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BitTorrent Client Library (Core)
There is a newer version: 1.10
/*
 * 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.service;

import bt.BtException;
import bt.net.PeerId;
import bt.tracker.SecretKey;
import com.google.inject.Inject;

import java.util.Optional;
import java.util.Random;

/**
 *Note that this class implements a service.
 * Hence, is not a part of the public API and is a subject to change.
 */
public class VersionAwareIdentityService implements IdentityService {

    private final PeerId peerId;

    @Inject
    public VersionAwareIdentityService(ApplicationService applicationService) {
        peerId = buildPeerId(buildVersionPrefix(applicationService.getVersion()));
    }

    private byte[] buildVersionPrefix(Version version) {

        int major = version.getMajor();
        if (major > Byte.MAX_VALUE) {
            throw new BtException("Invalid major version: " + major);
        }

        int minor = version.getMinor();
        if (minor > Byte.MAX_VALUE) {
            throw new BtException("Invalid major version: " + minor);
        }

        boolean snapshot = version.isSnapshot();
        return new byte[]{'-','B','t', (byte) major, (byte) minor,0, (byte) (snapshot? 1 : 0),'-'};
    }

    protected PeerId buildPeerId(byte[] versionPrefix) {

        if (versionPrefix.length >= PeerId.length()) {
            throw new IllegalArgumentException("Prefix is too long: " + versionPrefix.length);
        }

        byte[] tail = new byte[PeerId.length() - versionPrefix.length];
        Random random = new Random(System.currentTimeMillis());
        random.nextBytes(tail);

        byte[] peerId = new byte[PeerId.length()];
        System.arraycopy(versionPrefix, 0, peerId, 0, versionPrefix.length);
        System.arraycopy(tail, 0, peerId, versionPrefix.length, tail.length);
        return PeerId.fromBytes(peerId);
    }

    @Override
    public PeerId getLocalPeerId() {
        return peerId;
    }

    @Override
    public Optional getSecretKey() {
        return Optional.empty();
    }
}