XML::Validator::Schema - validate XML against a subset of W3C XML Schema

XML-Validator-Schema documentation Contained in the XML-Validator-Schema distribution.

Index

Code Index:

NAME

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XML::Validator::Schema - validate XML against a subset of W3C XML Schema

SYNOPSIS

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  use XML::SAX::ParserFactory;
  use XML::Validator::Schema;

  #
  # create a new validator object, using foo.xsd
  #
  $validator = XML::Validator::Schema->new(file => 'foo.xsd');

  #
  # create a SAX parser and assign the validator as a Handler
  #
  $parser = XML::SAX::ParserFactory->parser(Handler => $validator);

  #
  # validate foo.xml against foo.xsd
  #
  eval { $parser->parse_uri('foo.xml') };
  die "File failed validation: $@" if $@;

DESCRIPTION

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This module allows you to validate XML documents against a W3C XML Schema. This module does not implement the full W3C XML Schema recommendation (http://www.w3.org/XML/Schema), but a useful subset. See the SCHEMA SUPPORT|"SCHEMA SUPPORT" section below.

IMPORTANT NOTE: To get line and column numbers in the error messages generated by this module you must install XML::Filter::ExceptionLocator and use XML::SAX::ExpatXS as your SAX parser. This module is much more useful if you can tell where your errors are, so using these modules is highly recommeded!

INTERFACE

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RATIONALE

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I'm writing a piece of software which uses Xerces/C++ ( http://xml.apache.org/xerces-c/ ) to validate documents against XML Schema schemas. This works very well, but I'd like to release my project to the world. Requiring users to install Xerces is simply too onerous a requirement; few will have it already and the Xerces installation system leaves much to be desired.

On CPAN, the only available XML Schema validator is XML::Schema. Unfortunately, this module isn't ready for use as it lacks the ability to actually parse the XML Schema document format! I looked into enhancing XML::Schema but I must admit that I'm not smart enough to understand the code... One day, when XML::Schema is completed I will replace this module with a wrapper around it.

This module represents my attempt to support enough XML Schema syntax to be useful without attempting to tackle the full standard. I'm sure this will mean that it can't be used in all situations, but hopefully that won't prevent it from being used at all.

SCHEMA SUPPORT

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Supported Elements

The following elements are supported by the XML Schema parser. If you don't see an element or an attribute here then you definitely can't use it in a schema document.

You can expect that the schema document parser will produce an error if you include elements which are not supported. However, unsupported attributes may be silently ignored. This should not be misconstrued as a feature and will eventually be fixed.

All of these elements must be in the http://www.w3.org/2001/XMLSchema namespace, either using a default namespace or a prefix.

  <schema>

     Supported attributes: targetNamespace, elementFormDefault,
     attributeFormDefault

     Notes: the only supported values for elementFormDefault and
     attributeFormDefault are "unqualified."  As such, targetNamespace
     is essentially ignored.

  <element name="foo">

     Supported attributes: name, type, minOccurs, maxOccurs, ref

  <attribute>

     Supported attributes: name, type, use, ref

  <sequence>

     Supported attributes: minOccurs, maxOccurs

  <choice>

     Supported attributes: minOccurs, maxOccurs

  <all>

     Supported attributes: minOccurs, maxOccurs

  <complexType>

    Supported attributes: name

  <simpleContent>

    The only supported sub-element is <extension>.

  <extension>

    Supported attributes: base

    Notes: only allowed inside <simpleContent>

  <simpleType>

    Supported attributes: name

  <restriction>

    Supported attributes: base

    Notes: only allowed inside <simpleType>

  <whiteSpace>

    Supported attributes: value

  <pattern>

    Supported attributes: value

  <enumeration>

    Supported attributes: value

  <length>

    Supported attributes: value

  <minLength>

    Supported attributes: value

  <maxLength>

    Supported attributes: value

  <minInclusive>

    Supported attributes: value

  <minExclusive>

    Supported attributes: value

  <maxInclusive>

    Supported attributes: value

  <maxExclusive>

    Supported attributes: value

  <totalDigits>

    Supported attributes: value

  <fractionDigits>

    Supported attributes: value

  <annotation>

  <documentation>

    Supported attributes: name

  <union>
    Supported attributes: MemberTypes

Simple Type Support

Supported built-in types are:

  string

  normalizedString

  token

  NMTOKEN

   Notes: the spec says NMTOKEN should only be used for attributes,
   but this rule is not enforced.

  boolean

  decimal

   Notes: the enumeration facet is not supported on decimal or any
   types derived from decimal.

  integer

  int

  short

  byte

  unsignedInt

  unsignedShort

  unsignedByte

  positiveInteger

  negativeInteger

  nonPositiveInteger

  nonNegativeInteger

  dateTime

    Notes: Although dateTime correctly validates the lexical format it does not
    offer comparison facets (min*, max*, enumeration).

  double

    Notes: Although double correctly validates the lexical format it
    does not offer comparison facets (min*, max*, enumeration).  Also,
    minimum and maximum constraints as described in the spec are not
    checked.

  float

    Notes: The restrictions on double support apply to float as well.

  duration

  time

  date

  gYearMonth

  gYear

  gMonthDay

  gDay

  gMonth

  hexBinary

  base64Binary

  anyURI

  QName

  NOTATION

Miscellaneous Details

Other known devations from the specification:

CAVEATS

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Here are a few gotchas that you should know about:

BUGS

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Please use rt.cpan.org to report bugs in this module:

  http://rt.cpan.org

Please note that I will delete bugs which merely point out the lack of support for a particular feature of XML Schema. Those are feature requests, and believe me, I know we've got a long way to go.

SUPPORT

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This module is supported on the perl-xml mailing-list. Please join the list if you have questions, suggestions or patches:

  http://listserv.activestate.com/mailman/listinfo/perl-xml

CVS

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If you'd like to help develop XML::Validator::Schema you'll want to check out a copy of the CVS tree:

  http://sourceforge.net/cvs/?group_id=89764

CREDITS

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The following people have contributed bug reports, test cases and/or code:

  Russell B Cecala (aka Plankton)
  David Wheeler
  Toby Long-Leather
  Mathieu
  h.bridge@fasol.fujitsu.com
  michael.jacob@schering.de
  josef@clubphoto.com
  adamk@ali.as
  Jean Flouret

AUTHOR

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Sam Tregar <sam@tregar.com>

COPYRIGHT AND LICENSE

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Copyright (C) 2002-2003 Sam Tregar

This program is free software; you can redistribute it and/or modify it under the same terms as Perl 5 itself.

A NOTE ON DEVELOPMENT METHODOLOGY

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This module isn't just an XML Schema validator, it's also a test of the Test Driven Development methodology. I've been writing tests while I develop code for a while now, but TDD goes further by requiring tests to be written before code. One consequence of this is that the module code may seem naive; it really is just enough code to pass the current test suite. If I'm doing it right then there shouldn't be a single line of code that isn't directly related to passing a test. As I add functionality (by way of writing tests) I'll refactor the code a great deal, but I won't add code only to support future development.

For more information I recommend "Test Driven Development: By Example" by Kent Beck.

SEE ALSO

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XML::Schema

http://www.w3.org/XML/Schema

http://xml.apache.org/xerces-c/

XML-Validator-Schema documentation Contained in the XML-Validator-Schema distribution. 
package XML::Validator::Schema;

use 5.006;
use strict;
use warnings;

our $VERSION = '1.10';


use base qw(XML::SAX::Base); # this module is a SAX filter
use Carp qw(croak);          # make some noise
use XML::SAX::Exception;     # for real
use XML::Filter::BufferText; # keep text together
use XML::SAX::ParserFactory; # needed to parse the schema documents

use XML::Validator::Schema::Parser;
use XML::Validator::Schema::ElementNode;
use XML::Validator::Schema::ElementRefNode;
use XML::Validator::Schema::RootNode;
use XML::Validator::Schema::ComplexTypeNode;
use XML::Validator::Schema::SimpleTypeNode;
use XML::Validator::Schema::SimpleType;
use XML::Validator::Schema::TypeLibrary;
use XML::Validator::Schema::ElementLibrary;
use XML::Validator::Schema::AttributeLibrary;
use XML::Validator::Schema::ModelNode;
use XML::Validator::Schema::Attribute;
use XML::Validator::Schema::AttributeNode;

use XML::Validator::Schema::Util qw(_err);
our %CACHE;

our $DEBUG = 0;

# create a new validation filter
sub new {
    my $pkg  = shift;
    my $opt  = (@_ == 1)  ? { %{shift()} } : {@_};
    my $self = bless $opt, $pkg;

    $self->{debug} = exists $self->{debug} ? $self->{debug} : $DEBUG;

    # check options
    croak("Missing required 'file' option.") unless $self->{file};

    # if caching is on, check the cache
    if ($self->{cache} and
        exists $CACHE{$self->{file}} and 
        $CACHE{$self->{file}}{mtime} == (stat($self->{file}))[9]) {

        # load cached object
        $self->{node_stack} = $CACHE{$self->{file}}{node_stack};

        # might have nodes on it leftover from failed validation,
        # truncate to root
        $#{$self->{node_stack}} = 0;

        # clean up any lingering state from the last use of this tree
        $self->{node_stack}[0]->walk_down(
           { callback => sub { shift->clear_memory; 1; } });

    } else {
        # create an empty element stack
        $self->{node_stack} = [];

        # load the schema, filling in the element tree
        $self->parse_schema();

        # store to cache
        if ($self->{cache}) {
            $CACHE{$self->{file}}{mtime} = (stat($self->{file}))[9];
            $CACHE{$self->{file}}{node_stack} = $self->{node_stack};
        }
    }

    # buffer text for convenience
    my $bf = XML::Filter::BufferText->new( Handler => $self );

    # add line-numbers and column-numbers to errors if
    # XML::Filter::ExceptionLocator is available
    eval { require XML::Filter::ExceptionLocator; };
    if ($@) {
        # no luck, just return the buffer-text handler
        return $bf;
    } else {
        # create a new exception-locator and return it
        my $el = XML::Filter::ExceptionLocator->new( Handler => $bf );
        return $el;
    }
}

# parse an XML schema document, filling $self->{node_stack}
sub parse_schema {
    my $self = shift;

    _err("Specified schema file '$self->{file}' does not exist.")
      unless -e $self->{file};
    
    # initialize the schema parser
    my $parser = XML::Validator::Schema::Parser->new(schema => $self);

    # add line-numbers and column-numbers to errors if
    # XML::Filter::ExceptionLocator is available
    eval { require XML::Filter::ExceptionLocator; };
    unless ($@) {
        # create a new exception-locator and set it up above the parser
        $parser = XML::Filter::ExceptionLocator->new( Handler => $parser );
    }

    # parse the schema file
    $parser = XML::SAX::ParserFactory->parser(Handler => $parser);
    $parser->parse_uri($self->{file});
}

# check element start
sub start_element {
    my ($self, $data) = @_;
    my $name = $data->{LocalName};
    my $node_stack = $self->{node_stack};
    my $element = $node_stack->[-1];

    print STDERR "  " x scalar(@{$node_stack}), " o ", $name, "\n" 
      if $self->{debug};

    # check that this alright
    my $daughter = $element->check_daughter($name);

    # check attributes
    $daughter->check_attributes($data->{Attributes});
    
    if ($self->{debug}) {
        foreach my $att ( keys %{ $data->{Attributes} } ) {
            print STDERR "  " x (scalar(@{$node_stack}) + 2), " - ", 
              $data->{Attributes}->{$att}->{Name}, " = ", 
                $data->{Attributes}->{$att}->{Value}, "\n" 
            }
    }

    # enter daughter node
    push(@$node_stack, $daughter);

    $self->SUPER::start_element($data);
}

# check character content
sub characters {
    my ($self, $data) = @_;
    my $element = $self->{node_stack}[-1];
    $element->check_contents($data->{Data});
    $element->{checked_content} = 1;

    $self->SUPER::characters($data);
}

# finish element checking
sub end_element {
    my ($self, $data) = @_;
    my $node_stack = $self->{node_stack};
    my $element = $node_stack->[-1];

    # check empty content if haven't checked yet
    $element->check_contents('')
      unless $element->{checked_content};
    $element->{checked_content} = 0;

    # final model check
    $element->{model}->check_final_model($data->{LocalName},
                                         $element->{memory} || [])
      if $element->{model};

    # done
    $element->clear_memory();
    pop(@$node_stack);

    $self->SUPER::end_element($data);
}

1;