Merge pull request #2697 from fluent/fix-dual-stack-ipv6-issue

server helper: Fix IPv6 dual stack mode issue for tcp socket.

lib/fluent/plugin_helper/server.rb

@@ -355,7 +355,11 @@ def server_create_tcp_socket(shared, bind, port)
         sock = if shared
                  server_socket_manager_client.listen_tcp(bind, port)
                else
-                 TCPServer.new(bind, port) # this method call can create sockets for AF_INET6
+                 # TCPServer.new doesn't set IPV6_V6ONLY flag, so use Addrinfo class instead.
+                 # backlog will be set by the caller, we don't need to set backlog here
+                 tsock = Addrinfo.tcp(bind, port).listen
+                 tsock.autoclose = false
+                 TCPServer.for_fd(tsock.fileno)
                end
         # close-on-exec is set by default in Ruby 2.0 or later (, and it's unavailable on Windows)
         sock.fcntl(Fcntl::F_SETFL, Fcntl::O_NONBLOCK) # nonblock

test/plugin_helper/test_server.rb

@@ -538,6 +538,19 @@ class Dummy < Fluent::Plugin::TestBase
       assert_equal ["yayfoo\n", "yayfoo\n", "yayfoo\n"], lines
       assert_equal ["closed", "closed", "closed"], callback_results
     end
+
+    test 'can listen IPv4 / IPv6 together' do
+      omit "IPv6 unavailable here" unless ipv6_enabled?
+
+      assert_nothing_raised do
+        @d.server_create_tcp(:s_ipv4, PORT, bind: '0.0.0.0', shared: false) do |data, conn|
+          # ...
+        end
+        @d.server_create_tcp(:s_ipv6, PORT, bind: '::', shared: false) do |data, conn|
+          # ...
+        end
+      end
+    end
   end
 
   sub_test_case '#server_create_udp' do