Ignore IPv6 nameservers to prevent Socket::ResolutionError

lib/cool.io/dns_resolver.rb

@@ -67,8 +67,9 @@ def self.hosts(host, hostfile = Resolv::Hosts::DefaultFileName)
     # list of nameservers to query.  By default the resolver will
     # use nameservers listed in /etc/resolv.conf
     def initialize(hostname, *nameservers)
+      nameservers = reject_ipv6_nameservers(nameservers)
       if nameservers.empty?
-        nameservers = Resolv::DNS::Config.default_config_hash[:nameserver]
+        nameservers = reject_ipv6_nameservers(Resolv::DNS::Config.default_config_hash[:nameserver])
         raise RuntimeError, "no nameservers found" if nameservers.empty? # TODO just call resolve_failed, not raise [also handle Errno::ENOENT)]
       end
 
@@ -203,6 +204,12 @@ def response_address(message)
       nil
     end
 
+    private
+
+    def reject_ipv6_nameservers(nameservers)
+      nameservers.reject { |ns| ns.include?(':') }
+    end
+
     class Timeout < TimerWatcher
       def initialize(resolver)
         @resolver = resolver

spec/dns_spec.rb

@@ -56,4 +56,24 @@ def on_resolve_failed
       expect( Coolio::DNSResolver.hosts("localhost", file.path)).to eq @preferred_localhost_address
     end
   end
+
+  describe "IPv6 nameserver filtering" do
+    it "ignores IPv6 nameservers provided in arguments" do
+      resolver = Coolio::DNSResolver.new("example.com", "8.8.8.8", "2001:4860:4860::8888", "1.1.1.1")
+
+      nameservers = resolver.instance_variable_get(:@nameservers)
+      expect(nameservers).to eq(["8.8.8.8", "1.1.1.1"])
+    end
+
+    it "falls back to default IPv4 config if only IPv6 addresses are provided" do
+      allow(Resolv::DNS::Config).to receive(:default_config_hash).and_return({
+        nameserver: ["8.8.4.4", "2001:4860:4860::8844"]
+      })
+
+      resolver = Coolio::DNSResolver.new("example.com", "2001:4860:4860::8888")
+
+      nameservers = resolver.instance_variable_get(:@nameservers)
+      expect(nameservers).to eq(["8.8.4.4"])
+    end
+  end
 end