1 /*******************************************************************************
2  * Copyright (c) 2000, 2011 IBM Corporation and others.
3  *
4  * This program and the accompanying materials
5  * are made available under the terms of the Eclipse Public License 2.0
6  * which accompanies this distribution, and is available at
7  * https://www.eclipse.org/legal/epl-2.0/
8  *
9  * SPDX-License-Identifier: EPL-2.0
10  *
11  * Contributors:
12  *     IBM Corporation - initial API and implementation
13  *******************************************************************************/
14 package org.eclipse.swt.internal.image;
15 
16 
17 import java.io.*;
18 
19 import org.eclipse.swt.*;
20 
21 public class PngDecodingDataStream extends InputStream {
22 	InputStream stream;
23 	byte currentByte;
24 	int nextBitIndex;
25 
26 	PngLzBlockReader lzBlockReader;
27 	int adlerValue;
28 
29 	static final int PRIME = 65521;
30 	static final int MAX_BIT = 7;
31 
PngDecodingDataStream(InputStream stream)32 PngDecodingDataStream(InputStream stream) throws IOException {
33 	super();
34 	this.stream = stream;
35 	nextBitIndex = MAX_BIT + 1;
36 	adlerValue = 1;
37 	lzBlockReader = new PngLzBlockReader(this);
38 	readCompressedDataHeader();
39 	lzBlockReader.readNextBlockHeader();
40 }
41 
42 /**
43  * This method should be called when the image decoder thinks
44  * that all of the compressed image data has been read. This
45  * method will ensure that the next data value is an end of
46  * block marker. If there are more blocks after this one,
47  * the method will read them and ensure that they are empty.
48  */
assertImageDataAtEnd()49 void assertImageDataAtEnd() throws IOException {
50 	lzBlockReader.assertCompressedDataAtEnd();
51 }
52 
53 @Override
close()54 public void close() throws IOException {
55 	assertImageDataAtEnd();
56 	checkAdler();
57 }
58 
getNextIdatBits(int length)59 int getNextIdatBits(int length) throws IOException {
60 	int value = 0;
61 	for (int i = 0; i < length; i++) {
62 		value |= (getNextIdatBit() << i);
63 	}
64 	return value;
65 }
66 
getNextIdatBit()67 int getNextIdatBit() throws IOException {
68 	if (nextBitIndex > MAX_BIT) {
69 		currentByte = getNextIdatByte();
70 		nextBitIndex = 0;
71 	}
72 	return (currentByte & (1 << nextBitIndex)) >> nextBitIndex++;
73 }
74 
getNextIdatByte()75 byte getNextIdatByte() throws IOException {
76 	byte nextByte = (byte)stream.read();
77 	nextBitIndex = MAX_BIT + 1;
78 	return nextByte;
79 }
80 
updateAdler(byte value)81 void updateAdler(byte value) {
82 	int low = adlerValue & 0xFFFF;
83 	int high = (adlerValue >> 16) & 0xFFFF;
84 	int valueInt = value & 0xFF;
85 	low = (low + valueInt) % PRIME;
86 	high = (low + high) % PRIME;
87 	adlerValue = (high << 16) | low;
88 }
89 
90 @Override
read()91 public int read() throws IOException {
92 	byte nextDecodedByte = lzBlockReader.getNextByte();
93 	updateAdler(nextDecodedByte);
94 	return nextDecodedByte & 0xFF;
95 }
96 
97 @Override
read(byte[] buffer, int off, int len)98 public int read(byte[] buffer, int off, int len) throws IOException {
99 	for (int i = 0; i < len; i++) {
100 		int b = read();
101 		if (b == -1) return i;
102 		buffer[off + i] = (byte)b;
103 	}
104 	return len;
105 }
106 
error()107 void error() {
108 	SWT.error(SWT.ERROR_INVALID_IMAGE);
109 }
110 
readCompressedDataHeader()111 private void readCompressedDataHeader() throws IOException {
112 	byte headerByte1 = getNextIdatByte();
113 	byte headerByte2 = getNextIdatByte();
114 
115 	int number = ((headerByte1 & 0xFF) << 8) | (headerByte2 & 0xFF);
116 	if (number % 31 != 0) error();
117 
118 	int compressionMethod = headerByte1 & 0x0F;
119 	if (compressionMethod != 8) error();
120 
121 	int windowSizeHint = (headerByte1 & 0xF0) >> 4;
122 	if (windowSizeHint > 7) error();
123 	int windowSize = (1 << (windowSizeHint + 8));
124 	lzBlockReader.setWindowSize(windowSize);
125 
126 	int dictionary = (headerByte2 & (1 << 5));
127 	if (dictionary != 0) error();
128 
129 //	int compressionLevel = (headerByte2 & 0xC0) >> 6;
130 }
131 
checkAdler()132 void checkAdler() throws IOException {
133 	int storedAdler = ((getNextIdatByte() & 0xFF) << 24)
134 		| ((getNextIdatByte() & 0xFF) << 16)
135 		| ((getNextIdatByte() & 0xFF) << 8)
136 		| (getNextIdatByte() & 0xFF);
137 	if (storedAdler != adlerValue) error();
138 }
139 
140 }
141