NAME
XML::Bare - Minimal XML parser implemented via a C state engine
VERSION
0.40
SYNOPSIS
use XML::Bare;
my $ob = new XML::Bare( text => '<xml><name>Bob</name></xml>' );
# Parse the xml into a hash tree
my $root = $ob->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 $ob2 = new XML::Bare( file => 'test.xml' );
my $root2 = $ob2->parse();
$root2->{xml}->{name}->{value} = 'Tim';
# Save the changes back to the file
$ob2->save();
---
# Load xml and verify against XBS ( XML Bare Schema )
my $xml_text = '<xml><item name=bob/></xml>''
my $schema_text = '<xml><item* name=[a-z]+></item*></xml>'
my $ob = new XML::Bare( text => $xml_text, schema => { text => $schema_text } );
$ob->parse(); # this will error out if schema is invalidDESCRIPTION
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 struct tree from input text. That C struct 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.
The parser itself will only cease parsing if it encounters tags that are not closed properly. All other inputs will parse, even invalid inputs. To allowing checking for validity, a schema checker is included in the module as well.
The schema format is custom and is meant to be as simple as possible. It is based loosely around the way multiplicity is handled in Perl regular expressions.
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';
Schema Checking
Schema checking is done by providing the module with an XBS (XML::Bare Schema) to check the XML against. If the XML checks as valid against the schema, parsing will continue as normal. If the XML is invalid, the parse function will die, providing information about the failure.
The following information is provided in the error message:
The type of error
Where the error occured ( line and char )
A short snippet of the XML at the point of failure
XBS ( XML::Bare Schema ) Format
Required nodes
XML: <xml></xml> XBS: <xml/>Optional nodes - allow one
XML: <xml></xml> XBS: <xml item?/> or XBS: <xml><item?/></xml>Optional nodes - allow 0 or more
XML: <xml><item/></xml> XBS: <xml item*/>Required nodes - allow 1 or more
XML: <xml><item/><item/></xml> XBS: <xml item+/>Nodes - specified minimum and maximum number
XML: <xml><item/><item/></xml> XBS: <xml item{1,2}/> or XBS: <xml><item{1,2}/></xml> or XBS: <xml><item{1,2}></item{1,2}></xml>Multiple acceptable node formats
XML: <xml><item type=box volume=20/><item type=line length=10/></xml> XBS: <xml><item type=box volume/><item type=line length/></xml>Regular expressions checking for values
XML: <xml name=Bob dir=up num=10/> XBS: <xml name=[A-Za-z]+ dir=up|down num=[0-9]+/>Require multi_ tags
XML: <xml><multi_item/></xml> XBS: <xml item@/>
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 3 additional subnodes:
_i
The character offset within the original parsed XML of where the node begins. This is used to provide line information for errors when XML fails a schema check.
_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. ( note that multiple nodes of the same name are stored 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 of 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. Note that nodes of the same name with the same parent will be grouped together; the position of the first item to appear will determine the output position of the group.
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 may use no quotes, single quotes, quotes
Quoted attributes cannot contain escaped quotes
No escape character is recognized within quotes. As a result, regular quotes cannot be stored to XML, or the written XML will not be correct, due to all attributes always being written using quotes.
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
$tree = $object->simple()Alternate to the parse function which generates a tree similar to that generated by XML::Simple. Note that the sets of nodes are turned into arrays always, regardless of whether they have a 'name' attribute, unlike XML::Simple.
Note that currently the generated tree cannot be used with any of the functions in this module that operate upon trees. The function is provided purely as a quick and dirty way to read simple XML files.
Also note that you cannot rely upon this function being contained in future versions of XML::Bare; the function will likely be split off into an optimized version meant purely to operate in this fashion.
$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->add_node_after( [node], [node to insert after], [nodeset name], name => value, ... )Same as add_node, but the new node is added immediately after the specificed node.
$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>XML::Bare::del_by_perl( ... )Works exactly like find_by_perl, but deletes whatever matches.
XML::Bare::forcearray( [noderef] )Turns the node reference into an array reference, whether that node is just a single node, or is already an array reference.
XML::Bare::new_node( ... )Creates a new node...
XML::Bare::newhash( ... )Creates a new hash with the specified value.
XML::Bare::simplify( [noderef] )Take a node with children that have immediate values and creates a hashref to reference those values by the name of each child.
Functions Used Internally
XML::Bare::check()=item *XML::Bare::checkone()=item *XML::Bare::readxbs()=item *XML::Bare::lineinfo()=item *XML::Bare::c_parse()=item *XML::Bare::c_parsefile()=item *XML::Bare::free_tree()=item *XML::Bare::free_tree_c()=item *XML::Bare::xml2obj()=itme *XML::Bare::xml2obj_simple()=item *XML::Bare::obj2xml()=item *XML::Bare::get_root()
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 templated speed comparison mechanism has been created and included with XML::Bare.
The include makebench.pl file runs when you make the module and creates perl files within the bench directory corresponding to the .tmpl contained there.
Currently there are three types of modules that can be tested against, executable parsers ( exe.tmpl ), tree parsers ( tree.tmpl ), and parsers that do not generated trees ( notree.tmpl ).
A full list of modules currently tested against is as follows:
Tiny XML (exe)
EzXML (exe)
XMLIO (exe)
XML::LibXML (notree)
XML::Parser (notree)
XML::Parser::Expat (notree)
XML::Descent (notree)
XML::Parser::EasyTree
XML::Handler::Trees
XML::Twig
XML::Smart
XML::Simple using XML::Parser
XML::Simple using XML::SAX::PurePerl
XML::Simple using XML::LibXML::SAX::Parser
XML::Simple using XML::Bare::SAX::Parser
XML::TreePP
XML::Trivial
XML::SAX::Simple
XML::Grove::Builder
XML::XPath::XMLParser
XML::DOM
To run the comparisons, run the appropriate perl file within the bench directory. (exe.pl, tree.pl, or notree.pl )
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::TreePP 2.3063 33.1776 6.1598
XML::Parser::EasyTree 4.9405 25.7278 7.4571
XML::Handler::Trees 7.2303 26.5688 9.6447
XML::Trivial 5.0636 12.4715 7.3046
XML::Smart 6.8138 78.7939 15.8296
XML::Simple (XML::Parser) 2.3346 50.4772 10.7455
XML::Simple (PurePerl) 2.361 261.4571 33.6524
XML::Simple (LibXML) 2.3187 163.7501 23.1816
XML::Simple (XML::Bare) 2.3252 59.1254 10.9163
XML::SAX::Simple 8.7792 170.7313 28.3634
XML::Twig 27.8266 56.4476 31.3594
XML::Grove::Builder 7.1267 26.1672 9.4064
XML::XPath::XMLParser 9.7783 35.5486 13.0002
XML::LibXML (notree) 11.0038 4.5758 10.6881
XML::Parser (notree) 4.4698 17.6448 5.8609
XML::Parser::Expat(notree) 3.7681 50.0382 6.0069
XML::Descent (notree) 6.0525 37.0265 11.0322
Tiny XML (exe) 1.0095
EzXML (exe) 1.1284
XMLIO (exe) 1.0165Here 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::TreePP 2.3068 23.7554 7.6921
XML::Parser::EasyTree 4.8799 25.3691 9.6257
XML::Handler::Trees 6.8545 33.1007 13.0575
XML::Trivial 5.0105 32.0043 11.4113
XML::Simple (XML::Parser) 2.3498 41.9007 12.3062
XML::Simple (PurePerl) 2.3551 224.3027 51.7832
XML::Simple (LibXML) 2.3617 88.8741 23.215
XML::Simple (XML::Bare) 2.4319 37.7355 10.2343
XML::Simple 2.7168 90.7203 26.7525
XML::SAX::Simple 8.7386 94.8276 29.2166
XML::Twig 28.3206 48.1014 33.1222
XML::Grove::Builder 7.2021 30.7926 12.9334
XML::XPath::XMLParser 9.6869 43.5032 17.4941
XML::LibXML (notree) 11.0023 5.022 10.5214
XML::Parser (notree) 4.3748 25.0213 5.9803
XML::Parser::Expat(notree) 3.6555 51.6426 7.4316
XML::Descent (notree) 5.9206 155.0289 18.7767
Tiny XML (exe) 1.2212
EzXML (exe) 1.3618
XMLIO (exe) 1.0145These results show that XML::Bare is, at least on the test machine, running all tests within cygwin, faster at loading and parsing than everything being tested against.
The following things 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 tree in less time than all three binary parsers take just to parse.
Note that the executable parsers are not perl modules and are timed using dummy programs that just uses the library to load and parse the example files. The executables are not included with this program. Any source modifications used to generate the shown test results can be found in the bench/src directory of the distribution
LICENSE
Copyright (C) 2008 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.
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