    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 * Implements a buffered input stream, which allows to peek into the buffers first bytes. This comes in handy when
    025 * manually implementing scanners, lexers, parsers, and the like.
    026 */
    027public class PeekableInputStream extends CircularBufferInputStream {
    028
    029    /**
    030     * Creates a new instance, which filters the given input stream, and uses the given buffer size.
    031     *
    032     * @param inputStream The input stream, which is being buffered.
    033     * @param bufferSize The size of the {@link CircularByteBuffer}, which is used internally.
    034     */
    035    public PeekableInputStream(final InputStream inputStream, final int bufferSize) {
    036        super(inputStream, bufferSize);
    037    }
    038
    039    /**
    040     * Creates a new instance, which filters the given input stream, and uses a reasonable default buffer size (8192).
    041     *
    042     * @param inputStream The input stream, which is being buffered.
    043     */
    044    public PeekableInputStream(final InputStream inputStream) {
    045        super(inputStream);
    046    }
    047
    048    /**
    049     * Returns whether the next bytes in the buffer are as given by {@code sourceBuffer}. This is equivalent to
    050     * {@link #peek(byte[], int, int)} with {@code offset} == 0, and {@code length} == {@code sourceBuffer.length}
    051     *
    052     * @param sourceBuffer the buffer to compare against
    053     * @return true if the next bytes are as given
    054     * @throws IOException Refilling the buffer failed.
    055     */
    056    public boolean peek(final byte[] sourceBuffer) throws IOException {
    057        Objects.requireNonNull(sourceBuffer, "sourceBuffer");
    058        return peek(sourceBuffer, 0, sourceBuffer.length);
    059    }
    060
    061    /**
    062     * Returns whether the next bytes in the buffer are as given by {@code sourceBuffer}, {code offset}, and
    063     * {@code length}.
    064     *
    065     * @param sourceBuffer the buffer to compare against
    066     * @param offset the start offset
    067     * @param length the length to compare
    068     * @return true if the next bytes in the buffer are as given
    069     * @throws IOException if there is a problem calling fillBuffer()
    070     */
    071    public boolean peek(final byte[] sourceBuffer, final int offset, final int length) throws IOException {
    072        Objects.requireNonNull(sourceBuffer, "sourceBuffer");
    073        if (sourceBuffer.length > bufferSize) {
    074            throw new IllegalArgumentException("Peek request size of " + sourceBuffer.length
    075                + " bytes exceeds buffer size of " + bufferSize + " bytes");
    076        }
    077        if (buffer.getCurrentNumberOfBytes() < sourceBuffer.length) {
    078            fillBuffer();
    079        }
    080        return buffer.peek(sourceBuffer, offset, length);
    081    }
    082}