Source code: org/apache/batik/ext/awt/image/spi/MagicNumberRegistryEntry.java
1 /*
2
3 Copyright 2001,2003 The Apache Software Foundation
4
5 Licensed under the Apache License, Version 2.0 (the "License");
6 you may not use this file except in compliance with the License.
7 You may obtain a copy of the License at
8
9 http://www.apache.org/licenses/LICENSE-2.0
10
11 Unless required by applicable law or agreed to in writing, software
12 distributed under the License is distributed on an "AS IS" BASIS,
13 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 See the License for the specific language governing permissions and
15 limitations under the License.
16
17 */
18 package org.apache.batik.ext.awt.image.spi;
19
20 import java.io.IOException;
21 import java.io.InputStream;
22 import java.io.StreamCorruptedException;
23
24 /**
25 * This Image tag registry entry is built around the notion of magic
26 * numbers. These are strings of bytes that are at a well known
27 * location in the input stream (often the start).
28 *
29 * This base class can handle the compatiblity check based on a list
30 * of Magic Numbers that correspond to your format (Some formats have
31 * multiple magic numbers associated with them).
32 */
33 public abstract class MagicNumberRegistryEntry
34 extends AbstractRegistryEntry
35 implements StreamRegistryEntry {
36
37 public static final float PRIORITY = 1000;
38
39 /**
40 * Inner class that represents one magic number. Simply consists
41 * of an offset in bytes from the start of the file, and a byte
42 * array that must match.
43 */
44 public static class MagicNumber {
45 int offset;
46 byte [] magicNumber;
47 byte [] buffer;
48
49 /**
50 * Constructor.
51 * @param offset the location of the magic number in file.
52 * @param magicNumber the sequence of bytes that must match.
53 */
54 public MagicNumber(int offset, byte[]magicNumber) {
55 this.offset = offset;
56 this.magicNumber = (byte[])magicNumber.clone();
57 buffer = new byte[magicNumber.length];
58 }
59
60 /**
61 * Returns the maximum number of bytes that will be read for
62 * this magic number compairison.
63 */
64 int getReadlimit() {
65 return offset+magicNumber.length;
66 }
67
68 /**
69 * Performs the check of is.
70 */
71 boolean isMatch(InputStream is)
72 throws StreamCorruptedException {
73 int idx = 0;
74 is.mark(getReadlimit());
75 try {
76 // Skip to the offset location.
77 while (idx < offset) {
78 int rn = (int)is.skip(offset-idx);
79 if (rn == -1) return false;
80 idx += rn;
81 }
82
83 idx = 0;
84 while (idx < buffer.length) {
85 int rn = is.read(buffer, idx, buffer.length-idx);
86 if (rn == -1) return false;
87 idx += rn;
88 }
89
90 for (int i=0; i<magicNumber.length; i++) {
91 if (magicNumber[i] != buffer[i])
92 return false;
93 }
94 } catch (IOException ioe) {
95 return false;
96 } finally {
97 try {
98 // Make sure we always put back what we have read.
99 // If this throws an IOException then the current
100 // stream should be closed an reopend by the registry.
101 is.reset();
102 } catch (IOException ioe) {
103 throw new StreamCorruptedException(ioe.getMessage());
104 }
105 }
106 return true;
107 }
108 }
109
110 /** The list of magic numbers associated with this entry */
111 MagicNumber [] magicNumbers;
112
113 /**
114 * Constructor, simplifies construction of entry when only
115 * one extension and one magic number is required.
116 * @param name Format Name
117 * @param ext Standard extension
118 * @param offset Offset of magic number
119 * @param magicNumber byte array to match.
120 */
121 public MagicNumberRegistryEntry(String name,
122 String ext,
123 String mimeType,
124 int offset, byte[]magicNumber) {
125 super(name, PRIORITY, ext, mimeType);
126 magicNumbers = new MagicNumber[1];
127 magicNumbers[0] = new MagicNumber(offset, magicNumber);
128 }
129
130 /**
131 * Constructor, simplifies construction of entry when only
132 * one extension is required.
133 * @param name Format Name
134 * @param ext Standard extension
135 * @param magicNumbers Array of magic numbers any of which can match.
136 */
137 public MagicNumberRegistryEntry(String name,
138 String ext,
139 String mimeType,
140 MagicNumber [] magicNumbers) {
141 super(name, PRIORITY, ext, mimeType);
142 this.magicNumbers = magicNumbers;
143 }
144
145 /**
146 * Constructor, simplifies construction of entry when only
147 * one magic number is required.
148 * @param name Format Name
149 * @param exts Standard set of extensions
150 * @param offset Offset of magic number
151 * @param magicNumber byte array to match.
152 */
153 public MagicNumberRegistryEntry(String name,
154 String [] exts,
155 String [] mimeTypes,
156 int offset, byte[]magicNumber) {
157 super(name, PRIORITY, exts, mimeTypes);
158 magicNumbers = new MagicNumber[1];
159 magicNumbers[0] = new MagicNumber(offset, magicNumber);
160 }
161
162 /**
163 * Constructor
164 * @param name Format Name
165 * @param exts Standard set of extensions
166 * @param magicNumbers array of magic numbers any of which can match.
167 */
168 public MagicNumberRegistryEntry(String name,
169 String [] exts,
170 String [] mimeTypes,
171 MagicNumber [] magicNumbers) {
172 super(name, PRIORITY, exts, mimeTypes);
173 this.magicNumbers = magicNumbers;
174 }
175
176 /**
177 * Constructor, allows for overriding the default priority of
178 * magic number entries. This should be needed very rarely since
179 * magic number checks are fairly relyable and hence aren't usually
180 * sensative to order issues.
181 * @param name Format Name
182 * @param exts Standard set of extensions
183 * @param magicNumbers array of magic numbers any of which can match.
184 * @param priority The priority of this entry (1000 is baseline)
185 */
186 public MagicNumberRegistryEntry(String name,
187 String [] exts,
188 String [] mimeTypes,
189 MagicNumber [] magicNumbers,
190 float priority) {
191 super(name, priority, exts, mimeTypes);
192 this.magicNumbers = magicNumbers;
193 }
194
195 /**
196 * Returns the maximume read ahead needed for all magic numbers.
197 */
198 public int getReadlimit() {
199 int maxbuf = 0;
200 for (int i=0; i<magicNumbers.length; i++) {
201 int req = magicNumbers[i].getReadlimit();
202 if (req > maxbuf) maxbuf = req;
203 }
204 return maxbuf;
205 }
206
207 /**
208 * Check if the stream contains an image that can be
209 * handled by this format handler
210 */
211 public boolean isCompatibleStream(InputStream is)
212 throws StreamCorruptedException {
213 for (int i=0; i<magicNumbers.length; i++) {
214 if (magicNumbers[i].isMatch(is))
215 return true;
216 }
217
218 return false;
219 }
220 }