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Manual Reference Pages  -  HTML::MASON::PLUGIN (3)

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NAME

HTML::Mason::Plugin - Plugin Base class for Mason

CONTENTS

SYNOPIS



   package MasonX::Plugin::Timer;
   use base qw(HTML::Mason::Plugin);
   use Time::HiRes;

   sub start_component_hook {
       my ($self, $context) = @_;
       push @{$self->{ timers }}, Time::HiRes::time;
   }

   sub end_component_hook {
       my ($self, $context) = @_;
       my $elapsed = Time::HiRes::time - pop @{$self->{ timers }};
       printf STDERR "Component %s took %.1f seconds\n",
           $context->comp->title, $elapsed;
   }

   1;



DESCRIPTION

Use a Mason plugin to have actions occur at the beginning or end of requests or components. Plugins are activated by passing plugins in the interpreter or request object. Each plugin in the list can be specified as a class name (in which case the plugin object is created once for each request) or as an actual object of the plugin class.

If your plugin can be configured, place the configuration in class variables - for example,



    $MasonX::Plugin::Timer::Units = seconds;



These can be set either from httpd.conf via PerlSetVar directives, or in perl directly from a handler.pl file.

PLUGIN HOOKS

A plugin class defines one or more of the following hooks (methods): start_request_hook, end_request_hook, start_component_hook, and end_component_hook.

Every hook receives two arguments: the plugin object itself, and a context object with various methods.
start_request_hook start_request_hook is called before the Mason request begins execution. Its context has the following read-only methods:



    request # the current request ($m)
    args    # arguments the request was called with



When called in scalar context, args returns a list reference which may be modified to change or add to the arguments passed to the first component. When called in list context, args returns a list (which may be assigned to a hash).

Note that subrequests (see HTML::Mason::Request will create a new plugin object and execute this code again; you can skip your code for subrequests by checking is_subrequest on request. e.g.



   sub start_request_hook {
       my ($self, $context) = @_;
       unless ($context->request->is_subrequest()) {
           # perform hook action
       }
   }



Currently, this hook is called before any information about the requested component is available, so you cannot call methods like base_comp() or request_args() on the Request object.

end_request_hook end_request_hook is called before the Mason request exits. Its context has the following read-only methods:



    request     # the current request ($m)
    args        # arguments the request was called with
    output      # reference to the contents of the output buffer
    wantarray   # value of wantarray the request was called with
    result      # arrayref of value(s) that the request is about to return
    error       # reference to error, if any, that the request is about to throw



When called in scalar context, args returns a list reference; when called in list context, it returns a list (which may be assigned to a hash).

result always contains an array ref; if wantarray is 0, the return value is the the first element of that array. The plugin may modify output to affect what the request outputs, and result and error to affect what the request returns.

start_component_hook start_component_hook is called before a component begins executing. Its context has the following read-only methods:



    request     # the current request ($m)
    comp        # the component object
    args        # arrayref of arguments the component was called with



The plugin may NOT modify args currently.

end_component_hook end_component_hook() is called after a component has completed. Its context has the following read-only methods:



    request     # the current request ($m)
    comp        # the component object
    args        # arrayref of arguments the component was called with
    wantarray   # value of wantarray the component was called with
    result      # arrayref of value(s) that the component is about to return
    error       # reference to error, if any, that the component is about to throw



result always contains an array ref; if wantarray is 0, the return value is the first element of that array. The plugin may modify both result and error to affect how the request returns.

It would be desirable for this hook to have access to the component’s output as well as its return value, but this is currently impossible because output from multiple components combine into a single buffer.

WARNINGS

Do not keep an unweakened reference to a request or component object in your plugin object, or you will create a nasty circular reference.
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perl v5.20.3 HTML::MASON::PLUGIN (3) 2014-11-15

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