BufferDecoder.java

package nom.tam.util;

/*
 * #%L
 * nom.tam FITS library
 * %%
 * Copyright (C) 1996 - 2021 nom-tam-fits
 * %%
 * This is free and unencumbered software released into the public domain.
 * 
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 * 
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 * #L%
 */


import java.io.EOFException;
import java.io.IOException;

/**
 * @deprecated  This is a rusty rail implementation only, unsafe for general use.
 *      Use {@link FitsDecoder} instead, which provides a similar function but in
 *      a more consistent way and with a less misleading name, or else use {@link ArrayDecoder}
 *      as a base for implementing efficient custom decoding of binary inputs. 
 *      
 *      
 *
 * @see FitsDecoder
 */
@Deprecated
public abstract class BufferDecoder extends FitsDecoder {

   
    
    private BufferPointer p;
    
    /**
     * 
     * @param p     Unused, but the position and length fields are set/reset as to pretend that half of
     *              the buffer is perpetually available for reading.
     *              However, at no point will there be any data actually in the buffer of this object,
     *              and you should by all means avoid directly loading data from the stream into this
     *              dead-end buffer, other than the hopefully untiggered existing implementation
     *              of <code>checkBuffer(int)</code> (and it's safest if you don't override
     *              or ever call <code>checkBuffer(int)</code> from your code!).
     */
    public BufferDecoder(BufferPointer p) {
        super();
        
        this.p = p;
        
        pretendHalfPopulated();
        
        setInput(new InputReader() {
            private byte[] b1 = new byte[1];

            @Override
            public int read() throws IOException {
                int n = BufferDecoder.this.read(b1, 0, 1);
                if (n < 0) {
                    return n;
                }
                return b1[0];
            }

            @Override
            public int read(byte[] b, int from, int length) throws IOException {
                return BufferDecoder.this.read(b, from, length);
            }
            
        });
    }
    
    /**
     * We'll always pretend the buffer to be half populated at pos=0, in order to avoid triggering
     * a read from the input into the unused buffer of BufferPointer, or a write to the
     * output from that buffer... If the pointer has no buffer, length will be 0 also.
     */
    private void pretendHalfPopulated() {
        p.pos = 0; 
        p.length = p.buffer == null ? 0 : p.buffer.length >>> 1;   
    }
    
    @Override
    boolean makeAvailable(int needBytes) throws IOException {
        pretendHalfPopulated();
        boolean result = super.makeAvailable(needBytes);
        return result;
    }
    
    /**
     * @deprecated  No longer used internally, kept only for back-compatibility since it used to be a needed abstract method.
     *              It's safest if you never override or call this method from your code!
     *             
     * @param needBytes     the number of byte we need available to decode the next element
     * @throws IOException  if the data could not be made available due to an IO error of the underlying input.
     */
    protected void checkBuffer(int needBytes) throws IOException {
    }
    
    @Override
    protected int read(byte[] buf, int offset, int length) throws IOException {
        throw new UnsupportedOperationException("You need to override this with an implementation that reads from the desired input.");
    }
    
    /**
     * @deprecated  No longer used internally, kept only for back-compatibility since it used to be a needed abstract method.
     * 
     * @param e     the <code>EOFException</code> thrown by one of the read calls.
     * @param start the index of the first array element we wanted to fill
     * @param index the array index of the element during which the exception was thrown
     * @param elementSize the number of bytes per element we were processing
     * 
     * @return the numer of bytes successfully processed from the input before the exception occurred.
     * @throws EOFException
     *              if the input had no more data to process
     */
    protected int eofCheck(EOFException e, int start, int index, int elementSize) throws EOFException {
        return super.eofCheck(e, (index - start), -1) * elementSize;
    }
    
    /**
     * See the contract of {@link ArrayDataInput#readLArray(Object)}.
     * 
     * @param o
     *            an array, to be populated
     * @return the actual number of bytes read from the input, or -1 if already
     *         at the end-of-file.
     * @throws IllegalArgumentException
     *             if the argument is not an array or if it contains an element
     *             that is not supported for decoding.
     * @throws IOException
     *             if there was an IO error reading from the input
     */
    protected long readLArray(Object o) throws IOException {
        try { 
            return super.readArray(o); 
        } catch (IllegalArgumentException e) {
            throw new IOException(e);
        }
    }
 
    
}