POE::Filter::StackableUser Contributed Perl DocumentaPOE::Filter::Stackable(3)NAMEPOE::Filter::Stackable - combine multiple POE::Filter objects
SYNOPSIS
#!perl
use POE qw(
Wheel::FollowTail
Filter::Line Filter::Grep Filter::Stackable
);
POE::Session->create(
inline_states => {
_start => sub {
my $parse_input_as_lines = POE::Filter::Line->new();
my $select_sudo_log_lines = POE::Filter::Grep->new(
Put => sub { 1 },
Get => sub {
my $input = shift;
return $input =~ /sudo\[\d+\]/i;
},
);
my $filter_stack = POE::Filter::Stackable->new(
Filters => [
$parse_input_as_lines, # first on get, last on put
$select_sudo_log_lines, # first on put, last on get
]
);
$_[HEAP]{tailor} = POE::Wheel::FollowTail->new(
Filename => "/var/log/system.log",
InputEvent => "got_log_line",
Filter => $filter_stack,
);
},
got_log_line => sub {
print "Log: $_[ARG0]\n";
}
}
);
POE::Kernel->run();
exit;
DESCRIPTIONPOE::Filter::Stackable combines multiple filters together in such a way
that they appear to be a single filter. All the usual POE::Filter
methods work, but data is secretly passed through the stacked filters
before it is returned. POE::Wheel objects and stand-alone programs
need no modifications to work with a filter stack.
In the "SYNOPSIS", POE::Filter::Line and POE::Filter::Grep are combined
into one filter that only returns a particular kind of line. This can
be more efficient than filtering lines in application space, as fewer
events may need to be dispatched and handled.
Internally, filters are stored in an array.
Data added by get_one_start() will flow through the filter array in
increasing index order. Filter #0 will have first crack at it,
followed by filter #1 and so. The get_one() call will return an item
after it has passed through the last filter.
put() passes data through the filters in descending index order. Data
will go through the filter with the highest index first, and put() will
return the results after data has passed through filter #0.
PUBLIC FILTER METHODS
In addition to the usual POE::Filter methods, POE::Filter::Stackable
also supports the following.
new
By default, new() creates an empty filter stack that behaves like
POE::Filter::Stream. It may be given optional parameters to initialize
the stack with an array of filters.
my $sudo_lines = POE::Filter::Stackable->new(
Filters => [
POE::Filter::Line->new(),
POE::Filter::Grep->new(
Put => sub { 1 }, # put all items
Get => sub { shift() =~ /sudo\[\d+\]/i },
),
]
);
pop
Behaves like Perl's built-in pop() for the filter stack. The highest-
indexed filter is removed from the stack and returned. Any data
remaining in the filter's input buffer is lost, but an application may
always call "get_pending" in POE::Filter on the returned filter.
my $last_filter = $stackable->pop();
my $last_buffer = $last_filter->get_pending();
shift
Behaves like Perl's built-in shift() for the filter stack. The 0th
filter is removed from the stack and returned. Any data remaining in
the filter's input buffer is passed to the new head of the stack, or it
is lost if the stack becomes empty. An application may also call
"get_pending" in POE::Filter on the returned filter to examine the
filter's input buffer.
my $first_filter = $stackable->shift();
my $first_buffer = $first_filter->get_pending();
push FILTER[, FILTER]
push() adds one or more new FILTERs to the end of the stack. The newly
pushed FILTERs will process input last, and they will handle output
first.
# Reverse data read through the stack.
# rot13 encode data sent through the stack.
$stackable->push(
POE::Filter::Map->(
Get => sub { return scalar reverse shift() },
Put => sub { local $_ = shift(); tr[a-zA-Z][n-za-mN-ZA-M]; $_ },
)
);
unshift FILTER[, FILTER]
unshift() adds one or more new FILTERs to the beginning of the stack.
The newly unshifted FILTERs will process input first, and they will
handle output last.
filters
filters() returns a list of the filters inside the Stackable filter, in
the stack's native order.
Calling "<$filter_stack-"filters()>> in the "SYNOPSIS" would return a
list of two filter objects:
POE::Filter::Line=ARRAY(0x8b5ee0)
POE::Filter::Grep=ARRAY(0x8b5f7c)
filter_types
filter_types() returns a list of class names for each filter in the
stack, in the stack's native order.
Calling "<$filter_stack-"filter_types()>> in the "SYNOPSIS" would
return a list of two class names:
POE::FIlter::Line
POE::Filter::Grep
It could easily be replaced by:
my @filter_types = map { ref } $filter_stack->filters;
SEE ALSO
POE::Filter for more information about filters in general.
Specific filters, amongst which are: POE::Filter::Block,
POE::Filter::Grep, POE::Filter::HTTPD, POE::Filter::Line,
POE::Filter::Map, POE::Filter::RecordBlock, POE::Filter::Reference,
POE::Filter::Stream
BUGS
None currently known.
AUTHORS & COPYRIGHTS
The Stackable filter was contributed by Dieter Pearcey. Documentation
provided by Rocco Caputo.
Please see the POE manpage for more information about authors and
contributors.
perl v5.14.2 2011-12-15 POE::Filter::Stackable(3)
