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The Apache Commons IO library contains utility classes, stream implementations, file filters, file comparators, endian transformation classes, and much more.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */
package org.apache.commons.io.input.buffer;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Objects;


/**
 * Implementation of a buffered input stream, which is internally based on the
 * {@link CircularByteBuffer}. Unlike the {@link BufferedInputStream}, this one
 * doesn't need to reallocate byte arrays internally.
 */
public class CircularBufferInputStream extends InputStream {
	protected final InputStream in;
	protected final CircularByteBuffer buffer;
	protected final int bufferSize;
	private boolean eofSeen;

	/** Creates a new instance, which filters the given input stream, and
	 * uses the given buffer size.
	 * @param pIn The input stream, which is being buffered.
	 * @param pBufferSize The size of the {@link CircularByteBuffer}, which is
	 * used internally.
	 */
	public CircularBufferInputStream(InputStream pIn, int pBufferSize) {
		Objects.requireNonNull(pIn, "InputStream");
		if (pBufferSize <= 0) {
			throw new IllegalArgumentException("Invalid buffer size: " + pBufferSize);
		}
		in = pIn;
		buffer = new CircularByteBuffer(pBufferSize);
		bufferSize = pBufferSize;
		eofSeen = false;
	}

	/** Creates a new instance, which filters the given input stream, and
	 * uses a reasonable default buffer size (8192).
	 * @param pIn The input stream, which is being buffered.
	 */
	public CircularBufferInputStream(InputStream pIn) {
		this(pIn, 8192);
	}

	protected void fillBuffer() throws IOException {
		if (eofSeen) {
			return;
		}
		int space = buffer.getSpace();
		final byte[] buf = new byte[space];
		while (space > 0) {
			final int res = in.read(buf, 0, space);
			if (res == -1) {
				eofSeen = true;
				return;
			} else if (res > 0) {
				buffer.add(buf, 0, res);
				space -= res;
			}
		}
	}

	protected boolean haveBytes(int pNumber) throws IOException {
		if (buffer.getCurrentNumberOfBytes() < pNumber) {
			fillBuffer();
		}
		return buffer.hasBytes();
	}

	@Override
	public int read() throws IOException {
		if (!haveBytes(1)) {
			return -1;
		}
		return buffer.read();
	}

	@Override
	public int read(byte[] pBuffer) throws IOException {
		return read(pBuffer, 0, pBuffer.length);
	}

	@Override
	public int read(byte[] pBuffer, int pOffset, int pLength) throws IOException {
		Objects.requireNonNull(pBuffer, "Buffer");
		if (pOffset < 0) {
			throw new IllegalArgumentException("Offset must not be negative");
		}
		if (pLength < 0) {
			throw new IllegalArgumentException("Length must not be negative");
		}
		if (!haveBytes(pLength)) {
			return -1;
		}
		final int result = Math.min(pLength, buffer.getCurrentNumberOfBytes());
		for (int i = 0;  i < result;  i++) {
			pBuffer[pOffset+i] = buffer.read();
		}
		return result;
	}

	@Override
	public void close() throws IOException {
		in.close();
		eofSeen = true;
		buffer.clear();
	}
}