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JmDNS is a Java implementation of multi-cast DNS and can be used for service registration and discovery in local area networks. JmDNS is fully compatible with Apple's Bonjour. The project was originally started in December 2002 by Arthur van Hoff at Strangeberry. In November 2003 the project was moved to SourceForge, and the name was changed from JRendezvous to JmDNS for legal reasons. Many thanks to Stuart Cheshire for help and moral support.

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// Copyright 2003-2005 Arthur van Hoff, Rick Blair
// Licensed under Apache License version 2.0
// Original license LGPL

package javax.jmdns.impl.tasks.resolver;

import java.io.IOException;

import javax.jmdns.impl.DNSEntry;
import javax.jmdns.impl.DNSOutgoing;
import javax.jmdns.impl.DNSQuestion;
import javax.jmdns.impl.DNSRecord;
import javax.jmdns.impl.JmDNSImpl;
import javax.jmdns.impl.ServiceInfoImpl;
import javax.jmdns.impl.constants.DNSRecordClass;
import javax.jmdns.impl.constants.DNSRecordType;

/**
 * The ServiceInfoResolver queries up to three times consecutively for a service info, and then removes itself from the timer.
 * 
 * The ServiceInfoResolver will run only if JmDNS is in state ANNOUNCED. REMIND: Prevent having multiple service resolvers for the same info in the timer queue.
 */
public class ServiceInfoResolver extends DNSResolverTask {

    private final ServiceInfoImpl _info;

    public ServiceInfoResolver(JmDNSImpl jmDNSImpl, ServiceInfoImpl info) {
        super(jmDNSImpl);
        this._info = info;
        info.setDns(this.getDns());
        this.getDns().addListener(info, DNSQuestion.newQuestion(info.getQualifiedName(), DNSRecordType.TYPE_ANY, DNSRecordClass.CLASS_IN, DNSRecordClass.NOT_UNIQUE));
    }

    /*
     * (non-Javadoc)
     * @see javax.jmdns.impl.tasks.DNSTask#getName()
     */
    @Override
    public String getName() {
        return "ServiceInfoResolver(" + (this.getDns() != null ? this.getDns().getName() : "") + ")";
    }

    /*
     * (non-Javadoc)
     * @see java.util.TimerTask#cancel()
     */
    @Override
    public boolean cancel() {
        // We should not forget to remove the listener
        boolean result = super.cancel();
        if (!_info.isPersistent()) {
            this.getDns().removeListener(_info);
        }
        return result;
    }

    /*
     * (non-Javadoc)
     * @see javax.jmdns.impl.tasks.Resolver#addAnswers(javax.jmdns.impl.DNSOutgoing)
     */
    @Override
    protected DNSOutgoing addAnswers(DNSOutgoing out) throws IOException {
        DNSOutgoing newOut = out;
        if (!_info.hasData()) {
            long now = System.currentTimeMillis();
            newOut = this.addAnswer(newOut, (DNSRecord) this.getDns().getCache().getDNSEntry(_info.getQualifiedName(), DNSRecordType.TYPE_SRV, DNSRecordClass.CLASS_IN), now);
            newOut = this.addAnswer(newOut, (DNSRecord) this.getDns().getCache().getDNSEntry(_info.getQualifiedName(), DNSRecordType.TYPE_TXT, DNSRecordClass.CLASS_IN), now);
            if (_info.getServer().length() > 0) {
                for (DNSEntry addressEntry : this.getDns().getCache().getDNSEntryList(_info.getServer(), DNSRecordType.TYPE_A, DNSRecordClass.CLASS_IN)) {
                    newOut = this.addAnswer(newOut, (DNSRecord) addressEntry, now);
                }
                for (DNSEntry addressEntry : this.getDns().getCache().getDNSEntryList(_info.getServer(), DNSRecordType.TYPE_AAAA, DNSRecordClass.CLASS_IN)) {
                    newOut = this.addAnswer(newOut, (DNSRecord) addressEntry, now);
                }
            }
        }
        return newOut;
    }

    /*
     * (non-Javadoc)
     * @see javax.jmdns.impl.tasks.Resolver#addQuestions(javax.jmdns.impl.DNSOutgoing)
     */
    @Override
    protected DNSOutgoing addQuestions(DNSOutgoing out) throws IOException {
        DNSOutgoing newOut = out;
        if (!_info.hasData()) {
            newOut = this.addQuestion(newOut, DNSQuestion.newQuestion(_info.getQualifiedName(), DNSRecordType.TYPE_SRV, DNSRecordClass.CLASS_IN, DNSRecordClass.NOT_UNIQUE));
            newOut = this.addQuestion(newOut, DNSQuestion.newQuestion(_info.getQualifiedName(), DNSRecordType.TYPE_TXT, DNSRecordClass.CLASS_IN, DNSRecordClass.NOT_UNIQUE));
            if (_info.getServer().length() > 0) {
                newOut = this.addQuestion(newOut, DNSQuestion.newQuestion(_info.getServer(), DNSRecordType.TYPE_A, DNSRecordClass.CLASS_IN, DNSRecordClass.NOT_UNIQUE));
                newOut = this.addQuestion(newOut, DNSQuestion.newQuestion(_info.getServer(), DNSRecordType.TYPE_AAAA, DNSRecordClass.CLASS_IN, DNSRecordClass.NOT_UNIQUE));
            }
        }
        return newOut;
    }

    /*
     * (non-Javadoc)
     * @see javax.jmdns.impl.tasks.Resolver#description()
     */
    @Override
    protected String description() {
        return "querying service info: " + (_info != null ? _info.getQualifiedName() : "null");
    }

}