    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        public int read() throws IOException {
    048            int read = in.read();
    049            this.count(read < 0 ? -1 : 1);
    050            return read;
    051        }
    052
    053        /**
    054         * {@inheritDoc}
    055         *
    056         * @since Apache Commons Compress 1.1
    057         */
    058        public int read(byte[] b) throws IOException {
    059            int read = in.read(b);
    060            this.count(read);
    061            return read;
    062        }
    063
    064        /**
    065         * {@inheritDoc}
    066         *
    067         * @since Apache Commons Compress 1.1
    068         */
    069        public int read(byte[] b, int from, int length) throws IOException {
    070            int read = in.read(b, from, length);
    071            this.count(read);
    072            return read;
    073        }
    074
    075        /**
    076         * Checks if the signature matches what is expected for a gzip file.
    077         *
    078         * @param signature
    079         *            the bytes to check
    080         * @param length
    081         *            the number of bytes to check
    082         * @return true, if this stream is a gzipped compressed stream, false otherwise
    083         *
    084         * @since Apache Commons Compress 1.1
    085         */
    086        public static boolean matches(byte[] signature, int length) {
    087
    088            if (length < 2) {
    089                return false;
    090            }
    091
    092            if (signature[0] != 31) {
    093                return false;
    094            }
    095
    096            if (signature[1] != -117) {
    097                return false;
    098            }
    099
    100            return true;
    101        }
    102
    103    }