/*
 * $Id: InputEntity.java,v 1.3 2001/09/29 00:44:34 edwingo Exp $
 *
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 2000 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:  
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Crimson" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written 
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    nor may "Apache" appear in their name, without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, Sun Microsystems, Inc., 
 * http://www.sun.com.  For more information on the Apache Software 
 * Foundation, please see <http://www.apache.org/>.
 */


package org.apache.crimson.parser;

import java.io.CharConversionException;
import java.io.UnsupportedEncodingException;
import java.io.InputStreamReader;
import java.io.InputStream;
import java.io.IOException;
import java.io.Reader;
import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Locale;

import org.xml.sax.*;

import org.apache.crimson.util.XmlChars;


/**
 * This is how the parser talks to its input entities, of all kinds.
 * The entities are in a stack.
 * 
 * <P> For internal entities, the character arrays are referenced here,
 * and read from as needed (they're read-only).  External entities have
 * mutable buffers, that are read into as needed.
 *
 * <P> <em>Note:</em> This maps CRLF (and CR) to LF without regard for
 * whether it's in an external (parsed) entity or not.  The XML 1.0 spec
 * is inconsistent in explaining EOL handling; this is the sensible way.
 *
 * @author David Brownell
 * @version $Revision: 1.3 $
 */
final class InputEntity implements Locator
{
    private int			start, finish;
    private char		buf [];
    private int			lineNumber = 1;
    private boolean		returnedFirstHalf = false;
    private boolean		maybeInCRLF = false;

    // name of entity (never main document or unnamed DTD PE)
    private String		name;

    private InputEntity		next;

    // for system and public IDs in diagnostics
    private InputSource		input;

    // this is a buffer; some buffers can be replenished.
    private Reader		reader;
    private boolean		isClosed;

    private ErrorHandler    	errHandler;
    private Locale		locale;

    private StringBuffer	rememberedText;
    private int			startRemember;

    // record if this is a PE, so endParsedEntity won't be called
    private boolean		isPE;

    // InputStreamReader throws an internal per-read exception, so
    // we minimize reads.  We also add a byte to compensate for the
    // "ungetc" byte we keep, so that our downstream reads are as
    // nicely sized as we can make them.
    final private static int	BUFSIZ = 8 * 1024 + 1;

    final private static char	newline [] = { '\n' };

    public static InputEntity getInputEntity (ErrorHandler h, Locale l)
    {
	InputEntity retval = new InputEntity ();
	retval.errHandler = h;
	retval.locale = l;
	return retval;
    }

    private InputEntity () { }

    //
    // predicate:  return true iff this is an internal entity reader,
    // and so may safely be "popped" as needed.  external entities have
    // syntax to uphold; internal parameter entities have at most validity
    // constraints to monitor.  also, only external entities get decent
    // location diagnostics.
    //
    public boolean isInternal () { return reader == null; }

    //
    // predicate:  return true iff this is the toplevel document
    //
    public boolean isDocument () { return next == null; }

    //
    // predicate:  return true iff this is a PE expansion (so that
    // LexicalEventListner.endParsedEntity won't be called)
    //
    public boolean isParameterEntity () { return isPE; }

    //
    // return name of current entity
    //
    public String getName () { return name; }

    private static String convertToFileURL(String filename) {
        // On JDK 1.2 and later, simplify this to:
        // "path = file.toURL().toString()".
        String path = new File(filename).getAbsolutePath();
        if (File.separatorChar != '/') {
            path = path.replace(File.separatorChar, '/');
        }
        if (!path.startsWith("/")) {
            path = "/" + path;
        }
        return "file:" + path;
    }

    /**
     * Use this for an external parsed entity
     */
    public void init(InputSource in, String name, InputEntity stack,
                     boolean isPE)
        throws IOException, SAXException
    {
	input = in;
	this.isPE = isPE;
	reader = in.getCharacterStream ();

	if (reader == null) {
	    InputStream		bytes = in.getByteStream ();

	    if (bytes == null) {
                // When the app first provides an external InputSource, the
                // SystemId may not be a valid URI and just be a simple
                // filename.  In this case, convert the filename to a
                // "file:" URL instead of throwing an exception.  Note:
                // this does not strictly conform to the SAX spec but is
                // convenient for users.
                String systemId = in.getSystemId();
                URL url;
                try {
                    url = new URL(systemId);
                } catch (MalformedURLException e) {
                    String urlString = convertToFileURL(systemId);
                    in.setSystemId(urlString);
                    url = new URL(urlString);
                }

		reader = XmlReader.createReader(url.openStream());
	    } else if (in.getEncoding () != null)
		reader = XmlReader.createReader (
			in.getByteStream (),
			in.getEncoding ());
	    else
		reader = XmlReader.createReader (in.getByteStream ());
	}
	next = stack;
	buf = new char [BUFSIZ];
	this.name = name;
	checkRecursion (stack);
    }

    //
    // use this for an internal parsed entity; buffer is readonly
    //
    public void init (char b [], String name,
	InputEntity stack, boolean isPE)
    throws SAXException
    {
	next = stack;
	buf = b;
	finish = b.length;
	this.name = name;
	this.isPE = isPE;
	checkRecursion (stack);
    }

    private void checkRecursion (InputEntity stack) throws SAXException
    {
	if (stack == null)
	    return;
	for (stack = stack.next; stack != null; stack = stack.next) {
	    if (stack.name != null && stack.name.equals (name))
		fatal ("P-069", new Object [] { name });
	}
    }

    public InputEntity pop () throws IOException
    {
	// caller has ensured there's nothing left to read
	close ();
	return next;
    }

    /** returns true iff there's no more data to consume ... */
    public boolean isEOF ()
    throws IOException, SAXException
    {
	// called to ensure WF-ness of included entities and to pop
	// input entities appropriately ... EOF is not always legal.
	if (start >= finish) {
	    fillbuf ();
	    return start >= finish;
	} else
	    return false;
    }

    /**
     * Returns the name of the encoding in use, else null; the name
     * returned is in as standard a form as we can get.
     */
    public String getEncoding ()
    {
	if (reader == null)
	    return null;
	if (reader instanceof XmlReader)
	    return ((XmlReader)reader).getEncoding ();

	// XXX prefer a java2std() call to normalize names...

	if (reader instanceof InputStreamReader)
	    return ((InputStreamReader)reader).getEncoding ();
	return null;
    }


    /**
     * returns the next name char, or NUL ... faster than getc(),
     * and the common "name or nmtoken must be next" case won't
     * need ungetc().
     */
    public char getNameChar () throws IOException, SAXException
    {
	if (finish <= start)
	    fillbuf ();
	if (finish > start) {
	    char c = buf [start++];
	    if (XmlChars.isNameChar (c))
		return c;
	    start--;
	}
	return 0;
    }

    /**
     * gets the next Java character -- might be part of an XML
     * text character represented by a surrogate pair, or be
     * the end of the entity.
     */
    public char getc () throws IOException, SAXException
    {
	if (finish <= start)
	    fillbuf ();
	if (finish > start) {
	    char c = buf [start++];

	    // [2] Char ::= #x0009 | #x000A | #x000D
	    //			| [#x0020-#xD7FF]
	    //			| [#xE000-#xFFFD]
	    // plus surrogate _pairs_ representing [#x10000-#x10ffff]
	    if (returnedFirstHalf) {
		if (c >= 0xdc00 && c <= 0xdfff) {
		    returnedFirstHalf = false;
		    return c;
		} else
		    fatal ("P-070", new Object [] { Integer.toHexString (c) });
	    }
	    if ((c >= 0x0020 && c <= 0xD7FF)
			|| c == 0x0009
			// no surrogates!
			|| (c >= 0xE000 && c <= 0xFFFD))
		return c;

	    //
	    // CRLF and CR are both line ends; map both to LF, and
	    // keep line count correct.
	    //
	    else if (c == '\r' && !isInternal ()) {
		maybeInCRLF = true;
		c = getc ();
		if (c != '\n')
		    ungetc ();
		maybeInCRLF = false;

		lineNumber++;
		return '\n';

	    } else if (c == '\n' || c == '\r') { // LF, or 2nd char in CRLF
		if (!isInternal () && !maybeInCRLF)
		    lineNumber++;
		return c;
	    }

	    // surrogates...
	    if (c >= 0xd800 && c < 0xdc00) {
		returnedFirstHalf = true;
		return c;
	    }

	    fatal ("P-071", new Object [] { Integer.toHexString (c) });
	}
	throw new EndOfInputException ();
    }


    public boolean peekc (char c) throws IOException, SAXException
    {
	if (finish <= start)
	    fillbuf ();
	if (finish > start) {
	    if (buf [start] == c) {
		start++;
		return true;
	    } else
		return false;
	}
	return false;
    }


    /**
     * two character pushback is guaranteed
     */
    public void ungetc ()
    {
	if (start == 0)
	    throw new InternalError ("ungetc");
	start--;

	if (buf [start] == '\n' || buf [start] == '\r') {
	    if (!isInternal ())
		lineNumber--;
	} else if (returnedFirstHalf)
	    returnedFirstHalf = false;
    }


    /**
     * optional grammatical whitespace (discarded)
     */
    public boolean maybeWhitespace ()
    throws IOException, SAXException
    {
	char	c;
	boolean	isSpace = false;
	boolean	sawCR = false;

	// [3] S ::= #20 | #09 | #0D | #0A
	for (;;) {
	    if (finish <= start)
		fillbuf ();
	    if (finish <= start)
		return isSpace;

	    c = buf [start++];
	    if (c == 0x20 || c == 0x09 || c == '\n' || c == '\r') {
		isSpace = true;

		//
		// CR, LF are line endings ... CLRF is one, not two!
		//
		if ((c == '\n' || c == '\r') && !isInternal ()) {
		    if (!(c == '\n' && sawCR)) {
			lineNumber++;
			sawCR = false;
		    }
		    if (c == '\r')
			sawCR = true;
		}
	    } else {
		start--;
		return isSpace;
	    }
	}
    }


    /**
     * normal content; whitespace in markup may be handled
     * specially if the parser uses the content model.
     *
     * <P> content terminates with markup delimiter characters,
     * namely ampersand (&amp;) and left angle bracket (&lt;).
     *
     * <P> the document handler's characters() method is called
     * on all the content found
     */
    public boolean parsedContent (
	ContentHandler		contentHandler,
	ElementValidator	validator
    ) throws IOException, SAXException
    {
	// [14] CharData ::= [^<&]* - ([^<&]* ']]>' [^<&]*)

	int		first;		// first char to return
	int		last;		// last char to return
	boolean		sawContent;	// sent any chars?
	char		c;

	// deliver right out of the buffer, until delimiter, EOF,
	// or error, refilling as we go
	for (first = last = start, sawContent = false; ; last++) {

	    // buffer empty?
	    if (last >= finish) {
		if (last > first) {
		    validator.text ();
		    contentHandler.characters (buf, first, last - first);
		    sawContent = true;
		    start = last;
		}
		if (isEOF ())	// calls fillbuf
		    return sawContent;
		first = start;
		last = first - 1;	// incremented in loop
		continue;
	    }

	    c = buf [last];

	    //
	    // pass most chars through ASAP; this inlines the code of
	    // [2] !XmlChars.isChar(c) leaving only characters needing
	    // special treatment ... line ends, surrogates, and: 
	    //	0x0026 == '&'
	    //	0x003C == '<'
	    //	0x005D == ']'
	    // Comparisons ordered for speed on 'typical' text
	    //
	    if (       (c >  0x005D && c <= 0xD7FF)	// a-z and more
		    || (c <  0x0026 && c >= 0x0020)	// space & punct
		    || (c >  0x003C && c <  0x005D)	// A-Z & punct
		    || (c >  0x0026 && c <  0x003C)	// 0-9 & punct
		    ||  c == 0x0009
		    || (c >= 0xE000 && c <= 0xFFFD)
		    )
		continue;

	    // terminate on markup delimiters
	    if (c == '<' || c == '&')
		break;

	    // count lines
	    if (c == '\n') {
	        if (!isInternal ())
		    lineNumber++;
	        continue;
	    }

	    // External entities get CR, CRLF --> LF mapping
	    // Internal ones got it already, and we can't repeat
	    // else we break char ref handling!!
	    if (c == '\r') {
		if (isInternal ())
		    continue;

		contentHandler.characters (buf, first, last - first);
		contentHandler.characters (newline, 0, 1);
		sawContent = true;
		lineNumber++;
		if (finish > (last + 1)) {
		    if (buf [last + 1] == '\n')
			last++;
		} else {	// CR at end of buffer
// XXX case not yet handled:  CRLF here will look like two lines
		}
		first = start = last + 1;
		continue;
	    }

	    // ']]>' is a WF error -- must fail if we see it
	    if (c == ']') {
		switch (finish - last) {
		  // for suspicious end-of-buffer cases, get more data
		  // into the buffer to rule out this sequence.
		  case 2:
		    if (buf [last + 1] != ']')
			continue;
		    // FALLTHROUGH

		  case 1:
		    if (reader == null || isClosed)
			continue;
		    if (last == first)
			throw new InternalError ("fillbuf");
		    last--;
		    if (last > first) {
			validator.text ();
			contentHandler.characters (buf, first, last - first);
			sawContent = true;
			start = last;
		    }
		    fillbuf ();
		    first = last = start;
		    continue;

		  // otherwise any "]]>" would be buffered, and we can
		  // see right away if that's what we have
		  default:
		    if (buf [last + 1] == ']' && buf [last + 2] == '>')
			fatal ("P-072", null);
		    continue;
		} 
	    }

	    // correctly paired surrogates are OK
	    if (c >= 0xd800 && c <= 0xdfff) {
		if ((last + 1) >= finish) {
		    if (last > first) {
			validator.text ();
			contentHandler.characters (buf, first, last - first);
			sawContent = true;
			start = last + 1;
		    }
		    if (isEOF ()) {	// calls fillbuf
	    	       fatal ("P-081", 
			      new Object [] { Integer.toHexString (c) });
		    }
		    first = start;
		    last = first ;
		    continue;
		}
		if (checkSurrogatePair (last))
		    last++;
		else {
		    last--;
		    // also terminate on surrogate pair oddities
		    break;
		}
		continue;
	    } 

	    fatal ("P-071", new Object [] { Integer.toHexString (c) });
	}
	if (last == first)
	    return sawContent;
	validator.text ();
	contentHandler.characters (buf, first, last - first);
	start = last;
	return true;
    }


    /**
     * CDATA -- character data, terminated by "]]>" and optionally
     * including unescaped markup delimiters (ampersand and left angle
     * bracket).  This should otherwise be exactly like character data,
     * modulo differences in error report details.
     *
     * <P> The document handler's characters() or ignorableWhitespace()
     * methods are invoked on all the character data found
     *
     * @param contentHandler gets callbacks for character data
     * @param validator text() or ignorableWhitespace() methods are
     *	called appropriately
     * @param ignorableWhitespace if true, whitespace characters will
     *	be reported using contentHandler.ignorableWhitespace(); implicitly,
     *	non-whitespace characters will cause validation errors
     * @param standaloneWhitespaceInvalid if true, ignorable whitespace
     *	causes a validity error report as well as a callback
     */
    public void unparsedContent (
	ContentHandler		contentHandler,
	ElementValidator	validator,
	boolean			ignorableWhitespace,
	String			whitespaceInvalidMessage
    ) throws IOException, SAXException
    {
	// [18] CDSect ::= CDStart CData CDEnd
	// [19] CDStart ::= '<![CDATA['
	// [20] CData ::= (Char* - (Char* ']]>' Char*))
	// [21] CDEnd ::= ']]>'

	// Caller has already consumed the leading '<![CDATA[' so all that
        // remains to be parsed of [18] is "CData CDEnd"

	// only a literal ']]>' stops this ...
	int	last;

	for (;;) {		// until ']]>' seen
	    boolean	done = false;
	    char	c;

	    // don't report ignorable whitespace as "text" for
	    // validation purposes.
	    boolean	white = ignorableWhitespace;

	    for (last = start; last < finish; last++) {
		c = buf [last];

		//
		// Reject illegal characters.
		//
		if (!XmlChars.isChar (c)) {
		    white = false;
		    if (c >= 0xd800 && c <= 0xdfff) {
			if (checkSurrogatePair (last)) {
			    last++;
			    continue;
			} else {
			    last--;
			    break;
			}
		    }
		    fatal ("P-071", new Object []
			{ Integer.toHexString (buf [last]) });
		}
		if (c == '\n') {
		    if (!isInternal ())
			lineNumber++;
		    continue;
		}
		if (c == '\r') {
		    // As above, we can't repeat CR/CRLF --> LF mapping
		    if (isInternal ())
			continue;

		    if (white) {
			if (whitespaceInvalidMessage != null)
			    errHandler.error (new SAXParseException (
				Parser2.messages.getMessage (locale,
					whitespaceInvalidMessage),
				this));
			contentHandler.ignorableWhitespace (buf, start,
				last - start);
			contentHandler.ignorableWhitespace (newline, 0, 1);
		    } else {
			validator.text ();
			contentHandler.characters (buf, start, last - start);
			contentHandler.characters (newline, 0, 1);
		    }
		    lineNumber++;
		    if (finish > (last + 1)) {
			if (buf [last + 1] == '\n')
			    last++;
		    } else {	// CR at end of buffer
// XXX case not yet handled ... as above
		    }
		    start = last + 1;
		    continue;
		}
		if (c != ']') {
		    if (c != ' ' && c != '\t')
			white = false;
		    continue;
		}
                // assert(buf[last] == ']');
		if ((last + 2) < finish) {
		    if (buf [last + 1] == ']' && buf [last + 2] == '>') {
			done = true;
			break;
		    }
		    white = false;
		    continue;
		} else {
                    // "last" is at or one before end of buffered data.
                    // Report what we have so far, not including "last", by
                    // breaking and executing code below, outside inner
                    // loop, then continuing on to find end of CDATA section.
                    break;
		}
	    }
	    if (white) {
		if (whitespaceInvalidMessage != null)
		    errHandler.error (new SAXParseException (
			Parser2.messages.getMessage (locale,
				whitespaceInvalidMessage),
			this));
		contentHandler.ignorableWhitespace (buf, start, last - start);
	    } else {
		validator.text ();
		contentHandler.characters (buf, start, last - start);
	    }
	    if (done) {
		start = last + 3;
		break;
	    }
	    start = last;
            fillbuf();
	    if (isEOF ())
		fatal ("P-073", null);
	}
    }

    // return false to backstep at end of buffer)
    private boolean checkSurrogatePair (int offset)
    throws SAXException
    {
	if ((offset + 1) >= finish)
	    return false;

	char c1 = buf [offset++];
	char c2 = buf [offset];

	if ((c1 >= 0xd800 && c1 < 0xdc00) && (c2 >= 0xdc00 && c2 <= 0xdfff))
	    return true;
	fatal ("P-074", new Object [] {
		Integer.toHexString (c1 & 0x0ffff),
		Integer.toHexString (c2 & 0x0ffff)
	    });
	return false;
    }


    /**
     * whitespace in markup (flagged to app, discardable)
     *
     * <P> the document handler's ignorableWhitespace() method
     * is called on all the whitespace found
     */
    public boolean ignorableWhitespace (ContentHandler handler)
    throws IOException, SAXException
    {
	char	c;
	boolean	isSpace = false;
	int	first;

	// [3] S ::= #20 | #09 | #0D | #0A
	for (first = start;;) {
	    if (finish <= start) {
		if (isSpace)
		    handler.ignorableWhitespace (buf, first, start - first);
		fillbuf ();
		first = start;
	    }
	    if (finish <= start)
		return isSpace;

	    c = buf [start++];
	    switch (c) {
	      case '\n':
		if (!isInternal ())
		    lineNumber++;
// XXX handles Macintosh line endings wrong
		// fallthrough
	      case 0x09:
	      case 0x20:
		isSpace = true;
		continue;

	      case '\r':
		isSpace = true;
		if (!isInternal ())
		    lineNumber++;
		handler.ignorableWhitespace (buf, first,
		    (start - 1) - first);
		handler.ignorableWhitespace (newline, 0, 1);
		if (start < finish && buf [start] == '\n')
		    ++start;
		first = start;
		continue;

	      default:
		ungetc ();
		if (isSpace)
		    handler.ignorableWhitespace (buf, first, start - first);
		return isSpace;
	    }
	}
    }

    /**
     * returns false iff 'next' string isn't as provided,
     * else skips that text and returns true
     *
     * <P> NOTE:  two alternative string representations are
     * both passed in, since one is faster.
     */
    public boolean peek (String next, char chars [])
    throws IOException, SAXException
    {
	int	len;
	int	i;

	if (chars != null)
	    len = chars.length;
	else
	    len = next.length ();

	// buffer should hold the whole thing ... give it a
	// chance for the end-of-buffer case and cope with EOF
	// by letting fillbuf compact and fill
	if (finish <= start || (finish - start) < len)
	    fillbuf ();

	// can't peek past EOF
	if (finish <= start)
	    return false;

	// compare the string; consume iff it matches
	if (chars != null) {
	    for (i = 0; i < len && (start + i) < finish; i++) {
		if (buf [start + i] != chars [i])
		    return false;
	    }
	} else {
	    for (i = 0; i < len && (start + i) < finish; i++) {
		if (buf [start + i] != next.charAt (i))
		    return false;
	    }
	}

	// if the first fillbuf didn't get enough data, give
	// fillbuf another chance to read
	if (i < len) {
	    if (reader == null || isClosed)
		return false;
	    
	    //
	    // This diagnostic "knows" that the only way big strings would
	    // fail to be peeked is where it's a symbol ... e.g. for an
	    // </EndTag> construct.  That knowledge could also be applied
	    // to get rid of the symbol length constraint, since having
	    // the wrong symbol is a fatal error anyway ...
	    //
	    if (len > buf.length)
		fatal ("P-077", new Object [] { new Integer (buf.length) });

	    fillbuf ();
	    return peek (next, chars);
	}

	start += len;
	return true;
    }

    /**
     * This method is used to disambiguate between XMLDecl, TextDecl, and
     * PI by doing a lookahead w/o consuming any characters.  We look for
     * "<?xml" plus a whitespace character, but no more.  For example, we
     * could have input documents with the PI "<?xml-stylesheet ... >".
     *
     * @return true iff next chars match either the prefix for XMLDecl or
     *              TextDecl
     */
    boolean isXmlDeclOrTextDeclPrefix()
        throws IOException, SAXException
    {
        // [23] XMLDecl ::= '<?xml' VersionInfo EncodingDecl?
        //                      SDDecl? S? '>'
        // [77] TextDecl ::= '<?xml' VersionInfo? EncodingDecl S? '?>'
        // [24] VersionInfo ::= S 'version' Eq \'|\" versionNum \'|\"

        String match = "<?xml";
        int matchLen = match.length();

        // Length of the entire prefix including whitespace
        int prefixLen = matchLen + 1;

	// buffer should hold the whole thing ... give it a
	// chance for the end-of-buffer case and cope with EOF
	// by letting fillbuf compact and fill
	if (finish <= start || (finish - start) < prefixLen)
	    fillbuf ();

	// can't peek past EOF
	if (finish <= start)
	    return false;

	// Compare the non-whitespace part of the prefix
        int i;
        for (i = 0; i < matchLen && (start + i) < finish; i++) {
            if (buf [start + i] != match.charAt (i))
                return false;
        }

	// if the first fillbuf didn't get enough data, give
	// fillbuf another chance to read
	if (i < matchLen) {
	    if (reader == null || isClosed)
		return false;
	    
	    fillbuf ();
	    return isXmlDeclOrTextDeclPrefix();
	}

        // assert(i == matchLen);
        // Match whitespace
        if (!XmlChars.isSpace(buf[i])) {
            return false;
        }

	return true;
    }


    //
    // Support for reporting the internal DTD subset, so <!DOCTYPE...>
    // declarations can be recreated.  This is collected as a single
    // string; such subsets are normally small, and many applications
    // don't even care about this.
    //
    public void startRemembering ()
    {
	if (startRemember != 0)
	    throw new InternalError ();
	startRemember = start;
    }

    public String rememberText ()
    {
	String retval;

	// If the internal subset crossed a buffer boundary, we
	// created a temporary buffer.
	if (rememberedText != null) {
	    rememberedText.append (buf, startRemember,
		start - startRemember);
	    retval = rememberedText.toString ();
	} else
	    retval = new String (buf, startRemember,
		start - startRemember);

	startRemember = 0;
	rememberedText = null;
	return retval;
    }

    // LOCATOR METHODS

    private Locator getLocator ()
    {
	InputEntity	current = this;

	// don't report locations within internal entities!

	while (current != null && current.input == null)
	    current = current.next;
	return current == null ? this : current;
    }


    /** Returns the public ID of this input source, if known */
    public String getPublicId ()
    {
	Locator	where = getLocator ();
	if (where == this)
	    return input.getPublicId ();
	return where.getPublicId ();
    }

    /** Returns the system ID of this input source, if known */
    public String getSystemId ()
    {
	Locator	where = getLocator ();
	if (where == this)
	    return input.getSystemId ();
	return where.getSystemId ();
    }

    /** Returns the current line number in this input source */
    public int getLineNumber ()
    {
	Locator	where = getLocator ();
	if (where == this)
	    return lineNumber;
	return where.getLineNumber ();
    }

    /** returns -1; maintaining column numbers hurts performance */
    public int getColumnNumber ()
    {
	return -1;		// not maintained (speed)
    }



    //
    // n.b. for non-EOF end-of-buffer cases, reader should return
    // at least a handful of bytes so various lookaheads behave.
    //
    // two character pushback exists except at first; characters
    // represented by surrogate pairs can't be pushed back (they'd
    // only be in character data anyway).
    //
    // SAX exception thrown on char conversion problems; line number
    // will be low, as a rule.
    //
    private void fillbuf () throws IOException, SAXException
    {
	// don't touched fixed buffers, that'll usually
	// change entity values (and isn't needed anyway)
	// likewise, ignore closed streams
	if (reader == null || isClosed)
	    return;
	
	// if remembering DTD text, copy!
	if (startRemember != 0) {
	    if (rememberedText == null)
		rememberedText = new StringBuffer (buf.length);
	    rememberedText.append (buf, startRemember,
		start - startRemember);
	}

	boolean	extra = (finish > 0) && (start > 0);
	int	len;

	if (extra)		// extra pushback
	    start--;
	len = finish - start;

	System.arraycopy (buf, start, buf, 0, len);
	start = 0;
	finish = len;

	try {
	    len = buf.length - len;
	    len = reader.read (buf, finish, len);
	} catch (UnsupportedEncodingException e) {
	    fatal ("P-075", new Object [] { e.getMessage () });
	} catch (CharConversionException e) {
	    fatal ("P-076", new Object [] { e.getMessage () });
	}
	if (len >= 0)
	    finish += len;
	else
	    close ();
	if (extra)		// extra pushback
	    start++;

	if (startRemember != 0)
	    // assert extra == true
	    startRemember = 1;
    }

    public void close ()
    {
	try {
	    if (reader != null && !isClosed)
		reader.close ();
	    isClosed = true;
	} catch (IOException e) {
	    /* NOTHING */
	}
    }


    private void fatal (String messageId, Object params []) throws SAXException
    {
	SAXParseException	x = new SAXParseException (
	    Parser2.messages.getMessage (locale, messageId, params),
	    this);

	// not continuable ... e.g. WF errors
	close ();
	errHandler.fatalError (x);
	throw x;
    }    
}