[jdev] jso api for SRV lookup

[Matt Tucker]

Veronica,

Here's a code snippet that uses JNDI to do the lookup:

Regards,
Matt

/**
 * Utilty class to perform DNS lookups.
 *
 * @author Matt Tucker
 */
public class DNSUtil {

    private static DirContext context;

    static {
        try {
            Hashtable env = new Hashtable();
            env.put("java.naming.factory.initial",
"com.sun.jndi.dns.DnsContextFactory");
            context = new InitialDirContext(env);
        }
        catch (Exception e) {
            Log.error(e);
        }
    }

    /**
     * Returns the host name and port that the specified XMPP server can
be
     * reached at for server-to-server communication. A DNS lookup for a
SRV
     * record in the form "_xmpp-server._tcp.example.com" is attempted,
according
     * to section 14.4 of RFC 3920. If that lookup fails, a lookup in
the older form
     * of "_jabber._tcp.example.com" is attempted since servers that
implement an
     * older version of the protocol may be listed using that notation.
If that
     * lookup fails as well, it's assumed that the XMPP server lives at
the
     * host resolved by a DNS lookup at the specified domain on the
default port
     * of 5269.<p>
     *
     * As an example, a lookup for "example.com" may return
"im.example.com:5269".
     *
     * @param domain the domain.
     * @return a HostAddress, which encompasses the hostname and port
that the XMPP
     *      server can be reached at for the specified domain.
     */
    public static HostAddress resolveXMPPDomain(String domain) {
        if (context == null) {
            return new HostAddress(domain, 5269);
        }
        String host = domain;
        int port = 5269;
        try {
            Attributes dnsLookup =
context.getAttributes("_xmpp-server._tcp." + domain);
            String srvRecord = (String)dnsLookup.get("SRV").get();
            String [] srvRecordEntries = srvRecord.split(" ");
            port =
Integer.parseInt(srvRecordEntries[srvRecordEntries.length-2]);
            host = srvRecordEntries[srvRecordEntries.length-1];
        }
        catch (Exception e) {
            // Attempt lookup with older "jabber" name.
            try {
                Attributes dnsLookup =
context.getAttributes("_jabber._tcp." + domain);
                String srvRecord = (String)dnsLookup.get("SRV").get();
                String [] srvRecordEntries = srvRecord.split(" ");
                port =
Integer.parseInt(srvRecordEntries[srvRecordEntries.length-2]);
                host = srvRecordEntries[srvRecordEntries.length-1];
            }
            catch (Exception e2) { }
        }
        // Host entries in DNS should end with a ".".
        if (host.endsWith(".")) {
            host = host.substring(0, host.length()-1);
        }
        return new HostAddress(domain, port);
    }

    /**
     * Encapsulates a hostname and port.
     */
    public static class HostAddress {

        private String host;
        private int port;

        private HostAddress(String host, int port) {
            this.host = host;
            this.port = port;
        }

        /**
         * Returns the hostname.
         *
         * @return the hostname.
         */
        public String getHost() {
            return host;
        }

        /**
         * Returns the port.
         *
         * @return the port.
         */
        public int getPort() {
            return port;
        }

        public String toString() {
            return host + ":" + port;
        }
    }
} 

> -----Original Message-----
> From: jdev-bounces at jabber.org 
> [mailto:jdev-bounces at jabber.org] On Behalf Of Veronica Chau
> Sent: Wednesday, February 02, 2005 2:29 PM
> To: jdev at jabber.org
> Subject: [jdev] jso api for SRV lookup
> 
> Is there any api available to do the DNS SRV lookup?
> 
> Thanks.
> 
>       Veronica
> 
> 
> 
> 
> 
> 
> 
> 
> 	
> 		
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