[DNSResolver] Raise SocketError when there’s no connection.

lib/celluloid/io/dns_resolver.rb

@@ -5,6 +5,8 @@ module Celluloid
   module IO
     # Asynchronous DNS resolver using Celluloid::IO::UDPSocket
     class DNSResolver
+      class SocketNameResolutionError < SocketError; end
+
       # Maximum UDP packet we'll accept
       MAX_PACKET_SIZE = 512
       DNS_PORT        = 53
@@ -29,7 +31,9 @@ def initialize
 
         # The non-blocking secret sauce is here, as this is actually a
         # Celluloid::IO::UDPSocket
-        @socket = UDPSocket.new(@server.family)
+        unless @socket = UDPSocket.new(@server.family)
+          fail SocketNameResolutionError, "nodename nor servname provided, or not known"
+        end
       end
 
       def resolve(hostname)

spec/celluloid/io/dns_resolver_spec.rb

@@ -39,5 +39,10 @@
         expect(results).to be_an_instance_of(Resolv::IPv4)
       end
     end
+
+    it "raises SocketError if unable to connect to the nameserver" do
+      allow(Celluloid::IO::UDPSocket).to receive(:new).and_return(nil)
+      expect { Celluloid::IO::DNSResolver.new }.to raise_error(Celluloid::IO::DNSResolver::SocketNameResolutionError)
+    end
   end
 end