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BitTorrent Client Library (Core)
There is a newer version: 1.7
/*
 * Copyright (c) 2016—2017 Andrei Tomashpolskiy and individual contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package bt.net.extended;

import bt.metainfo.TorrentId;
import bt.net.HandshakeHandler;
import bt.net.PeerConnection;
import bt.protocol.Handshake;
import bt.protocol.IExtendedHandshakeFactory;
import bt.protocol.extended.ExtendedHandshake;
import com.google.inject.Inject;

import java.io.IOException;

/**
 * Sets a reserved bit, indicating that
 * BEP-10: Extension Protocol is supported by the local client.
 *
 * @since 1.0
 */
public class ExtendedProtocolHandshakeHandler implements HandshakeHandler {

    private static final int EXTENDED_FLAG_BIT_INDEX = 43;

    private IExtendedHandshakeFactory extendedHandshakeFactory;

    @Inject
    public ExtendedProtocolHandshakeHandler(IExtendedHandshakeFactory extendedHandshakeFactory) {
        this.extendedHandshakeFactory = extendedHandshakeFactory;
    }

    @Override
    public void processIncomingHandshake(PeerConnection connection, Handshake peerHandshake) {
        ExtendedHandshake extendedHandshake = getHandshake(peerHandshake.getTorrentId());
        // do not send the extended handshake
        // if local client does not have any extensions turned on
        if (!extendedHandshake.getData().isEmpty()) {
            try {
                connection.postMessage(extendedHandshake);
            } catch (IOException e) {
                throw new RuntimeException("Failed to send extended handshake to peer: " + connection.getRemotePeer(), e);
            }
        }
    }

    @Override
    public void processOutgoingHandshake(Handshake handshake) {
        ExtendedHandshake extendedHandshake = getHandshake(handshake.getTorrentId());
        // do not advertise support for the extended protocol
        // if local client does not have any extensions turned on
        if (!extendedHandshake.getData().isEmpty()) {
            handshake.setReservedBit(EXTENDED_FLAG_BIT_INDEX);
        }
    }

    private ExtendedHandshake getHandshake(TorrentId torrentId) {
        return extendedHandshakeFactory.getHandshake(torrentId);
    }
}