Multicast DNS (mDNS) [RFC 6762] & DNS-Based Service Discovery (DNS-SD) [RFC6763] in Java
The Multicast DNS (mDNS) [RFC 6762] & DNS-Based Service Discovery (DNS-SD) [RFC 6763] in Java (mdnsjava) project is an extension of dnsjava (dnsjava.org) that implements Multicast DNS (mDNS) [RFC 6762] and DNS-Based Service Discovery (DNS-SD) [RFC 6763] in Java (aka. Bonjour in Java). Unlike other mDNS/DNS-SD implementations mdnsjava does not artificially bind the mDNS and DNS-SD functionality into a single API, instead treating each as a separate feature that is independent from, but related to, the other. This allows clients to use Multicast DNS (mDNS) [RFC 6762] for name resolution without having to worry about service discovery and simplifies the use of DNS-Base Service Discovery using plain old Unicast DNS (mDNS can be used as a substitiute for DNS for name resolution and DNS can be used as a substitute for mDNS for service discovery).
This project depends on:
$java -jar mdnsjava.jar
or
$java -cp mdnsjava.jar:dnsjava.jar dnssd
Command Line: dnssd <option> [parameters]
dnssd -E (Enumerate recommended registration domains)
dnssd -F (Enumerate recommended browsing domains)
dnssd -B <Type> [<Domain>] (Browse for services instances)
dnssd -L <Name> <Type> [<Domain>] (Look up a service instance)
dnssd -R <Name> <Type> <Domain> <Port> <Host> [<TXT>...] (Register a service)
dnssd -Q <FQDN> <rrtype> <rrclass> (Generic query for any record type)
dnssd -G v4/v6/v4v6 <Hostname> (Get address information for hostname)
dnssd -V (Get version of currently running daemon / system service)
$
The following are examples of mdnsjava API usage.
All domain names in mdnsjava are considered to be relative to the domain search path unless they end with a period ..
For example:
posick.net. will be treated as an absolute domain name, looking up records in the posick.net domain.posick.net will be treated as a relative domain name and will be prepended to each domain listed in the DNS search path, ex, posick.net.local., posick.net.posick.net., etc...Lookup lookup = new Lookup(MulticastDNSService.DEFAULT_REGISTRATION_DOMAIN_NAME,
MulticastDNSService.REGISTRATION_DOMAIN_NAME,
MulticastDNSService.DEFAULT_BROWSE_DOMAIN_NAME,
MulticastDNSService.BROWSE_DOMAIN_NAME,
MulticastDNSService.LEGACY_BROWSE_DOMAIN_NAME);
Domain[] domains = lookup.lookupDomains();
for (Domain domain : domains)
{
System.out.println(domain);
}
lookup.close();
Lookup lookup = new Resolve("Test._org.smpte.st2071.service:service_v1.0._sub._mdc._tcp.local.");
ServiceInstance[] services = lookup.lookupServices();
for (ServiceInstance service : services)
{
System.out.println(service);
}
String[] serviceTypes = new String[]
{
"_http._tcp.", // Web pages
"_printer._sub._http._tcp", // Printer configuration web pages
"_org.smpte.st2071.device:device_v1.0._sub._mdc._tcp", // SMPTE ST2071 Devices
"_org.smpte.st2071.service:service_v1.0._sub._mdc._tcp" // SMPTE ST2071 Services
};
Browse browse = new Browse(serviceTypes);
browse.start(new DNSSDListener()
{
public void serviceDiscovered(Object id, ServiceInstance service)
{
System.out.println("Service Discovered - " + service);
}
public void serviceRemoved(Object id, ServiceInstance service)
{
System.out.println("Service Removed - " + service);
}
public void handleException(Object id, Exception e)
{
System.err.println("Exception: " + e.getMessage());
e.printStackTrace(System.err);
}
});
while (true)
{
Thread.sleep(10);
if (System.in.read() == 'q')
{
break;
}
}
browse.close();
Lookup lookup = new Lookup("Test._mdc._tcp.local.", Type.ANY, DClass.IN);
Record[] records = lookup.lookupRecords();
for (Record record : records)
{
System.out.println(records);
}
Lookup lookup = new Lookup("Test._mdc._tcp.local.", Type.ANY, DClass.IN);
Record[] records = Lookup. LookupRecordsAsych(new RecordListener()
{
public void receiveRecord(Object id, Record record)
{
System.out.println("Record Found - " + record);
}
public void handleException(Object id, Exception e)
{
System.err.println("Exception: " + e.getMessage());
e.printStackTrace(System.err);
}
});
Thread.sleep(1000);
resolve.close();
MulticastDNSService mDNSService = new MulticastDNSService();
ServiceInstance service = new ServiceInstance(serviceName, 0, 0, port, hostname, MulticastDNSService.DEFAULT_SRV_TTL, addresses, txtValues);
ServiceInstance registeredService = mDNSService.register(service);
if (registeredService != null)
{
System.out.println("Services Successfully Registered: \n\t" + registeredService);
} else
{
System.err.println("Services Registration Failed!");
}
while (true)
{
Thread.sleep(10);
if (System.in.read() == 'q')
{
if (mDNSService.unregister(registeredService))
{
System.out.println("Services Successfully Unregistered: \n\t" + service);
} else
{
System.err.println("Services Unregistration Failed!");
}
break;
}
}
mDNSService.close();
Numerous bugs have been reported with Java's support of IPv6. Among them is an issue where the IP header's Time To Live (TTL) value for datagrams does not get set properly. If the IP header's Time To Live (TTL) value is not set to 255, then the Java VM must be started with IPv6 disabled, using the "-Djava.net.preferIPv4Stack=true" VM option. This is true for IPv4 datagrams as well. Disabling IPv6 fixes the TTL issue for IPv4.
For Example:
java -Djava.net.preferIPv4Stack=true -jar mdnsjava.jar dnssd -E
DNS-based Service Discovery is an efficient service discovery protocol developed by Apple, originally as Bonjour. DNS-SD is part of the [Zeroconf] specification and sclaes from the link-local network up to the Internet. Link-local network support is provided via mDNS using the local. domain name, while scaling to networks ouside than the link-local network is achieved thru Unicast DNS and regular domain names, for example posick.net..
This project was originally created for the development of a proof of concept application for the Society of Motion Picture and Television Engineers (SMPTE) suite of standards on Media & Device Control over IP networks, [SMPTE ST2071]. The SMPTE ST2071 suite of standards defines an open standard for the representation of devices and services within an Internet of Things (IoT) and defines extensions to the DNS-SD protocol that allows for the service discovery DNS infrastructure to be seperate from the DNS infrastructure used for name resolution.
The SMPTE ST2071 standard defines Capabilities as uniquely identified interfaces that describe an atomic of behavior or feature. Devices and Services are then described by listing the identities of the uniquely identified interfaces. The standard defines the DNS naming convention for these Capabilities to be in the form:
'_' ${namespace} ':' ${interface_name} '_sub._mdc._tcp.' ${domain}
and for each device and service to also be registered using the DNS-SD name
'_mdc._tcp.' ${domain}
The registration of all services using the _mdc._tcp name facilitates the search of all registered ST2071 devices, services and Capability enpoints.
mdnsjava was created by Steve Posick (@posicks) as part of a Proof of Concept application for the Society of Motion Picture and Television Engineers (SMPTE) suite of standards on Media & Device Control over IP networks, [SMPTE ST2071]. The SMPTE ST2071 suite of standards defines an open standard for the representation of devices and services within an Internet of Things (IoT) using uniquely identified feature interfaces, similar in principle to uniquely identified Microservice interfaces, and defines extensions for the DNS-SD protocol that allow for the service discovery DNS infrastructure to be separated from the name resolution DNS infrastructure.
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