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/* Copyright 2002, 2003, 2005 Elliotte Rusty Harold
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This library is free software; you can redistribute it and/or modify
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it under the terms of version 2.1 of the GNU Lesser General Public
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License as published by the Free Software Foundation.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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Boston, MA 02111-1307 USA
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You can contact Elliotte Rusty Harold by sending e-mail to
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elharo@metalab.unc.edu. Please include the word "XOM" in the
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subject line. The XOM home page is located at http://www.xom.nu/
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package nu.xom.xinclude;
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import java.io.IOException;
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import java.io.InputStream;
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* <code>EncodingHeuristics</code> reads from a stream
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* (which should be buffered) and attempts to guess
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* what the encoding of the text in the stream is.
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* Byte order marks are stripped from the stream.
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* If it fails to determine the type of the encoding,
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* it returns the default UTF-8.
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* @author Elliotte Rusty Harold
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class EncodingHeuristics {
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// No instances allowed
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private EncodingHeuristics() {}
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* This utility method uses a variety of heuristics to
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* attempt to guess the encoding from the initial
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* @param in <code>InputStream</code> to read from.
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* @return String The name of the encoding.
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* @throws IOException if the stream cannot be reset back
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* to where it was when the method was invoked.
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public static String readEncodingFromStream(InputStream in)
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// This may fail if there are a lot of space
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// characters before the end of the encoding declaration
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// Lots of things can go wrong here. If any do,
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// return "UTF-8" as the default.
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int byte1 = in.read();
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int byte2 = in.read();
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if (byte1 == 0xFE && byte2 == 0xFF) {
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// Don't reset because the byte order mark should not be
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// included per section 4.3 of the XInclude spec
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else if (byte1 == 0xFF && byte2 == 0xFE) {
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// Don't reset because the byte order mark should not be
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// included per section 4.3 of the XInclude spec
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return "UnicodeLittle";
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/* In accordance with the Character Model,
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when the text format is a Unicode encoding, the XInclude
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processor must fail the inclusion when the text in the
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selected range is non-normalized. When transcoding
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characters to a Unicode encoding from a legacy encoding,
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a normalizing transcoder must be used. */
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int byte3 = in.read();
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// check for UTF-8 byte order mark
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if (byte1 == 0xEF && byte2 == 0xBB && byte3 == 0xBF) {
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// Don't reset because the byte order mark should not be
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// included per section 4.3 of the XInclude spec
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int byte4 = in.read();
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&& byte2 == 0x00 && byte3 == 0xFE && byte4 == 0xFF) {
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// Don't reset because the byte order mark should not be
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// included per section 4.3 of the XInclude spec
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// Most Java VMs don't support this next one
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else if (byte1 == 0x00 && byte2 == 0x00
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&& byte3 == 0xFF && byte4 == 0xFE) {
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// Don't reset because the byte order mark should not be
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// included per section 4.3 of the XInclude spec
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// Most Java VMs don't support this next one
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// no byte order mark present; first character must be
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// less than sign or white space
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// Let's look for less-than signs first
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if (byte1 == 0x00 && byte2 == 0x00
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&& byte3 == 0x00 && byte4 == '<') {
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else if (byte1 == '<' && byte2 == 0x00
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&& byte3 == 0x00 && byte4 == 0x00) {
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else if (byte1 == 0x00 && byte2 == '<'
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&& byte3 == 0x00 && byte4 == '?') {
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return "UnicodeBigUnmarked";
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else if (byte1 == '<' && byte2 == 0x00
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&& byte3 == '?' && byte4 == 0x00) {
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return "UnicodeLittleUnmarked";
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else if (byte1 == '<' && byte2 == '?'
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&& byte3 == 'x' && byte4 == 'm') {
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// ASCII compatible, must read encoding declaration.
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// 1024 bytes will be far enough to read most
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byte[] data = new byte[1024];
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data[0] = (byte) byte1;
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data[1] = (byte) byte2;
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data[2] = (byte) byte3;
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data[3] = (byte) byte4;
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int length = in.read(data, 4, 1020) + 4;
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// Use Latin-1 (ISO-8859-1) because it's ASCII compatible
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// and all byte sequences are legal Latin-1 sequences
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// so I don't have to worry about encoding errors if I
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// slip past the end of the XML/text declaration
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String declaration=new String(data, 0, length, "8859_1");
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// If any of these throw a
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// StringIndexOutOfBoundsException,
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// we just fall into the catch block and return null
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// since this can't be well-formed XML
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String encoding = findEncodingDeclaration(declaration);
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else if (byte1 == 0x4C && byte2 == 0x6F
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&& byte3 == 0xA7 && byte4 == 0x94) {
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// EBCDIC compatible, must read encoding declaration
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byte[] buffer = new byte[1016];
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for (int i = 0; i < buffer.length; i++) {
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buffer[i] = (byte) c;
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// Most EBCDIC encodings are compatible with Cp037 over
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// the range we care about
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return findEncodingDeclaration(new String(buffer, "Cp037"));
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catch (Exception ex) {
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// no XML or text declaration present
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private static String findEncodingDeclaration(String declaration)
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int position = declaration.indexOf("encoding") + 8;
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// get rid of white space before equals sign
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c = declaration.charAt(position++);
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if (c !=' ' && c != '\t' && c != '\r' && c != '\n') {
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if (c != '=') { // malformed
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throw new IOException("Couldn't determine encoding");
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// get rid of white space after equals sign
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c = declaration.charAt(position++);
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if (c !=' ' && c != '\t' && c != '\r' && c != '\n') {
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if (delimiter != '\'' && delimiter != '"') { // malformed
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// now positioned to read encoding name
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StringBuffer encodingName = new StringBuffer();
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c = declaration.charAt(position++);
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if (c == delimiter) break;
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encodingName.append(c);
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return encodingName.toString();
b'\\ No newline at end of file'
added
removed
src/nu/xom/xinclude/EncodingHeuristics.java
