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/*
* Copyright 2002-2017 Drew Noakes
*
* Licensed 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.
*
* More information about this project is available at:
*
* https://drewnoakes.com/code/exif/
* https://github.com/drewnoakes/metadata-extractor
*/
package com.drew.metadata.iptc;
import com.drew.lang.annotations.NotNull;
import com.drew.lang.annotations.Nullable;
import java.nio.ByteBuffer;
import java.nio.charset.CharacterCodingException;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
public final class Iso2022Converter
{
private static final String ISO_8859_1 = "ISO-8859-1";
private static final String UTF_8 = "UTF-8";
private static final byte LATIN_CAPITAL_A = 0x41;
private static final int DOT = 0xe280a2;
private static final byte LATIN_CAPITAL_G = 0x47;
private static final byte PERCENT_SIGN = 0x25;
private static final byte ESC = 0x1B;
/**
* Converts the given ISO2022 char set to a Java charset name.
*
* @param bytes string data encoded using ISO2022
* @return the Java charset name as a string, or <code>null</code> if the conversion was not possible
*/
@Nullable
public static String convertISO2022CharsetToJavaCharset(@NotNull final byte[] bytes)
{
if (bytes.length > 2 && bytes[0] == ESC && bytes[1] == PERCENT_SIGN && bytes[2] == LATIN_CAPITAL_G)
return UTF_8;
if (bytes.length > 3 && bytes[0] == ESC && (bytes[3] & 0xFF | ((bytes[2] & 0xFF) << 8) | ((bytes[1] & 0xFF) << 16)) == DOT && bytes[4] == LATIN_CAPITAL_A)
return ISO_8859_1;
return null;
}
/**
* Attempts to guess the {@link Charset} of a string provided as a byte array.
* <p>
* Charsets trialled are, in order:
* <ul>
* <li>UTF-8</li>
* <li><code>System.getProperty("file.encoding")</code></li>
* <li>ISO-8859-1</li>
* </ul>
* <p>
* Its only purpose is to guess the Charset if and only if IPTC tag coded character set is not set. If the
* encoding is not UTF-8, the tag should be set. Otherwise it is bad practice. This method tries to
* workaround this issue since some metadata manipulating tools do not prevent such bad practice.
* <p>
* About the reliability of this method: The check if some bytes are UTF-8 or not has a very high reliability.
* The two other checks are less reliable.
*
* @param bytes some text as bytes
* @return the name of the encoding or null if none could be guessed
*/
@Nullable
static Charset guessCharSet(@NotNull final byte[] bytes)
{
String[] encodings = { UTF_8, System.getProperty("file.encoding"), ISO_8859_1 };
for (String encoding : encodings)
{
Charset charset = Charset.forName(encoding);
CharsetDecoder cs = charset.newDecoder();
try {
cs.decode(ByteBuffer.wrap(bytes));
return charset;
} catch (CharacterCodingException e) {
// fall through...
}
}
// No encodings succeeded. Return null.
return null;
}
private Iso2022Converter()
{}
}
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