package org.masukomi.aspirin.core.dns;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.Vector;
import javax.mail.URLName;
import org.masukomi.aspirin.core.AspirinInternal;
import org.xbill.DNS.Lookup;
import org.xbill.DNS.MXRecord;
import org.xbill.DNS.Record;
import org.xbill.DNS.TextParseException;
import org.xbill.DNS.Type;
/**
* This object checks all DNS contents and get MX records for emails.
* TODO Create DNS cache
*
* @author Laszlo Solova
*
*/
public class DnsResolver {
public static final String SMTP_PROTOCOL_PREFIX = "smtp://";
/**
* <p>This method gives back the host name(s) where we can send the email.
* It is copied from it's original place in RemoteDelivery object.</p>
*
* <p>First time we ask DNS to find MX record(s) of a domain name. If no MX
* records are found, we check the upper level domains (if exists). At last
* we try to get the domain A record, because the MX server could be same as
* the normal domain handler server. If only upper level domain has MX
* record then we append the A record of original hostname (if exists) as
* first element of record collection. If none of these tries are
* successful, we give back an empty collection.</p>
*
* Special Thanks to Tim Motika (tmotika at ionami dot com) for
* his reworking of this method.
*
* @param hostName We search the associated MX server of this hostname.
* @return Collection of URLName objects. If no MX server found, then it
* gives back an empty collection.
*
*/
public static Collection<URLName> getMXRecordsForHost(String hostName) {
Vector<URLName> recordsColl = null;
try {
boolean foundOriginalMX = true;
Record[] records = new Lookup(hostName, Type.MX).run();
/*
* Sometimes we should send an email to a subdomain which does not
* have own MX record and MX server. At this point we should find an
* upper level domain and server where we can deliver our email.
*
* Example: subA.subB.domain.name has not own MX record and
* subB.domain.name is the mail exchange master of the subA domain
* too.
*/
if( records == null || records.length == 0 )
{
foundOriginalMX = false;
String upperLevelHostName = hostName;
while( records == null &&
upperLevelHostName.indexOf(".") != upperLevelHostName.lastIndexOf(".") &&
upperLevelHostName.lastIndexOf(".") != -1
)
{
upperLevelHostName = upperLevelHostName.substring(upperLevelHostName.indexOf(".")+1);
records = new Lookup(upperLevelHostName, Type.MX).run();
}
}
if( records != null )
{
// Sort in MX priority (higher number is lower priority)
Arrays.sort(records, new Comparator<Record>() {
@Override
public int compare(Record arg0, Record arg1) {
return ((MXRecord)arg0).getPriority()-((MXRecord)arg1).getPriority();
}
});
// Create records collection
recordsColl = new Vector<URLName>(records.length);
for (int i = 0; i < records.length; i++)
{
MXRecord mx = (MXRecord) records[i];
String targetString = mx.getTarget().toString();
URLName uName = new URLName(
SMTP_PROTOCOL_PREFIX +
targetString.substring(0, targetString.length() - 1)
);
recordsColl.add(uName);
}
}else
{
foundOriginalMX = false;
recordsColl = new Vector<URLName>();
}
/*
* If we found no MX record for the original hostname (the upper
* level domains does not matter), then we add the original domain
* name (identified with an A record) to the record collection,
* because the mail exchange server could be the main server too.
*
* We append the A record to the first place of the record
* collection, because the standard says if no MX record found then
* we should to try send email to the server identified by the A
* record.
*/
if( !foundOriginalMX )
{
Record[] recordsTypeA = new Lookup(hostName, Type.A).run();
if (recordsTypeA != null && recordsTypeA.length > 0)
{
recordsColl.add(0, new URLName(SMTP_PROTOCOL_PREFIX + hostName));
}
}
} catch (TextParseException e) {
AspirinInternal.getConfiguration().getLogger().warn("DnsResolver.getMXRecordsForHost(): Failed get MX record for host '"+hostName+"'.",e);
}
return recordsColl;
}
}