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 }