xincludefilter.java

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/*
 * Copyright (C) 2001-2002 David Brownell
 * 
 * This file is part of GNU JAXP, a library.
 *
 * GNU JAXP 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.
 * 
 * GNU JAXP 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.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * As a special exception, if you link this library with other files to
 * produce an executable, this library does not by itself cause the
 * resulting executable to be covered by the GNU General Public License.
 * This exception does not however invalidate any other reasons why the
 * executable file might be covered by the GNU General Public License. 
 */

package gnu.xml.pipeline;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL; 
import java.net.URLConnection; 
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Stack;
import java.util.Vector;

import org.xml.sax.Attributes;
import org.xml.sax.ErrorHandler;
import org.xml.sax.InputSource;
import org.xml.sax.Locator;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.XMLReaderFactory;

import gnu.xml.util.Resolver;



/**
 * Filter to process an XPointer-free subset of
 * <a href="http://www.w3.org/TR/xinclude">XInclude</a>, supporting its
 * use as a kind of replacement for parsed general entities.
 * XInclude works much like the <code>#include</code> of C/C++ but
 * works for XML documents as well as unparsed text files.
 * Restrictions from the 17-Sept-2002 CR draft of XInclude are as follows:
 *
 * <ul>
 *
 * <li> URIs must not include fragment identifiers.
 * The CR specifies support for XPointer <em>element()</em> fragment IDs,
 * which is not currently implemented here.
 *
 * <li> <em>xi:fallback</em> handling of resource errors is not
 * currently supported.
 *
 * <li> DTDs are not supported in included files, since the SAX DTD events
 * must have completely preceded any included file. 
 * The CR explicitly allows the DTD related portions of the infoset to
 * grow as an effect of including XML documents.
 *
 * <li> <em>xml:base</em> fixup isn't done.
 *
 * </ul>
 *
 * <p> XML documents that are included will normally be processed using
 * the default SAX namespace rules, meaning that prefix information may
 * be discarded.  This may be changed with {@link #setSavingPrefixes
 * setSavingPrefixes()}.  <em>You are strongly advised to do this.</em>
 *
 * <p> Note that XInclude allows highly incompatible implementations, which
 * are specialized to handle application-specific infoset extensions.  Some
 * such implementations can be implemented by subclassing this one, but
 * they may only be substituted in applications at "user option".
 *
 * <p>TBD: "IURI" handling.
 *
 * @author David Brownell
 */
public class XIncludeFilter extends EventFilter implements Locator
{
    private Hashtable		extEntities = new Hashtable (5, 5);
    private int			ignoreCount;
    private Stack		uris = new Stack ();
    private Locator		locator;
    private Vector		inclusions = new Vector (5, 5);
    private boolean		savingPrefixes;

    /**
     */
    public XIncludeFilter (EventConsumer next)
    throws SAXException
    {
	super (next);
	setContentHandler (this);
	// DTDHandler callbacks pass straight through
	setProperty (DECL_HANDLER, this);
	setProperty (LEXICAL_HANDLER, this);
    }

    private void fatal (SAXParseException e) throws SAXException
    {
	ErrorHandler		eh;
	
	eh = getErrorHandler ();
	if (eh != null)
	    eh.fatalError (e);
	throw e;
    }

    /**
     * Passes "this" down the filter chain as a proxy locator.
     */
    public void setDocumentLocator (Locator locator)
    {
	this.locator = locator;
	super.setDocumentLocator (this);
    }

    /** Used for proxy locator; do not call directly. */
    public String getSystemId ()
	{ return (locator == null) ? null : locator.getSystemId (); }
    /** Used for proxy locator; do not call directly. */
    public String getPublicId ()
	{ return (locator == null) ? null : locator.getPublicId (); }
    /** Used for proxy locator; do not call directly. */
    public int getLineNumber ()
	{ return (locator == null) ? -1 : locator.getLineNumber (); }
    /** Used for proxy locator; do not call directly. */
    public int getColumnNumber ()
	{ return (locator == null) ? -1 : locator.getColumnNumber (); }

    /**
     * Assigns the flag controlling the setting of the SAX2
     * <em>namespace-prefixes</em> flag.
     */
    public void setSavingPrefixes (boolean flag)
	{ savingPrefixes = flag; }

    /**
     * Returns the flag controlling the setting of the SAX2
     * <em>namespace-prefixes</em> flag when parsing included documents.
     * The default value is the SAX2 default (false), which discards
     * information that can be useful.
     */
    public boolean isSavingPrefixes ()
	{ return savingPrefixes; }

    //
    // Two mechanisms are interacting here.
    // 
    //	- XML Base implies a stack of base URIs, updated both by
    //	  "real entity" boundaries and element boundaries.
    //
    //	- Active "Real Entities" (for document and general entities,
    //	  and by xincluded files) are tracked to prevent circular
    //	  inclusions.
    //
    private String addMarker (String uri)
    throws SAXException
    {
	if (locator != null && locator.getSystemId () != null)
	    uri = locator.getSystemId ();

	// guard against InputSource objects without system IDs
	if (uri == null)
	    fatal (new SAXParseException ("Entity URI is unknown", locator));

	try {
	    URL	url = new URL (uri);

	    uri = url.toString ();
	    if (inclusions.contains (uri))
		fatal (new SAXParseException (
			"XInclude, circular inclusion", locator));
	    inclusions.addElement (uri);
	    uris.push (url);
	} catch (IOException e) {
	    // guard against illegal relative URIs (Xerces)
	    fatal (new SAXParseException ("parser bug: relative URI",
		locator, e));
	}
	return uri;
    }

    private void pop (String uri)
    {
	inclusions.removeElement (uri);
	uris.pop ();
    }

    //
    // Document entity boundaries get both treatments.
    //
    public void startDocument () throws SAXException
    {
	ignoreCount = 0;
	addMarker (null);
	super.startDocument ();
    }

    public void endDocument () throws SAXException
    {
	inclusions.setSize (0);
	extEntities.clear ();
	uris.setSize (0);
	super.endDocument ();
    }

    //
    // External general entity boundaries get both treatments.
    //
    public void externalEntityDecl (String name,
    	String publicId, String systemId)
    throws SAXException
    {
	if (name.charAt (0) == '%')
	    return;
	try {
	    URL	url = new URL (locator.getSystemId ());
	    systemId = new URL (url, systemId).toString ();
	} catch (IOException e) {
	    // what could we do?
	}
	extEntities.put (name, systemId);
    }

    public void startEntity (String name)
    throws SAXException
    {
	if (ignoreCount != 0) {
	    ignoreCount++;
	    return;
	}

	String	uri = (String) extEntities.get (name);
	if (uri != null)
	    addMarker (uri);
	super.startEntity (name);
    }

    public void endEntity (String name)
    throws SAXException
    {
	if (ignoreCount != 0) {
	    if (--ignoreCount != 0)
		return;
	}

	String	uri = (String) extEntities.get (name);

	if (uri != null)
	    pop (uri);
	super.endEntity (name);
    }
    
    //
    // element boundaries only affect the base URI stack,
    // unless they're XInclude elements.
    //
    public void
    startElement (String uri, String localName, String qName, Attributes atts)
    throws SAXException
    {
	if (ignoreCount != 0) {
	    ignoreCount++;
	    return;
	}

	URL	baseURI = (URL) uris.peek ();
	String	base;

	base = atts.getValue ("http://www.w3.org/XML/1998/namespace", "base");