/*
* This file is part of muCommander, http://www.mucommander.com
* Copyright (C) 2002-2016 Maxence Bernard
*
* muCommander is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* muCommander 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package com.mucommander.commons.io;
import com.mucommander.commons.io.bom.BOM;
import com.mucommander.commons.io.bom.BOMConstants;
import com.mucommander.commons.io.bom.BOMInputStream;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
/**
* This class provides methods to determine whether some data is binary data or text data.
* As there is no formal characterization of what binary data really is, this method is an approximation at best
* and should not be trusted for anything critical.
*
* <p>The {@link #RECOMMENDED_BYTE_SIZE} field indicates how many bytes should be provided for the detector to be
* confident enough.</p>
*
* @see com.mucommander.commons.io.EncodingDetector
* @author Maxence Bernard
*/
public class BinaryDetector {
/** Provides an indication as to the number of bytes that should fed to the detector for it to have enough
* confidence. */
public final static int RECOMMENDED_BYTE_SIZE = 1024;
/**
* This method is a shorthand for {@link #guessBinary(byte[], int, int) guessBinary(b, 0, b.length)}.
*
* @param b the data to analyze
* @return true if BinaryDetector thinks that the specified data is binary
*/
public static boolean guessBinary(byte b[]) {
return guessBinary(b, 0, b.length);
}
/**
* Tries and detect whether the given bytes correspond to binary or text data. The specified bytes can typically
* be the beginning of a file.</br>
* This method returns <code>true</code> if it thinks that the bytes correspond to binary data.
*
* @param b the data to analyze
* @param off specifies where to start reading the array
* @param len specifies where to stop reading the array
* @return true if BinaryDetector thinks that the specified data is binary
*/
public static boolean guessBinary(byte b[], int off, int len) {
try {
// Returns true if any of the bytes are the NUL character. The NUL character is usually not found in a text
// file, except for UTF-16 and UTF-32 streams.
// So first, we try and look for a BOM (byte-order mark) to see if the stream is UTF-16 or UTF-32 encoded.
BOMInputStream bin = new BOMInputStream(new ByteArrayInputStream(b, off, len));
BOM bom = bin.getBOM();
if(bom!=null) {
if(bom.equals(BOMConstants.UTF16_BE_BOM) || bom.equals(BOMConstants.UTF16_LE_BOM)
|| bom.equals(BOMConstants.UTF32_BE_BOM) || bom.equals(BOMConstants.UTF32_LE_BOM)) {
return false;
}
}
// No BOM, start looking for zeros
int i;
while((i=bin.read())!=-1)
if(i==0x00)
return true;
}
catch(IOException e) {
// Can never happen in practice with a ByteArrayInputStream.
}
return false;
}
/**
* Tries and detect whether the given stream contains binary or text data.</br>
* This method returns <code>true</code> if it thinks that the bytes correspond to binary data.
*
* <p>A maximum of {@link #RECOMMENDED_BYTE_SIZE} will be read from the <code>InputStream</code>. The
* stream will not be closed and will not be repositionned after the bytes have been read. It is up to the calling
* method to use the <code>InputStream#mark()</code> and <code>InputStream#reset()</code> methods (if supported)
* or reopen the stream if needed.
* </p>
*
* @param in the stream to analyze
* @return true if BinaryDetector thinks that the specified data is binary
* @throws IOException if an error occurred while reading the InputStream.
*/
public static boolean guessBinary(InputStream in) throws IOException {
byte[] bytes = new byte[RECOMMENDED_BYTE_SIZE];
return guessBinary(bytes, 0, StreamUtils.readUpTo(in, bytes));
}
}