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jRTPS - An implementation of RTPS protocol by OMG
There is a newer version: 1.5.1
package net.sf.jrtps.message;

import net.sf.jrtps.transport.RTPSByteBuffer;
import net.sf.jrtps.types.EntityId;
import net.sf.jrtps.types.SequenceNumber;

/**
 * This message is sent from an RTPS Writer to an RTPS Reader to communicate the
 * sequence numbers of changes that the Writer has available.
 * 
 * see 8.3.7.5
 * 
 * @author mcr70
 */
public class Heartbeat extends SubMessage {
    public static final int KIND = 0x07;

    private EntityId readerId;
    private EntityId writerId;
    private SequenceNumber firstSN;
    private SequenceNumber lastSN;
    private int count;

    public Heartbeat(EntityId readerId, EntityId writerId, long firstSeqNum, long lastSeqNum, int count) {
        super(new SubMessageHeader(KIND));

        this.readerId = readerId;
        this.writerId = writerId;
        this.count = count;
        firstSN = new SequenceNumber(firstSeqNum);
        lastSN = new SequenceNumber(lastSeqNum);

        header.flags |= 2; // set FinalFlag. No response needed.
    }

    Heartbeat(SubMessageHeader smh, RTPSByteBuffer bb) {
        super(smh);

        readMessage(bb);
    }

    /**
     * Appears in the Submessage header flags. Indicates whether the Reader is
     * required to respond to the Heartbeat or if it is just an advisory
     * heartbeat. If finalFlag is set, Reader is not required to respond with
     * AckNack.
     * 
     * @return true if final flag is set and reader is not required to respond
     */
    public boolean finalFlag() {
        return (header.flags & 0x2) != 0;
    }

    /**
     * Sets the finalFlag to given value.
     * 
     * @param flag
     */
    public void finalFlag(boolean flag) {
        if (flag) {
            header.flags |= 0x2;
        } else {
            header.flags &= ~0x2;
        }
    }

    /**
     * Appears in the Submessage header flags. Indicates that the DDS DataWriter
     * associated with the RTPS Writer of the message has manually asserted its
     * LIVELINESS.
     * 
     * @return true, if liveliness flag is set
     */
    public boolean livelinessFlag() {
        return (header.flags & 0x4) != 0;
    }

    /**
     * Sets the livelinessFlag to given value
     * 
     * @param livelinessFlag
     */
    public void livelinessFlag(boolean livelinessFlag) {
        if (livelinessFlag) {
            header.flags |= 0x4;
        } else {
            header.flags &= ~0x4;
        }
    }

    /**
     * Identifies the Reader Entity that is being informed of the availability
     * of a set of sequence numbers. Can be set to ENTITYID_UNKNOWN to indicate
     * all readers for the writer that sent the message.
     */
    public EntityId getReaderId() {
        return readerId;
    }

    /**
     * Identifies the Writer Entity to which the range of sequence numbers
     * applies.
     */
    public EntityId getWriterId() {
        return writerId;
    }

    /**
     * Identifies the first (lowest) sequence number that is available in the
     * Writer.
     */
    public long getFirstSequenceNumber() {
        return firstSN.getAsLong();
    }

    /**
     * Identifies the last (highest) sequence number that is available in the
     * Writer.
     */
    public long getLastSequenceNumber() {
        return lastSN.getAsLong();
    }

    /**
     * A counter that is incremented each time a new Heartbeat message is sent.
     * Provides the means for a Reader to detect duplicate Heartbeat messages
     * that can result from the presence of redundant communication paths.
     */
    public int getCount() {
        return count;
    }

    private void readMessage(RTPSByteBuffer bb) {
        this.readerId = EntityId.readEntityId(bb);
        this.writerId = EntityId.readEntityId(bb);
        this.firstSN = new SequenceNumber(bb);
        this.lastSN = new SequenceNumber(bb);

        this.count = bb.read_long();
    }

    @Override
    public void writeTo(RTPSByteBuffer bb) {
        readerId.writeTo(bb);
        writerId.writeTo(bb);
        firstSN.writeTo(bb);
        lastSN.writeTo(bb);

        bb.write_long(count);
    }

    public String toString() {
        return super.toString() + " #" + count + ", " + readerId + ", " + writerId + ", " + firstSN + ", " + lastSN
                + ", F:" + finalFlag() + ", L:" + livelinessFlag();
    }
}