NAME

XML::Handler::YAWriter - Yet another Perl SAX XML Writer

SYNOPSIS

use XML::Handler::YAWriter;

my $ya = new XML::Handler::YAWriter( %options );
my $perlsax = new XML::Parser::PerlSAX( 'Handler' => $ya );

DESCRIPTION

YAWriter implements Yet Another XML::Hander::Writer. The reasons for this one are that I needed a flexible escaping technique, and want some kind of pretty printing. If an instances of YAWriter is created without any options, the default behavior is to produce an array of strings containing the XML in :

@{$ya->{Strings}}

Options

Options are given in the usual 'key' => 'value' ideom.

Output IO::File

This option tells YAWriter to use an already open file for output, instead of using $ya->{Strings} to store the array of strings. It should be noted that the only thing the object needs to implement is the print method. So anything can be used to receive a stream of strings from YAWriter.

AsFile string

This option will cause start_document to open named file and end_document to close it. Use the literal dash "-" if you want to print on standard output.

AsArray boolean

This option will force to store the XML in $ya->{Strings} even, if the Output option is given.

AsString boolean

This option will cause end_document to return the complete XML document in a single string. Most SAX drivers return the value of end_document as a result of their parse method. As this may not work with any combinations of SAX drivers and filters, a join of $ya->{Strings} in the controling method is prefered.

Encoding string

This will change the default encoding from UTF-8 to anything you like. You should ensure that given data is already in this encoding or provide a Escape hash, to tell YAWriter the recoding.

Escape hash

The Escape hash defines substitutions that have to be done to any string, with the execption of the processing_intruction and doctype_decl methods, where I think that escaping of target and data would cause more trouble, than necessary.

The default value for Escape is

$XML::Handler::YAWriter::escape = {
		'&'  => '&',
		'<'  => '&lt;',
		'>'  => '&gt;',
		'"'  => '&quot;',
		'--' => '&#45;&#45;'
		};

YAWriter will use an evaluated sub to make the recoding based on a given Escape hash resonable fast. Future versions may use XS to improve this performance bottleneck.

Pretty hash

Hash of string => boolean tuples, to define kind of prettyprinting. Default to undef. Possible string values:

AddHiddenNewline boolean

Add hidden newline before ">"

AddHiddenAttrTab boolean

Add hidden tabulation for attributes

CatchEmptyElement boolean

Catch emtpy Elements apply "/>" compression

CatchWhiteSpace boolean

Catch whitespace with comments

IsSGML boolean

This option will cause start_document, processing_instruction and doctype_decl to appear as SGML. The SGML is still wellformed of course, if your SAX events are wellformed.

NoComments boolean

Supress Comments

NoDTD boolean

Supress DTD

NoPI boolean

Supress Processing Instructions

NoProlog boolean

Supress <?xml ... ?> Prolog

NoWhiteSpace boolean

Supress WhiteSpace to clean documents from prior pretty printing.

PrettyWhiteIndent boolean

Add visible indent before any eventstring

PrettyWhiteNewline boolean

Add visible newlines before any eventstring

SAX1 boolean (not yet implemented)

Output only SAX1 compilant eventstrings

Notes:

The the correct handling of start_document and end_document is required!

The YAWriter Object initialises its structures during start_document and does its cleanup during end_document. If you forget to call start_document, any other method will break during the run. Most likely place is the encode method, trying to eval undef as a subroutine. If you forget to call end_document, you should not use a single instance of YAWriter more than once.

For small documents AsArray may be the fastest method and AsString the easiest one to receive the output of YAWriter. But AsString and AsArray may run out of memory with infinitve SAX streams. The only method XML::Handler::Writer calls on a given Output object is the print method. So its easy to use a self written Output object to improve streaming.

A single instance of XML::Handler::YAWriter is able to produce more than one file in a single run. Ensure to provide a fresh IO::File as Output before you call start_document and close this File after calling end_document. Or provide a filename in AsFile, so start_document and end_document can open and close its own filehandle.

Automatic recoding between 8bit and 16bit does not yet work correctly !

I have Perl-5.00563 at home and here I can claim "use utf8;" in the right places to make recoding work. But I dislike to claim "use 5.00555;" because many systems run 5.00503.

If you use some 8bit character set internaly and want use national characters, state either your character as Encoding to be ISO-8859-1, or provide an Escape hash similar to the following :

$ya->{'Escape'} = {
		'&'  => '&',
		'<'  => '&lt;',
		'>'  => '&gt;',
		'"'  => '&quot;',
		'--' => '&#45;&#45;'
		'ö' => '&ouml;'
		'ä' => '&auml;'
		'ü' => '&uuml;'
		'Ö' => '&Ouml;'
		'Ä' => '&Auml;'
		'Ü' => '&Uuml;'
		'ß' => '&szlig;'
		};

You may abuse YAWriter to clean XML documents from whitespace. Take a look at test.pl, doing just that with an XML::Edifact message, without querying the DTD. This may work in 99% of the cases, where you want to get rid of ignorable whitespace that is caused by the various forms of pretty printing.

my $ya = new XML::Handler::YAWriter( 
	'Output' => new IO::File ( ">-" );
	'Pretty' => {
		'NoWhiteSpace'=>1,
		'NoComments'=>1,
		'AddHiddenNewline'=>1,
		'AddHiddenAttrTab'=>1,
	} );

XML::Handler::Writer implements any method XML::Parser::PerlSAX wants. This extens the Java SAX1.0 specifcation. I think to use Pretty=>SAX1=>1 to disable this feature, if abusing YAWriter for a SAX proxy.

AUTHOR

Michael Koehne, Kraehe@Copyleft.De

Thanks

"Derksen, Eduard (Enno), CSCIO" <enno@att.com> helped me with the Escape hash and gave quite a lot of usefull comments.

SEE ALSO

perl and XML::Parser::PerlSAX