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package org.glassfish.jersey.internal.util.collection;

import java.io.IOException;
import java.io.InputStream;

/**
 * An abstract {@link InputStream} extension that defines contract for non-blocking
 * streaming {@code read} operations.
 *
 * @author Marek Potociar (marek.potociar at oracle.com)
 */
public abstract class NonBlockingInputStream extends InputStream {
    /**
     * Constant used as a return value from {@link #tryRead()} method, to indicate that nothing
     * has been read.
     */
    public static final int NOTHING = Integer.MIN_VALUE;

    /**
     * Returns an estimate of the number of bytes that can be read (or
     * skipped over) from this input stream without blocking by the next
     * invocation of a method for this input stream. The next invocation
     * might be the same thread or another thread.  A single read or skip of this
     * many bytes will not block, but may read or skip fewer bytes.
     * 

* Note that while some implementations of {@code InputStream} will return * the total number of bytes in the stream, many will not. It is * never correct to use the return value of this method to allocate * a buffer intended to hold all data in this stream. *

*

* A subclass' implementation of this method may choose to throw an * {@link java.io.IOException} if this input stream has been closed by * invoking the {@link #close()} method. *

*

* The default implementation of this method in {@code NonBlockingInputStream} * throws an {@link UnsupportedOperationException}. This method must be overridden * by subclasses. The overriding implementations must guarantee non-blocking behavior * of the method. The overriding implementation must also guarantee that a non-empty * stream does not return zero from the method. IOW, it must be possible to use the * method for empty check: {@code stream.available() == 0} *

* * @return an estimate of the number of bytes that can be read (or skipped * over) from this input stream without blocking or {@code 0} when * it reaches the end of the input stream or the stream is empty. * @throws java.io.IOException if an I/O error occurs. */ @Override public int available() throws IOException { throw new UnsupportedOperationException(); } /** * Behaves mostly like {@link java.io.InputStream#read()}. * * The main difference is that this method is non-blocking. In case there are no * data available to be read, the method returns {@link #NOTHING} immediately. * * @return next byte of data, {@code -1} if end of the stream has been reached or * {@link #NOTHING} in case no data are available to be read at the moment. * @throws java.io.IOException if an I/O error occurs. */ public abstract int tryRead() throws IOException; /** * Behaves mostly like {@link java.io.InputStream#read(byte[])}. * * The main difference is that this method is non-blocking. In case there are no * data available to be read, the method returns zero immediately. * * @param b the buffer into which the data is read. * @return the total number of bytes read into the buffer or {@code -1} if end of the * stream has been reached or {@code 0} in case no data are available to be * read at the moment. * @throws java.io.IOException if an I/O error occurs. */ public abstract int tryRead(byte b[]) throws IOException; /** * Behaves mostly like {@link java.io.InputStream#read(byte[], int, int)}. * * The main difference is that this method is non-blocking. In case there are no * data available to be read, the method returns zero immediately. * * @param b the buffer into which the data is read. * @param off the start offset in array {@code b} * at which the data is written. * @param len the maximum number of bytes to read. * @return the total number of bytes read into the buffer or {@code -1} if end of the * stream has been reached or {@code 0} in case no data are available to be * read at the moment. * @throws java.io.IOException if an I/O error occurs. */ public abstract int tryRead(byte b[], int off, int len) throws IOException; }




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