/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.io.input;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.text.MessageFormat;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.commons.io.ByteOrderMark;

/**
 * Character stream that handles all the necessary Voodo to figure out the
 * charset encoding of the XML document within the stream.
 * <p>
 * IMPORTANT: This class is not related in any way to the org.xml.sax.XMLReader.
 * This one IS a character stream.
 * <p>
 * All this has to be done without consuming characters from the stream, if not
 * the XML parser will not recognized the document as a valid XML. This is not
 * 100% true, but it's close enough (UTF-8 BOM is not handled by all parsers
 * right now, XmlStreamReader handles it and things work in all parsers).
 * <p>
 * The XmlStreamReader class handles the charset encoding of XML documents in
 * Files, raw streams and HTTP streams by offering a wide set of constructors.
 * <p>
 * By default the charset encoding detection is lenient, the constructor with
 * the lenient flag can be used for an script (following HTTP MIME and XML
 * specifications). All this is nicely explained by Mark Pilgrim in his blog, <a
 * href="http://diveintomark.org/archives/2004/02/13/xml-media-types">
 * Determining the character encoding of a feed</a>.
 * <p>
 * Originally developed for <a href="http://rome.dev.java.net">ROME</a> under
 * Apache License 2.0.
 *
 * @author Alejandro Abdelnur
 * @version $Id: XmlStreamReader.java,v 1.1.2.1 2011/01/15 20:32:23 caniszczyk Exp $
 * @see org.apache.commons.io.output.XmlStreamWriter
 * @since Commons IO 2.0
 */
public class XmlStreamReader extends Reader {
    private static final int BUFFER_SIZE = 4096;

    private static final String UTF_8 = "UTF-8";

    private static final String US_ASCII = "US-ASCII";

    private static final String UTF_16BE = "UTF-16BE";

    private static final String UTF_16LE = "UTF-16LE";

    private static final String UTF_16 = "UTF-16";

    private static final String EBCDIC = "CP1047";

    private static final ByteOrderMark[] BOMS = new ByteOrderMark[] {
        ByteOrderMark.UTF_8,
        ByteOrderMark.UTF_16BE,
        ByteOrderMark.UTF_16LE
    };
    private static final ByteOrderMark[] XML_GUESS_BYTES = new ByteOrderMark[] {
        new ByteOrderMark(UTF_8,    0x3C, 0x3F, 0x78, 0x6D),
        new ByteOrderMark(UTF_16BE, 0x00, 0x3C, 0x00, 0x3F),
        new ByteOrderMark(UTF_16LE, 0x3C, 0x00, 0x3F, 0x00),
        new ByteOrderMark(EBCDIC,   0x4C, 0x6F, 0xA7, 0x94)
    };


    private final Reader reader;

    private final String encoding;

    private final String defaultEncoding;

    /**
     * Returns the default encoding to use if none is set in HTTP content-type,
     * XML prolog and the rules based on content-type are not adequate.
     * <p>
     * If it is NULL the content-type based rules are used.
     *
     * @return the default encoding to use.
     */
    public String getDefaultEncoding() {
        return defaultEncoding;
    }

    /**
     * Creates a Reader for a File.
     * <p>
     * It looks for the UTF-8 BOM first, if none sniffs the XML prolog charset,
     * if this is also missing defaults to UTF-8.
     * <p>
     * It does a lenient charset encoding detection, check the constructor with
     * the lenient parameter for details.
     *
     * @param file File to create a Reader from.
     * @throws IOException thrown if there is a problem reading the file.
     */
    public XmlStreamReader(File file) throws IOException {
        this(new FileInputStream(file));
    }

    /**
     * Creates a Reader for a raw InputStream.
     * <p>
     * It follows the same logic used for files.
     * <p>
     * It does a lenient charset encoding detection, check the constructor with
     * the lenient parameter for details.
     *
     * @param is InputStream to create a Reader from.
     * @throws IOException thrown if there is a problem reading the stream.
     */
    public XmlStreamReader(InputStream is) throws IOException {
        this(is, true);
    }

    /**
     * Creates a Reader for a raw InputStream.
     * <p>
     * It follows the same logic used for files.
     * <p>
     * If lenient detection is indicated and the detection above fails as per
     * specifications it then attempts the following:
     * <p>
     * If the content type was 'text/html' it replaces it with 'text/xml' and
     * tries the detection again.
     * <p>
     * Else if the XML prolog had a charset encoding that encoding is used.
     * <p>
     * Else if the content type had a charset encoding that encoding is used.
     * <p>
     * Else 'UTF-8' is used.
     * <p>
     * If lenient detection is indicated an XmlStreamReaderException is never
     * thrown.
     *
     * @param is InputStream to create a Reader from.
     * @param lenient indicates if the charset encoding detection should be
     *        relaxed.
     * @throws IOException thrown if there is a problem reading the stream.
     * @throws XmlStreamReaderException thrown if the charset encoding could not
     *         be determined according to the specs.
     */
    public XmlStreamReader(InputStream is, boolean lenient) throws IOException {
        this(is, lenient, null);
    }

    /**
     * Creates a Reader for a raw InputStream.
     * <p>
     * It follows the same logic used for files.
     * <p>
     * If lenient detection is indicated and the detection above fails as per
     * specifications it then attempts the following:
     * <p>
     * If the content type was 'text/html' it replaces it with 'text/xml' and
     * tries the detection again.
     * <p>
     * Else if the XML prolog had a charset encoding that encoding is used.
     * <p>
     * Else if the content type had a charset encoding that encoding is used.
     * <p>
     * Else 'UTF-8' is used.
     * <p>
     * If lenient detection is indicated an XmlStreamReaderException is never
     * thrown.
     *
     * @param is InputStream to create a Reader from.
     * @param lenient indicates if the charset encoding detection should be
     *        relaxed.
     * @param defaultEncoding The default encoding
     * @throws IOException thrown if there is a problem reading the stream.
     * @throws XmlStreamReaderException thrown if the charset encoding could not
     *         be determined according to the specs.
     */
    public XmlStreamReader(InputStream is, boolean lenient, String defaultEncoding) throws IOException {
        this.defaultEncoding = defaultEncoding;
        BOMInputStream bom = new BOMInputStream(new BufferedInputStream(is, BUFFER_SIZE), false, BOMS);
        BOMInputStream pis = new BOMInputStream(bom, true, XML_GUESS_BYTES);
        this.encoding = doRawStream(bom, pis, lenient);
        this.reader = new InputStreamReader(pis, encoding);
    }

    /**
     * Creates a Reader using the InputStream of a URL.
     * <p>
     * If the URL is not of type HTTP and there is not 'content-type' header in
     * the fetched data it uses the same logic used for Files.
     * <p>
     * If the URL is a HTTP Url or there is a 'content-type' header in the
     * fetched data it uses the same logic used for an InputStream with
     * content-type.
     * <p>
     * It does a lenient charset encoding detection, check the constructor with
     * the lenient parameter for details.
     *
     * @param url URL to create a Reader from.
     * @throws IOException thrown if there is a problem reading the stream of
     *         the URL.
     */
    public XmlStreamReader(URL url) throws IOException {
        this(url.openConnection(), null);
    }

    /**
     * Creates a Reader using the InputStream of a URLConnection.
     * <p>
     * If the URLConnection is not of type HttpURLConnection and there is not
     * 'content-type' header in the fetched data it uses the same logic used for
     * files.
     * <p>
     * If the URLConnection is a HTTP Url or there is a 'content-type' header in
     * the fetched data it uses the same logic used for an InputStream with
     * content-type.
     * <p>
     * It does a lenient charset encoding detection, check the constructor with
     * the lenient parameter for details.
     *
     * @param conn URLConnection to create a Reader from.
     * @param defaultEncoding The default encoding
     * @throws IOException thrown if there is a problem reading the stream of
     *         the URLConnection.
     */
    public XmlStreamReader(URLConnection conn, String defaultEncoding) throws IOException {
        this.defaultEncoding = defaultEncoding;
        boolean lenient = true;
        String contentType = conn.getContentType();
        InputStream is = conn.getInputStream();
        BOMInputStream bom = new BOMInputStream(new BufferedInputStream(is, BUFFER_SIZE), false, BOMS);
        BOMInputStream pis = new BOMInputStream(bom, true, XML_GUESS_BYTES);
        if (conn instanceof HttpURLConnection || contentType != null) {
            this.encoding = doHttpStream(bom, pis, contentType, lenient);
        } else {
            this.encoding = doRawStream(bom, pis, lenient);
        }
        this.reader = new InputStreamReader(pis, encoding);
    }

    /**
     * Creates a Reader using an InputStream an the associated content-type
     * header.
     * <p>
     * First it checks if the stream has BOM. If there is not BOM checks the
     * content-type encoding. If there is not content-type encoding checks the
     * XML prolog encoding. If there is not XML prolog encoding uses the default
     * encoding mandated by the content-type MIME type.
     * <p>
     * It does a lenient charset encoding detection, check the constructor with
     * the lenient parameter for details.
     *
     * @param is InputStream to create the reader from.
     * @param httpContentType content-type header to use for the resolution of
     *        the charset encoding.
     * @throws IOException thrown if there is a problem reading the file.
     */
    public XmlStreamReader(InputStream is, String httpContentType)
            throws IOException {
        this(is, httpContentType, true);
    }

    /**
     * Creates a Reader using an InputStream an the associated content-type
     * header. This constructor is lenient regarding the encoding detection.
     * <p>
     * First it checks if the stream has BOM. If there is not BOM checks the
     * content-type encoding. If there is not content-type encoding checks the
     * XML prolog encoding. If there is not XML prolog encoding uses the default
     * encoding mandated by the content-type MIME type.
     * <p>
     * If lenient detection is indicated and the detection above fails as per
     * specifications it then attempts the following:
     * <p>
     * If the content type was 'text/html' it replaces it with 'text/xml' and
     * tries the detection again.
     * <p>
     * Else if the XML prolog had a charset encoding that encoding is used.
     * <p>
     * Else if the content type had a charset encoding that encoding is used.
     * <p>
     * Else 'UTF-8' is used.
     * <p>
     * If lenient detection is indicated an XmlStreamReaderException is never
     * thrown.
     *
     * @param is InputStream to create the reader from.
     * @param httpContentType content-type header to use for the resolution of
     *        the charset encoding.
     * @param lenient indicates if the charset encoding detection should be
     *        relaxed.
     * @param defaultEncoding The default encoding
     * @throws IOException thrown if there is a problem reading the file.
     * @throws XmlStreamReaderException thrown if the charset encoding could not
     *         be determined according to the specs.
     */
    public XmlStreamReader(InputStream is, String httpContentType,
            boolean lenient, String defaultEncoding) throws IOException {
        this.defaultEncoding = defaultEncoding;
        BOMInputStream bom = new BOMInputStream(new BufferedInputStream(is, BUFFER_SIZE), false, BOMS);
        BOMInputStream pis = new BOMInputStream(bom, true, XML_GUESS_BYTES);
        this.encoding = doHttpStream(bom, pis, httpContentType, lenient);
        this.reader = new InputStreamReader(pis, encoding);
    }

    /**
     * Creates a Reader using an InputStream an the associated content-type
     * header. This constructor is lenient regarding the encoding detection.
     * <p>
     * First it checks if the stream has BOM. If there is not BOM checks the
     * content-type encoding. If there is not content-type encoding checks the
     * XML prolog encoding. If there is not XML prolog encoding uses the default
     * encoding mandated by the content-type MIME type.
     * <p>
     * If lenient detection is indicated and the detection above fails as per
     * specifications it then attempts the following:
     * <p>
     * If the content type was 'text/html' it replaces it with 'text/xml' and
     * tries the detection again.
     * <p>
     * Else if the XML prolog had a charset encoding that encoding is used.
     * <p>
     * Else if the content type had a charset encoding that encoding is used.
     * <p>
     * Else 'UTF-8' is used.
     * <p>
     * If lenient detection is indicated an XmlStreamReaderException is never
     * thrown.
     *
     * @param is InputStream to create the reader from.
     * @param httpContentType content-type header to use for the resolution of
     *        the charset encoding.
     * @param lenient indicates if the charset encoding detection should be
     *        relaxed.
     * @throws IOException thrown if there is a problem reading the file.
     * @throws XmlStreamReaderException thrown if the charset encoding could not
     *         be determined according to the specs.
     */
    public XmlStreamReader(InputStream is, String httpContentType,
            boolean lenient) throws IOException {
        this(is, httpContentType, lenient, null);
    }

    /**
     * Returns the charset encoding of the XmlStreamReader.
     *
     * @return charset encoding.
     */
    public String getEncoding() {
        return encoding;
    }

    /**
     * Invokes the underlying reader's <code>read(char[], int, int)</code> method.
     * @param buf the buffer to read the characters into
     * @param offset The start offset
     * @param len The number of bytes to read
     * @return the number of characters read or -1 if the end of stream
     * @throws IOException if an I/O error occurs
     */
    @Override
    public int read(char[] buf, int offset, int len) throws IOException {
        return reader.read(buf, offset, len);
    }

    /**
     * Closes the XmlStreamReader stream.
     *
     * @throws IOException thrown if there was a problem closing the stream.
     */
    @Override
    public void close() throws IOException {
        reader.close();
    }

    /**
     * Process the raw stream.
     *
     * @param bom BOMInputStream to detect byte order marks
     * @param pis BOMInputStream to guess XML encoding
     * @param lenient indicates if the charset encoding detection should be
     *        relaxed.
     * @return the encoding to be used
     * @throws IOException thrown if there is a problem reading the stream.
     */
    private String doRawStream(BOMInputStream bom, BOMInputStream pis, boolean lenient)
            throws IOException {
        String bomEnc      = bom.getBOMCharsetName();
        String xmlGuessEnc = pis.getBOMCharsetName();
        String xmlEnc = getXmlProlog(pis, xmlGuessEnc);
        try {
            return calculateRawEncoding(bomEnc, xmlGuessEnc, xmlEnc);
        } catch (XmlStreamReaderException ex) {
            if (lenient) {
                return doLenientDetection(null, ex);
            } else {
                throw ex;
            }
        }
    }

    /**
     * Process a HTTP stream.
     *
     * @param bom BOMInputStream to detect byte order marks
     * @param pis BOMInputStream to guess XML encoding
     * @param httpContentType The HTTP content type
     * @param lenient indicates if the charset encoding detection should be
     *        relaxed.
     * @return the encoding to be used
     * @throws IOException thrown if there is a problem reading the stream.
     */
    private String doHttpStream(BOMInputStream bom, BOMInputStream pis, String httpContentType,
            boolean lenient) throws IOException {
        String bomEnc      = bom.getBOMCharsetName();
        String xmlGuessEnc = pis.getBOMCharsetName();
        String xmlEnc = getXmlProlog(pis, xmlGuessEnc);
        try {
            return calculateHttpEncoding(httpContentType, bomEnc,
                    xmlGuessEnc, xmlEnc, lenient);
        } catch (XmlStreamReaderException ex) {
            if (lenient) {
                return doLenientDetection(httpContentType, ex);
            } else {
                throw ex;
            }
        }
    }

    /**
     * Do lenient detection.
     *
     * @param httpContentType content-type header to use for the resolution of
     *        the charset encoding.
     * @param ex The thrown exception
     * @return the encoding
     * @throws IOException thrown if there is a problem reading the stream.
     */
    private String doLenientDetection(String httpContentType,
            XmlStreamReaderException ex) throws IOException {
        if (httpContentType != null && httpContentType.startsWith("text/html")) {
            httpContentType = httpContentType.substring("text/html".length());
            httpContentType = "text/xml" + httpContentType;
            try {
                return calculateHttpEncoding(httpContentType, ex.getBomEncoding(),
                        ex.getXmlGuessEncoding(), ex.getXmlEncoding(), true);
            } catch (XmlStreamReaderException ex2) {
                ex = ex2;
            }
        }
        String encoding = ex.getXmlEncoding();
        if (encoding == null) {
            encoding = ex.getContentTypeEncoding();
        }
        if (encoding == null) {
            encoding = (defaultEncoding == null) ? UTF_8 : defaultEncoding;
        }
        return encoding;
    }

    /**
     * Calculate the raw encoding.
     *
     * @param bomEnc BOM encoding
     * @param xmlGuessEnc XML Guess encoding
     * @param xmlEnc XML encoding
     * @return the raw encoding
     * @throws IOException thrown if there is a problem reading the stream.
     */
    String calculateRawEncoding(String bomEnc, String xmlGuessEnc,
            String xmlEnc) throws IOException {

        // BOM is Null
        if (bomEnc == null) {
            if (xmlGuessEnc == null || xmlEnc == null) {
                return (defaultEncoding == null ? UTF_8 : defaultEncoding);
            }
            if (xmlEnc.equals(UTF_16) &&
               (xmlGuessEnc.equals(UTF_16BE) || xmlGuessEnc.equals(UTF_16LE))) {
                return xmlGuessEnc;
            }
            return xmlEnc;
        }

        // BOM is UTF-8
        if (bomEnc.equals(UTF_8)) {
            if (xmlGuessEnc != null && !xmlGuessEnc.equals(UTF_8)) {
                String msg = MessageFormat.format(RAW_EX_1, new Object[] { bomEnc, xmlGuessEnc, xmlEnc });
                throw new XmlStreamReaderException(msg, bomEnc, xmlGuessEnc, xmlEnc);
            }
            if (xmlEnc != null && !xmlEnc.equals(UTF_8)) {
                String msg = MessageFormat.format(RAW_EX_1, new Object[] { bomEnc, xmlGuessEnc, xmlEnc });
                throw new XmlStreamReaderException(msg, bomEnc, xmlGuessEnc, xmlEnc);
            }
            return bomEnc;
        }

        // BOM is UTF-16BE or UTF-16LE
        if (bomEnc.equals(UTF_16BE) || bomEnc.equals(UTF_16LE)) {
            if (xmlGuessEnc != null && !xmlGuessEnc.equals(bomEnc)) {
                String msg = MessageFormat.format(RAW_EX_1, new Object[] { bomEnc, xmlGuessEnc, xmlEnc });
                throw new XmlStreamReaderException(msg, bomEnc, xmlGuessEnc, xmlEnc);
            }
            if (xmlEnc != null && !xmlEnc.equals(UTF_16) && !xmlEnc.equals(bomEnc)) {
                String msg = MessageFormat.format(RAW_EX_1, new Object[] { bomEnc, xmlGuessEnc, xmlEnc });
                throw new XmlStreamReaderException(msg, bomEnc, xmlGuessEnc, xmlEnc);
            }
            return bomEnc;
        }

        // BOM is something else
        String msg = MessageFormat.format(RAW_EX_2, new Object[] { bomEnc, xmlGuessEnc, xmlEnc });
        throw new XmlStreamReaderException(msg, bomEnc, xmlGuessEnc, xmlEnc);
    }


    /**
     * Calculate the HTTP encoding.
     *
     * @param httpContentType The HTTP content type
     * @param bomEnc BOM encoding
     * @param xmlGuessEnc XML Guess encoding
     * @param xmlEnc XML encoding
     * @param lenient indicates if the charset encoding detection should be
     *        relaxed.
     * @return the HTTP encoding
     * @throws IOException thrown if there is a problem reading the stream.
     */
    String calculateHttpEncoding(String httpContentType,
            String bomEnc, String xmlGuessEnc, String xmlEnc,
            boolean lenient) throws IOException {

        // Lenient and has XML encoding
        if (lenient && xmlEnc != null) {
            return xmlEnc;
        }

        // Determine mime/encoding content types from HTTP Content Type
        String cTMime = getContentTypeMime(httpContentType);
        String cTEnc  = getContentTypeEncoding(httpContentType);
        boolean appXml  = isAppXml(cTMime);
        boolean textXml = isTextXml(cTMime);

        // Mime type NOT "application/xml" or "text/xml"
        if (!appXml && !textXml) {
            String msg = MessageFormat.format(HTTP_EX_3, cTMime, cTEnc, bomEnc, xmlGuessEnc, xmlEnc);
            throw new XmlStreamReaderException(msg, cTMime, cTEnc, bomEnc, xmlGuessEnc, xmlEnc);
        }

        // No content type encoding
        if (cTEnc == null) {
            if (appXml) {
                return calculateRawEncoding(bomEnc, xmlGuessEnc, xmlEnc);
            } else {
                return (defaultEncoding == null) ? US_ASCII : defaultEncoding;
            }
        }

        // UTF-16BE or UTF-16LE content type encoding
        if (cTEnc.equals(UTF_16BE) || cTEnc.equals(UTF_16LE)) {
            if (bomEnc != null) {
                String msg = MessageFormat.format(HTTP_EX_1, cTMime, cTEnc, bomEnc, xmlGuessEnc, xmlEnc);
                throw new XmlStreamReaderException(msg, cTMime, cTEnc, bomEnc, xmlGuessEnc, xmlEnc);
            }
            return cTEnc;
        }

        // UTF-16 content type encoding
        if (cTEnc.equals(UTF_16)) {
            if (bomEnc != null && bomEnc.startsWith(UTF_16)) {
                return bomEnc;
            }
            String msg = MessageFormat.format(HTTP_EX_2, cTMime, cTEnc, bomEnc, xmlGuessEnc, xmlEnc);
            throw new XmlStreamReaderException(msg, cTMime, cTEnc, bomEnc, xmlGuessEnc, xmlEnc);
        }

        return cTEnc;
    }

    /**
     * Returns MIME type or NULL if httpContentType is NULL.
     *
     * @param httpContentType the HTTP content type
     * @return The mime content type
     */
    static String getContentTypeMime(String httpContentType) {
        String mime = null;
        if (httpContentType != null) {
            int i = httpContentType.indexOf(";");
            if (i >= 0) {
                mime = httpContentType.substring(0, i);
            } else {
                mime = httpContentType;
            }
            mime = mime.trim();
        }
        return mime;
    }

    private static final Pattern CHARSET_PATTERN = Pattern
            .compile("charset=[\"']?([.[^; \"']]*)[\"']?");

    /**
     * Returns charset parameter value, NULL if not present, NULL if
     * httpContentType is NULL.
     *
     * @param httpContentType the HTTP content type
     * @return The content type encoding
     */
    static String getContentTypeEncoding(String httpContentType) {
        String encoding = null;
        if (httpContentType != null) {
            int i = httpContentType.indexOf(";");
            if (i > -1) {
                String postMime = httpContentType.substring(i + 1);
                Matcher m = CHARSET_PATTERN.matcher(postMime);
                encoding = (m.find()) ? m.group(1) : null;
                encoding = (encoding != null) ? encoding.toUpperCase() : null;
            }
        }
        return encoding;
    }

    public static final Pattern ENCODING_PATTERN = Pattern.compile(
            "<\\?xml.*encoding[\\s]*=[\\s]*((?:\".[^\"]*\")|(?:'.[^']*'))",
            Pattern.MULTILINE);

    /**
     * Returns the encoding declared in the <?xml encoding=...?>, NULL if none.
     *
     * @param is InputStream to create the reader from.
     * @param guessedEnc guessed encoding
     * @return the encoding declared in the <?xml encoding=...?>
     * @throws IOException thrown if there is a problem reading the stream.
     */
    private static String getXmlProlog(InputStream is, String guessedEnc)
            throws IOException {
        String encoding = null;
        if (guessedEnc != null) {
            byte[] bytes = new byte[BUFFER_SIZE];
            is.mark(BUFFER_SIZE);
            int offset = 0;
            int max = BUFFER_SIZE;
            int c = is.read(bytes, offset, max);
            int firstGT = -1;
            String xmlProlog = null;
            while (c != -1 && firstGT == -1 && offset < BUFFER_SIZE) {
                offset += c;
                max -= c;
                c = is.read(bytes, offset, max);
                xmlProlog = new String(bytes, 0, offset, guessedEnc);
                firstGT = xmlProlog.indexOf('>');
            }
            if (firstGT == -1) {
                if (c == -1) {
                    throw new IOException("Unexpected end of XML stream");
                } else {
                    throw new IOException(
                            "XML prolog or ROOT element not found on first "
                                    + offset + " bytes");
                }
            }
            int bytesRead = offset;
            if (bytesRead > 0) {
                is.reset();
                BufferedReader bReader = new BufferedReader(new StringReader(
                        xmlProlog.substring(0, firstGT + 1)));
                StringBuffer prolog = new StringBuffer();
                String line = bReader.readLine();
                while (line != null) {
                    prolog.append(line);
                    line = bReader.readLine();
                }
                Matcher m = ENCODING_PATTERN.matcher(prolog);
                if (m.find()) {
                    encoding = m.group(1).toUpperCase();
                    encoding = encoding.substring(1, encoding.length() - 1);
                }
            }
        }
        return encoding;
    }

    /**
     * Indicates if the MIME type belongs to the APPLICATION XML family.
     * 
     * @param mime The mime type
     * @return true if the mime type belongs to the APPLICATION XML family,
     * otherwise false
     */
    static boolean isAppXml(String mime) {
        return mime != null &&
               (mime.equals("application/xml") || 
                mime.equals("application/xml-dtd") ||
                mime.equals("application/xml-external-parsed-entity") ||
               (mime.startsWith("application/") && mime.endsWith("+xml")));
    }

    /**
     * Indicates if the MIME type belongs to the TEXT XML family.
     * 
     * @param mime The mime type
     * @return true if the mime type belongs to the TEXT XML family,
     * otherwise false
     */
    static boolean isTextXml(String mime) {
        return mime != null &&
              (mime.equals("text/xml") ||
               mime.equals("text/xml-external-parsed-entity") ||
              (mime.startsWith("text/") && mime.endsWith("+xml")));
    }

    private static final String RAW_EX_1 =
        "Invalid encoding, BOM [{0}] XML guess [{1}] XML prolog [{2}] encoding mismatch";

    private static final String RAW_EX_2 =
        "Invalid encoding, BOM [{0}] XML guess [{1}] XML prolog [{2}] unknown BOM";

    private static final String HTTP_EX_1 =
        "Invalid encoding, CT-MIME [{0}] CT-Enc [{1}] BOM [{2}] XML guess [{3}] XML prolog [{4}], BOM must be NULL";

    private static final String HTTP_EX_2 =
        "Invalid encoding, CT-MIME [{0}] CT-Enc [{1}] BOM [{2}] XML guess [{3}] XML prolog [{4}], encoding mismatch";

    private static final String HTTP_EX_3 =
        "Invalid encoding, CT-MIME [{0}] CT-Enc [{1}] BOM [{2}] XML guess [{3}] XML prolog [{4}], Invalid MIME";

}
