plucky (3) XML::CompactTree.3pm.gz
NAME
XML::CompactTree - builder of compact tree structures from XML documents
VERSION
Version 0.03
SYNOPSIS
use XML::CompactTree;
use XML::LibXML::Reader;
my $reader = XML::LibXML::Reader->new(location => $url);
...
my $tree = XML::CompactTree::readSubtreeToPerl($reader);
...
DESCRIPTION
This module provides functions that use XML::LibXML::Reader to parse an XML document into a parse tree
formed of nested arrays (and hashes).
It aims to be fast in doing that and to presreve all relevant information from the XML (including
namespaces, document order, mixed content, etc.). It sacrifices user friendliness for speed.
IMPORTANT: There is an even more efficient XS implementation of this module called XML::CompactTree::XS
with 100% equivalent functionality.
PURPOSE
I wrote this module because I noticed that repeated calls to methods implemented in C (XS) were very
expensive in Perl.
Therefore traversing a large DOM tree using XML::LibXML or iterating over an XML stream using
XML::LibXML::Reader was much slower than traversing similarly large and structured native Perl data
structures.
This module allows the user to build a document parse tree consisting of native Perl data structures
(arrays and optionally hashes) using XML::LibXML::Reader with minimal number of XS calls.
(Note that there XML::CompactTree::XS is 100% equivalent of this module that manages the same with just
one XS call.)
It does not provide full DOM navigation but attempts to provide maximum amount of information. Its
memory footprint should be somewhat smaller than that of a corresponding XML::LibXML DOM tree.
EXPORT
By default, the following constants are exported (":flags" export tag) to be used as flags for the tree
builder:
XCT_IGNORE_WS
XCT_IGNORE_SIGNIFICANT_WS
XCT_IGNORE_PROCESSING_INSTRUCTIONS
XCT_IGNORE_COMMENTS
XCT_USE_QNAMES /* not yet implemented */
XCT_KEEP_NS_DECLS
XCT_TEXT_AS_STRING /* not yet implemented */
XCT_ATTRIBUTE_ARRAY
XCT_PRESERVE_PARENT /* not yet implemented */
XCT_MERGE_TEXT_NODES /* not yet implemented */
XCT_DOCUMENT_ROOT
FUNCTIONS
readSubtreeToPerl( $reader, $flags, \my %ns )
Uses a given XML::LibXML::Reader parser objects to parse a subtree at the current reader position to
build a tree formed of nested arrays (see "OUTPUT FORMAT").
reader
A XML::LibXML::Reader object to use as the reader. While building the tree, the reader moves to the
next node on the current or higher level.
flags
An integer consisting of 1 bit flags (see constants in the EXPORT section). Use binary or (|) to
combine individual flags.
The following flags are NOT implemented yet:
XCT_USE_QNAMES, XCT_TEXT_AS_STRING, XCT_PRESERVE_PARENT, XCT_MERGE_TEXT_NODES
ns You may pass an empty hash reference that will be populated by a namespace_uri to namespace_index
map, that can be used to decode namespace indexes in the resulting data structure (see OUTPUT
FORMAT).
readLevelToPerl( $reader, $flags, $ns )
Like "readSubtreeToPerl", but reads the subtree at the current reader position and all its following
siblings. It returns an array reference of representations of these subtrees as in the format described
in "OUTPUT FORMAT".
OUTPUT FORMAT
The result of parsing a subtree is a Perl array reference $node contains a node type followed by node
data whose interpretation on further positions in $node depends on the node type, as described below:
Any Node
• $node->[0] is an integer representing the node type. Use XML::LibXML::Reader node-tye constants,
e.g. XML_READER_TYPE_ELEMENT for an element node, XML_READER_TYPE_TEXT for text node, etc.
Document or Document Fragment Nodes
• $node->[1] contains the document encoding
• $node->[2] is an array reference containing similar represention of all the child nodes of the
document (fragment).
Note: XML::LibXML::Reader does not document node by default, which means that calling readSubtreeToPerl
on a reader object in its initial state only parses the first node in the document (which can be the root
element, but also a comment or a processing instruction). Use XCT_DOCUMENT_ROOT flag to force creating a
document node in such case.
Element nodes
• $node->[1] is the local name (UTF-8 encoded character string)
• $node->[2] is the namespace index (see NAMESPACES below)
• $node->[3] is undef if the element has no attributes. Otherwise if XCT_ATTRIBUTE_ARRAY flag was
used, $node->[3] is an array reference of the form "[ name1, value1, name2, value2, ....]" of
attribute names and corresponding values. If XCT_ATTRIBUTE_ARRAY flag was not used, then $node->[3]
is a hash reference mapping attribute names to the corresponding attribute values "{ name1="value1,
name2=>value2...}>
The flag XCT_KEEP_NS_DECLS controls whether namespace declarations (xmlns=... or xmlns:prefix=...)
are included along with normal attributes or not.
Note: there is no support for namespaced attributes yet, but the attribute names are stored as
QNames, so one can always use XCT_KEEP_NS_DECLS to keep track of namespace prefix declarations and
do the resolving manually. Support for namespaced attributes is planned.
• If XTC_LINE_NUMBERS flag was used, $node->[4] contains the line number of the element and $node->[5]
contains an array reference containing similar representions of the child nodes of the current node.
• If XTC_LINE_NUMBERS flag was NOT used, $node->[4] contains an array reference of similar
representations of the child nodes of the current node.
Text, CDATA, Comment and White-Space Nodes
• $node->[1] contains the node value (UTF-8 encoded character string)
Unparsed Entity, Processing-Instruction, and Notation Nodes
• $node->[1] contains the local name (there is no support for namespaces on these types of nodes yet)
• $node->[2] contains the node value
Skipping Less-Significant Nodes
White-space (non-significant or significant), processing-instruction and comment nodes can be completely
skipped, using the following flags:
XCT_IGNORE_WS
XCT_IGNORE_SIGNIFICANT_WS
XCT_IGNORE_PROCESSING_INSTRUCTIONS
XCT_IGNORE_COMMENTS
NAMESPACES
Namespaces of element nodes are stored in the element node as an integer. 0 always represents nodes
without namespace, all other namespaces are assigned unique numbers in an increasing order as they
appear. You can pass an empty hash reference to the parsing functions to obtain the mapping.
Example
use XML::CompactTree;
use XML::LibXML::Reader;
my $reader = XML::LibXML::Reader->new(location => $ARGV[0]);
my %ns;
my $data = XML::CompactTree::readSubtreeToPerl( $reader, XCT_DOCUMENT_ROOT, \%ns );
$ns_map[$ns{$_}]=$_ for keys %ns;
my @nodes = ($data);
while (@nodes) {
my $node = shift @nodes;
my $type = $node->[0];
if ($type == XML_READER_TYPE_ELEMENT) {
print "element $node->[1] is from ns $node->[2] '$ns_map[$node->[2]]'\n";
push @nodes, @{$node->[4]}; # queue children
} elsif ($type == XML_READER_TYPE_DOCUMENT) {
push @nodes, @{$node->[2]}; # queue children
}
}
PLANNED FEATURES
Planned flags:
XCT_USE_QNAMES - use QNames instead of local names for all nodes
XCT_TEXT_AS_STRING - put text nodes into the tree as plain scalars
XCT_PRESERVE_PARENT - add a slot with a weak reference to the parent node
XCT_MERGE_TEXT_NODES - merge adjacent text/cdata nodes together
Features: allow blessing the array refs to default or user-specified classes; the default classes would
provide a very small subset of DOM methods to retrieve node information, manipulate the tree, and
possibly serialize the parse tree back to XML.
AUTHOR
Petr Pajas, "<pajas@matfyz.cz>"
BUGS
Please report any bugs or feature requests to "bug-xml-compacttree-xs@rt.cpan.org", or through the web interface at <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=XML-CompactTree-XS>. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.
COPYRIGHT & LICENSE
Copyright 2008-2009 Petr Pajas, All Rights Reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.
SEE ALSO
XML::CompactTree::XS
XML::LibXML::Reader