001// Copyright 2013 The Apache Software Foundation
002//
003// Licensed under the Apache License, Version 2.0 (the "License");
004// you may not use this file except in compliance with the License.
005// You may obtain a copy of the License at
006//
007// http://www.apache.org/licenses/LICENSE-2.0
008//
009// Unless required by applicable law or agreed to in writing, software
010// distributed under the License is distributed on an "AS IS" BASIS,
011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012// See the License for the specific language governing permissions and
013// limitations under the License.
014
015package org.apache.tapestry5.internal.services.assets;
016
017import org.apache.tapestry5.commons.Resource;
018import org.apache.tapestry5.commons.util.CollectionFactory;
019import org.apache.tapestry5.services.assets.AssetChecksumGenerator;
020import org.apache.tapestry5.services.assets.StreamableResource;
021import org.apache.tapestry5.services.assets.StreamableResourceProcessing;
022import org.apache.tapestry5.services.assets.StreamableResourceSource;
023
024import java.io.IOException;
025import java.io.InputStream;
026import java.util.Map;
027import java.util.zip.Adler32;
028
029public class AssetChecksumGeneratorImpl implements AssetChecksumGenerator
030{
031
032    private final StreamableResourceSource streamableResourceSource;
033
034    private final ResourceChangeTracker tracker;
035
036    private final Map<Integer, String> cache = CollectionFactory.newConcurrentMap();
037
038    public AssetChecksumGeneratorImpl(StreamableResourceSource streamableResourceSource, ResourceChangeTracker tracker)
039    {
040        this.streamableResourceSource = streamableResourceSource;
041        this.tracker = tracker;
042
043        tracker.clearOnInvalidation(cache);
044    }
045
046    public String generateChecksum(Resource resource) throws IOException
047    {
048        StreamableResource streamable = streamableResourceSource.getStreamableResource(resource, StreamableResourceProcessing.COMPRESSION_DISABLED,
049                tracker);
050
051        return generateChecksum(streamable);
052    }
053
054    public String generateChecksum(StreamableResource resource) throws IOException
055    {
056        return cache.computeIfAbsent(resource.hashCode(), 
057                r -> {
058                    try {
059                        return toChecksum(resource.openStream());
060                    } catch (IOException e) {
061                        throw new RuntimeException(e);
062                    }
063                });
064    }
065
066    private String toChecksum(InputStream is) throws IOException
067    {
068        // Adler32 is very fast and suitable for these purposes (MD5 and SHA are slower, and
069        // are targetted at cryptographic solutions).
070        Adler32 checksum = new Adler32();
071
072        byte[] buffer = new byte[1024];
073
074        try
075        {
076            while (true)
077            {
078                int length = is.read(buffer);
079
080                if (length < 0)
081                {
082                    break;
083                }
084
085                checksum.update(buffer, 0, length);
086            }
087
088            // Reduces it down to just 32 bits which we express in hex.
089            return Long.toHexString(checksum.getValue());
090        } finally
091        {
092            is.close();
093        }
094    }
095}