Provided by: libxml-sax-machines-perl_0.42-1_all bug

NAME

       XML::Filter::Merger - Assemble multiple SAX streams in to one document

SYNOPSIS

           ## See XML::SAX::Manifold and XML::SAX::ByRecord for easy ways
           ## to use this processor.

           my $w = XML::SAX::Writer->new(           Output => \*STDOUT );
           my $h = XML::Filter::Merger->new(        Handler => $w );
           my $p = XML::SAX::ParserFactory->parser( Handler => $h );

           ## To insert second and later docs in to the first doc:
           $h->start_manifold_document( {} );
           $p->parse_file( $_ ) for @ARGV;
           $h->end_manifold_document( {} );

           ## To insert multiple docs inline (especially useful if
           ## a subclass does the inline parse):
           $h->start_document( {} );
           $h->start_element( { ... } );
           ....
           $h->start_element( { Name => "foo", ... } );
           $p->parse_uri( $uri );   ## Body of $uri inserted in <foo>...</foo>
           $h->end_element( { Name => "foo", ... } );
           ...

DESCRIPTION

       Combines several documents in to one "manifold" document.  This can be done in two ways,
       both of which start by parsing a master document in to which (the guts of) secondary
       documents will be inserted.

   Inlining Secondary Documents
       The most SAX-like way is to simply pause the parsing of the master document between the
       two events where you want to insert a secondard document and parse the complete secondard
       document right then and there so it's events are inserted in the pipeline at the right
       spot.  XML::Filter::Merger only passes the content of the secondary document's root
       element:

           my $h = XML::Filter::Merger->new( Handler => $w );
           $h->start_document( {} );
           $h->start_element( { Name => "foo1" } );
               $p->parse_string( "<foo2><baz /></foo2>" );
           $h->end_element( { Name => "foo1" } );
           $h->end_document( {} );

       results in $w seeing a document like "<foo1><baz/></foo1>".

       This technique is especially useful when subclassing XML::Filter::Merger to implement
       XInclude-like behavior.  Here's a useless example that inserts some content after each
       "characters()" event:

           package Subclass;

           use vars qw( @ISA );

           @ISA = qw( XML::Filter::Merger );

           sub characters {
               my $self = shift;

               return $self->SUPER::characters( @_ )  ## **
                   unless $self->in_master_document;  ## **

               my $r = $self->SUPER::characters( @_ );

               $self->set_include_all_roots( 1 );

               XML::SAX::PurePerl->new( Handler => $self )->parse_string( "<hey/>" );
               return $r;
           }

           ## **: It is often important to use the recursion guard shown here
           ## to protect the decision making logic that should only be run on
           ## the events in the master document from being run on events in the
           ## subdocument.  Of course, if you want to apply the logic
           ## recursively, just leave the guard code out (and, yes, in this
           ## example, th guard code is phrased in a slightly redundant fashion,
           ## but we want to make the idiom clear).

       Feeding this filter "<foo> </foo>" results in "<foo> <hey/></foo>".  We've called
       set_include_all_roots( 1 ) to get the secondary document's root element included.

   Inserting Manifold Documents
       A more involved way suitable to handling consecutive documents it to use the two non-SAX
       events--"start_manifold_document" and "end_manifold_document"--that are called before the
       first document to be combined and after the last one, respectively.

       The first document to be started after the "start_manifold_document" is the master
       document and is emitted as-is except that it will contain the contents of all of the other
       documents just before the root "end_element()" tag.  For example:

           $h->start_manifold_document( {} );
           $p->parse_string( "<foo1><bar /></foo1>" );
           $p->parse_string( "<foo2><baz /></foo2>" );
           $h->end_manifold_document( {} );

       results in "<foo><bar /><baz /></foo>".

   The details
       In case the above was a bit vague, here are the rules this filter lives by.

       For the master document:

       ·   Events before the root "end_element" are forwarded as received.  Because of the rules
           for secondary documents, any secondary documents sent to the filter in the midst of a
           master document will be inserted inline as their events are received.

       ·   All remaining events, from the root "end_element" are buffered until the
           end_manifold_document() received, and are then forwarded on.

       For secondary documents:

       ·   All events before the root "start_element" are discarded.  There is no way to recover
           these (though we can add an option for most non-DTD events, I believe).

       ·   The root "start_element" is discarded by default, or forwarded if
           "set_include_all_roots( $v )" has been used to set a true value.

       ·   All events up to, but not including, the root "end_element" are forwarded as received.

       ·   The root "end_element" is discarded or forwarded if the matching "start_element" was.

       ·   All remaining events until and including the "end_document" are forwarded and
           processing.

       ·   Secondary documents may contain other secondary documents.

       ·   Secondary documents need not be well formed.  The must, however, be well balanced.

       This requires very little buffering and is "most natural" with the limitations:

       ·   All of each secondary document's events must all be received between two consecutive
           events of it's master document.  This is because most master document events are not
           buffered and this filter cannot tell from which upstream source a document came.

       ·   If the master document should happen to have some egregiously large amount of
           whitespace, commentary, or illegal events after the root element, buffer memory could
           be huge.  This should be exceedingly rare, even non-existent in the real world.

       ·   If any documents are not well balanced, the result won't be.

       ·

METHODS

       new
               my $d = XML::Filter::Merger->new( \%options );

       reset
           Clears the filter after an accident.  Useful when reusing the filter.  new() and
           start_manifold_document() both call this.

       start_manifold_document
           This must be called before the master document's "start_document()" if you want
           XML::Filter::Merger to insert documents that will be sent after the master document.

           It does not need to be called if you are going to insert secondary documents by
           sending their events in the midst of processing the master document.

           It is passed an empty ({}) data structure.

Additional Methods

       These are provided to make it easy for subclasses to find out roughly where they are in
       the document structure.  Generally, these should be called after calling
       SUPER::start_...() and before calling SUPER::end_...() to be accurate.

       in_master_document
           Returns TRUE if the current event is in the first top level document.

       document_depth
           Gets how many nested documents surround the current document.  0 means that you are in
           a top level document.  In manifold mode, This may or may not be a secondary document:
           secondary documents may also follow the primary document, in which case they have a
           document depth of 0.

       element_depth
           Gets how many nested elements surround the current element in the current input
           document.  Does not count elements from documents surrounding this document.

       top_level_document_number
           Returns the number of the top level document in a manifold document.  This is 0 for
           the first top level document, which is always the master document.

       end_manifold_document
           This must be called after the last document's end_document is called.  It is passed an
           empty ({}) data structure which is passed on to the next processor's end_document()
           call.  This call also causes the end_element() for the root element to be passed on.

       set_include_all_roots
               $h->set_include_all_roots( 1 );

           Setting this option causes the merger to include all root element nodes, not just the
           first document's.  This means that later documents are treated as subdocuments of the
           output document, rather than as envelopes carrying subdocuments.

           Given two documents received are:

            Doc1:   <root1><foo></root1>

            Doc1:   <root2><bar></root2>

            Doc3:   <root3><baz></root3>

           then with this option cleared (the default), the result looks like:

               <root1><foo><bar><baz></root1>

           .  This is useful when processing document oriented XML and each upstream filter
           channel gets a complete copy of the document.  This is the case with the machine
           XML::SAX::Manifold and the splitting filter XML::Filter::Distributor.

           With this option set, the result looks like:

               <root1><foo><root2><bar></root2><root3><baz></root3></root1>

           This is useful when processing record oriented XML, where the first document only
           contains the preamble and postamble for the records and not all of the records.  This
           is the case with the machine XML::SAX::ByRecord and the splitting filter
           XML::Filter::DocSplitter.

           The two splitter filters mentioned set this feature appropriately.

LIMITATIONS

       The events before and after a secondary document's root element events are discarded.  It
       is conceivable that characters, PIs and commentary outside the root element might need to
       be kept.  This may be added as an option.

       The DocumentLocators are not properly managed: they should be saved and restored around
       each each secondary document.

       Does not yet buffer all events after the first document's root end_element event.

       If these bite you, contact me.

AUTHOR

           Barrie Slaymaker <barries@slaysys.com>

COPYRIGHT

           Copyright 2002, Barrie Slaymaker, All Rights Reserved.

       You may use this module under the terms of the Artistic, GNU Public, or BSD licenses, you
       choice.