    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one
    003     * or more contributor license agreements.  See the NOTICE file
    004     * distributed with this work for additional information
    005     * regarding copyright ownership.  The ASF licenses this file
    006     * to you under the Apache License, Version 2.0 (the
    007     * "License"); you may not use this file except in compliance
    008     * with the License.  You may obtain a copy of the License at
    009     *
    010     * http://www.apache.org/licenses/LICENSE-2.0
    011     *
    012     * Unless required by applicable law or agreed to in writing,
    013     * software distributed under the License is distributed on an
    014     * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    015     * KIND, either express or implied.  See the License for the
    016     * specific language governing permissions and limitations
    017     * under the License.
    018     */
    019    package org.apache.commons.compress.compressors.gzip;
    020
    021    import java.io.IOException;
    022    import java.io.InputStream;
    023    import java.util.zip.GZIPInputStream;
    024
    025    import org.apache.commons.compress.compressors.CompressorInputStream;
    026
    027    /**
    028     * Implements the "gz" compression format as an input stream.
    029     * This classes wraps the standard java classes for working with gz.
    030     */
    031    public class GzipCompressorInputStream extends CompressorInputStream {
    032        /* reference to the compressed stream */
    033        private final GZIPInputStream in;
    034
    035        /**
    036         * Constructs a new GZip compressed input stream by the referenced
    037         * InputStream.
    038         *
    039         * @param inputStream the InputStream from which this object should be created of
    040         * @throws IOException if the stream could not be created
    041         */
    042        public GzipCompressorInputStream(InputStream inputStream) throws IOException {
    043            in = new GZIPInputStream(inputStream);
    044        }
    045
    046        /** {@inheritDoc} */
    047        @Override
    048        public int read() throws IOException {
    049            int read = in.read();
    050            this.count(read < 0 ? -1 : 1);
    051            return read;
    052        }
    053
    054        /**
    055         * {@inheritDoc}
    056         *
    057         * @since Apache Commons Compress 1.1
    058         */
    059        @Override
    060        public int read(byte[] b) throws IOException {
    061            int read = in.read(b);
    062            this.count(read);
    063            return read;
    064        }
    065
    066        /**
    067         * {@inheritDoc}
    068         *
    069         * @since Apache Commons Compress 1.1
    070         */
    071        @Override
    072        public int read(byte[] b, int from, int length) throws IOException {
    073            int read = in.read(b, from, length);
    074            this.count(read);
    075            return read;
    076        }
    077
    078        /**
    079         * Checks if the signature matches what is expected for a gzip file.
    080         *
    081         * @param signature
    082         *            the bytes to check
    083         * @param length
    084         *            the number of bytes to check
    085         * @return true, if this stream is a gzipped compressed stream, false otherwise
    086         *
    087         * @since Apache Commons Compress 1.1
    088         */
    089        public static boolean matches(byte[] signature, int length) {
    090
    091            if (length < 2) {
    092                return false;
    093            }
    094
    095            if (signature[0] != 31) {
    096                return false;
    097            }
    098
    099            if (signature[1] != -117) {
    100                return false;
    101            }
    102
    103            return true;
    104        }
    105
    106        /**
    107         * Closes the input stream (unless it is System.in).
    108         *
    109         * @since 1.2
    110         */
    111        @Override
    112        public void close() throws IOException {
    113            if (this.in != System.in) {
    114                this.in.close();
    115            }
    116        }
    117    }