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Dave Rolsky


HTML::Mason::Request - Mason Request Class


    $m->abort (...)
    $m->comp (...)


The Request API is your gateway to all Mason features not provided by syntactic tags. Mason creates a new Request object for every web request. Inside a component you access the current request object via the global $m. Outside of a component, you can use the class method instance.


The methods Request->comp, Request->comp_exists, and Request->fetch_comp take a component path argument. Component paths are like URL paths, and always use a forward slash (/) as the separator, regardless of what your operating system uses.

  • If the path is absolute (starting with a '/'), then the component is found relative to the component root.

  • If the path is relative (no leading '/'), then the component is found relative to the current component directory.

  • If the path matches both a subcomponent and file-based component, the subcomponent takes precedence.



True or false, default is false. Indicates whether to flush the output buffer after every string is output. Turn on autoflush if you need to send partial output to the client, for example in a progress meter.


The class to use when creating buffers. Defaults to HTML::Mason::Buffer.


The $m->cache API to use. '1.1', the default, indicates the newer API documented in this manual. '1.0' indicates the old API documented in 1.0x and earlier. This compatibility layer is provided as a convenience for users upgrading from older versions of Mason, but will not be supported indefinitely.


A hash reference of default options to use for the $m->cache command. For example, to use the MemoryCache implementation by default,

    data_cache_defaults => {cache_class => 'MemoryCache'}

These settings are overriden by options given to particular $m->cache calls.


File name used for dhandlers. Default is "dhandler".


Indicates how errors are formatted. The built-in choices are

  • brief - just the error message with no trace information

  • text - a multi-line text format

  • line - a single-line text format, with different pieces of information separated by tabs (useful for log files)

  • html - a fancy html format

The default format under Apache and CGI is either line or html depending on whether the error mode is fatal or output, respectively. The default for standalone mode is text.

The formats correspond to HTML::Mason::Exception methods named as_format. You can define your own format by creating an appropriately named method; for example, to define an "xml" format, create a method HTML::Mason::Exception::as_xml patterned after one of the built-in methods.


Indicates how errors are returned to the caller. The choices are fatal, meaning die with the error, and output, meaning output the error just like regular output.

The default under Apache and CGI is output, causing the error to be displayed in the browser. The default for standalone mode is fatal.


The maximum recursion depth for the component stack, for the request stack, and for the inheritance stack. An error is signalled if the maximum is exceeded. Default is 32.


Indicates where to send output. If out_method is a reference to a scalar, output is appended to the scalar. If out_method is a reference to a subroutine, the subroutine is called with each output string. For example, to send output to a file called "mason.out":

    my $fh = new IO::File ">mason.out";
    out_method => sub { $fh->print($_[0]) }

By default, out_method prints to standard output. Under Apache, standard output is redirected to $r->print.


    abort ([return value])

    Ends the current request, finishing the page without returning through components. The optional argument specifies the return value from Interp::exec; in a web environment, this ultimately becomes the HTTP status code.

    abort is implemented by throwing an HTML::Mason::Exception::Abort object and can thus be caught by eval(). The aborted method is a shortcut for determining whether a caught error was generated by abort.

    If abort is called from a component that has a <%filter>, than any output generated up to that point is filtered, unless abort is called from a <%shared> block.

    aborted ([$err])

    Returns true or undef indicating whether the specified $err was generated by abort. If no $err was passed, use $@.

    In this code, we catch and process fatal errors while letting abort exceptions pass through:

        eval { code_that_may_fail_or_abort() };
        if ($@) {
            die $@ if $m->aborted;
            # handle fatal errors...

    $@ can lose its value quickly, so if you are planning to call $m->aborted more than a few lines after the eval, you should save $@ to a temporary variable.


    Returns the current base component for method and attributes. Initially, the base component is the same as the requested component (returned by $m->request_comp. However, whenever a component call is made, the base component changes to the called component, unless the component call was made uses a component object for its first argument, or the call starts with SELF:, PARENT:, or REQUEST.

    cache (cache_class=>'...', [cache_options])

    $m->cache returns a new cache object with a namespace specific to this component.

    cache_class specifies the class of cache object to create. It defaults to FileCache in most cases, or MemoryCache if the interpreter has no data directory, and must be a backend subclass of Cache::Cache. The prefix "Cache::" need not be included. See the Cache::Cache package for a full list of backend subclasses.

    cache_options may include any valid options to the new() method of the cache class. e.g. for FileCache, valid options include default_expires_in and cache_depth.

    See the data caching section of the developer's manual for a caching tutorial and examples. See the HTML::Mason::Cache::BaseCache documentation for a method reference.

    Note: users upgrading from 1.0x and earlier can continue to use the old $m->cache API by setting data_cache_api to '1.0'. This support will be removed at a later date.

    cache_self ([expires_in => '...'], [key => '...'], [get_options], [cache_options])

    $m->cache_self caches the entire output and return result of a component.

    cache_self either returns undef, or a list containing the return value of the component followed by '1'. You should return immediately upon getting the latter result, as this indicates that you are inside the second invocation of the component.

    cache_self takes any of parameters to $m->cache (e.g. cache_depth), any of the optional parameters to $cache->get (expire_if, busy_lock), and two additional options:

    • expire_in or expires_in: Indicates when the cache expires - it is passed as the third argument to $cache->set. e.g. '10 sec', '5 min', '2 hours'.

    • key: An identifier used to uniquely identify the cache results - it is passed as the first argument to $cache->get and $cache->set. The default key is '__mason_cache_self__'.

    To cache the component's output:

        return if $m->cache_self(expire_in => '10 sec'[, key => 'fookey']);
        ... <rest of init> ...

    To cache the component's scalar return value:

        my ($result, $cached) = $m->cache_self(expire_in => '5 min'[, key => 'fookey']);
        return $result if $cached;
        ... <rest of init> ...

    To cache the component's list return value:

        my (@retval) = $m->cache_self(expire_in => '3 hours'[, key => 'fookey']);
        return @retval if pop @retval;
        ... <rest of init> ...

    We call pop on @retval to remove the mandatory '1' at the end of the list.

    If a component has a <%filter> block, then the filtered output is cached.

    Note: users upgrading from 1.0x and earlier can continue to use the old $m->cache_self API by setting data_cache_api to '1.0'. This support will be removed at a later date.


    Returns the arguments passed by the component at the specified stack level. Use a positive argument to count from the current component and a negative argument to count from the component at the bottom of the stack. e.g.

        $m->caller_args(0)   # arguments passed to current component
        $m->caller_args(1)   # arguments passed to component that called us
        $m->caller_args(-1)  # arguments passed to first component executed

    When called in scalar context, a hash reference is returned. When called in list context, a list of arguments (which may be assigned to a hash) is returned.


    With no arguments, returns the current component stack as a list of component objects, starting with the current component and ending with the top-level component. With one numeric argument, returns the component object at that index in the list. Use a positive argument to count from the current component and a negative argument to count from the component at the bottom of the stack. e.g.

        my @comps = $m->callers   # all components
        $m->callers(0)            # current component
        $m->callers(1)            # component that called us
        $m->callers(-1)           # first component executed


    A synonym for $m->caller(1), i.e. the component that called the currently executing component.

    call_next ([args...])

    Calls the next component in the content wrapping chain; usually called from an autohandler. With no arguments, the original arguments are passed to the component. Any arguments specified here serve to augment and override (in case of conflict) the original arguments. Works like $m->comp in terms of return value and scalar/list context. See the autohandlers section of the developer's manual for examples.

    call_self (output, return)

    This method allows a component to call itself so that it can filter both its output and return values. It is fairly advanced; for most purposes the <%filter> tag will be sufficient and simpler.

    $m->call_self takes two arguments. The first is a scalar reference and will be populated with the component output. The second is either a scalar or list reference and will be populated with the component return value; the type of reference determines whether the component will be called in scalar or list context. Both of these arguments are optional; you may pass undef for either of them.

    $m->call_self acts like a fork() in the sense that it will return twice with different values. When it returns 0, you allow control to pass through to the rest of your component. When it returns 1, that means the component has finished and you can begin filtering the output and/or return value. (Don't worry, it doesn't really do a fork! See next section for explanation.)

    The following examples would generally appear at the top of a <%init> section. Here is a no-op $m->call_self that leaves the output and return value untouched:

        my ($output, $retval);
        if ($m->call_self(\$output, \$retval)) {
            return $retval;

    Here is a simple output filter that makes the output all uppercase. Note that we ignore both the original and the final return value.

        my $output;
        if ($m->call_self(\$output, undef)) {
            $m->print(uc $output);

    Here is a piece of code that traps all errors occuring anywhere in the component or its children, e.g. for the purpose of handling application-specific exceptions. This is difficult to do with a manual eval because it would have to span multiple code sections and the main component body.

        # Run this component with an eval around it
        my $in_parent = eval { $m->call_self() };
        if ($@) {
            # check $@ and do something with it
        return if $in_parent;


    Clears the Mason output buffer. Any output sent before this line is discarded. Useful for handling error conditions that can only be detected in the middle of a request.

    clear_buffer is, of course, thwarted by flush_buffer.

    comp (comp, args...)

    Calls the component designated by comp with the specified option/value pairs. comp may be a component path or a component object.

    Components work exactly like Perl subroutines in terms of return values and context. A component can return any type of value, which is then returned from the $m->comp call.

    The <& &> tag provides a convenient shortcut for $m->comp.

    As of 1.10, component calls can accept an initial hash reference of modifiers. The only currently supported modifier is store, which stores the component's output in a scalar reference. For example:

      my $buf;
      my $return = $m->comp( { store => \$buf }, '/some/comp', type => 'big' );

    This mostly duplicates the behavior of scomp, but can be useful in rare cases where you need to capture both a component's output and return value.

    This modifier can be used with the <& &> tag as well, for example:

      <& { store => \$buf }, '/some/comp', size => 'medium' &>

    comp_exists (comp_path)

    Returns 1 if comp_path is the path of an existing component, 0 otherwise. That path given may be relative, in which case the current component's directory path will be prepended.


    Evaluates the content (passed between <&| comp &> and </&> tags) of the current component, and returns the resulting text.

    Returns undef if there is no content.


    Returns the number of this request, which is unique for a given request and interpreter.


    Returns the current component object.


    Used from a top-level component or dhandler, this method clears the output buffer, aborts the current request and restarts with the next applicable dhandler up the tree. If no dhandler is available, an error occurs. This method bears no relation to the Apache DECLINED status except in name.


    Returns the current size of the component stack. The lowest possible value is 1, which indicates we are in the top-level component.


    If the request has been handled by a dhandler, this method returns the remainder of the URI or Interp::exec path when the dhandler directory is removed. Otherwise returns undef.

    dhandler_arg may be called from any component in the request, not just the dhandler.

    exec (comp, args...)

    Starts the request by executing the top-level component and arguments. This is normally called for you on the main request, but you can use it to execute subrequests.

    A request can only be executed once; e.g. it is an error to call this recursively on the same request.

    fetch_comp (comp_path)

    Given a comp_path, returns the corresponding component object or undef if no such component exists.


    Returns the next component in the content wrapping chain, or undef if there is no next component. Usually called from an autohandler. See the autohandlers section of the developer's manual for usage and examples.


    Returns a list of the remaining components in the content wrapping chain. Usually called from an autohandler. See the autohandlers section of the developer's manual for usage and examples.

    file (filename)

    Returns the contents of filename as a string. If filename is a relative path, Mason prepends the current component directory.


    Flushes the Mason output buffer. Under mod_perl, also sends HTTP headers if they haven't been sent and calls $r->rflush to flush the Apache buffer. Flushing the initial bytes of output can make your servers appear more responsive.

    Attempts to flush the buffers are ignored within the context of a call to $m->scomp or when output is being stored in a scalar reference, as with the { store = \$out } > component call modifier.

    Additionally, if a component has a <%filter> block, that component is buffered until its entire output is generated. This means that inside that component and any components that it calls, the buffer cannot be flushed.


    This class method returns the HTML::Mason:::Request currently in use. If called when no Mason request is active it will return undef.

    If called inside a subrequest, it returns the subrequest object.


    Returns the Interp object associated with this request.

    make_subrequest (comp => path, args => arrayref, other parameters)

    This method creates a new Request object which inherits its parent's settable properties, such as autoflush and out_method. These values may be overridden by passing parameters to this method.

    The "comp" parameter is required, while all other parameters are optional.

    See the subrequests section of the developer's manual for more information about subrequests.

    out (string)

    A synonym for $m->print.

    print (string)

    Print the given string. Rarely needed, since normally all text is just placed in the component body and output implicitly. $m->print is useful if you need to output something in the middle of a Perl block.

    In 1.1 and on, print and $r->print are remapped to $m->print, so they may be used interchangeably. Before 1.1, one should only use $m->print.


    Returns the arguments originally passed to the top level component (see Request->request_comp for definition). When called in scalar context, a hash reference is returned. When called in list context, a list of arguments (which may be assigned to a hash) is returned.


    Returns the component originally called in the request. Without autohandlers, this is the same as the first component executed. With autohandlers, this is the component at the end of the $m->call_next chain.

    scomp (comp, args...)

    Like comp, but returns the component output as a string instead of printing it. (Think sprintf versus printf.) The component's return value is discarded.

    subexec (comp, args...)

    This method creates a new subrequest with the specified top-level component and arguments, and executes it. This is most often used to perform an "internal redirect" to a new component such that autohandlers and dhandlers take effect.


    Returns the interpreter's notion of the current time (deprecated).


These additional methods are available when running Mason with mod_perl and the ApacheHandler.


    Returns the ApacheHandler object associated with this request.


    Returns the Apache request object. This is also available in the global $r.


    True or false, default is true. Indicates whether Mason should automatically send HTTP headers before sending content back to the client. If you set to false, you should call $r->send_http_header manually.

    See the sending HTTP headers section of the developer's manual for more details about the automatic header feature.


This additional method is available when running Mason with the CGIHandler module.


    Returns the Apache request emulation object, which is available as $r inside components.

    See the CGIHandler docs for more details.


This method is available when Mason is running under either the ApacheHandler or CGIHandler modules.


    Returns the CGI object used to parse any CGI parameters submitted to the component, assuming that you have not changed the default value of the ApacheHandler args_method parameter. If you are using the 'mod_perl' args method, then calling this method is a fatal error. See the ApacheHandler and CGIHandler documentation for more details.

    redirect ($url, [$status])

    Given a url, this generates a proper HTTP redirect for that URL. It uses $m->clear_buffer to clear out any previous output, and $m->abort to abort the request. By default, the status code used is 302, but this can be overridden by the user.

    Since this is implemented using $m->abort, it will be trapped by an eval {} block. If you are using an eval {} block in your code to trap errors, you need to make sure to rethrow these exceptions, like this:

      eval {
      die $@ if $m->aborted;
      # handle other exceptions


Jonathan Swartz <swartz@pobox.com>, Dave Rolsky <autarch@urth.org>, Ken Williams <ken@mathforum.org>


HTML::Mason, HTML::Mason::Devel, HTML::Mason::Component

4 POD Errors

The following errors were encountered while parsing the POD:

Around line 1416:

You can't have =items (as at line 1420) unless the first thing after the =over is an =item

Around line 1923:

You can't have =items (as at line 1927) unless the first thing after the =over is an =item

Around line 1957:

You can't have =items (as at line 1961) unless the first thing after the =over is an =item

Around line 1976:

You can't have =items (as at line 1980) unless the first thing after the =over is an =item