WarpPI/desktop/src/main/java/ar/com/hjg/pngj/BufferedStreamFeeder.java

package ar.com.hjg.pngj;

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

/**
 * Reads bytes from an input stream, and feeds a IBytesConsumer.
 */
public class BufferedStreamFeeder {

	private InputStream stream;
	private byte[] buf;
	private int pendinglen; // bytes read and stored in buf that have not yet still been fed to
							// IBytesConsumer
	private int offset;
	private boolean eof = false;
	private boolean closeStream = true;
	private boolean failIfNoFeed = false;

	private static final int DEFAULTSIZE = 8192;

	/** By default, the stream will be closed on close() */
	public BufferedStreamFeeder(InputStream is) {
		this(is, DEFAULTSIZE);
	}

	public BufferedStreamFeeder(InputStream is, int bufsize) {
		this.stream = is;
		buf = new byte[bufsize < 1 ? DEFAULTSIZE : bufsize];
	}

	/**
	 * Returns inputstream
	 * 
	 * @return Input Stream from which bytes are read
	 */
	public InputStream getStream() {
		return stream;
	}

	/**
	 * Feeds bytes to the consumer <br>
	 * Returns bytes actually consumed <br>
	 * This should return 0 only if the stream is EOF or the consumer is done
	 */
	public int feed(IBytesConsumer consumer) {
		return feed(consumer, Integer.MAX_VALUE);
	}

	/**
	 * Feeds the consumer (with at most maxbytes) <br>
	 * Returns 0 only if the stream is EOF (or maxbytes=0). Returns negative is
	 * the consumer is done.<br>
	 * It can return less than maxbytes (that doesn't mean that the consumer or
	 * the input stream is done)
	 */
	public int feed(IBytesConsumer consumer, int maxbytes) {
		if (pendinglen == 0)
			refillBuffer();
		int tofeed = maxbytes >= 0 && maxbytes < pendinglen ? maxbytes : pendinglen;
		int n = 0;
		if (tofeed > 0) {
			n = consumer.consume(buf, offset, tofeed);
			if (n > 0) {
				offset += n;
				pendinglen -= n;
			}
		}
		if (n < 1 && failIfNoFeed)
			throw new PngjInputException("Failed to feed bytes (premature ending?)");
		return n;
	}

	/**
	 * Feeds as much bytes as it can to the consumer, in a loop. <br>
	 * Returns bytes actually consumed <br>
	 * This will stop when either the input stream is eof, or when the consumer
	 * refuses to eat more bytes. The caller can
	 * distinguish both cases by calling {@link #hasMoreToFeed()}
	 */
	public long feedAll(IBytesConsumer consumer) {
		long n = 0;
		while (hasMoreToFeed()) {
			int n1 = feed(consumer);
			if (n1 < 1)
				break;
			n += n1;
		}
		return n;
	}

	/**
	 * Feeds exactly nbytes, retrying if necessary
	 * 
	 * @param consumer
	 *            Consumer
	 * @param nbytes
	 *            Number of bytes
	 * @return true if success, false otherwise (EOF on stream, or consumer is
	 *         done)
	 */
	public boolean feedFixed(IBytesConsumer consumer, int nbytes) {
		int remain = nbytes;
		while (remain > 0) {
			int n = feed(consumer, remain);
			if (n < 1)
				return false;
			remain -= n;
		}
		return true;
	}

	/**
	 * If there are not pending bytes to be consumed tries to fill the buffer
	 * with bytes from the stream.
	 */
	protected void refillBuffer() {
		if (pendinglen > 0 || eof)
			return; // only if not pending data
		try {
			// try to read
			offset = 0;
			pendinglen = stream.read(buf);
			if (pendinglen < 0) {
				close();
				return;
			} else
				return;
		} catch (IOException e) {
			throw new PngjInputException(e);
		}
	}

	/**
	 * Returuns true if we have more data to fed the consumer. This internally
	 * tries to grabs more bytes from the stream
	 * if necessary
	 */
	public boolean hasMoreToFeed() {
		if (eof)
			return pendinglen > 0;
		else
			refillBuffer();
		return pendinglen > 0;
	}

	/**
	 * @param closeStream
	 *            If true, the underlying stream will be closed on when close()
	 *            is called
	 */
	public void setCloseStream(boolean closeStream) {
		this.closeStream = closeStream;
	}

	/**
	 * Closes this object.
	 * 
	 * Sets EOF=true, and closes the stream if <tt>closeStream</tt> is true
	 * 
	 * This can be called internally, or from outside.
	 * 
	 * Idempotent, secure, never throws exception.
	 **/
	public void close() {
		eof = true;
		buf = null;
		pendinglen = 0;
		offset = 0;
		if (stream != null && closeStream) {
			try {
				stream.close();
			} catch (Exception e) {
				// PngHelperInternal.LOGGER.log(Level.WARNING, "Exception closing stream", e);
			}
		}
		stream = null;
	}

	/**
	 * Sets a new underlying inputstream. This allows to reuse this object. The
	 * old underlying is not closed and the state
	 * is not reset (you should call close() previously if you want that)
	 * 
	 * @param is
	 */
	public void setInputStream(InputStream is) { // to reuse this object
		this.stream = is;
		eof = false;
	}

	/**
	 * @return EOF on stream, or close() was called
	 */
	public boolean isEof() {
		return eof;
	}

	/**
	 * If this flag is set (default: false), any call to feed() that returns
	 * zero (no byte feed) will throw an exception.
	 * This is useful to be sure of avoid infinite loops in some scenarios.
	 * 
	 * @param failIfNoFeed
	 */
	public void setFailIfNoFeed(boolean failIfNoFeed) {
		this.failIfNoFeed = failIfNoFeed;
	}
}