NAME
XML::Bare - Minimal XML parser implemented via a C state engine
VERSION
0.23
SYNOPSIS
use XML::Bare;
my $xml = new XML::Bare( text => '<xml><name>Bob</name></xml>' );
# Parse the xml into a hash tree
my $root = $xml->parse();
# Print the content of the name node
print $root->{xml}->{name}->{value};
# Load xml from a file ( assume same contents as first example )
my $xml2 = new XML::Bare( file => 'test.xml' );
my $root2 = $xml2->parse();
$root2->{xml}->{name}->{value} = 'Tim';
# Save the changes back to the file
$xml2->save(); DESCRIPTION
This module is a 'Bare' XML parser. It is implemented in C++. The parser itself is a simple state engine that is less than 500 lines of C++. The parser builds a C++ class tree from input text. That C++ class tree is converted to a Perl hash by a Perl function that makes basic calls back to the C++ to go through the nodes sequentially.
Supported XML
To demonstrate what sort of XML is supported, consider the following examples. Each of the PERL statements evaluates to true.
Node containing just text
XML: <xml>blah</xml> PERL: $root->{xml}->{value} eq "blah";Subset nodes
XML: <xml><name>Bob</name></xml> PERL: $root->{xml}->{name}->{value} eq "Bob";Attributes unquoted
XML: <xml><a href=index.htm>Link</a></xml> PERL: $root->{xml}->{a}->{href}->{value} eq "index.htm";Attributes quoted
XML: <xml><a href="index.htm">Link</a></xml> PERL: $root->{xml}->{a}->{href}->{value} eq "index.htm";CDATA nodes
XML: <xml><raw><![CDATA[some raw $~<!bad xml<>]]></raw></xml> PERL: $root->{xml}->{raw}->{value} eq "some raw \$~<!bad xml<>";Multiple nodes; form array
XML: <xml><item>1</item><item>2</item></xml> PERL: $root->{xml}->{item}->[0]->{value} eq "1";Forcing array creation
XML: <xml><multi_item/><item>1</item></xml> PERL: $root->{xml}->{item}->[0]->{value} eq "1";One comment supported per node
XML: <xml><!--test--></xml> PERL: $root->{xml}->{comment} eq 'test';
Parsed Hash Structure
The hash structure returned from XML parsing is created in a specific format. Besides as described above, the structure contains some additional nodes in order to preserve information that will allow that structure to be correctly converted back to XML.
Nodes may contain the following 2 additional subnodes:
pos
This is a number indicating the ordering of nodes. It is used to allow items in a perl hash to be sorted when writing back to xml. Note that items are not sorted after parsing in order to save time if all you are doing is reading and you do not care about the order.
In future versions of this module an option will be added to allow you to sort your nodes so that you can read them in order.
att
This is a boolean value that exists and is 1 iff the node is an attribute.
Parsing Limitations / Features
CDATA parsed correctly, but stripped if unneeded
Currently the contents of a node that are CDATA are read and put into the value hash, but the hash structure does not have a value indicating the node contains CDATA.
When converting back to XML, the contents are the value hash are parsed to check for xml incompatible data using a regular expression. If 'CDATA like' stuff is encountered, the node is output as CDATA.
Node position stored, but hash remains unsorted
The ordering of nodes is noted using the 'pos' value, but the hash itself is not ordered after parsing. Currently items will be out of order when looking at them in the hash.
Note that when converted back to XML, the nodes are then sorted and output in the correct order to XML.
Comments are parsed but only one is stored per node.
For each node, there can be a comment within it, and that comment will be saved and output back when dumping to XML.
Comments override output of immediate value
If a node contains only a comment node and a text value, only the comment node will be displayed. This is in line with treating a comment node as a node and only displaying immediate values when a node contains no subnodes.
PI sections are parsed, but discarded
Unknown
<!sections are parsed, but discardedAttributes must use double quotes if quoted
Attributes in XML can be used, with or without quotes, but if quotes are used they must be double quotes. If single quotes are used, the value will end up starting with a single quote and continue until a space or a node end.
Quoted attributes cannot contain escaped quotes
No escape character is recognized within quotes. As a result, there is no way to store a double quote character in an attribute value.
Attributes are always written back to XML with quotes
Nodes cannot contain subnodes as well as an immediate value
Actually nodes can in fact contain a value as well, but that value will be discarded if you write back to XML. That value is equal to the first continuous string of text besides a subnode.
<node>text<subnode/>text2</node> ( the value of node is text ) <node><subnode/>text</node> ( the value of node is text ) <node> <subnode/>text </node> ( the value of node is "\n " )
Module Functions
$ob = new XML::Bare( text => "[some xml]" )Create a new XML object, with the given text as the xml source.
$object = new XML::Bare( file => "[filename]" )Create a new XML object, with the given filename/path as the xml source
$object = new XML::Bare( text => "[some xml]", file => "[filename]" )Create a new XML object, with the given text as the xml input, and the given filename/path as the potential output ( used by save() )
$tree = $object->parse()Parse the xml of the object and return a tree reference
$text = $object->xml( [root] )Take the hash tree in [root] and turn it into cleanly indented ( 2 spaces ) XML text.
$object->save()The the current tree in the object, cleanly indent it, and save it to the file paramter specified when creating the object.
$text = XML::Bare::clean( text => "[some xml]" )Shortcut to creating an xml object and immediately turning it into clean xml text.
$text = XML::Bare::clean( file => "[filename]" )Similar to previous.
XML::Bare::clean( file => "[filename]", save => 1 )Clean up the xml in the file, saving the results back to the file
XML::Bare::clean( text => "[some xml]", save => "[filename]" )Clean up the xml provided, and save it into the specified file.
XML::Bare::clean( file => "[filename1]", save => "[filename2]" )Clean up the xml in filename1 and save the results to filename2.
$object->add_node( [node], [nodeset name], name => value, name2 => value2, ... )Example: $object->add_node( $root->{xml}, 'item', name => 'Bob' ); Result: <xml> <item> <name>Bob</name> </item> </xml>$object->del_node( [node], [nodeset name], name => value )Example: Starting XML: <xml> <a> <b>1</b> </a> <a> <b>2</b> </a> </xml> Code: $xml->del_node( $root->{xml}, 'a', b=>'1' ); Ending XML: <xml> <a> <b>2</b> </a> </xml>$object->find_node( [node], [nodeset name], name => value )Example: Starting XML: <xml> <ob> <key>1</key> <val>a</val> </ob> <ob> <key>2</key> <val>b</val> </ob> </xml> Code: $object->find_node( $root->{xml}, 'ob', key => '1' )->{val}->{value} = 'test'; Ending XML: <xml> <ob> <key>1</key> <val>test</val> </ob> <ob> <key>2</key> <val>b</val> </ob> </xml>$object->find_by_perl( [nodeset], "[perl code]" )find_by_perl evaluates some perl code for each node in a set of nodes, and returns the nodes where the perl code evaluates as true. In order to easily reference node values, node values can be directly referred to from within the perl code by the name of the node with a dash(-) in front of the name. See the example below.
Note that this function returns an array reference as opposed to a single node unlike the find_node function.
Example: Starting XML: <xml> <ob> <key>1</key> <val>a</val> </ob> <ob> <key>2</key> <val>b</val> </ob> </xml> Code: $object->find_by_perl( $root->{xml}->{ob}, "-key eq '1'" )->[0]->{val}->{value} = 'test'; Ending XML: <xml> <ob> <key>1</key> <val>test</val> </ob> <ob> <key>2</key> <val>b</val> </ob> </xml>XML::Bare::merge( [nodeset1], [nodeset2], [id node name] )Merges the nodes from nodeset2 into nodeset1, matching the contents of each node based up the content in the id node.
Example:
Code: my $ob1 = new XML::Bare( text => " <xml> <multi_a/> <a>bob</a> <a> <id>1</id> <color>blue</color> </a> </xml>" ); my $ob2 = new XML::Bare( text => " <xml> <multi_a/> <a>john</a> <a> <id>1</id> <name>bob</name> <bob>1</bob> </a> </xml>" ); my $root1 = $ob1->parse(); my $root2 = $ob2->parse(); merge( $root1->{'xml'}->{'a'}, $root2->{'xml'}->{'a'}, 'id' ); print $ob1->xml( $root1 ); Output: <xml> <multi_a></multi_a> <a>bob</a> <a> <id>1</id> <color>blue</color> <name>bob</name> <bob>1</bob> </a> </xml>
Performance
In comparison to other available perl xml parsers that create trees, XML::Bare is extremely fast. In order to measure the performance of loading and parsing compared to the alternatives, a test script has been created and is included with the distribution as 'test.pl'.
The test script can compare the speed of XML::Bare against the following alternatives:
XML::Parser::EasyTree
XML::Handler::Trees
XML::Twig
XML::LibXML
Note that basic LibXML is included in the comparison, despite the fact that it does not create a tree.
XML::Smart
XML::Simple
To run the comparison, you must provide a number, 1-12, as a paramter to the script in order to choose which module to compare against. The script works this way because some of the modules have parts used by the other modules, which hides the loading time for the module tested later...
The script measures the milliseconds of loading and parsing, and compares the time against the time of XML::Bare. So a 7 means it takes 7 times as long as XML::Bare.
Here is a combined table of the script run against each alternative using the included test.xml:
-Module- load parse total
XML::Bare 1 1 1
XML::Parser::EasyTree 5.6811 29.2881 8.5366
XML::Handler::Trees 7.8083 30.1434 10.503
XML::Twig 31.0709 60.7735 34.5892
XML::LibXML (no tree) 13.1591 1.8211 11.7857
XML::Smart 6.9198 93.2242 17.1124
XML::Simple 3.4242 207.0007 29.5704
XML::SAX::Simple 9.82 191.0584 31.1326
XML::Trivial 5.8321 7.009 6.3731
XML::TreePP 2.5766 35.0588 6.4429
XML::XPath::XMLParser 12.4321 41.0182 16.651
XML::DOM::Lite 16.3544 14.8667 16.1905
TinyXML 4.2033Here is a combined table of the script run against each alternative using the included feed2.xml:
-Module- load parse total
XML::Bare 1 1 1
XML::Parser::EasyTree 5.442 23.234 10.0313
XML::Handler::Trees 5.9811 20.5755 9.6939
XML::Twig 32.0006 44.811 35.3799
XML::LibXML (no tree) 13.5665 1.2518 10.0492
XML::Smart 6.8234 42.8422 16.2711
XML::Simple 3.9487 111.1732 31.6937
XML::SAX::Simple 10.1525 90.7282 32.7888
XML::Trivial 5.7941 28.5549 11.7381
XML::TreePP 2.8155 4.5963 3.9556
XML::XPath::XMLParser 11.9291 63.184 26.5266
XML::DOM::Lite 17.1702 13.8642 16.286
TinyXML 6.5016These results show that XML::Bare is, at least on the test machine, ~3-30 times faster loading and ~10-150 times faster parsing than any of the alternative tree parsers.
The following are shown as well: - XML::Bare can parse XML and create a hash tree in less time than it takes LibXML just to parse. - XML::Bare can parse XML and create a hash tree in 1/4 the time it takes TinyXML just to parse
Note that TinyXML is not a perl module and is timed by a dummy program that just uses the library to load and parse the example files.
LICENSE
Copyright (C) 2007 David Helkowski
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version. You may also can
redistribute it and/or modify it under the terms of the Perl
Artistic License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.