NAME¶
XML::SAX::Machine - Manage a collection of SAX processors
VERSION¶
version 0.46
SYNOPSIS¶
## Note: See XML::SAX::Pipeline and XML::SAX::Machines first,
## this is the gory, detailed interface.
use My::SAX::Machines qw( Machine );
use My::SAX::Filter2;
use My::SAX::Filter3;
my $filter3 = My::SAX::Filter3->new;
## A simple pipeline. My::SAX::Filter1 will be autoloaded.
my $m = Machine(
#
# Name => Class/object => handler(s)
#
[ Intake => "My::SAX::Filter1" => "B" ],
[ B => My::SAX::Filter2->new() => "C" ],
[ C => $filter3 => "D" ],
[ D => \*STDOUT ],
);
## A parser will be created unless My::SAX::Filter1 can parse_file
$m->parse_file( "foo.revml" );
my $m = Machine(
[ Intake => "My::SAX::Filter1" => qw( Tee ) ],
[ Tee => "XML::Filter::SAXT" => qw( Foo Bar ) ],
[ Foo => "My::SAX::Filter2" => qw( Out1 ) ],
[ Out1 => \$log ],
[ Bar => "My::SAX::Filter3" => qw( Exhaust ) ],
);
DESCRIPTION¶
WARNING: This API is alpha!!! It
will be changing.
A generic SAX machine (an instance of XML::SAX::Machine) is a container of SAX
processors (referred to as "parts") connected in arbitrary ways.
Each parameter to "Machine()" (or "XML::SAX::Machine-"
new()>) represents one top level part of the machine. Each part has
a name, a processor, and one or more handlers (usually specified by name, as
shown in the SYNOPSIS).
Since SAX machines may be passed in as single top level parts, you can also
create nested, complex machines ($filter3 in the SYNOPSIS could be a Pipeline,
for example).
A SAX machines can act as a normal SAX processors by connecting them to other
SAX processors:
my $w = My::Writer->new();
my $m = Machine( ...., { Handler => $w } );
my $g = My::Parser->new( Handler => $w );
Part Names¶
Although it's not required, each part in a machine can be named. This is useful
for retrieving and manipulating the parts (see "part", for
instance), and for debugging, since debugging output (see
"trace_parts" and "trace_all_parts") includes the names.
Part names must be valid Perl subroutine names, beginning with an uppercase
character. This is to allow convenience part accessors methods like
$c = $m->NameOfAFilter;
to work without ever colliding with the name of a method (all method names are
completely lower case). Only filters named like this can be accessed using the
magical accessor functions.
Reserved Names: Intake and Exhaust¶
The names c<Intake> and "Exhaust" are reserved.
"Intake" refers to the first part in the processing chain. This is
not necessarily the first part in the constructor list, just the first part to
receive external events.
"Exhaust" refers to the output of the machine; no part may be named
"Exhaust", and any parts with a handler named "Exhaust"
will deliver their output to the machine's handler. Normally, only one part
should deliver it's output to the Exhaust port.
Calling $m->
set_handler() alters the Exhaust port, assuming any
processors pointing to the "Exhaust" provide a
"set_handler()" method like XML::SAX::Base's.
"Intake" and "Exhaust" are usually assigned automatically by
single-purpose machines like XML::SAX::Pipeline and XML::SAX::Manifold.
SAX Processor Support¶
The XML::SAX::Machine class is very agnostic about what SAX processors it
supports; about the only constraint is that it must be a blessed reference (of
any type) that does not happen to be a Perl IO::Handle (which are assumed to
be input or output filehandles).
The major constraint placed on SAX processors is that they must provide either a
"set_handler" or "set_handlers" method (depending on how
many handlers a processor can feed) to allow the SAX::Machine to disconnect
and reconnect them. Luckily, this is true of almost any processor derived from
XML::SAX::Base. Unfortunately, many SAX older (SAX1) processors do not meet
this requirement; they assume that SAX processors will only ever be connected
together using their constructors.
Connections¶
SAX machines allow you to connect the parts however you like; each part is given
a name and a list of named handlers to feed. The number of handlers a part is
allowed depends on the part; most filters only allow once downstream handler,
but filters like XML::Filter::SAXT and XML::Filter::Distributor are meant to
feed multiple handlers.
Parts may not be connected in loops ("cycles" in graph theory terms).
The machines specified by:
[ A => "Foo" => "A" ], ## Illegal!
and
[ A => "Foo" => "B" ], ## Illegal!
[ B => "Foo" => "A" ],
. Configuring a machine this way would cause events to flow in an infinite loop,
and/or cause the first processor in the cycle to start receiving events from
the end of the cycle before the input document was complete. Besides, it's not
a very useful topology :).
SAX machines detect loops at construction time.
NAME¶
XML::SAX::Machine - Manage a collection of SAX processors
API¶
Public Methods¶
These methods are meant to be used by users of SAX machines.
- new()
-
my $m = $self->new( @machine_spec, \%options );
Creates $self using %options, and compiles the machine spec. This is the
longhand form of "Machines( ... )".
- find_part
- Gets a part contained by this machine by name, number or object reference:
$c = $m->find_part( $name );
$c = $m->find_part( $number );
$c = $m->find_part( $obj ); ## useful only to see if $obj is in $m
If a machine contains other machines, parts of the contained machines may be
accessed by name using unix directory syntax:
$c = $m->find_part( "/Intake/Foo/Bar" );
(all paths must be absolute).
Parts may also be accessed by number using array indexing:
$c = $m->find_part(0); ## Returns first part or undef if none
$c = $m->find_part(-1); ## Returns last part or undef if none
$c = $m->find_part( "Foo/0/1/-1" );
There is no way to guarantee that a part's position number means anything,
since parts can be reconnected after their position numbers are assigned,
so using a part name is recommended.
Throws an exception if the part is not found, so doing things like
$m->find_part( "Foo" )->bar()
garner informative messages when "Foo" is not found. If you want
to test a result code, do something like
my $p = eval { $m->find_part };
unless ( $p ) {
...handle lookup failure...
}
- parts
-
for ( $m->parts ) { ... }
Gets an arbitrarily ordered list of top level parts in this machine. This is
all of the parts directly contained by this machine and none of the parts
that may be inside them. So if a machine contains an XML::SAX::Pipeline as
one of it's parts, the pipeline will be returned but not the parts inside
the pipeline.
- all_parts
-
for ( $m->all_parts ) { ... }
Gets all parts in this machine, not just top level ones. This includes any
machines contained by this machine and their parts.
- set_handler
-
$m->set_handler( $handler );
$m->set_handler( DTDHandler => $handler );
Sets the machine's handler and sets the handlers for all parts that have
"Exhaust" specified as their handlers. Requires that any such
parts provide a "set_handler" or (if the part has multiple
handlers) a "set_handlers" method.
NOTE: handler types other than "Handler" are only supported if
they are supported by whatever parts point at the "Exhaust". If
the handler type is "Handler", then the appropriate method is
called as:
$part->set_handler( $handler );
$part->set_handlers( $handler0, $handler1, ... );
If the type is some other handler type, these are called as:
$part->set_handler( $type => $handler );
$part->set_handlers( { $type0 => $handler0 }, ... );
- trace_parts
-
$m->trace_parts; ## trace all top-level parts
$m->trace_parts( @ids ); ## trace the indicated parts
Uses Devel::TraceSAX to enable tracing of all events received by the parts
of this machine. Does not enable tracing of parts contained in machines in
this machine; for that, see trace_all_parts.
- trace_all_parts
-
$m->trace_all_parts; ## trace all parts
Uses Devel::TraceSAX to trace all events received by the parts of this
machine.
- untracify_parts
-
$m->untracify_parts( @ids );
Converts the indicated parts to SAX processors with tracing enabled. This
may not work with processors that use AUTOLOAD.
Events and parse routines¶
XML::SAX::Machine provides all SAX1 and SAX2 events and delgates them to the
processor indicated by $m->find_part( "Intake" ). This adds some
overhead, so if you are concerned about overhead, you might want to direct SAX
events directly to the Intake instead of to the machine.
It also provides parse...() routines so it can whip up a parser if need be. This
means:
parse(),
parse_uri(),
parse_string(), and
parse_file() (see XML::SAX::EventMethodMaker for details). There is no
way to pass methods directly to the parser unless you know that the Intake is
a parser and call it directly. This is not so important for parsing, because
the overhead it takes to delegate is minor compared to the effort needed to
parse an XML document.
Internal and Helper Methods¶
These methods are meant to be used/overridden by subclasses.
- _compile_specs
-
my @comp = $self->_compile_specs( @_ );
Runs through a list of module names, output specifiers, etc., and builds the
machine.
$scalar --> "$scalar"->new
$ARRAY_ref --> pipeline @$ARRAY_ref
$SCALAR_ref --> XML::SAX::Writer->new( Output => $SCALAR_ref )
$GLOB_ref --> XML::SAX::Writer->new( Output => $GLOB_ref )
- generate_description
-
$m->generate_description( $h );
$m->generate_description( Handler => $h );
$m->generate_description( Pipeline ... );
Generates a series of SAX events to the handler of your choice.
See XML::Handler::Machine2GraphViz on CPAN for a way of visualizing machine
innards.
TODO¶
- •
- Separate initialization from construction time; there should be somthing
like a $m->connect( ....machine_spec... ) that new() calls to
allow you to delay parts speficication and reconfigure existing
machines.
- •
- Allow an XML doc to be passed in as a machine spec.
LIMITATIONS¶
AUTHOR¶
Barrie Slaymaker <barries@slaysys.com>
LICENSE¶
Artistic or GPL, any version.
AUTHORS¶
- •
- Barry Slaymaker
- •
- Chris Prather <chris@prather.org>
COPYRIGHT AND LICENSE¶
This software is copyright (c) 2013 by Barry Slaymaker.
This is free software; you can redistribute it and/or modify it under the same
terms as the Perl 5 programming language system itself.