    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
    023import org.apache.commons.io.IOUtils;
    024
    025/**
    026 * Implements a buffered input stream, which allows to peek into the buffers first bytes. This comes in handy when
    027 * manually implementing scanners, lexers, parsers, and the like.
    028 *
    029 * @since 2.7
    030 */
    031public class PeekableInputStream extends CircularBufferInputStream {
    032
    033    /**
    034     * Constructs a new instance, which filters the given input stream, and uses a reasonable default buffer size ({@link IOUtils#DEFAULT_BUFFER_SIZE}).
    035     *
    036     * @param inputStream The input stream, which is being buffered.
    037     */
    038    public PeekableInputStream(final InputStream inputStream) {
    039        super(inputStream);
    040    }
    041
    042    /**
    043     * Constructs a new instance, which filters the given input stream, and uses the given buffer size.
    044     *
    045     * @param inputStream The input stream, which is being buffered.
    046     * @param bufferSize The size of the {@link CircularByteBuffer}, which is used internally.
    047     */
    048    public PeekableInputStream(final InputStream inputStream, final int bufferSize) {
    049        super(inputStream, bufferSize);
    050    }
    051
    052    /**
    053     * Returns whether the next bytes in the buffer are as given by {@code sourceBuffer}. This is equivalent to
    054     * {@link #peek(byte[], int, int)} with {@code offset} == 0, and {@code length} == {@code sourceBuffer.length}
    055     *
    056     * @param sourceBuffer the buffer to compare against
    057     * @return true if the next bytes are as given
    058     * @throws IOException Refilling the buffer failed.
    059     */
    060    public boolean peek(final byte[] sourceBuffer) throws IOException {
    061        Objects.requireNonNull(sourceBuffer, "sourceBuffer");
    062        return peek(sourceBuffer, 0, sourceBuffer.length);
    063    }
    064
    065    /**
    066     * Returns whether the next bytes in the buffer are as given by {@code sourceBuffer}, {code offset}, and
    067     * {@code length}.
    068     *
    069     * @param sourceBuffer the buffer to compare against
    070     * @param offset the start offset
    071     * @param length the length to compare
    072     * @return true if the next bytes in the buffer are as given
    073     * @throws IOException if there is a problem calling fillBuffer()
    074     */
    075    public boolean peek(final byte[] sourceBuffer, final int offset, final int length) throws IOException {
    076        Objects.requireNonNull(sourceBuffer, "sourceBuffer");
    077        if (sourceBuffer.length > bufferSize) {
    078            throw new IllegalArgumentException("Peek request size of " + sourceBuffer.length
    079                + " bytes exceeds buffer size of " + bufferSize + " bytes");
    080        }
    081        if (buffer.getCurrentNumberOfBytes() < sourceBuffer.length) {
    082            fillBuffer();
    083        }
    084        return buffer.peek(sourceBuffer, offset, length);
    085    }
    086}