/*

 * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package sun.security.ssl;

import java.io.IOException;

import javax.net.ssl.SSLProtocolException;

/*

 * [RFC6066] TLS specifies a fixed maximum plaintext fragment length of

 * 2^14 bytes.  It may be desirable for constrained clients to negotiate

 * a smaller maximum fragment length due to memory limitations or bandwidth

 * limitations.

 *

 * In order to negotiate smaller maximum fragment lengths, clients MAY

 * include an extension of type "max_fragment_length" in the (extended)

 * client hello.  The "extension_data" field of this extension SHALL

 * contain:

 *

 *    enum{

 *        2^9(1), 2^10(2), 2^11(3), 2^12(4), (255)

 *    } MaxFragmentLength;

 *

 * whose value is the desired maximum fragment length.

 */

final class MaxFragmentLengthExtension extends HelloExtension {

    private static final int MAX_FRAGMENT_LENGTH_512  = 1;      // 2^9

    private static final int MAX_FRAGMENT_LENGTH_1024 = 2;      // 2^10

    private static final int MAX_FRAGMENT_LENGTH_2048 = 3;      // 2^11

    private static final int MAX_FRAGMENT_LENGTH_4096 = 4;      // 2^12

    final int maxFragmentLength;

    MaxFragmentLengthExtension(int fragmentSize) {

        super(ExtensionType.EXT_MAX_FRAGMENT_LENGTH);

        if (fragmentSize < 1024) {

            maxFragmentLength = MAX_FRAGMENT_LENGTH_512;

        } else if (fragmentSize < 2048) {

            maxFragmentLength = MAX_FRAGMENT_LENGTH_1024;

        } else if (fragmentSize < 4096) {

            maxFragmentLength = MAX_FRAGMENT_LENGTH_2048;

        } else {

            maxFragmentLength = MAX_FRAGMENT_LENGTH_4096;

        }

    }

    MaxFragmentLengthExtension(HandshakeInStream s, int len)

                throws IOException {

        super(ExtensionType.EXT_MAX_FRAGMENT_LENGTH);

        // check the extension length

        if (len != 1) {

            throw new SSLProtocolException("Invalid " + type + " extension");

        }

        maxFragmentLength = s.getInt8();

        if ((maxFragmentLength > 4) || (maxFragmentLength < 1)) {

            throw new SSLProtocolException("Invalid " + type + " extension");

        }

    }

    // Length of the encoded extension, including the type and length fields

    @Override

    int length() {

        return 5;               // 4: extension type and length fields

                                // 1: MaxFragmentLength field

    }

    @Override

    void send(HandshakeOutStream s) throws IOException {

        s.putInt16(type.id);

        s.putInt16(1);

        s.putInt8(maxFragmentLength);

    }

    int getMaxFragLen() {

        switch (maxFragmentLength) {

            case MAX_FRAGMENT_LENGTH_512:

                return 512;

            case MAX_FRAGMENT_LENGTH_1024:

                return 1024;

            case MAX_FRAGMENT_LENGTH_2048:

                return 2048;

            case MAX_FRAGMENT_LENGTH_4096:

                return 4096;

        }

        // unlikely to happen

        return -1;

    }

    static boolean needFragLenNego(int fragmentSize) {

        return (fragmentSize > 0) && (fragmentSize <= 4096);

    }

    static int getValidMaxFragLen(int fragmentSize) {

        if (fragmentSize < 1024) {

            return 512;

        } else if (fragmentSize < 2048) {

            return 1024;

        } else if (fragmentSize < 4096) {

            return 2048;

        } else if (fragmentSize == 4096) {

            return 4096;

        } else {

            return 16384;

        }

    }

    @Override

    public String toString() {

        return "Extension " + type + ", max_fragment_length: " +

                "(2^" + (maxFragmentLength + 8) + ")";

    }

}