001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.io.input.buffer;
018
019import java.io.IOException;
020import java.io.InputStream;
021import java.util.Objects;
022
023
024/**
025 * Implementation of a buffered input stream, which allows to peek into
026 * the buffers first bytes. This comes in handy when manually implementing
027 * scanners, lexers, parsers, or the like.
028 */
029public class PeekableInputStream extends CircularBufferInputStream {
030
031    /**
032     * Creates a new instance, which filters the given input stream, and
033     * uses the given buffer size.
034     *
035     * @param inputStream         The input stream, which is being buffered.
036     * @param bufferSize The size of the {@link CircularByteBuffer}, which is
037     *                    used internally.
038     */
039    public PeekableInputStream(final InputStream inputStream, final int bufferSize) {
040        super(inputStream, bufferSize);
041    }
042
043    /**
044     * Creates a new instance, which filters the given input stream, and
045     * uses a reasonable default buffer size (8192).
046     *
047     * @param inputStream The input stream, which is being buffered.
048     */
049    public PeekableInputStream(final InputStream inputStream) {
050        super(inputStream);
051    }
052
053    /**
054     * Returns, whether the next bytes in the buffer are as given by
055     * {@code sourceBuffer}. This is equivalent to {@link #peek(byte[], int, int)}
056     * with {@code offset} == 0, and {@code length} == {@code sourceBuffer.length}
057     *
058     * @param sourceBuffer the buffer to compare against
059     * @return true if the next bytes are as given
060     * @throws IOException Refilling the buffer failed.
061     */
062    public boolean peek(final byte[] sourceBuffer) throws IOException {
063        Objects.requireNonNull(sourceBuffer, "Buffer");
064        if (sourceBuffer.length > bufferSize) {
065            throw new IllegalArgumentException("Peek request size of " + sourceBuffer.length
066                    + " bytes exceeds buffer size of " + bufferSize + " bytes");
067        }
068        if (buffer.getCurrentNumberOfBytes() < sourceBuffer.length) {
069            fillBuffer();
070        }
071        return buffer.peek(sourceBuffer, 0, sourceBuffer.length);
072    }
073
074    /**
075     * Returns, whether the next bytes in the buffer are as given by
076     * {@code sourceBuffer}, {code offset}, and {@code length}.
077     *
078     * @param sourceBuffer the buffer to compare against
079     * @param offset the start offset
080     * @param length the length to compare
081     * @return true if the next bytes in the buffer are as given
082     * @throws IOException if there is a problem calling fillBuffer()
083     */
084    public boolean peek(final byte[] sourceBuffer, final int offset, final int length) throws IOException {
085        Objects.requireNonNull(sourceBuffer, "Buffer");
086        if (sourceBuffer.length > bufferSize) {
087            throw new IllegalArgumentException("Peek request size of " + sourceBuffer.length
088                    + " bytes exceeds buffer size of " + bufferSize + " bytes");
089        }
090        if (buffer.getCurrentNumberOfBytes() < sourceBuffer.length) {
091            fillBuffer();
092        }
093        return buffer.peek(sourceBuffer, offset, length);
094    }
095}