1 /*
2 * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package sun.security.ssl;
27
28 import java.io.IOException;
29 import javax.net.ssl.SSLProtocolException;
30
31 /*
32 * [RFC6066] TLS specifies a fixed maximum plaintext fragment length of
33 * 2^14 bytes. It may be desirable for constrained clients to negotiate
34 * a smaller maximum fragment length due to memory limitations or bandwidth
35 * limitations.
36 *
37 * In order to negotiate smaller maximum fragment lengths, clients MAY
38 * include an extension of type "max_fragment_length" in the (extended)
39 * client hello. The "extension_data" field of this extension SHALL
40 * contain:
41 *
42 * enum{
43 * 2^9(1), 2^10(2), 2^11(3), 2^12(4), (255)
44 * } MaxFragmentLength;
45 *
46 * whose value is the desired maximum fragment length.
47 */
48 final class MaxFragmentLengthExtension extends HelloExtension {
49
50 private static final int MAX_FRAGMENT_LENGTH_512 = 1; // 2^9
51 private static final int MAX_FRAGMENT_LENGTH_1024 = 2; // 2^10
52 private static final int MAX_FRAGMENT_LENGTH_2048 = 3; // 2^11
53 private static final int MAX_FRAGMENT_LENGTH_4096 = 4; // 2^12
54
55 final int maxFragmentLength;
56
57 MaxFragmentLengthExtension(int fragmentSize) {
58 super(ExtensionType.EXT_MAX_FRAGMENT_LENGTH);
59
60 if (fragmentSize < 1024) {
61 maxFragmentLength = MAX_FRAGMENT_LENGTH_512;
62 } else if (fragmentSize < 2048) {
63 maxFragmentLength = MAX_FRAGMENT_LENGTH_1024;
64 } else if (fragmentSize < 4096) {
65 maxFragmentLength = MAX_FRAGMENT_LENGTH_2048;
66 } else {
67 maxFragmentLength = MAX_FRAGMENT_LENGTH_4096;
68 }
69 }
70
71 MaxFragmentLengthExtension(HandshakeInStream s, int len)
72 throws IOException {
73 super(ExtensionType.EXT_MAX_FRAGMENT_LENGTH);
74
75 // check the extension length
76 if (len != 1) {
77 throw new SSLProtocolException("Invalid " + type + " extension");
78 }
79
80 maxFragmentLength = s.getInt8();
81 if ((maxFragmentLength > 4) || (maxFragmentLength < 1)) {
82 throw new SSLProtocolException("Invalid " + type + " extension");
83 }
84 }
85
86 // Length of the encoded extension, including the type and length fields
87 @Override
88 int length() {
89 return 5; // 4: extension type and length fields
90 // 1: MaxFragmentLength field
91 }
92
93 @Override
94 void send(HandshakeOutStream s) throws IOException {
95 s.putInt16(type.id);
96 s.putInt16(1);
97 s.putInt8(maxFragmentLength);
98 }
99
100 int getMaxFragLen() {
101 switch (maxFragmentLength) {
102 case MAX_FRAGMENT_LENGTH_512:
103 return 512;
104 case MAX_FRAGMENT_LENGTH_1024:
105 return 1024;
106 case MAX_FRAGMENT_LENGTH_2048:
107 return 2048;
108 case MAX_FRAGMENT_LENGTH_4096:
109 return 4096;
110 }
111
112 // unlikely to happen
113 return -1;
114 }
115
116 static boolean needFragLenNego(int fragmentSize) {
117 return (fragmentSize > 0) && (fragmentSize <= 4096);
118 }
119
120 static int getValidMaxFragLen(int fragmentSize) {
121 if (fragmentSize < 1024) {
122 return 512;
123 } else if (fragmentSize < 2048) {
124 return 1024;
125 } else if (fragmentSize < 4096) {
126 return 2048;
127 } else if (fragmentSize == 4096) {
128 return 4096;
129 } else {
130 return 16384;
131 }
132 }
133
134 @Override
135 public String toString() {
136 return "Extension " + type + ", max_fragment_length: " +
137 "(2^" + (maxFragmentLength + 8) + ")";
138 }
139 }