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    }