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HTML::Mason::Admin - Mason Administrator's Manual
This manual is written for the sysadmin/webmaster in charge of
installing, configuring, or tuning a Mason system. The bulk of the
documentation assumes that you are using mod_perl. See ЗАПУСК ВНЕ MOD_PERL
for more details. For more details on mod_perl, visit
the mod_perl website at http://perl.apache.org/.
Mason includes a module specifically designed to integrate Mason and
mod_perl (1 and 2), HTML::Mason::ApacheHandler. By telling
mod_perl to hand content requests to this module, you can use Mason to
generate web pages. There are two ways to configure Mason under
mod_perl.
- Basic
Mason provides reasonable default behavior under mod_perl, so using
Mason can be as simple as adding two directives to your Apache
configuration file. Throughout this document, we will assume that
your Apache configuration file is called httpd.conf. By adding
more configuration parameters to this file you can implement more
complex behaviors.
- Advanced
If the basic method does not provide enough flexibility for you, you
can wrap Mason in a custom mod_perl handler. The wrapper code you
write can create its own Mason objects, or it can take advantage of
httpd.conf configuration parameters and let Mason create the
objects it needs by itself.
We recommend that you start with the basic method and work your way
forward as the need for flexibility arises.
Mason is very flexible, and you can replace parts of it by creating
your own classes. This documentation assumes that you are simply
using the classes provided in the Mason distribution. Subclassing is
covered in the Subclassing document. The
two topics are orthogonal, as you can mix the configuration techniques
discussed here with your own custom subclasses.
The absolutely most minimal configuration looks like this:
PerlModule HTML::Mason::ApacheHandler
<Location />
SetHandler perl-script
PerlHandler HTML::Mason::ApacheHandler
</Location>
This configuration tells Apache to serve all URLs through Mason (see
the next section for a more realistic strategy). We use the
PerlModule line to tell mod_perl to load Mason once at startup time,
saving time and memory. This example does not set any Mason
configuration parameters, so Mason uses its default values.
If this is your first time installing and using Mason, we recommend
that you use the above configuration in a test webserver to start
with. This will let you play with Mason under mod_perl with a minimum
of fuss. Once you've gotten this working, then come back and read the
rest of the document for further possibilities.
As it turns out, serving every URL through Mason is a bad idea for two
reasons:
-
Mason should be prevented from handling images, tarballs, and other
binary files. Not only will performance suffer, but binary files may
inadvertently contain a Mason character sequence such as ``<%''. These
files should be instead served by Apache's default content handler.
-
Mason should be prevented from serving private (non-top-level) Mason
components to users. For example, if you used a utility component for
performing arbitrary sql queries, you wouldn't want external users to
be able to access it via a URL. Requests for private components should
simply result in a 404 NOT_FOUND.
The easiest way to distinguish between different types of files is
with filename extensions. While many naming schemes are possible, we
suggest using ``normal'' extensions for top-level components and
adding an ``m'' prefix for private components. For example,
Top-level Private
Component outputs HTML .html .mhtml
Component outputs text .txt .mtxt
Component executes Perl .pl .mpl
This scheme minimizes the chance of confusing browsers about content
type, scales well for new classes of content (e.g. .js/.mjs for
javascript), and makes transparent the fact that you are using Mason
versus some other package.
Here is a configuration that enforces this naming scheme:
PerlModule HTML::Mason::ApacheHandler
<LocationMatch "(\.html|\.txt|\.pl)$">
SetHandler perl-script
PerlHandler HTML::Mason::ApacheHandler
</LocationMatch>
<LocationMatch "(\.m(html|txt|pl)|dhandler|autohandler)$">
SetHandler perl-script
PerlInitHandler Apache::Constants::NOT_FOUND
</LocationMatch>
The first block causes URLs ending in .html, .txt, or .pl to be served
through Mason. The second block causes requests to private components
to return 404 NOT_FOUND, preventing unscrupulous users from even
knowing which private components exist. Any other file extensions
(e.g. .gif, .tgz) will be served by Apache's default content handler.
You might prefer FilesMatch to LocationMatch. However, be aware
that LocationMatch will work best in conjunction with Mason's
dhandlers.
Mason allows you to flexibly configure its behavior via httpd.conf
configuration parameters.
These configuration parameters are set via mod_perl's PerlSetVar
and PerlAddVar directives. Though these parameters are all strings
in your httpd.conf file, Mason treats different directives as
containing different types of values:
- string
The variable's value is simply taken literally and used. The string
should be surrounded by quotes if the it contains whitespace. The
quotes will be automatically removed by Apache before Mason sees the
variable.
- boolean
The variable's value is used as a boolean, and is subject to Perl's
rules on truth/falseness. It is recommended that you use 0 (false) or
1 (true) for these arguments.
- code
The string is treated as a piece of code and eval'ed. This is used
for parameters that expect subroutine references. For example, an
anonymous subroutine might look like:
PerlSetVar MasonOutMode "sub { ... }"
A named subroutine reference would look like this:
PerlSetVar MasonOutMode "\&Some::Module::handle_output"
- list
To set a list parameter, use PerlAddVar for the values, like this:
PerlAddVar MasonPreloads /foo/bar/baz.comp
PerlAddVar MasonPreloads /foo/bar/quux.comp
- hash_list
Just like a list parameter, use PerlAddVar for the values.
However, in the case of a hash_list, each element should be a
key/value pair separated by ``=>'':
PerlAddVar MasonDataCacheDefaults "cache_class => MemoryCache"
PerlAddVar MasonDataCacheDefaults "namespace => foo"
Take note that the right hand side of the each pair should not be
quoted.
See HTML::Mason::Params for a full list
of parameters, and their associated types.
The component root (comp_root) marks the top of your component
hierarchy. When running Mason with the ApacheHandler or CGIHandler
modules, this defaults to your document root.
The component root defines how component paths are translated into
real file paths. If your component root is /usr/local/httpd/docs, a
component path of /products/index.html translates to the file
/usr/local/httpd/docs/products/index.html.
One cannot call a component outside the component root. If Apache
passes a file through Mason that is outside the component root (say,
as the result of an Alias) you will get a 404 and a warning in the
logs.
You may also specify multiple component roots in the spirit of Perl's
@INC. Each root is assigned a key that identifies the root
mnemonically. For example, in httpd.conf:
PerlAddVar MasonCompRoot "private => /usr/home/joe/comps"
PerlAddVar MasonCompRoot "main => /usr/local/www/htdocs"
This specifies two component roots, a main component tree and a
private tree which overrides certain components. The order is
respected ala @INC, so private is searched first and main
second.
The component root keys must be unique in a case-insensitive
comparison. The keys are used in several ways. They help to
distinguish component caches and object files between different
component roots, and they appear in the title() of a component.
The data directory (data_dir) is a writable directory that Mason
uses for various features and optimizations. By default, it is a
directory called ``mason'' under your Apache server root. Because Mason
will not use a default data directory under a top-level directory,
you will need to change this on certain systems that assign a
high-level server root such as /usr or /etc.
Mason will create the directory on startup, if necessary, and set its
permissions according to the web server User/Group.
Components will often need access to external Perl modules. There are
several ways to load them.
-
The httpd PerlModule directive:
PerlModule CGI
PerlModule LWP
-
In the <%once> section of the component(s) that use the module.
<%once>
use CGI ':standard';
use LWP;
</%once>
Each method has its own trade-offs:
The first method ensures that the module will be loaded by the Apache
parent process at startup time, saving time and memory. The second
method, in contrast, will cause the modules to be loaded by each
server child. On the other hand this could save memory if the
component and module are rarely used. See the mod_perl guide's tuning
section and Vivek Khera's mod_perl tuning guide for more details on
this issue.
The second method uses the modules from inside the package used by
components (HTML::Mason::Commands), meaning that exported method
names and other symbols will be usable from components. The first
method, in contrast, will import symbols into the main package. The
significance of this depends on whether the modules export symbols and
whether you want to use them from components.
If you want to preload the modules in your httpd.conf file, and
still have them export symbols into the HTML::Mason::Commands
namespace, you can do this:
<Perl>
{ package HTML::Mason::Commands;
use CGI;
use LWP;
}
</Perl>
A Perl section will also work for including local library paths:
<Perl>
use lib '/path/to/local/lib';
</Perl>
By default Mason will decline requests for directories, leaving Apache
to serve up a directory index or a FORBIDDEN as appropriate.
Unfortunately this rule applies even if there is a dhandler in the
directory: /foo/bar/dhandler does not get a chance to
handle a request for /foo/bar/.
If you would like Mason to handle directory requests, set
decline_dirs to 0. The dhandler that catches a directory request
is responsible for setting a reasonable content type via
$r->content_type().
These examples extend the single site configurations given so far.
If you want to share some components between your sites, arrange your
httpd.conf so that all DocumentRoots live under a single component
space:
# Web site #1
<VirtualHost www.site1.com>
DocumentRoot /usr/local/www/htdocs/site1
<LocationMatch ...>
SetHandler perl-script
PerlHandler HTML::Mason::ApacheHandler
</LocationMatch>
</VirtualHost>
# Web site #2
<VirtualHost www.site2.com>
DocumentRoot /usr/local/www/htdocs/site2
<LocationMatch ...>
SetHandler perl-script
PerlHandler HTML::Mason::ApacheHandler
</LocationMatch>
</VirtualHost>
# Mason configuration
PerlSetVar MasonCompRoot /usr/local/www/htdocs
PerlSetVar MasonDataDir /usr/local/mason
PerlModule HTML::Mason::ApacheHandler
The directory structure for this scenario might look like:
/usr/local/www/htdocs/ # component root
+- shared/ # shared components
+- site1/ # DocumentRoot for first site
+- site2/ # DocumentRoot for second site
Incoming URLs for each site can only request components in their
respective DocumentRoots, while components internally can call other
components anywhere in the component space. The shared/ directory
is a private directory for use by components, inaccessible from the
Web.
If your sites need to have completely distinct component hierarchies,
e.g. if you are providing Mason ISP services for multiple users, then
the component root must change depending on the site requested.
<VirtualHost www.site1.com>
DocumentRoot /usr/local/www/htdocs/site1
# Mason configuration
PerlSetVar MasonCompRoot /usr/local/www/htdocs/site1
PerlSetVar MasonDataDir /usr/local/mason/site1
<LocationMatch ...>
SetHandler perl-script
PerlHandler HTML::Mason::ApacheHandler
</LocationMatch>
</VirtualHost>
# Web site #2
<VirtualHost www.site2.com>
DocumentRoot /usr/local/www/htdocs/site2
# Mason configuration
PerlSetVar MasonCompRoot /usr/local/www/htdocs/site2
PerlSetVar MasonDataDir /usr/local/mason/site2
<LocationMatch ...>
SetHandler perl-script
PerlHandler HTML::Mason::ApacheHandler
</LocationMatch>
</VirtualHost>
As mentioned previously, it is possible to write a custom mod_perl
content handler that wraps around Mason and provides basically
unlimited flexibility when handling requests. In this section, we
show some basic wrappers and re-implement some of the functionality
previously discussed, such as declining image requests and protecting
private components.
In addition, we discuss some of the possibilities that become
available when you create a custom wrapper around Mason's request
handling mechanism. This wrapper generally consists of two parts.
The initialization portion, run at server startup, will load any
needed modules and create objects. The other portion is the
handler() subroutine, which handles web page requests.
To create a wrapper, you simply need to define a handler()
subroutine in the package of your choice, and tell mod_perl to use it
as a content handler. The file that defines the handler()
subroutine can be a module, or you can simply load a simple file that
contains this subroutine definition. The latter solution was, for a
long time, the only way to configure Mason, and the file used was
traditionally called handler.pl.
Nowadays, we recommend that you create a custom module in the
appropriate namespace and define your handler() subroutine there.
The advantage to this approach is that it uses well-known techniques
for creating and installing modules, but it does require a bit more
work than simply dropping a script file into the Apache configuration
directory. But because the process is better defined, it may ``feel''
more solid to some folks than the script approach.
The eg/ directory of the Mason distribution contains a couple
sample modules that define handler() subroutines. Let's assume
that your module, like the example, defines a handler() in the
package MyApp::Mason. In this case, your Apache configuration
would look like this:
PerlModule MyApp::Mason
<LocationMatch ...>
SetHandler perl-script
PerlHandler MyApp::Mason
</LocationMatch>
You may still see references to a handler.pl file in the Mason
users list archives, as well as the FAQ. These references will
generally be applicable to any custom code wrapping Mason.
Sometimes people attempt to write a wrapper and configure Mason
with PerlSetVar directives in their Apache configuration file.
This does not work. When you give mod_perl this configuration:
PerlHandler HTML::Mason::ApacheHandler
it will dispatch directly to the <
HTML::Mason::ApacheHandler-handler() >> method, without ever
executing your wrapper code. However, you can mix the two methods.
See Mixing httpd.conf Configuration with a Wrapper
You can also put your wrapper code in a <Perl> block as part of
your httpd.conf file. The result is no different than loading a
file via the PerlRequire directive.
Regardless of how you load your wrapper code, it will always work the
same way. The handler() subroutine should expect to receive the
Apache request object representing the current request. This request
object is used by the ApacheHandler module to determine what component
is being called.
Let's look at the guts of some wrapper code. Here's a first version:
package MyApp::Mason;
use strict;
use HTML::Mason::ApacheHandler;
my $ah =
HTML::Mason::ApacheHandler->new
( comp_root => '/path/to/comp/root',
data_dir => '/path/to/data/dir' );
sub handler {
my ($r) = @_;
return $ah->handle_request($r);
}
This wrapper is fully functional, but it doesn't actually do anything
you couldn't do more easily by configuring Mason via the httpd.conf
file. However, it does serve as a good skeleton to which additional
functionality can easily be added.
Since you are loading an arbitrary piece of code to define your
wrapper, you can easily load other modules needed for your application
at the same time. For example, you might simple add these lines to
the wrapper code above:
{
package HTML::Mason::Commands;
use MIME::Base64;
}
Explicitly setting the package to HTML::Mason::Commands makes sure
that any symbols that the loaded modules export (constants,
subroutines, etc.) get exported into the namespace under which
components run. Of course, if you've changed the component namespace,
make sure to change the package name here as well.
Alternatively, you might consider creating a separate piece of code to
load the modules you need. For example, you might create a module
called MyApp::MasonInit:
{
package HTML::Mason::Commands;
use Apache::Constants qw(:common);
use Apache::URI;
use File::Temp;
}
1;
This can be loaded via a PerlModule directive in the httpd.conf
file, or in the wrapper code itself via use.
An example of something you can only do with wrapper code is deciding
at run-time whether a component can be accessed at the top-level based
on a complex property of the component. For example, here's a piece
of code that uses the current user and a component's access_level
attribute to control access:
sub handler {
my ($r) = @_;
my $req = $ah->prepare_request($r);
my $comp = $req->request_comp;
# this is done via magic hand-waving ...
my $user = get_user_from_cookie();
# remember, attributes are inherited so this could come from a
# component higher up the inheritance chain
my $required_access = $comp->attr('access_level');
return NOT_FOUND
if $user->access_level < $required_access;
return $req->exec;
}
If you had several virtual hosts, each of which had a separate
component root, you'd need to create a separate ApacheHandler object
for each host, one for each host. Here's some sample code for that:
my %ah;
foreach my $site ( qw( site1 site2 site3 ) ) {
$ah{$site} =
HTML::Mason::ApacheHandler->new
( comp_root => "/usr/local/www/$site",
data_dir => "/usr/local/mason/$site" );
}
sub handler {
my ($r) = @_;
my $site = $r->dir_config('SiteName');
return DECLINED unless exists $ah{$site};
return $ah{$site}->handle_request($r);
}
This code assumes that you set the SiteName variable via a
PerlSetVar directive in each VirtualHost block, like this:
<VirtualHost site1.example.com>
PerlSetVar SiteName site1
<LocationMatch ...>
SetHandler perl-script
PerlHandler MyApp::Mason
</LocationMatch>
</VirtualHost>
You might also consider creating ApacheHandler objects on the fly,
like this:
my %ah;
sub handler {
my ($r) = @_;
my $site = $r->dir_config('SiteName');
return DECLINED unless $site;
unless exists($ah{$site}) {
$ah{$site} = HTML::Mason::ApacheHandler->new( ... );
}
$ah{$site}->handle_request($r);
}
This is more flexible but you lose the memory savings of creating all
your objects during server startup.
If you have some code which must always run after a request, then
the only way to guarantee that this happens is to wrap the $ah->handle_request()
call in an eval {} block, and then run the
needed code after the request returns. You can then handle errors
however you like.
You can take advantage of Mason's httpd.conf configuration system
while at the same time providing your own wrapper code. The key to
doing this is not creating your own ApacheHandler object. Instead,
you call the HTML::Mason::ApacheHandler->handler() class method
from your handler() subroutine. Here's a complete wrapper that
does this:
package MyApp::Mason;
use strict;
use HTML::Mason::ApacheHandler;
sub handler {
my ($r) = @_;
return HTML::Mason::ApacheHandler->handler($r);
}
The HTML::Mason::ApacheHandler->handler method will create an
ApacheHandler object based on the configuration directives it finds in
your httpd.conf file. Obviously, this wrapper is again a skeleton,
but you could mix and match this wrapper code with any of the code
shown above.
Alternately you could subclass the HTML::Mason::ApacheHandler
class, and override the handler() method it provides. See the
Subclassing documentation for more
details. Of course, you could even create a subclass and write a
wrapper that called it.
This section describes how to set up common developer features.
Global variables can make programs harder to read, maintain, and
debug, and this is no less true for Mason components. Due to the
persistent mod_perl environment, globals require extra initialization
and cleanup care.
That said, there are times when it is very useful to make a value
available to all Mason components: a DBI database handle, a hash of
user session information, the server root for forming absolute URLs.
Because Mason by default parses components in strict mode, you'll
need to declare a global if you don't want to access it with an
explicit package name. The easiest way to declare a global is with
the allow_globals parameter.
Since all components run in the same package, you'll be able to set
the global in one component and access it in all the others.
Autohandlers are common places to assign values to globals. Use the
<%once> section if the global only needs to be
initialized at load time, or the <%init> section if it
needs to be initialized every request.
Mason does not have a built-in session mechanism, but you can use the
MasonX::Request::WithApacheSession module, available from CPAN, to
add a session to every request. It can also automatically set and
read cookies containing the session id.
Data caching is implemented with DeWitt Clinton's Cache::Cache
module. For full understanding of this section you should read the
documentation for Cache::Cache as well as for relevant subclasses
(e.g. Cache::FileCache).
- Cache files
-
By default, Cache::FileCache is the subclass used for data caching,
although this may be overriden by the developer. Cache::FileCache
creates a separate subdirectory for every component that uses caching,
and one file some number of levels underneath that subdirectory for
each cached item. The root of the cache tree is
data_dir/cache. The name of the cache subdirectory for a component
is determined by the function HTML::Mason::Utils::data_cache_namespace.
- Default constructor options
-
Ordinarily, when $m->cache is called, Mason passes to the cache
constructor the namespace, and cache_root options, along with
any other options given in the $m->cache method.
-
You may specify other default constructor options with the
data_cache_defaults parameter. For example,
-
PerlSetVar MasonDataCacheDefaults "cache_class => SizeAwareFileCache"
PerlAddVar MasonDataCacheDefaults "cache_depth => 2"
PerlAddVar MasonDataCacheDefaults "default_expires_in => 1 hour"
-
Any options passed to individual $m->cache calls override these
defaults.
- Disabling data caching
-
If for some reason you want to disable data caching entirely, set the
default cache_class to ``NullCache''. This subclass faithfully
implements the cache API but never stores data.
This section explains Mason's various performance enhancements and how
to administer them. One of the best ways to maximize performance on
your production server is run in static_source mode; see the third
subsection below.
When Mason loads a component, it places it in a memory cache. By
default, the cache has no limit, but you can specify a maximum number
of components to cache with the code_cache_max_size parameter. In
this case, Mason will free up space as needed by discarding
components. The discard algorithm is least frequently used (LFU), with
a periodic decay to gradually eliminate old frequency information. In
a nutshell, the components called most often in recent history should
remain in the cache.
Previous versions of Mason attempted to estimate the size of each
component, but this proved so inaccurate as to be virtually useless
for cache policy. The max size is now specified purely in number of
components.
Mason can use certain optimizations with an unlimited cache,
especially in conjunction with static_source, so don't limit the
cache unless experience shows that your servers are growing too
large. Many dynamic sites can be served comfortably with all
components in memory.
You can prepopulate the cache with components that you know will be
accessed often; see Preloading Components.
Note that preloaded components possess no special status in the cache
and can be discarded like any others.
Naturally, a cache entry is invalidated if the corresponding component
source file changes.
To turn off code caching completely, set code_cache_max_size to 0.
The in-memory code cache is only useful on a per-process basis. Each
process must build and maintain its own cache. Shared memory caches
are conceivable in the future, but even those will not survive between
web server restarts.
As a secondary, longer-term cache mechanism, Mason stores a compiled
form of each component in an object file under data_dir/obj. Any
server process can eval the object file and save time on parsing the
component source file. The object file is recreated whenever the
source file changes.
The object file pathname is formed from three parts:
Besides improving performance, object files can be useful for
debugging. If you feel the need to see what your source has been
translated into, you can peek inside an object file to see exactly how
Mason converted a given component to a Perl object. This was crucial
for pre-1.10 Mason, in which error line numbers were based on the
object file rather than the source file.
If for some reason you don't want Mason to create object files, set
use_object_files to 0.
In static_source mode, Mason assumes that the component hierarchy
is unchanging and thus does not check source timestamps when using an
in-memory cached component or object file. This significantly reduces
filesystem stats and other overhead. We've seen speedups by a factor
of two or three as a result of this mode, though of course YMMV.
When in static_source mode, you must remove object files and call
$interp->flush_code_cache in order for the server to recognize
component changes. The easiest way to arrange this is to point
static_source_touch_file to a file that can be touched whenever
components change.
We highly recommend running in this mode in production if you can
manage it. Many of Mason's future optimizations will be designed for
this mode. On development servers, of course, it makes sense to keep
this off so that components are reloaded automatically.
To support the dynamic autoflush feature, Mason has to check for
autoflush mode after printing every piece of text. If you can commit
to not using autoflush, setting enable_autoflush to 0 will allow
Mason to compile components more efficiently. Consider whether a few
well-placed $m->flush_buffer calls would be just as good as
autoflush.
Writing your own handler() subroutine which uses an ApacheHandler
object (or objects) created during server startup is slightly faster
(around 5% or so) than configuring mason via your httpd.conf file
and letting Mason create its own ApacheHandler objects internally.
You can tell Mason to preload a set of components in the parent
process, rather than loading them on demand, using the preloads
parameter. Each child server will start with those components loaded
in the memory cache. The trade-offs are:
- time
-
a small one-time startup cost, but children save time by not
having to load the components
- memory
-
a fatter initial server, but the memory for preloaded components are
shared by all children. This is similar to the advantage of using
modules only in the parent process.
Try to preload components that are used frequently and do not change
often. (If a preloaded component changes, all the children will have
to reload it from scratch.)
You can set buffer_preallocate_size to set the size of the
preallocated output buffer for each request. This can reduce the
number of reallocations Perl performs as components output text.
When an error occurs, Mason can respond by:
-
showing a detailed error message in the browser in HTML.
-
die'ing, which sends a 500 status to the browser and lets the error
message go to the error logs.
The first behavior is ideal for development, where you want immediate
feedback on the error. The second behavior is usually desired for
production so that users are not exposed to messy error messages. You
choose the behavior by setting error_mode to ``output'' or ``fatal''
respectively.
Error formatting is controlled by the error_format parameter. When
showing errors in the browser, Mason defaults to the ``html'' format.
When the error_mode is set to ``fatal'', the default format is
``line'', which puts the entire error message on one line in a format
suitable for web server error logs. Mason also offers other formats,
which are covered in the Request class
documentation.
Finally, you can use Apache's ErrorDocument directive to specify a
custom error handler for 500 errors. In this case, you'd set the
error_mode to ``fatal''. The URL specified by the ErrorDocument
directive could point to a Mason component.
The way that Mason really reports errors is through the use of
exception objects, which are implemented with the Exception::Class
module from CPAN, and some custom code in the
HTML::Mason::Exceptions module.
If, during the execution of a component, execution stops because some
code calls die(), then Mason will catch this exception. If the
exception being thrown is just a string, then it will be converted to
an HTML::Mason::Exception object. If the exception being thrown is
an object with a rethrow() method, then this method will be called.
Otherwise, Mason simply leaves the exception untouched and calls
die() again.
Returning to the topic of wrapper code that we covered earlier, what
if you wanted to handle all request errors by calling an error
handling component? There is no way to do this without wrapper code.
Here's an example handler() subroutine that does this:
sub handler {
my ($r) = @_;
my $return = eval { $ah->handle_request($r) };
if ( my $err = $@ )
{
$r->pnotes( error => $err );
$r->filename( $r->document_root . '/error/500.html' );
return $ah->handle_request($r);
}
return $return;
}
First, we wrap our call to $ah->handle_request() in an
eval{} block. If an error occurs, we store it in the request
object using the $r->pnotes() method. Then we change the
filename property of the Apache request object to point to our
error-handling component and call the $ah->handle_request()
method again, passing it the altered request object. We could have
put the exception in $r->args, but we want to leave this
untouched so that the error-handling component can see the original
arguments.
Here's what that component error-handling component might look like:
<html>
<head>
<title>Error</title>
</head>
<body>
<p>
Looks like our application broke. Whatever you did, don't do it again!
</p>
<p>
If you have further questions, please feel free to contact us at <a
href="mailto:support@example.com">support@example.com</a>.
</p>
<p><a href="/">Click here</a> to continue.</p>
</body>
</html>
<%init>
my $error = $r->pnotes('error');
my $error_text = "Page is " . $r->parsed_uri->unparse . "\n\n";
$error_text .= UNIVERSAL::can( $error, 'as_text' ) ? $error->as_text : $error;
$r->log_error($error_text);
my $mail =
MIME::Lite->new
( From => 'error-handler@example.com',
To => 'rt@example.com',
Subject => 'Application error',
Data => $error_text,
);
$r->register_cleanup( sub { $mail->send } );
</%init>
<%flags>
inherit => undef
</%flags>
This component does several things. First of all, it logs the
complete error to the Apache error logs, along with the complete URL,
including query string, that was requested. The $r->parsed_uri()
method that we use above is only available if the Apache::URI
module has been loaded.
The component also sends an email containing the error, in this case
to an RT installation, so that the error is logged in a bug tracking
system. Finally, it displays a less technical error message to the
user.
For this to work properly, you must set error_mode to ``fatal'', so
that Mason doesn't just display its own HTML error page.
Although Mason is most commonly used in conjunction with mod_perl, the
APIs are flexible enough to use in any environment. Below we describe
the two most common alternative environments, CGI and standalone
scripts.
The easiest way to use Mason via a CGI script is with the CGIHandler module module.
Here is a skeleton CGI script that calls a component and sends the
output to the browser.
#!/usr/bin/perl
use HTML::Mason::CGIHandler;
my $h = HTML::Mason::CGIHandler->new
(
data_dir => '/home/jethro/code/mason_data',
);
$h->handle_request;
The relevant portions of the httpd.conf file look like:
DocumentRoot /path/to/comp/root
ScriptAlias /cgi-bin/ /path/to/cgi-bin/
<LocationMatch "\.html$">
Action html-mason /cgi-bin/mason_handler.cgi
AddHandler html-mason .html
</LocationMatch>
<LocationMatch "^/cgi-bin/">
RemoveHandler .html
</LocationMatch>
<FilesMatch "(autohandler|dhandler)$">
Order allow,deny
Deny from all
</FilesMatch>
This simply causes Apache to call the mason_handler.cgi script every
time a URL ending in ``.html'' under the component root is requested.
To exclude certian directories from being under Mason control, you can
use something like the following:
<LocationMatch "^/(dir1|dir2|dir3)/">
RemoveHandler .html
</LocationMatch>
This script uses the CGIHandler class to do
most of the heavy lifting. See that class's documentation for more
details.
Mason can be used as a pure text templating solution -- like
Text::Template and its brethren, but with more power (and of course
more complexity).
Here is a bare-bones script that calls a component file and sends
the result to standard output:
#!/usr/bin/perl
use HTML::Mason;
use strict;
my $interp = HTML::Mason::Interp->new ();
$interp->exec(<relative path to file>, <args>...);
Because no component root was specified, the root is set to your
current working directory. If you have a well defined and contained
component tree, you'll probably want to specify a component root.
Because no data directory was specified, object files will not be
created and data caching will not work in the default manner. If
performance is an issue, you will want to specify a data directory.
Here's a slightly fuller script that specifies a component root and
data directory, and captures the result in a variable rather than
sending to standard output:
#!/usr/bin/perl
use HTML::Mason;
use strict;
my $outbuf;
my $interp = HTML::Mason::Interp->new
(comp_root => '/path/to/comp_root',
data_dir => '/path/to/data_dir',
out_method => \$outbuf
);
$interp->exec(<component-path>, <args>...);
# Do something with $outbuf
Jonathan Swartz <swartz@pobox.com>, Dave Rolsky <autarch@urth.org>, Ken Williams <ken@mathforum.org>
HTML::Mason,
HTML::Mason::Interp,
HTML::Mason::ApacheHandler,
HTML::Mason::Lexer,
HTML::Mason::Compiler
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