Use IPv6 on CI.

lib/async/dns/resolver.rb

@@ -103,7 +103,11 @@ def records_for(name, resource_classes)
 			end
 		end
 
-		ADDRESS_RESOURCE_CLASSES = [Resolv::DNS::Resource::IN::A, Resolv::DNS::Resource::IN::AAAA]
+		if System.use_ipv6?
+			ADDRESS_RESOURCE_CLASSES = [Resolv::DNS::Resource::IN::A, Resolv::DNS::Resource::IN::AAAA]
+		else
+			ADDRESS_RESOURCE_CLASSES = [Resolv::DNS::Resource::IN::A]
+		end
 
 		# Yields a list of `Resolv::IPv4` and `Resolv::IPv6` addresses for the given `name` and `resource_class`. Raises a ResolutionFailure if no severs respond.
 		def addresses_for(name, resource_classes = ADDRESS_RESOURCE_CLASSES)

lib/async/dns/system.rb

@@ -14,117 +14,127 @@ module Async::DNS
 	module System
 		RESOLV_CONF = "/etc/resolv.conf"
 		HOSTS = "/etc/hosts"
-
+		
 		def self.hosts_path
 			if RUBY_PLATFORM =~ /mswin32|mingw|bccwin/
 				Win32::Resolv.get_hosts_path
 			else
 				HOSTS
 			end
 		end
-
+
+		def self.use_ipv6?
+			begin
+				list = Socket.ip_address_list
+			rescue NotImplementedError
+				return true
+			end
+
+			list.any? {|a| a.ipv6? && !a.ipv6_loopback? && !a.ipv6_linklocal? }
+		end
+
 		# This code is very experimental
 		class Hosts
 			def initialize
 				@addresses = {}
 				@names = {}
 			end
-
+			
 			attr :addresses
 			attr :names
-
+			
 			# This is used to match names against the list of known hosts:
 			def call(name)
 				@names.include?(name)
 			end
-
+			
 			def lookup(name)
 				addresses = @names[name]
-
+				
 				if addresses
 					addresses.last
 				else
 					nil
 				end
 			end
-
+			
 			alias [] lookup
-
+			
 			def add(address, names)
 				@addresses[address] ||= []
 				@addresses[address] += names
-
+				
 				names.each do |name|
 					@names[name] ||= []
 					@names[name] << address
 				end
 			end
-
+			
 			def parse_hosts(io)
 				io.each do |line|
 					line.sub!(/#.*/, '')
 					address, hostname, *aliases = line.split(/\s+/)
-
+					
 					add(address, [hostname] + aliases)
 				end
 			end
-
+			
 			def self.local
 				hosts = self.new
-
+				
 				path = System::hosts_path
-
+				
 				if path and File.exist?(path)
 					File.open(path) do |file|
 						hosts.parse_hosts(file)
 					end
 				end
-
+				
 				return hosts
 			end
 		end
-
+		
 		def self.parse_resolv_configuration(path)
 			nameservers = []
 			File.open(path) do |file|
 				file.each do |line|
 					# Remove any comments:
 					line.sub!(/[#;].*/, '')
-
+					
 					# Extract resolv.conf command:
 					keyword, *args = line.split(/\s+/)
-
+					
 					case keyword
 					when 'nameserver'
 						nameservers += args
 					end
 				end
 			end
-
+			
 			return nameservers
 		end
-
+		
 		def self.standard_connections(nameservers, **options)
 			connections = []
-
+			
 			nameservers.each do |host|
 				connections << IO::Endpoint.udp(host, 53, **options)
 				connections << IO::Endpoint.tcp(host, 53, **options)
 			end
-
+			
 			return IO::Endpoint.composite(connections)
 		end
-
+		
 		# Get a list of standard nameserver connections which can be used for querying any standard servers that the system has been configured with. There is no equivalent facility to use the `hosts` file at present.
 		def self.nameservers(**options)
 			nameservers = []
-
+			
 			if File.exist? RESOLV_CONF
 				nameservers = parse_resolv_configuration(RESOLV_CONF)
 			elsif defined?(Win32::Resolv) and RUBY_PLATFORM =~ /mswin32|cygwin|mingw|bccwin/
 				search, nameservers = Win32::Resolv.get_resolv_info
 			end
-
+			
 			return standard_connections(nameservers, **options)
 		end