001// Copyright 2005 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.tapestry.record;
016
017import java.io.BufferedInputStream;
018import java.io.BufferedOutputStream;
019import java.io.ByteArrayInputStream;
020import java.io.ByteArrayOutputStream;
021import java.io.IOException;
022import java.io.InputStream;
023import java.io.ObjectInputStream;
024import java.io.ObjectOutputStream;
025import java.util.ArrayList;
026import java.util.Collections;
027import java.util.Iterator;
028import java.util.List;
029import java.util.zip.GZIPInputStream;
030import java.util.zip.GZIPOutputStream;
031
032import org.apache.commons.codec.binary.Base64;
033import org.apache.hivemind.ApplicationRuntimeException;
034import org.apache.hivemind.ClassResolver;
035import org.apache.hivemind.HiveMind;
036import org.apache.hivemind.util.Defense;
037import org.apache.tapestry.util.io.ResolvingObjectInputStream;
038import org.apache.tapestry.util.io.TeeOutputStream;
039
040/**
041 * Responsible for converting lists of {@link org.apache.tapestry.record.PropertyChange}s back and
042 * forth to a URL safe encoded string.
043 * <p>
044 * A possible improvement would be to encode the binary data with encryption both on and off, and
045 * select the shortest (prefixing with a character that identifies whether encryption should be used
046 * to decode).
047 * 
048 * @author Howard M. Lewis Ship
049 * @since 4.0
050 */
051public class PersistentPropertyDataEncoderImpl implements PersistentPropertyDataEncoder
052{
053    private ClassResolver _classResolver;
054
055    /**
056     * Prefix on the MIME encoding that indicates that the encoded data is not encoded.
057     */
058
059    public static final String BYTESTREAM_PREFIX = "B";
060
061    /**
062     * Prefix on the MIME encoding that indicates that the encoded data is encoded with GZIP.
063     */
064
065    public static final String GZIP_BYTESTREAM_PREFIX = "Z";
066
067    public String encodePageChanges(List changes)
068    {
069        Defense.notNull(changes, "changes");
070
071        if (changes.isEmpty())
072            return "";
073
074        try
075        {
076            ByteArrayOutputStream bosPlain = new ByteArrayOutputStream();
077            ByteArrayOutputStream bosCompressed = new ByteArrayOutputStream();
078
079            GZIPOutputStream gos = new GZIPOutputStream(bosCompressed);
080
081            TeeOutputStream tos = new TeeOutputStream(bosPlain, gos);
082
083            ObjectOutputStream oos = new ObjectOutputStream(new BufferedOutputStream(tos));
084
085            writeChangesToStream(changes, oos);
086
087            oos.close();
088
089            boolean useCompressed = bosCompressed.size() < bosPlain.size();
090
091            byte[] data = useCompressed ? bosCompressed.toByteArray() : bosPlain.toByteArray();
092
093            byte[] encoded = Base64.encodeBase64(data);
094
095            String prefix = useCompressed ? GZIP_BYTESTREAM_PREFIX : BYTESTREAM_PREFIX;
096
097            return prefix + new String(encoded);
098        }
099        catch (Exception ex)
100        {
101            throw new ApplicationRuntimeException(RecordMessages.encodeFailure(ex), ex);
102        }
103    }
104
105    public List decodePageChanges(String encoded)
106    {
107        if (HiveMind.isBlank(encoded))
108            return Collections.EMPTY_LIST;
109
110        String prefix = encoded.substring(0, 1);
111
112        if (!(prefix.equals(BYTESTREAM_PREFIX) || prefix.equals(GZIP_BYTESTREAM_PREFIX)))
113            throw new ApplicationRuntimeException(RecordMessages.unknownPrefix(prefix));
114
115        try
116        {
117            // Strip off the prefix, feed that in as a MIME stream.
118
119            byte[] decoded = Base64.decodeBase64(encoded.substring(1).getBytes());
120
121            InputStream is = new ByteArrayInputStream(decoded);
122
123            if (prefix.equals(GZIP_BYTESTREAM_PREFIX))
124                is = new GZIPInputStream(is);
125
126            // I believe this is more efficient; the buffered input stream should ask the
127            // GZIP stream for large blocks of un-gzipped bytes, with should be more efficient.
128            // The object input stream will probably be looking for just a few bytes at
129            // a time. We use a resolving object input stream that knows how to find
130            // classes not normally acessible.
131
132            ObjectInputStream ois = new ResolvingObjectInputStream(_classResolver,
133                    new BufferedInputStream(is));
134
135            List result = readChangesFromStream(ois);
136
137            ois.close();
138
139            return result;
140        }
141        catch (Exception ex)
142        {
143            throw new ApplicationRuntimeException(RecordMessages.decodeFailure(ex), ex);
144        }
145    }
146
147    private void writeChangesToStream(List changes, ObjectOutputStream oos) throws IOException
148    {
149        oos.writeInt(changes.size());
150
151        Iterator i = changes.iterator();
152        while (i.hasNext())
153        {
154            PropertyChange pc = (PropertyChange) i.next();
155
156            String componentPath = pc.getComponentPath();
157            String propertyName = pc.getPropertyName();
158            Object value = pc.getNewValue();
159
160            oos.writeBoolean(componentPath != null);
161
162            if (componentPath != null)
163                oos.writeUTF(componentPath);
164
165            oos.writeUTF(propertyName);
166            oos.writeObject(value);
167        }
168    }
169
170    private List readChangesFromStream(ObjectInputStream ois) throws IOException,
171            ClassNotFoundException
172    {
173        List result = new ArrayList();
174
175        int count = ois.readInt();
176
177        for (int i = 0; i < count; i++)
178        {
179            boolean hasPath = ois.readBoolean();
180            String componentPath = hasPath ? ois.readUTF() : null;
181            String propertyName = ois.readUTF();
182            Object value = ois.readObject();
183
184            PropertyChangeImpl pc = new PropertyChangeImpl(componentPath, propertyName, value);
185
186            result.add(pc);
187        }
188
189        return result;
190    }
191
192    public void setClassResolver(ClassResolver resolver)
193    {
194        _classResolver = resolver;
195    }
196}