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    }