Class: DNSSD

Inherits:
Object
  • Object
show all
Includes:
ResourceCache
Defined in:
lib/dns-sd.rb,
lib/dns-sd/target.rb,
lib/dns-sd/service.rb,
lib/dns-sd/resource_cache.rb,
lib/dns-sd/service_instance.rb

Overview

Interact with RFC6763 DNS-SD records.

Given a domain to work in, instances of this class use the standard Ruby DNS resolution mechanisms to look up services, service instances, and the individual servers that make up service instances. You can also obtain the "metadata" associated with service instances.

If you know the service, or even service instance, you wish to connect to, you can go straight there, using #service or #service_instance (as appropriate). Otherwise, if you're just curious about what is available, you can use #services to get a list of everything advertised under the "Service Type Enumeration" record for the domain.

Defined Under Namespace

Modules: ResourceCache Classes: Service, ServiceInstance, Target

Instance Method Summary collapse

Constructor Details

#initialize(domain) ⇒ DNSSD

Create a new DNS-SD instance.

Parameters:

  • domain (String, Resolv::DNS::Name) —

    Specify the base domain under which all the records we're interested in are registered.



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# File 'lib/dns-sd.rb', line 27

def initialize(domain)
  @domain = if domain.is_a?(Resolv::DNS::Name)
    domain
  else
    Resolv::DNS::Name.create(domain)
  end
end

Instance Method Details

#domain ⇒ String

The current search domain.

Returns:

  • (String) 


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# File 'lib/dns-sd.rb', line 39

def domain
  @domain.to_s
end

#service(name, protocol) ⇒ DNSSD::Service

Create a new instance of DNSSD::Service for this given name and protocol.

If you know the name and protocol of the service you wish to query for, this is the method for you! Note that just calling this method doesn't make any DNS requests, so you may get a service that has no instances.

Parameters:

  • name (String) —

    the name of the service, without the leading underscore that goes into the DNS name.

  • protocol (Symbol) —

    One of :TCP or :UDP, to indicate that you want to talk to a TCP or non-TCP service, respectively. Yes, :UDP means "non-TCP"; for more laughs, read RFC6763 s. 7.

Returns:



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# File 'lib/dns-sd.rb', line 58

def service(name, protocol)
  proto = case protocol
          when :TCP
            "_tcp"
          when :UDP
            "_udp"
          else
            raise ArgumentError,
              "Invalid protocol (must be one of :TCP or :UDP)"
  end

  DNSSD::Service.new(Resolv::DNS::Name.new(["_#{name}", proto] + @domain.to_a))
end

#service_instance(name, service_name, service_protocol) ⇒ DNSSD::ServiceInstance

Create a new DNSSD::ServiceInstance.

If you know everything about what you're trying to talk to except the server list, you can go straight to the boss level with this method.

Parameters:

  • name (String) —

    the name of the service instance.

  • service_name (String) —

    the generic name of the service which the desired instance implements, without the leading underscore that is in the DNS name.

  • service_protocol (Symbol) —

    one of :TCP or :UDP.

Returns:



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# File 'lib/dns-sd.rb', line 87

def service_instance(name, service_name, service_protocol)
  service(service_name, service_protocol).instance(name)
end

#services ⇒ Hash<String, DNSSD::Service>

Enumerate all known services in the domain.

RFC6763 s. 9 provides a special "Service Type Enumeration" DNS record, _services._dns-sd._udp.<domain>, which is a list of PTR records for the services available in the domain. If your DNS-SD registration system provisions names in there, you can use this to enumerate the available services.

Returns:

  • (Hash<String, DNSSD::Service>) —

    the list of services, indexed by the service name.



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# File 'lib/dns-sd.rb', line 102

def services
  {}.tap do |services|
    cached_resources(Resolv::DNS::Name.new(["_services", "_dns-sd", "_udp"] + @domain.to_a), Resolv::DNS::Resource::IN::PTR).each do |ptr|
      svc = DNSSD::Service.new(ptr.name)
      services[svc.name] = svc
    end
  end
end