration | |
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Writing Apache Modules with Perl and C
By Lincoln Stein, Doug MacEachern |
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Embedding Perl in HTML with Mason
By Dave Rolsky, Ken Williams |
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The mod_perl Developer's Cookbook
By Geoffrey Young, Paul Lindner, Randy Kobes |
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mod_perl Pocket Reference
By Andrew Ford |
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This section documents the various configuration options available for Apache and mod_perl, as well as the Perl startup files, and more esoteric possibilites such as configuring Apache with Perl.
The next step after building and installing your new mod_perl enabled Apache server is to configure the server. There are two separate parts to configure: Apache and mod_perl. Each has its own set of directives.
To configure your mod_perl enabled Apache server, the only file that you should need to edit is httpd.conf. By default, httpd.conf is put into the conf directory under the server root directory. The default server root is /usr/local/apache/ on many UNIX platforms, but within reason it can be any directory you choose. If you are new to Apache and mod_perl, you will probably find it helpful to keep to the directory layouts we use in this Guide if you can.
Apache versions 1.3.4 and later are distributed with the configuration directives in a single file -- httpd.conf. This Guide uses the same approach in its examples. Prior to version 1.3.4, the default Apache installation used three configuration files -- httpd.conf, srm.conf, and access.conf. If you wish you can still use all three files, by setting the AccessConfig and ResourceConfig directives in httpd.conf. You will also see later on that we use other files, for example perl.conf and startup.pl. This is just for our convenience, you could still do everything in httpd.conf if you wished.
Apache configuration can be confusing. To minimize the number of things that can go wrong, it can be a good idea first to configure Apache itself without mod_perl. This will give you the confidence that it works and maybe that you have some idea how to configure it.
There is a warning in the httpd.conf distributed with Apache about simply editing httpd.conf and running the server, without understanding all the implications. This is another warning. Modifying the configuration file and adding new directives can introduce security problems, and have performance implications.
The Apache distribution comes with an extensive configuration manual, and in addition each section of the distributed configuration file includes helpful comments explaining how every directive should be configured and what the defaults values are.
If you haven't moved Apache's directories around, the installation
program will have configured everything for you. You can just start
the server and test it. To start the server use the apachectl
utility which comes bundled with the Apache distribution. It resides
in the same directory as httpd, the Apache server itself. Execute:
/usr/local/apache/bin/apachectl start
Now you can test the server, for example by accessing http://localhost from a browser running on the same host.
For a basic setup there are just a few things to configure. If you have moved any directories you have to update them in httpd.conf. There are many of them, here are just a couple of examples:
ServerRoot "/usr/local/apache" DocumentRoot "/home/httpd/docs"
If you want to run it on a port other than port 80 edit the Port
directive:
Port 8080
You might want to change the user and group names the server will run under. Note that if started as the root user (which is generally the case), the parent process will continue to run as root, but its children will run as the user and group you have specified. For example:
User httpd Group httpd
There are many other directives that you might need to configure as
well. In addition to directives which take a single value there are
whole sections of the configuration (such as the <Directory> and
<Location> sections) which apply only to certain areas of your Web
space. As mentioned earlier you will find them all in httpd.conf.
If there is a file with the name .htaccess in any directory, Apache scans it for further configuration directives which it then applies only to that directory (and its subdirectories). The name .htaccess is confusing because it can contain any configuration directives, not just those related to access to resources. You will not be surprised to find that a configuration directive can change the names of the files used in this way.
Note that if there is a
<Directory />
AllowOverride None
</Directory>
directive in httpd.conf, Apache will not try to look for .htaccess at all.
I'll explain just the basics of the <Directory>, <Location> and
<Files> sections. Remember that there is more to know and the rest
of the information is available in the Apache documentation. The
information I'll present here is just what is important for
understanding the mod_perl configuration sections.
Apache considers directories and files on your machine all to be resources. For each resource you can determine a particular behaviour which will apply to every request for information from that particular resource.
Obviously the directives in <Directory> sections apply to specific
directories on your host machine, and those in <Files> sections
apply only to specific files (actually groups of files with names
which have something in common). In addition to these sections,
Apache has the concept of a <Location>, which is also just a
resource. <Location> sections apply to specific URIs. Locations
are based at the document root, directories are based at the
filesystem root. For example, if you have the default server
directory layout where the server root is /usr/local/apache and the
document root is /usr/local/apache/htdocs then static files in the
directory /usr/local/apache/htdocs/pub are in the location /pub.
It is up to you to decide which directories on your host machine are mapped to which locations. You should be careful how you do it, because the security of your server may be at stake.
Locations do not necessarily have to refer to existing physical directories, but may refer to virtual resources which the server creates for the duration of a single browser request. As you will see, this is often the case for a mod_perl server.
When a browser asks for a resource from your server, Apache determines
from its configuration whether or not to serve the request, whether to
pass the request to another server, what (if any) authorization is
required for access to the resource, and how to reply. For any given
resource, the various sections in your configuration may provide
conflicting information. For example you may have a <Directory>
section which tells Apache that authorization is required for access
to the resource but you may have a <Files> section which says that
it is not. It is not always obvious which directive takes precedence
in these cases. This can be a trap for the unwary.
Can appear in server and virtual host configurations.
<Directory> and </Directory> are used to enclose a group of
directives which will apply only to the named directory and
sub-directories of that directory. Any directive which is allowed in
a directory context (see the Apache documentation) may be used.
The path given in the <Directory> directive is either the full path
to a directory, or a wild-card string. In a wild-card string, ?
matches any single character, * matches any sequence of characters,
and [] matches character ranges. (This is similar to the shell's
file globs.) None of the wildcards will match a / character.
For example:
<Directory /home/httpd/docs>
Options Indexes
</Directory>
If you want to use a regular expression to match then you should use
the syntax <DirectoryMatch regex> ... </DirectoryMatch>.
If multiple (non-regular expression) directory sections match the directory (or its parents) containing a document, then the directives are applied in the order of shortest match first, interspersed with the directives from any .htaccess files. For example, with
<Directory />
AllowOverride None
</Directory>
<Directory /home/httpd/docs/*>
AllowOverride FileInfo
</Directory>
for access to the document /home/httpd/docs/index.html the steps are:
<Files filename> ... </Files>
Can appear in server and virtual host configurations, and .htaccess files as well.
The <Files> directive provides for access control by
filename. It is comparable to the <Directory> and
<Location> directives. It should be closed with the
</Files> directive. The directives given within this
section will be applied to any object with a basename (last component
of filename) matching the specified filename.
<Files> sections are processed in the order they appear in
the configuration file, after the <Directory> sections and
.htaccess files are read, but before <Location>
sections. Note that <Files> can be nested inside
<Directory> sections to restrict the portion of the
filesystem they apply to. <Files> cannot be nested inside
<Location> sections however.
The filename argument should include a filename, or a wild-card
string, where ? matches any single character, and * matches any
sequence of characters. Extended regular expressions can also be used,
simply place a tilde character ~ between the directive and the
regular expression. The regular expression should be in quotes. The
dollar symbol refers to the end of the string. The pipe character
indicates alternatives. Special characters in extended regular
expressions must escaped with a backslash. For example:
<Files ~ "\.(gif|jpe?g|png)$">
would match most common Internet graphics formats. Alternatively you
can use the <FilesMatch regex> ... </FilesMatch>
syntax.
Can appear in server and virtual host configurations.
The <Location> directive provides for access control by
URL. It is similar to the <Directory> directive, and
starts a section which is terminated with the </Location>
directive.
<Location> sections are processed in the order they appear
in the configuration file, after the <Directory> sections,
.htaccess files and <Files> sections are read.
The <Location> section is the directive that is used most
often with mod_perl.
URLs do not have to refer to real directories or files within the
filesystem at all, <Location> operates completely outside
the filesystem. Indeed it may sometimes be wise to ensure that
<Location>s do not match real paths to avoid confusion.
The URL may use wildcards. In a wild-card string, ? matches any
single character, and * matches any sequences of characters, []
groups characters to match. For regular expression matches use the
<LocationMatch regex> ... </LocationMatch>
syntax.
The <Location> functionality is especially useful when
combined with the SetHandler directive. For example to enable
status requests, but allow them only from browsers at example.com,
you might use:
<Location /status>
SetHandler server-status
order deny,allow
deny from all
allow from .example.com
</Location>
When configuring the server, it's important to understand the order in which the rules of each section apply to requests. The order of merging is:
<Directory> (except regular expressions) and
.htaccess are processed simultaneously, with .htaccess
overriding <Directory>
<DirectoryMatch>, and <Directory> with
regular expressions
<Files> and <FilesMatch> are processed
simultaneously
<Location> and <LocationMatch> are
processed simultaneously
Apart from <Directory>, each group is processed in the
order that it appears in the configuration files.
<Directory> (group 1 above) is processed in the order
shortest directory component to longest. If multiple
<Directory> sections apply to the same directory then they
are processed in the configuration file order.
Sections inside <VirtualHost> sections are applied as if
you were running several independent servers. The directives inside
<VirtualHost> sections do not interact with each other.
They are applied after first processing any sections outside the
virtual host definition. This allows virtual host configurations to
override the main server configuration.
Later sections override earlier ones.
Let's say that you want all files, except for a few of the files in a
specific directory and below, to be handled in the same way. For
example if you want all the files in /home/http/docs to be served
as plain files, but any files with ending .html and .txt to be
processed by the content handler of your Apache::MyFilter module.
<Directory /home/httpd/docs>
<FilesMatch "\.(html|txt)$">
SetHandler perl-script
PerlHandler Apache::MyFilter
</FilesMatch>
</Directory>
Thus it is possible to embed sections inside sections to create
subgroups which have their own distinct behavior. Alternatively you
could use a <Files> section inside an .htaccess file.
Note that you can't put <Files> or <FilesMatch>
sections inside a <Location> section, but you can put them
inside a <Directory> section.
Normally, if multiple Options directives apply to a directory, then
the most specific one is taken complete; the options are not merged.
However if all the options on the Options directive are preceded by
a + or - symbol, the options are merged. Any options preceded
by + are added to the options currently in force, and any options
preceded by - are removed.
For example, without any + and - symbols:
<Directory /home/httpd/docs>
Options Indexes FollowSymLinks
</Directory>
<Directory /home/httpd/docs/shtml>
Options Includes
</Directory>
then only Includes will be set for the /home/httpd/docs/shtml
directory. However if the second Options directive uses the +
and - symbols:
<Directory /home/httpd/docs>
Options Indexes FollowSymLinks
</Directory>
<Directory /home/httpd/docs/shtml>
Options +Includes -Indexes
</Directory>
then the options FollowSymLinks and Includes are set for the
/home/httpd/docs/shtml directory.
When you have tested that the Apache server works on your machine, it's time to configure mod_perl. Some of the configuration directives are already familiar to you, but mod_perl introduces a few new ones.
It can be a good idea to keep all the mod_perl related configuration at the end of the configuration file, after the native Apache configuration directives.
To ease maintenance and to simplify multiple server installations, the
Apache/mod_perl configuration system allows you several alternative
ways to keep your configuration directives in separate places. The
Include directive in httpd.conf allow you to include the
contents of other files, just as if the information were all contained
in httpd.conf. This is a feature of Apache itself. For example if
you want all your mod_perl configuration to be placed in a separate
file mod_perl.conf you can do that by adding to httpd.conf this
directive:
Include conf/mod_perl.conf
If you want to include this configuration conditionally, depending on
whether your apache has been compiled with mod_perl, you can use the
IfModule directive:
<IfModule mod_perl.c>
Include conf/mod_perl.conf
</IfModule>
mod_perl adds two further directives: <Perl> sections allow
you to execute Perl code from within any configuration file at server
startup time, and as you will see later, a file containing any Perl
program can be executed (also at server startup time) simply by
mentioning its name in a PerlRequire or PerlModule directive.
The ScriptAlias and Alias directives provide a mapping of a URI
to a file system directory. The directive:
Alias /foo /home/httpd/foo
will map all requests starting with /foo onto the files starting with /home/httpd/foo/. So when Apache gets a request http://www.example.com/foo/test.pl the server will map this into the file test.pl in the directory /home/httpd/foo/.
In addition ScriptAlias assigns all the requests that match the URI
(i.e. /cgi-bin) to be executed under mod_cgi.
ScriptAlias /cgi-bin /home/httpd/cgi-bin
is actually the same as:
Alias /cgi-bin /home/httpd/cgi-bin
<Location /cgi-bin>
SetHandler cgi-script
Options +ExecCGI
</Location>
where latter directive invokes mod_cgi. You shouldn't use the
ScriptAlias directive unless you want the request to be processed
under mod_cgi. Therefore when you configure mod_perl sections use
Alias instead.
Under mod_perl the Alias directive will be followed by two further
directives. The first is the SetHandler perl-script directive,
which tells Apache to invoke mod_perl to run the script. The second
directive (for example PerlHandler) tells mod_perl which handler
(Perl module) the script should be run under, and hence for which
phase of the request. Refer to the section
Perl*Handlers for more information about
handlers for the various request phases.
When you have decided which methods to use to run your scripts and where you will keep them, you can add the configuration directive(s) to httpd.conf. They will look like those below, but they will of course reflect the locations of your scripts in your file-system and the decisions you have made about how to run the scripts:
ScriptAlias /cgi-bin/ /home/httpd/cgi-bin/ Alias /perl/ /home/httpd/perl/
In the examples above all the requests issued for URIs starting with /cgi-bin will be served from the directory /home/httpd/cgi-bin/, and starting with /perl from the directory /home/httpd/perl/.
# Typical for plain cgi scripts:
ScriptAlias /cgi-bin/ /home/httpd/perl/
# Typical for Apache::Registry scripts:
Alias /perl/ /home/httpd/perl/
# Typical for Apache::PerlRun scripts:
Alias /cgi-perl/ /home/httpd/perl/
In the examples above we have mapped the three different URIs (http://www.example.com/perl/test.pl http://www.example.com/cgi-bin/test.pl and http://www.example.com/cgi-perl/test.pl) all to the same file /home/httpd/perl/test.pl. This means that we can have all our CGI scripts located at the same place in the file-system, and call the script in any of three ways simply by changing one component of the URI (cgi-bin|perl|cgi-perl).
This technique makes it easy to migrate your scripts to mod_perl. If
your script does not seem to be working while running under mod_perl,
then in most cases you can easily call the script in straight mod_cgi
mode or under Apache::PerlRun without making any script changes.
Simply change the URL you use to invoke it.
Although in the configuration above we have configured all three Aliases to point to the same directory within our file system, you can of course have them point to different directories if you prefer.
You should remember that it is undesirable to run scripts in plain mod_cgi mode from a mod_perl-enabled server--the resource consumption is too high. It is better to run these on a plain Apache server. See Standalone mod_perl Enabled Apache Server.
The <Location> section assigns a number of rules which the
server should follow when the request's URI matches the
Location. Just as it is the widely accepted convention to use
/cgi-bin for your mod_cgi scripts, it is conventional to use
/perl as the base URI of the perl scripts which you are running
under mod_perl. Let's review the following very widely used
<Location> section:
Alias /perl/ /home/httpd/perl/
PerlModule Apache::Registry
<Location /perl>
SetHandler perl-script
PerlHandler Apache::Registry
Options ExecCGI
allow from all
PerlSendHeader On
</Location>
This configuration causes all requests for URIs starting with /perl
to be handled by the mod_perl Apache module with the handler from the
Apache::Registry Perl module. Let's review the directives inside
the <Location> section in the example:
<Location /perl>
Remember the Alias from the above section? We use the same Alias
here; if you were to use a <Location> that does not have
the same Alias, the server would fail to locate the script in the
file system. You need the Alias setting only if the code that
should be executed is located in the file. So Alias just provides
the URI to filepath translation rule.
Sometimes there is no script to be executed. Instead there is some
module whose method is being executed, similar to /perl-status,
where the code is stored in an Apache module. In such cases we don't
need Alias settings for those <Location>s.
SetHandler perl-script
This assigns the mod_perl Apache module to handle the content generation phase.
PerlHandler Apache::Registry
Here we tell Apache to use the Apache::Registry Perl module for the
actual content generation.
Options ExecCGI
The Options directive accepts various parameters (options), one of
which is ExecCGI. This tells the server that the file is a program
and should be executed, instead of just being displayed like a static
file (like HTML file). If you omit this option then the script will
either be rendered as plain text or else it will trigger a Save-As
dialog, depending on the client's configuration.
allow from all
This directive is used to set access control based on domain. The above settings allow clients from any domain to run the script.
PerlSendHeader On
PerlSendHeader On tells the server to send an HTTP headers to the
browser on every script invocation. You will want to turn this off
for nph (non-parsed-headers) scripts.
The PerlSendHeader On setting invokes the Apache's
ap_send_http_header() method after parsing the headers generated by
the script. It is only meant for emulation of mod_cgi behavior with
regard to headers.
To send the HTTP headers it's always better either to use the
$r->send_http_header method using the Apache Perl API or to use
the $q->header method from the CGI.pm module.
</Location>
Closes the <Location> section definition.
Note that sometimes you will have to preload the module before using
it in the <Location> section. In the case of
Apache::Registry the configuration will look like this:
PerlModule Apache::Registry
<Location /perl>
SetHandler perl-script
PerlHandler Apache::Registry
Options ExecCGI
allow from all
PerlSendHeader On
</Location>
PerlModule is equivalent to Perl's native use() function call.
No changes are required to the /cgi-bin location (mod_cgi), since it has nothing to do with mod_perl.
Here is another very similar example, this time using
Apache::PerlRun (For more information see
Apache::PerlRun):
<Location /cgi-perl>
SetHandler perl-script
PerlHandler Apache::PerlRun
Options ExecCGI
allow from all
PerlSendHeader On
</Location>
The only difference from the Apache::Registry configuration is the
argument of the PerlHandler directive, where Apache::Registry
has been replaced with Apache::PerlRun.
So if you have:
<Location /foo>
SetHandler perl-script
PerlHandler My::Module
</Location>
If you want to remove a mod_perl handler setting from a location beneath a location where the handler was set (i.e. /foo/bar), all you have to do is to reset it, like this:
<Location /foo/bar>
SetHandler default-handler
</Location>
Now, all the requests starting with /foo/bar would be served by Apache's default handler.
As we saw earlier, a module should be loaded before it is used.
PerlModule and PerlRequire are the two mod_perl directives which
are used to load modules and code. They are almost equivalent to
Perl's use() and require() functions respectively and called
from the Apache configuration file. You can pass one or more module
names as arguments to PerlModule:
PerlModule Apache::DBI CGI DBD::Mysql
Generally the modules are preloaded from the startup script, which is
usually called startup.pl. This is a file containing plain Perl
code which is executed through the PerlRequire directive. For
example:
PerlRequire /home/httpd/perl/lib/startup.pl
A PerlRequire file name can be absolute or relative to
ServerRoot or a path in @INC.
As with any file with Perl code that gets use()'d or
require()'d, it must return a true value. To ensure that this
happens don't forget to add 1; at the end of startup.pl.
Notice that unless mod_perl is compiled as DSO and unless
PerlFreshRestart is set to On, one needs to
fully stop and start Apache for any changes to take affect, if the
files and modules have been modified.
As you probably know Apache traverses a loop for each HTTP request it receives.
After you have compiled and installed mod_perl, your Apache mod_perl
configuration directives tell Apache to invoke the module mod_perl as
the handler for some request which it receives. Although it could in
fact handle all the phases of the request loop, usually it does not.
You tell mod_perl which phases it is to handle (and so which to leave
to other modules, or to the default Apache routines) by putting
Perl*Handler directives in the configuration files.
Because you need the Perl interpreter to be present for your Perl
script to do any processing at all, there is a slight difference
between the way that you configure Perl and C handlers to handle parts
of the request loop. Ordinarily a C module is written, compiled and
configured to hook into a specific phase of the request loop. For a
Perl handler you compile mod_perl itself to hook into the appropriate
phases, as if it were to handle the phases itself. Then you put
Perl*Handler directives in your configuration file to tell mod_perl
that it is to pass the responsibility for handling that part of the
request phase to your Perl module.
mod_perl is an Apache module written in C. As most programmers will
only need to handle the response phase, in the default compilation
most of the Perl*Handlers are disabled. When you configure the
Makefile.PL file for its compilation, you must specify whether or
not you will want to handle parts of the request loop other than the
usual content generation phase. If so you need to specify which
parts. See the "Callback Hooks" section for
how to do this.
Apache specifies about eleven phases of the request loop, namely (and
in order of processing): Post-Read-Request, URI Translation, Header
Parsing, Access Control, Authentication, Authorization, MIME type
checking, FixUp, Response (also known as the Content handling phase),
Logging and finally Cleanup. These are the stages of a request where
the Apache API allows a module to step in and do something. There is
a dedicated Perl*Handler for each of these stages plus a couple of
others which don't correspond to parts of the request loop.
We call them Perl*Handler directives because the names of the many
mod_perl handler directives for the various phases of the request loop
all follow the same format. The * in Perl*Handler is a
placeholder to be replaced by something which identifies the phase to
be handled. For example PerlLogHandler is a Perl Handler which
(fairly obviously) handles the logging phase.
The slight exception is PerlHandler, which you can think of as
PerlResponseHandler. It is the content generation handler and so
it is probably the one that you will use most frequently.
Note that it is mod_perl which recognizes these directives, and not Apache. They are mod_perl directives, and an ordinary Apache does not recognize them. If you get error messages about these directives being "perhaps mis-spelled" it is a sure sign that the appropriate part of mod_perl (or the entire mod_perl module!) is not present in your copy of Apache executable.
The full list of Perl*Handlers follows. They are in the order that
they are processed by Apache and mod_perl:
PerlChildInitHandler
PerlPostReadRequestHandler
PerlInitHandler
PerlTransHandler
PerlHeaderParserHandler
PerlAccessHandler
PerlAuthenHandler
PerlAuthzHandler
PerlTypeHandler
PerlFixupHandler
PerlHandler
PerlLogHandler
PerlCleanupHandler
PerlChildExitHandler
PerlDispatchHandler
PerlRestartHandler
PerlChildInitHandler and PerlChildExitHandler do not refer to
parts of the request loop, they are to allow your modules to
initialize data structures and to clean up at the child process
start-up and shutdown respectively, for example by allocating and
deallocating memory.
All <Location>, <Directory> and
<Files> sections contain a physical path specification.
Like PerlChildInitHandler and PerlChildExitHandler, the
directives PerlPostReadRequestHandler and PerlTransHandler
cannot be used in these sections, nor in .htaccess files, because
it is not until the end of the Translation Handler
(PerlTransHandler) phase that the path translation is completed and
a physical path is known.
PerlInitHandler changes its behaviour depending upon where it is
used. In any case it is the first handler to be invoked in serving a
request. If found outside any <Location>,
<Directory> or <Files> section (at the top
level), it is an alias for PerlPostReadRequestHandler. When inside
any such section it is an alias for PerlHeaderParserHandler.
Starting from PerlHeaderParserHandler the requested URI has been
mapped to a physical server pathname, and thus it can be used to match
a <Location>, <Directory> or <Files>
configuration section, or to look in a .htaccess file if such a
file exists in the specified directory in the translated path.
PerlDispatchHandler and PerlRestartHandler do not correspond to
parts of the Apache API, but allow you to fine-tune the mod_perl API.
The Apache documentation will tell you all about these stages and what your modules can do. By default, most of these hooks are disabled at compile time, see the"Callback Hooks" section for information on enabling them.
By default the mod_perl API expects a subroutine called handler()
to handle the request in the registered Perl*Handler module. Thus if
your module implements this subroutine, you can register the handler
with mod_perl like this:
Perl*Handler Apache::Foo
Replace Perl*Handler with the name of a specific handler from the
list given above. mod_perl will preload the specified module for you.
Please note that this approach will not preload the module at startup.
To make sure it gets loaded you have three options: you can explicitly
preload it with the PerlModule directive:
PerlModule Apache::Foo
You can preload it at the startup file:
use Apache::Foo ();
Or you can use a nice shortcut that the Perl*Handler syntax
provides:
Perl*Handler +Apache::Foo
Note the leading + character. This directive is equivalent to:
PerlModule Apache::Foo Perl*Handler Apache::Foo
If you decide to give the handler routine a name other than
handler, for example my_handler, you must preload the module and
explicitly give the name of the handler subroutine:
PerlModule Apache::Foo Perl*Handler Apache::Foo::my_handler
As you have seen, this will preload the module at server startup.
If a module needs to know which handler is currently being run, it can find out with the current_callback method. This method is most useful to PerlDispatchHandlers which wish to take action for certain phases only.
if ($r->current_callback eq "PerlLogHandler") {
$r->warn("Logging request");
}
With the mod_perl stacked handlers mechanism, during any stage of a
request it is possible for more than one Perl*Handler to be defined
and run.
Perl*Handler directives (in your configuration files) can define
any number of subroutines. For example:
PerlTransHandler OneTrans TwoTrans RedTrans BlueTrans
With the method Apache->push_handlers(), callbacks (handlers)
can be added to a stack at runtime by mod_perl scripts.
Apache->push_handlers() takes the callback hook name as its
first argument and a subroutine name or reference as its second.
Here's an example:
use Apache::Constants qw(:common);
sub my_logger {
#some code here
return OK;
}
Apache->push_handlers("PerlLogHandler", \&my_logger);
Here's another one:
use Apache::Constants qw(:common);
$r->push_handlers("PerlLogHandler", sub {
print STDERR "__ANON__ called\n";
return OK;
});
After each request, this stack is erased.
All handlers will be called unless a handler returns a status other
than OK or DECLINED.
Example uses:
CGI.pm maintains a global object for its plain function interface.
Since the object is global, it does not go out of scope, DESTROY is
never called. CGI->new can call:
Apache->push_handlers("PerlCleanupHandler", \&CGI::_reset_globals);
This function will be called during the final stage of a request,
refreshing CGI.pm's globals before the next request comes in.
Apache::DCELogin establishes a DCE login context which must exist
for the lifetime of a request, so the DCE::Login object is stored
in a global variable. Without stacked handlers, users must set
PerlCleanupHandler Apache::DCELogin::purge
in the configuration files to destroy the context. This is not
"user-friendly". Now, Apache::DCELogin::handler can call:
Apache->push_handlers("PerlCleanupHandler", \&purge);
Persistent database connection modules such as Apache::DBI could
push a PerlCleanupHandler handler that iterates over %Connected,
refreshing connections or just checking that connections have not gone
stale. Remember, by the time we get to PerlCleanupHandler, the
client has what it wants and has gone away, so we can spend as much
time as we want here without slowing down response time to the client
(although the process itself is unavailable for serving new requests
before the operation is completed).
PerlTransHandlers (e.g. Apache::MsqlProxy) may decide, based on
the URI or some arbitrary condition, whether or not to handle a
request. Without stacked handlers, users must configure it
themselves:
PerlTransHandler Apache::MsqlProxy::translate PerlHandler Apache::MsqlProxy
PerlHandler is never actually invoked unless translate() sees
that the request is a proxy request ($r->proxyreq). If it is a
proxy request, translate() sets $r->handler("perl-script"),
and 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().
Imagine that you want to include footers, headers, etc., piecing together a document, without using SSI. The following example shows how to implement it. First we prepare the code as follows:
Test/Compose.pm
---------------
package Test::Compose;
use Apache::Constants qw(:common);
sub header {
my $r = shift;
$r->content_type("text/plain");
$r->send_http_header;
$r->print("header text\n");
return OK;
}
sub body { shift->print("body text\n") ; return OK}
sub footer { shift->print("footer text\n") ; return OK}
1;
__END__
# in httpd.conf or perl.conf
PerlModule Test::Compose
<Location /foo>
SetHandler "perl-script"
PerlHandler Test::Compose::header Test::Compose::body Test::Compose::footer
</Location>
Parsing the output of another PerlHandler? This is a little 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 it to its 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 $_ for example:
$self->{r}->print($_ . "[insert stuff]");
}
}
1;
__END__
To build in this feature, configure with:
% perl Makefile.PL PERL_STACKED_HANDLERS=1 [ ... ]
If you want to test whether your running mod_perl Apache can stack
handlers, the method Apache->can_stack_handlers will return
TRUE if mod_perl was configured with PERL_STACKED_HANDLERS=1,
and FALSE otherwise.
If a Perl*Handler is prototyped with $$, this handler will be
invoked as a method. For example:
package MyClass;
@ISA = qw(BaseClass);
sub handler ($$) {
my ($class, $r) = @_;
...;
}
package BaseClass;
sub method ($$) {
my ($class, $r) = @_;
...;
}
1;
Configuration:
PerlHandler MyClass
or
PerlHandler MyClass->handler
Since the handler is invoked as a method, it may inherit from other classes:
PerlHandler MyClass->method
In this case, the MyClass class inherits this method from
BaseClass. This means that any method of MyClass or any of its
parent classes can serve as a mod_perl handler, and that you can apply
good OO methodology within your mod_perl handlers.
For instance, you could have this base class:
package ServeContent;
use Apache::Constants qw(OK);
sub handler($$) {
my ($class, $r) = @_;
$r->send_http_header('text/plain');
$r->print($class->get_content());
return OK;
}
sub get_content {
return 'Hello World';
}
1;
And then use the same base class for different contents:
package HelloWorld;
use ServeContent;
@ISA = qw(ServeContent);
sub get_content {
return 'Hello, happy world!';
}
package GoodbyeWorld;
use ServeContent;
@ISA = qw(ServeContent);
sub get_content {
return 'Goodbye, cruel world!';
}
1;
Now you can keep the same handler subroutine for a group of modules which are similiar. The following configuration will enable the handlers from the subclasses:
<Location /hello>
SetHandler perl-script
PerlHandler HelloWorld->handler
</Location>
<Location /bye>
SetHandler perl-script
PerlHandler GoodbyeWorld->handler
</Location>
To build in this feature, configure with:
% perl Makefile.PL PERL_METHOD_HANDLERS=1 [ ... ]
To reload PerlRequire, PerlModule and other use()'d modules,
and to flush the Apache::Registry cache on server restart, add to
httpd.conf:
PerlFreshRestart On
Make sure you read Evil things might happen when using PerlFreshRestart.
Starting from mod_perl version 1.22 PerlFreshRestart is ignored
when mod_perl is compiled as a DSO. But it almost doesn't matter,
since mod_perl as a DSO will do a full tear-down (perl_destruct()).
So it's still a FreshRestart, just fresher than static (non-DSO)
mod_perl :)
But note that even if you have
PerlFreshRestart Off
and mod_perl as a DSO you will still get a FreshRestart.
PerlSetEnv key val PerlPassEnv key
PerlPassEnv passes, PerlSetEnv sets and passes ENVironment
variables to your scripts. You can access them in your scripts
through %ENV (e.g. $ENV{"key"}). These commands are useful to
pass information to your handlers or scripts, or to any modules you
use that require some additional configuration.
For example, the Oracle RDBMS requires a number of ORACLE_*
environment variables to be set so that you can connect to it through
DBI. So you might want to put this in your httpd.conf:
PerlSetEnv ORACLE_BASE /oracle
PerlSetEnv ORACLE_HOME /oracle
: :
You can then use DBI to access your oracle server without having to
set the environment variables in your handlers.
PerlPassEnv proposes another approach: you might want to set the
corresponding environment variables in your shell, and not reproduce
the information in your httpd.conf. For example, you might have
this in your .bash_profile:
ORACLE_BASE=/oracle ORACLE_HOME=/oracle export ORACLE_BASE ORACLE_HOME
However, Apache (or mod_perl) don't pass on environment variables from
the shell by default; you'll have to specify these using either the
standard PassEnv or mod_perl's PerlPassEnv directives.
PerlPassEnv ORACLE_BASE ORACLE_HOME
One thing to be aware of is that when you start Apache under a shell
different than the one you are logged in from, the environment
variables could be totally different, so don't be surprised if you get
a different value when using Passenv/PerlPassEnv or none at
all. Check the environment Apache is started from. Often it's started
from a special account like apache, or nobody, and can be
anything else. Check the value of User variable in httpd.conf to
find out the right answer. Once you figure that out, make sure that
the shell Apache starts from has the desired environment variables
right. And may be it's a better idea not to rely on the shell
variables, but instead set those explicitly using
Setenv/PerlSetEnv.
Regarding the setting of PerlPassEnv PERL5LIB in httpd.conf: if
you turn on taint checks (PerlTaintCheck On), $ENV{PERL5LIB}
will be ignored (unset). See the 'Switches -w, -T' section.
While the Apache's SetEnv/PassEnv and mod_perl's
PerlSetEnv/PerlPassEnv apparently do the same thing, the former
doesn't happen until the fixup phase, the latter happens as soon as
possible, so those variables are available before then, e.g. in
PerlAuthenHandler for $ENV{ORACLE_HOME} (or another environment
variable that you need in these early request processing stages).
PerlSetVar is very similar to PerlSetEnv; however, variables set
using PerlSetVar are only available through the mod_perl API, and
is thus more suitable for configuration. For example, environment
variables are available to all, and might show up on casual "print
environment" scripts, which you might not like. PerlSetVar is
well-suited for modules needing some configuration, but not wanting to
implement first-class configuration handlers just to get some
information.
PerlSetVar foo bar
or
<Perl>
push @{ $Location{"/"}->{PerlSetVar} }, [ foo => 'bar' ];
</Perl>
and in the code you read it with:
my $r = Apache->request;
print $r->dir_config('foo');
The above prints:
bar
Note that you cannot do this:
push @{ $Location{"/"}->{PerlSetVar} }, [ foo => \%bar ];
All values are treated as strings, so you will get a stringified
reference to a hash as a value (something which will look like
"HASH(0x87a5108)"). This cannot be turned back into a reference
and therefore into the original hash upon retrieval.
However you can use the PerlAddVar directive to push more values
into the variable, emulating arrays. For example:
PerlSetVar foo bar PerlAddVar foo bar1 PerlAddVar foo bar2
or the equivalent:
PerlAddVar foo bar PerlAddVar foo bar1 PerlAddVar foo bar2
To retrieve the values use the $r->dir_config->get()
method:
my @foo = $r->dir_config->get('foo');
or
my %foo = $r->dir_config->get('foo');
Make sure that you use an even number of elements if you store the retrieved values in a hash, like this:
PerlAddVar foo key1 PerlAddVar foo value1 PerlAddVar foo key2 PerlAddVar foo value2
Then %foo will have a structure like this:
%foo = (
key1 => 'value1',
key2 => 'value2',
);
There are some things you should know about sub requests and $r->dir_config. For
$r->lookup_uri, everything works as expected, because all
normal phases are run. You can then retrieve variables set in the
server scope of the configuration, in <VirtualHost>
sections, in <Location> sections, etc.
However, when using the $r->lookup_file method, you are
effectively skipping the URI translation phase. This means that the
URI won't be known by Apache, only the file name to retrieve. As such,
<Location> sections won't be applied. This means that if
you were using:
Alias /perl-subr/ /home/httpd/perl-subr/
<Location /perl-subr>
PerlSetVar foo bar
PerlSetVar foo2 bar2
</Location>
And issue a subrequest using $r->lookup_file and try to
retrieve its directory configuration (Apache::SubRequest class is
just a subclass of Apache):
my $subr = $r->lookup_file('/home/httpd/perl-subr/script.pl');
print $subr->dir_config('foo');
You won't get the results you wanted.
As a side note: the issue we discussed here means that
/perl-subr/script.pl won't even run under mod_perl if configured in
the normal Apache::Registry way (using a <Location>
section), because the <Location> blocks won't be
applied. You'd have to use a <Directory> or
<Files> section configuration to achieve the desired
effect. As to the PerlSetVar discussion, using
<Directory> or <Files> section would solve the
problem.
PerlSetupEnv On will allow you to access the environment variables
like $ENV{REQUEST_URI}, which are available under CGI. However,
when programming handlers, there are always better ways to access
these variables through the Apache API. Therefore, it is recommended
to turn it Off except for scripts which absolutely require it. See
PerlSetupEnv Off.
For PerlWarn and PerlTaintCheck directives see the 'Switches -w, -T' section.
MinSpareServers, MaxSpareServers, StartServers and
MaxClients are standard Apache configuration directives that
control the number of servers that will be launched at server startup
and kept alive during the server's operation.
MaxRequestsPerChild lets you specify the maximum number of requests
which each child will be allowed to serve. When a process has served
MaxRequestsPerChild requests the parent kills it and replaces it
with a new one. There may also be other reasons why a child is
killed, so it does not mean that each child will in fact serve this
many requests, only that it will not be allowed to serve more than
that number.
These five directives are very important for achieving the best performance from your server. The section ' Performance Tuning by Tweaking Apache Configuration' provides all the details.
At server startup, before child processes are spawned to receive incoming requests, there is more that can be done than just preloading files. You might want to register code that will initialize a database connection for each child when it is forked, tie read-only dbm files, etc.
The startup.pl file is an ideal place to put the code that should be executed when the server starts. Once you have prepared the code, load it in httpd.conf before the rest of the mod_perl configuration directives like this:
PerlRequire /home/httpd/perl/lib/startup.pl
I must stress that all the code that is run at server initialization
time is run with root privileges if you are executing it as the root
user (which you have to do unless you choose to run the server on an
unprivileged port, above 1024). This means that anyone who has write
access to a script or module that is loaded by PerlModule or
PerlRequire effectively has root access to the system. You might
want to take a look at the new and experimental PerlOpmask
directive and PERL_OPMASK_DEFAULT compile time option to try to
disable some of the more dangerous operations.
Since the startup file is a file written in plain Perl, one can validate its syntax with:
% perl -c /home/httpd/perl/lib/startup.pl
Let's look at a real world startup file:
startup.pl
----------
use strict;
# Extend @INC if needed
use lib qw(/dir/foo /dir/bar);
# Make sure we are in a sane environment.
$ENV{MOD_PERL} or die "not running under mod_perl!";
# For things in the "/perl" URL
use Apache::Registry;
# Load Perl modules of your choice here
# This code is interpreted *once* when the server starts
use LWP::UserAgent ();
use Apache::DBI ();
use DBI ();
# Tell me more about warnings
use Carp ();
$SIG{__WARN__} = \&Carp::cluck;
# Load CGI.pm and call its compile() method to precompile
# (but not to import) its autoloaded methods.
use CGI ();
CGI->compile(':all');
# Initialize the database connections for each child
Apache::DBI->connect_on_init
("DBI:mysql:database=test;host=localhost",
"user","password",
{
PrintError => 1, # warn() on errors
RaiseError => 0, # don't die on error
AutoCommit => 1, # commit executes immediately
}
);
1;
Now we'll review the code explaining why each line is used.
use strict;
This pragma is worth using in every script longer than half a dozen lines. It will save a lot of time and debugging later on.
use lib qw(/dir/foo /dir/bar);
The only chance to permanently modify @INC before the server is
started is with this command. Later the running code can modify
@INC just for the moment it require()'s some file, and then
@INC's value gets reset to what it was originally.
$ENV{MOD_PERL} or die "not running under mod_perl!";
A sanity check, if Apache/mod_perl wasn't properly built, the above code will abort the server startup.
use Apache::Registry; use LWP::UserAgent (); use Apache::DBI (); use DBI ();
Preload the modules that get used by our Perl code serving the
requests. Unless you need the symbols (variables and subroutines)
exported by the modules you preload to accomplish something within
the startup file, don't import them, since it's just a waste of
startup time. Instead use the empty list () to tell the import()
function not to import anything.
use Carp ();
$SIG{__WARN__} = \&Carp::cluck;
This is a useful snippet to enable extended warnings logged in the error_log file. In addition to basic warnings, a trace of calls is added. This makes the tracking of the potential problem a much easier task, since you know who called whom. For example, with normal warnings you might see:
Use of uninitialized value at
/usr/lib/perl5/site_perl/5.005/Apache/DBI.pm line 110.
but you have no idea where it was called from. When we use Carp as
shown above we might see:
Use of uninitialized value at
/usr/lib/perl5/site_perl/5.005/Apache/DBI.pm line 110.
Apache::DBI::connect(undef, 'mydb::localhost', 'user',
'passwd', 'HASH(0x87a5108)') called at
/usr/lib/perl5/site_perl/5.005/i386-linux/DBI.pm line 382
DBI::connect('DBI', 'DBI:mysql:mydb::localhost', 'user',
'passwd', 'HASH(0x8375e4c)') called at
/usr/lib/perl5/site_perl/5.005/Apache/DBI.pm line 36
Apache::DBI::__ANON__('Apache=SCALAR(0x87a50c0)') called at
PerlChildInitHandler subroutine
`Apache::DBI::__ANON__' line 0
eval {...} called at PerlChildInitHandler subroutine
`Apache::DBI::__ANON__' line 0
we clearly see that the warning was triggered by eval()'uating the
Apache::DBI::__ANON__ which called DBI::connect (with the
arguments that we see as well), which in turn called the
Apache::DBI::connect method. Now we know where to look for our
problem.
use CGI ();
CGI->compile(':all');
Some modules create their subroutines at run time to improve their
load time. This helps when the module includes many subroutines, but
only a few are actually used. CGI.pm falls into this
category. Since with mod_perl the module is loaded only once, it might
be a good idea to precompile all or a part of its methods.
CGI.pm's compile() method performs this task. Notice that this is a
proprietary function of this module, other modules can implement this
feature or not and use this or some other name for this
functionality. As with all modules we preload in the startup file, we
don't import symbols from them as they will be lost when they go out
of the file's scope.
Note that starting with CGI.pm version 2.46, the recommended method
to precompile the code in CGI.pm is:
use CGI qw(-compile :all);
But the old method is still available for backward compatibility.
1;
As startup.pl is run through Perl's require(), it has to return
a true value so that Perl can make sure it has been successfully
loaded. Don't forget this (it's very easy to forget it).
See also the 'Apache::Status -- Embedded interpreter status information' section.
Every module loaded at server startup will be shared among the server children, saving a lot of RAM on your machine. Usually I put most of the code I develop into modules and preload them.
You can even preload your CGI script with Apache::RegistryLoader
(See Preload Perl modules at server startup)
and you can get the children to preopen their database connections
with Apache::DBI.
Some people wonder why you need to duplicate the use() clause in
the startup file and in the script itself. The confusion arises due to
misunderstanding the use() function. use() normally performs two
operations, namely require() and import(), called within a
BEGIN block. See the section "use()" for a detailed
explanation of the use(), require() and import() functions.
In the startup file we don't want to import any symbols since they will be lost when we leave the scope of the startup file anyway, i.e. they won't be visible to any of the child processes which run our mod_perl scripts. Instead we want to preload the module in the startup file and then import any symbols that we actually need in each script individually.
Normally when we write use MyModule;, use() will both load the
module and import its symbols; so for the startup file we write use
MyModule (); and the empty parentheses will ensure that the module is
loaded but that no symbols are imported. Then in the actual mod_perl
script we write use() in the standard way, e.g. use MyModule;.
Since the module has already been preloaded, the only action taken is
to import the symbols. For example in the startup file you write:
use CGI ();
since you probably don't need any symbols to be imported there. But in your code you would probably write:
use CGI qw(:html);
For example, if you have use()'d Apache::Constants in the
startup file, it does not mean you can have the following handler:
package MyModule;
sub handler {
my $r = shift;
## Cool stuff goes here
return OK;
}
1;
You would either need to add:
use Apache::Constants qw( OK );
Or use the fully qualified name:
return Apache::Constants::OK;
If you want to use the function interface without exporting the
symbols, use fully qualified function names, e.g. CGI::param. The
same rule applies to variables, you can import variables and you can
access them by their full name. e g. $My::Module::bar. When you use
the object oriented (method) interface you don't need to export the
method symbols.
Technically, you aren't required to supply the use() statement in your
(handler?) code if it was already loaded during server startup
(i.e. by 'PerlRequire startup.pl'). When writing your code,
however, you should not assume the module code has been preloaded. In
the future, you or someone else will revisit this code and will not
understand how it is possible to use a module's methods without first
loading the module itself.
Read the Exporter and perlmod manpages for more information
about import().
With <Perl>...</Perl> sections, it is possible
to configure your server entirely in Perl.
<Perl> sections can contain any and as much Perl code as
you wish. These sections are compiled into a special package whose
symbol table mod_perl can then walk and grind the names and values of
Perl variables/structures through the Apache core configuration gears.
Most of the configuration directives can be represented as scalars
($scalar) or lists (@list). A @list inside these sections is
simply converted into a space delimited string for you. Here is an
example:
httpd.conf ------------ <Perl> @PerlModule = qw(Mail::Send Devel::Peek); #run the server as whoever starts it $User = getpwuid($>) || $>; $Group = getgrgid($)) || $); $ServerAdmin = $User; </Perl>
Block sections such as <Location>..</Location>
are represented in a %Location hash, e.g.:
<Perl>
$Location{"/~dougm/"} = {
AuthUserFile => '/tmp/htpasswd',
AuthType => 'Basic',
AuthName => 'test',
DirectoryIndex => [qw(index.html index.htm)],
Limit => {
METHODS => 'GET POST',
require => 'user dougm',
},
};
</Perl>
If an Apache directive can take two or three arguments you may push
strings (the lowest number of arguments will be shifted off the
@list) or use an array reference to handle any number greater than
the minimum for that directive:
push @Redirect, "/foo", "http://www.foo.com/"; push @Redirect, "/imdb", "http://www.imdb.com/"; push @Redirect, [qw(temp "/here" "http://www.there.com")];
Other section counterparts include %VirtualHost, %Directory and
%Files.
To pass all environment variables to the children with a single
configuration directive, rather than listing each one via PassEnv
or PerlPassEnv, a <Perl> section could read in a file and:
push @PerlPassEnv, [$key => $val];
or
Apache->httpd_conf("PerlPassEnv $key $val");
These are somewhat simple examples, but they should give you the basic idea. You can mix in any Perl code you desire. See eg/httpd.conf.pl and eg/perl_sections.txt in the mod_perl distribution for more examples.
Assume that you have a cluster of machines with similar configurations
and only small distinctions between them: ideally you would want to
maintain a single configuration file, but because the configurations
aren't exactly the same (e.g. the ServerName directive) it's not
quite that simple.
<Perl> sections come to rescue. Now you have a single
configuration file and the full power of Perl to tweak the local
configuration. For example to solve the problem of the ServerName
directive you might have this <Perl> section:
<Perl> $ServerName = `hostname`; </Perl>
For example if you want to allow personal directories on all machines except the ones whose names start with secure:
<Perl>
$ServerName = `hostname`;
if ( $ServerName !~ /^secure/) {
$UserDir = "public.html";
} else {
$UserDir = "DISABLED";
}
</Perl>
Behind the scenes, mod_perl defines a package called
Apache::ReadConfig. Here it keeps all the variables that you
define inside the <Perl> sections. Therefore it's not
necessarily to configure the server within the <Perl>
sections. Actually what you can do is to write the Perl code to
configure the server just like you'd do in the <Perl>
sections, but instead place it into a separate file that should be
called during the configuration parsing with either PerlModule or
PerlRequire directives, or from within the startup file. All you
have to do is to declare the package Apache::ReadConfig within this
file. Using the last example:
apache_config.pl
----------------
package Apache::ReadConfig;
$ServerName = `hostname`;
if ( $ServerName !~ /^secure/) {
$UserDir = "public.html";
} else {
$UserDir = "DISABLED";
}
1;
httpd.conf
----------
PerlRequire /home/httpd/perl/lib/apache_config.pl
To enable <Perl> sections you should build mod_perl with
perl Makefile.PL PERL_SECTIONS=1 [ ... ].
Be careful when you declare package names inside <Perl>
sections, for example this code has a problem:
<Perl>
package My::Trans;
use Apache::Constants qw(:common);
sub handler{ OK }
$PerlTransHandler = "My::Trans";
</Perl>
When you put code inside a <Perl> section, by default it
actually goes into the Apache::ReadConfig package, which is already
declared for you. This means that the PerlTransHandler we have
tried to define above is actually undefined. If you define a
different package name within a <Perl> section you must
make sure to close the scope of that package and return to the
Apache::ReadConfig package when you want to define the
configuration directives, like this:
<Perl>
package My::Trans;
use Apache::Constants qw(:common);
sub handler{ OK }
package Apache::ReadConfig;
$PerlTransHandler = "My::Trans";
</Perl>
This section shows how to check and dump the configuration you have
made with the help of <Perl> sections in httpd.conf.
To check the <Perl> section syntax outside of httpd, we
make it look like a Perl script:
<Perl> # !perl # ... code here ... __END__ </Perl>
Now you may run:
perl -cx httpd.conf
In a running httpd you can see how you have configured the
<Perl> sections through the URI
/perl-status, by choosing Perl
Section Configuration from the menu. In order to make this item show
up in the menu you should set $Apache::Server::SaveConfig to a true
value. When you do that the Apache::ReadConfig namespace (in which
the configuration data is stored) will not be flushed, making
configuration data available to Perl modules at request time.
Example:
<Perl> $Apache::Server::SaveConfig = 1; $DocumentRoot = ... ... </Perl>
At request time, the value of $DocumentRoot can be accessed with the fully qualified name $Apache::ReadConfig::DocumentRoot.
You can dump the configuration of <Perl> sections like
this:
<Perl> use Apache::PerlSections(); ... # Configuration Perl code here ... print STDERR Apache::PerlSections->dump(); </Perl>
Alternatively you can store it in a file:
Apache::PerlSections->store("httpd_config.pl");
You can then require() that file in some other <Perl>
section.
<Perl> SectionsIf the Perl code doesn't compile, the server won't start. If the
generated Apache config is invalid, <Perl> sections have
always just logged an error and carried on, since there might be
globals in the section that are not intended for the config.
The variable $Apache::Server::StrictPerlSections has been added in
mod_perl version 1.22. If you set this variable to a true value, for
example
$Apache::Server::StrictPerlSections = 1;
then mod_perl will not tolerate invalid Apache configuration syntax
and will croak (die) if this is the case. At the time of writing the
default value is 0.
If you compile mod_perl with PERL_TRACE=1 and set the environment
variable MOD_PERL_TRACE then you should see
some useful diagnostics when mod_perl is processing <Perl>
sections.
The Perl %ENV is cleared during startup, but the C environment is
left intact and so you can use it to set @PassEnv.
For more info see Writing Apache Modules with Perl and C, Chapter 8: http://modperl.com:9000/book/chapters/ch8.html
apachectl configtest tests the configuration file without starting
the server. You can safely validate the configuration file on your
production server, if you run this test before you restart the server
with apachectl restart. Of course it is not 100% perfect, but it
will reveal any syntax errors you might have made while editing the
file.
'apachectl configtest' is the same as 'httpd -t' and it doesn't
just parse the code in startup.pl, it actually executes it.
<Perl> configuration has always started Perl during the
configuration read, and Perl{Require,Module} do so as well.
Of course we assume that the code that gets called during this test
cannot cause any harm to your running production environment. The
following hint shows how to prevent the code in the startup script and
<Perl> from being executed during the syntax check, if
that's what you want.
If you want your startup code to get control over the -t
(configtest) server launch, start the server configuration test
with:
httpd -t -Dsyntax_check
and, if for example you want to prevent your startup code from being executed, at the top of the code add:
return if Apache->define('syntax_check');
The nifty mod_info module displays the complete server configuration in your browser. In order to use it you have compile it in or, if the server was compiled with DSO mode enabled, load it as an object. Then just uncomment the ready-prepared section in the httpd.conf file:
<Location /server-info>
SetHandler server-info
Order deny,allow
Deny from all
Allow from www.example.com
</Location>
Now restart the server and issue the request:
http://www.example.com/server-info
If you are using a two-server setup, with a mod_perl server listening on a high port, it is advised that you do not publish the number of the high port number in URLs. Rather use a proxying rewrite rule in the non-mod_perl server:
RewriteEngine On RewriteLogLevel 0 RewriteRule ^/perl/(.*) http://localhost:8080/perl/$1 [P] ProxyPassReverse / http://localhost/
I was told one problem with publishing high port numbers is that IE 4.x has a bug when re-posting data to a non-port-80 URL. It drops the port designator, and uses port 80 anyway.
Another reason is that firewalls probably will have the high port closed, therefore users behind the firewalls will be unable to reach your service, running on the blocked port.
mod_macro is an Apache module written by Fabien Coelho that lets you define and use macros in the Apache configuration file.
mod_macro can be really useful when you have many virtual hosts, and where each virtual host has a number of scripts/modules, most of them with a moderately complex configuration setup.
First download the latest version of mod_macro from http://www.cri.ensmp.fr/~coelho/mod_macro/ , and configure your Apache server to use this module.
Here are some useful macros for mod_perl users:
# set up a registry script <Macro registry> SetHandler "perl-script" PerlHandler Apache::Registry Options +ExecCGI </Macro> # example Alias /stuff /usr/www/scripts/stuff <Location /stuff> Use registry </Location>
If your registry scripts are all located in the same directory, and your aliasing rules consistent, you can use this macro:
# set up a registry script for a specific location <Macro registry $location $script> Alias /$location /home/httpd/perl/scripts/$script <Location /$location> SetHandler "perl-script" PerlHandler Apache::Registry Options +ExecCGI </Location> </Macro> # example Use registry stuff stuff.pl
If you're using content handlers packaged as modules, you can use the following macro:
# set up a mod_perl content handler module <Macro modperl $module> SetHandler "perl-script" Options +ExecCGI PerlHandler $module </Macro> #examples <Location /perl-status> PerlSetVar StatusPeek On PerlSetVar StatusGraph On PerlSetVar StatusDumper On Use modperl Apache::Status </Location>
The following macro sets up a Location for use with HTML::Embperl.
Here we define all ".html" files to be processed by Embperl.
<Macro embperl> SetHandler "perl-script" Options +ExecCGI PerlHandler HTML::Embperl PerlSetEnv EMBPERL_FILESMATCH \.html$ </Macro> # examples <Location /mrtg> Use embperl </Location>
Macros are also very useful for things that tend to be verbose, such as setting up Basic Authentication:
# Sets up Basic Authentication <Macro BasicAuth $realm $group> Order deny,allow Satisfy any AuthType Basic AuthName $realm AuthGroupFile /usr/www/auth/groups AuthUserFile /usr/www/auth/users Require group $group Deny from all </Macro> # example of use <Location /stats> Use BasicAuth WebStats Admin </Location>
Finally, here is a complete example that uses macros to set up simple
virtual hosts. It uses the BasicAuth macro defined previously (yes,
macros can be nested!).
<Macro vhost $ip $domain $docroot $admingroup> <VirtualHost $ip> ServerAdmin webmaster@$domain DocumentRoot /usr/www/htdocs/$docroot ServerName www.$domain <Location /stats> Use BasicAuth Stats-$domain $admingroup </Location> </VirtualHost> </Macro> # define some virtual hosts Use vhost 10.1.1.1 example.com example example-admin Use vhost 10.1.1.2 example.net examplenet examplenet-admin
mod_macro is also useful in a non vhost setting. Some sites for example have lots of scripts which people use to view various statistics, email settings and etc. It is much easier to read things like:
use /forwards email/showforwards use /webstats web/showstats
The actual macros for the last example are left as an exercise to reader. These can be easily constructed based on the examples presented in this section.
Check your configuration files and make sure that the ExecCGI is
turned on in your configurations.
<Location /perl>
SetHandler perl-script
PerlHandler Apache::Registry
Options ExecCGI
allow from all
PerlSendHeader On
</Location>
Did you put PerlSendHeader On in the configuration part of the
<Location foo></Location>.
No. Any virtual host will be able to see the routines from a startup.pl loaded for any other virtual host.
You can use PerlSetEnv PERL5LIB ... or a PerlFixupHandler with
the lib pragma (use lib qw(...)).
A better way is to use Apache::PerlVINC
This has been a bug before, last fixed in 1.15_01, i.e. if you are
running 1.15, that could be the problem. You should set this variable
in a startup file (which you load with PerlRequire in
httpd.conf):
$Apache::Registry::NameWithVirtualHost = 1;
But, as we know sometimes a bug turns out to be a feature. If the same
script is running for more than one Virtual host on the same machine,
this can be a waste, right? Set it to 0 in a startup script if you
want to turn it off and have this bug as a feature. (Only makes sense
if you are sure that there will be no other scripts with the same
path/name). It also saves you some memory as well.
$Apache::Registry::NameWithVirtualHost = 0;
The problem was reported by users who declared mod_perl configuration
inside a <Directory> section for all files matching *.pl. The
problem went away after placing the directives in a <Files>
section.
The mod_alias and mod_rewrite are both Trans handlers in the normal case. So in the setup where both are used, if mod_alias runs first and matches it will return OK and mod_rewrite won't see the request.
The opposite can happen as well, where mod_rewrite rules apply but the
Alias directives are completely ignored.
The behavior is not random, but depends on the Apache modules loading order. Apache modules are being executed in reverse order, i.e. module that was Added first will be executed last.
The solution is not to mix mod_rewrite and mod_alias. mod_rewrite
does everything mod_alias does--except for ScriptAlias which is not
really relevant to mod_perl anyway. Don't rely on the module ordering,
but use explicitly disjoint URL namespaces for Alias and
Rewrite. In other words any URL regex that can potentially match a
Rewrite rule should not be used in an Alias, and vice
versa. Given that mod_rewrite can easily do what mod_alias does, it's
no problem.
Here is one of the examples where Alias is replaced with
RedirectMatch. This is a snippet of configuration at the light
non-mod_perl Apache server:
RewriteEngine on RewriteLogLevel 0 RewriteRule ^/(perl.*)$ http://127.0.0.1:8045/$1 [P,L] RewriteRule ^/(mail.*)$ http://127.0.0.1:8045/$1 [P,L] NoCache * ProxyPassReverse / http://www.example.com/ RedirectMatch permanent ^/$ /pages/index RedirectMatch permanent ^/foo$ /pages/bar
This configuration works fine because any URI that matches one of the redirects will never match one of the rewrite rules.
In the above setup we proxy requests starting with /perl or /mail to the mod_perl server, forbid proxy requests to the external sites, and make sure that the proxied requests will use the http://www.example.com/ as their URL on the way back to the client.
The RedirectMatch settings work exactly like if you'd write:
Alias / /pages/index Alias /foo /pages/bar
But as we told before we don't want to mix the two.
Here is another example where the redirect is done by a rewrite rule:
RewriteEngine on
RewriteLogLevel 0
RewriteMap lowercase int:tolower
RewriteRule ^/(perl.*)$ http://127.0.0.1:8042/$1 [P,L]
RewriteRule ^/$ /pages/welcome.htm [R=301,L]
RewriteRule ^(.*)$ ${lowercase:$1}
NoCache *
ProxyPassReverse / http://www.example.com/
If we omit the rewrite rule that matches ^/$, and instead use a
redirect, it will never be called, because the URL is still matched by
the last rule ^(.*)$. This is a somewhat contrived example because
that last regex could be rewritten as ^(/.+)$ and all would be
well.
No, they don't.
So for example if you do:
PerlSetEnv foo bar
It'll be seen from mod_perl, but not mod_cgi or any other module.
The more modules you have in your web server, the more complex the code.
The more complex the code in your web server, the more chances for bugs.
The more chances for bugs, the more chance that some of those bugs may involve security breaches.
Because mod_perl runs within an httpd child process, it runs with the
User ID and Group ID specified in the httpd.conf file. This
User/Group should have the lowest possible privileges. It
should only have access to world readable files, even better only
files that belongs to this user. Even so, careless scripts can give
away information. You would not want your /etc/passwd file to be
readable over the net, for instance, even if you use shadow passwords.
When a handler needs write permissions, make sure that only the user, the server is running under, has write permissions to the files. Sometimes you need group write permissions, but be very careful, because a buggy or malicious code run in the server may destroy files writable by the server.
Make sure to run the server under:
PerlTaintCheck On
setting in the httpd.conf file. Taint checking doesn't ensure that your code is completely safe from external hacks, but it does forces you to improve your code to prevent many potential security problems.
It is better not to expose the mod_perl server to the outside world, for it creates a potential security risk by revealing which Apache modules used by the server and the OS the server is running on.
You can see what information is revealed by your server, by telneting to it and issuing some request. For example:
% telnet localhost 8080 Trying 127.0.0.1 Connected to localhost Escape character is '^]'. HEAD / HTTP1.0 HTTP/1.1 200 OK Date: Sun, 16 Apr 2000 11:06:25 GMT Server: Apache/1.3.12 (Unix) mod_perl/1.22 mod_ssl/2.6.2 OpenSSL/0.9.5 [more lines snipped]
So as you see that a lot of information is revealed and a Full
ServerTokens has been used.
We never were completely sure why the default of the ServerTokens
directive in Apache is Full rather than Minimal. Seems like you
would only make it Full if you are debugging. Probably the reason
for using the ServerTokens Full is for a show-off, so Netcraft
(http://netcraft.com) and other similar survey services will count
more Apache servers, which is good for all of us, but you really want
to reveal as little information as possible to the potential crackers.
Another approach is to modify httpd sources to reveal no unwanted
information, so all responses will return an empty or phony Server:
field.
From the other point of view, security by obscurity is a lack of security. Any determined cracker will eventually figure out what version of Apache run and what third party modules you have built in.
An even better approach is to completely hide the mod_perl server behind a front-end or a proxy server, so the server cannot be accessed directly.
When the server is restarted, the configuration and module
initialization phases are called twice in total before the children
are forked. The second restart is done in order to ensure that future
restarts will work correctly, by making sure that all modules can
survive a restart (SIGHUP). This is very important if you restart a
production server.
You can control what code will be executed on the start or restart by
checking the value of $Apache::Server::Starting and
$Apache::Server::ReStarting respectively. The former variable is
true when the server is starting and the latter is true when
it's restarting.
For example:
<Perl> print STDERR "Server is Starting\n" if $Apache::Server::Starting; print STDERR "Server is ReStarting\n" if $Apache::Server::ReStarting; </Perl>
The startup.pl file and similar loaded via PerlModule or
PerlRequire are compiled only once. Because once the module is
compiled it enters the special %INC hash. When Apache
restarts--Perl checks whether the module or script in question is
already registered in %INC and won't try to compile it again.
So the only code that you might need to protect from running on
restart is the one in the <Perl> sections. But since one
usually uses the <Perl> sections mainly for on the fly
configuration creation, there shouldn't be a reason why it'd be
undesirable to run the code more than once.
Let's say that you have a frontend server running mod_ssl, mod_rewrite and mod_proxy. You want to make sure that your user is using a secure connection for some specific actions like login information submission. You don't want to let the user login unless the request was submitted through a secure port.
Since you have to proxy_pass the request between front and backend servers, you cannot know where the connection has come from. Neither is using the HTTP headers reliable.
A possible solution for this problem is to have the mod_perl
server listen on two different ports (e.g. 8000 and 8001) and have the
mod_rewrite proxy rule in the regular server redirect to port 8000 and
the mod_rewrite proxy rule in the SSL virtual host redirect to port
8001. In the mod_perl server just check the PORT variable to tell
if the connection is secure.
This is covered in the Eagle Book in a great detail. This is just a simple example, showing how to add your own Configuration directives.
Makefile.PL
-----------
package Apache::TestDirective;
use ExtUtils::MakeMaker;
use Apache::ExtUtils qw(command_table);
use Apache::src ();
my @directives = ({
name => 'Directive4',
errmsg => 'Anything',
args_how => 'RAW_ARGS',
req_override=> 'OR_ALL',
});
command_table(\@directives);
WriteMakefile(
NAME => 'Apache::TestDirective',
VERSION_FROM => 'TestDirective.pm',
INC => Apache::src->new->inc,
);
TestDirective.pm
----------------
package Apache::TestDirective;
use strict;
use Apache::ModuleConfig ();
use DynaLoader ();
if ($ENV{MOD_PERL}) {
no strict;
$VERSION = '0.01';
@ISA = qw(DynaLoader);
__PACKAGE__->bootstrap($VERSION); #command table, etc.
}
sub Directive4 {
warn "Directive4 @_\n";
}
1;
__END__
In the mod_perl source tree, add this to t/docs/startup.pl:
use blib qw(/home/dougm/test/Apache/TestDirective);
and at the bottom of t/conf/httpd.conf:
PerlModule Apache::TestDirective Directive4 hi
Test it:
% make start_httpd % make kill_httpd
You should see:
Directive4 Apache::TestDirective=HASH(0x83379d0) Apache::CmdParms=SCALAR(0x862b80c) hi
And in the error log file:
% grep Directive4 t/logs/error_log Directive4 Apache::TestDirective=HASH(0x83119dc) Apache::CmdParms=SCALAR(0x8326878) hi
If it didn't work as expected try building mod_perl with PERL_TRACE=1,
then do:
setenv MOD_PERL_TRACE all
before starting the server. Now you should get some useful diagnostics.
Maintainer is the person(s) you should contact with updates, corrections and patches.
Stas Bekman [http://stason.org/]
Stas Bekman [http://stason.org/]
Only the major authors are listed above. For contributors see the Changes file.
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Last modified Sat Feb 15 17:38:37 2014
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