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.\" ========================================================================
.\"
.IX Title "XML::SAX::Writer 3"
.TH XML::SAX::Writer 3 "2017-07-17" "perl v5.26.3" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
XML::SAX::Writer \- SAX2 XML Writer
.SH "VERSION"
.IX Header "VERSION"
version 0.57
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&  use XML::SAX::Writer;
\&  use XML::SAX::SomeDriver;
\&
\&  my $w = XML::SAX::Writer\->new;
\&  my $d = XML::SAX::SomeDriver\->new(Handler => $w);
\&
\&  $d\->parse(\*(Aqsome options...\*(Aq);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
.SS "Why yet another \s-1XML\s0 Writer ?"
.IX Subsection "Why yet another XML Writer ?"
A new \s-1XML\s0 Writer was needed to match the \s-1SAX2\s0 effort because quite
naturally no existing writer understood \s-1SAX2.\s0 My first intention had
been to start patching XML::Handler::YAWriter as it had previously
been my favourite writer in the \s-1SAX1\s0 world.
.PP
However the more I patched it the more I realised that what I thought
was going to be a simple patch (mostly adding a few event handlers and
changing the attribute syntax) was turning out to be a rewrite due to
various ideas I'd been collecting along the way. Besides, I couldn't
find a way to elegantly make it work with \s-1SAX2\s0 without breaking the
\&\s-1SAX1\s0 compatibility which people are probably still using. There are of
course ways to do that, but most require user interaction which is
something I wanted to avoid.
.PP
So in the end there was a new writer. I think it's in fact better this
way as it helps keep \s-1SAX1\s0 and \s-1SAX2\s0 separated.
.SH "METHODS"
.IX Header "METHODS"
.IP "\(bu" 4
new(%hash)
.Sp
This is the constructor for this object. It takes a number of
parameters, all of which are optional.
.IP "\(bu" 4
Output
.Sp
This parameter can be one of several things. If it is a simple
scalar, it is interpreted as a filename which will be opened for
writing. If it is a scalar reference, output will be appended to this
scalar. If it is an array reference, output will be pushed onto this
array as it is generated. If it is a filehandle, then output will be
sent to this filehandle.
.Sp
Finally, it is possible to pass an object for this parameter, in which
case it is assumed to be an object that implements the consumer
interface described later in the documentation.
.Sp
If this parameter is not provided, then output is sent to \s-1STDOUT.\s0
.Sp
Note that there is no means to set an encoding layer on filehandles
created by this module; if this is necessary, the calling code should
first open a filehandle with the appropriate encoding set, and pass
that filehandle to this module.
.IP "\(bu" 4
Escape
.Sp
This should be a hash reference where the keys are characters
sequences that should be escaped and the values are the escaped form
of the sequence. By default, this module will escape the ampersand
(&), less than (<), greater than (>), double quote ("), and apostrophe
('). Note that some browsers don't support the &apos; escape used for
apostrophes so that you should be careful when outputting \s-1XHTML.\s0
.Sp
If you only want to add entries to the Escape hash, you can first
copy the contents of \f(CW%XML::SAX::Writer::DEFAULT_ESCAPE\fR.
.IP "\(bu" 4
CommentEscape
.Sp
Comment content often needs to be escaped differently from other
content. This option works exactly as the previous one except that
by default it only escapes the double dash (\-\-) and that the contents
can be copied from \f(CW%XML::SAX::Writer::COMMENT_ESCAPE\fR.
.IP "\(bu" 4
EncodeFrom
.Sp
The character set encoding in which incoming data will be provided.
This defaults to \s-1UTF\-8,\s0 which works for US-ASCII as well.
.Sp
Set this to \f(CW\*(C`undef\*(C'\fR if you do not wish to decode your data.
.IP "\(bu" 4
EncodeTo
.Sp
The character set encoding in which output should be encoded. Again,
this defaults to \s-1UTF\-8.\s0
.Sp
Set this to \f(CW\*(C`undef\*(C'\fR if you do not with to encode your data.
.IP "\(bu" 4
QuoteCharacter
.Sp
Set the character used to quote attributes. This defaults to single quotes (') 
for backwards compatibility.
.SH "THE CONSUMER INTERFACE"
.IX Header "THE CONSUMER INTERFACE"
XML::SAX::Writer can receive pluggable consumer objects that will be
in charge of writing out what is formatted by this module. Setting a
Consumer is done by setting the Output option to the object of your
choice instead of to an array, scalar, or file handle as is more
commonly done (internally those in fact map to Consumer classes and
and simply available as options for your convenience).
.PP
If you don't understand this, don't worry. You don't need it most of
the time.
.PP
That object can be from any class, but must have two methods in its
\&\s-1API.\s0 It is also strongly recommended that it inherits from
XML::SAX::Writer::ConsumerInterface so that it will not break if that
interface evolves over time. There are examples at the end of
XML::SAX::Writer's code.
.PP
The two methods that it needs to implement are:
.IP "\(bu" 4
output \s-1STRING\s0
.Sp
(Required)
.Sp
This is called whenever the Writer wants to output a string formatted
in \s-1XML.\s0 Encoding conversion, character escaping, and formatting have
already taken place. It's up to the consumer to do whatever it wants
with the string.
.IP "\(bu" 4
\&\fBfinalize()\fR
.Sp
(Optional)
.Sp
This is called once the document has been output in its entirety,
during the end_document event. end_document will in fact return
whatever \fBfinalize()\fR returns, and that in turn should be returned
by \fBparse()\fR for whatever parser was invoked. It might be useful if
you need to provide feedback of some sort.
.PP
Here's an example of a custom consumer.  Note the extra \f(CW\*(C`$\*(C'\fR signs in
front of \f(CW$self\fR; the base class is optimized for the overwhelmingly
common case where only one data member is required and \f(CW$self\fR is a
reference to that data member.
.PP
.Vb 1
\&    package MyConsumer;
\&
\&    @ISA = qw( XML::SAX::Writer::ConsumerInterface );
\&
\&    use strict;
\&
\&    sub new {
\&        my $self = shift\->SUPER::new( my $output );
\&
\&        $$self = \*(Aq\*(Aq;      # Note the extra \*(Aq$\*(Aq
\&
\&        return $self;
\&    }
\&
\&    sub output {
\&        my $self = shift;
\&        $$self .= uc shift;
\&    }
\&
\&    sub get_output {
\&        my $self = shift;
\&        return $$self;
\&    }
.Ve
.PP
And here is one way to use it:
.PP
.Vb 2
\&    my $c = MyConsumer\->new;
\&    my $w = XML::SAX::Writer\->new( Output => $c );
\&
\&    ## ... send events to $w ...
\&
\&    print $c\->get_output;
.Ve
.PP
If you need to store more that one data member, pass in an array or hash
reference:
.PP
.Vb 1
\&        my $self = shift\->SUPER::new( {} );
.Ve
.PP
and access it like:
.PP
.Vb 4
\&    sub output {
\&        my $self = shift;
\&        $$self\->{Output} .= uc shift;
\&    }
.Ve
.SH "THE ENCODER INTERFACE"
.IX Header "THE ENCODER INTERFACE"
Encoders can be plugged in to allow one to use one's favourite encoder
object. Presently there are two encoders: Encode and NullEncoder. They
need to implement two methods, and may inherit from
XML::SAX::Writer::NullConverter if they wish to
.IP "new \s-1FROM_ENCODING, TO_ENCODING\s0" 4
.IX Item "new FROM_ENCODING, TO_ENCODING"
Creates a new Encoder. The arguments are the chosen encodings.
.IP "convert \s-1STRING\s0" 4
.IX Item "convert STRING"
Converts that string and returns it.
.PP
Note that the return value of the convert method is \fBnot\fR checked. Output may
be truncated if a character couldn't be converted correctly. To avoid problems
the encoder should take care encoding errors itself, for example by raising an
exception.
.SH "CUSTOM OUTPUT"
.IX Header "CUSTOM OUTPUT"
This module is generally used to write \s-1XML\s0 \*(-- which it does most of the
time \*(-- but just like the rest of \s-1SAX\s0 it can be used as a generic
framework to output data, the opposite of a non-XML \s-1SAX\s0 parser.
.PP
Of course there's only so much that one can abstract, so depending on
your format this may or may not be useful. If it is, you'll need to
know the following \s-1API\s0 (and probably to have a look inside
\&\f(CW\*(C`XML::SAX::Writer::XML\*(C'\fR, the default Writer).
.IP "init" 4
.IX Item "init"
Called before the writing starts, it's a chance for the subclass to do
some initialisation if it needs it.
.IP "setConverter" 4
.IX Item "setConverter"
This is used to set the proper converter for character encodings. The
default implementation should suffice but you can override it. It must
set \f(CW\*(C`$self\->{Encoder}\*(C'\fR to an Encoder object. Subclasses *should* call
it.
.IP "setConsumer" 4
.IX Item "setConsumer"
Same as above, except that it is for the Consumer object, and that it
must set \f(CW\*(C`$self\->{Consumer}\*(C'\fR.
.IP "setEscaperRegex" 4
.IX Item "setEscaperRegex"
Will initialise the escaping regex \f(CW\*(C`$self\->{EscaperRegex}\*(C'\fR based on
what is needed.
.IP "escape \s-1STRING\s0" 4
.IX Item "escape STRING"
Takes a string and escapes it properly.
.IP "setCommentEscaperRegex and escapeComment \s-1STRING\s0" 4
.IX Item "setCommentEscaperRegex and escapeComment STRING"
These work exactly the same as the two above, except that they are meant
to operate on comment contents, which often have different escaping rules
than those that apply to regular content.
.SH "TODO"
.IX Header "TODO"
.Vb 1
\&    \- proper UTF\-16 handling
\&
\&    \- the formatting options need to be developed.
\&
\&    \- test, test, test (and then some tests)
\&
\&    \- doc, doc, doc (actually this part is in better shape)
\&
\&    \- remove the xml_decl and replace it with intelligent logic, as
\&    discussed on perl\-xml
\&
\&    \- make a the Consumer selecting code available in the API, to avoid
\&    duplicating
\&
\&    \- add an Apache output Consumer, triggered by passing $r as Output
.Ve
.SH "CREDITS"
.IX Header "CREDITS"
Michael Koehne (XML::Handler::YAWriter) for much inspiration and Barrie
Slaymaker for the Consumer pattern idea, the coderef output option and
miscellaneous bugfixes and performance tweaks. Of course the usual
suspects (Kip Hampton and Matt Sergeant) helped in the usual ways.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
XML::SAX::*
.SH "AUTHORS"
.IX Header "AUTHORS"
.IP "\(bu" 4
Robin Berjon <robin@knowscape.com>
.IP "\(bu" 4
Chris Prather <chris@prather.org>
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
This software is copyright (c) 2014 by Robin Berjon.
.PP
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.