diff --git a/ChangeLog b/ChangeLog
index 4184f916d6..ba2ebc4553 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Tue Feb 10 21:26:33 2009  Tanaka Akira  <akr@fsij.org>
+
+	* ext/socket/lib/socket.rb (Socket.udp_server_sockets): new method.
+	  (Socket.udp_server_loop_on): new method.
+	  (Socket.udp_server_loop): new method
+	  (Socket.ip_sockets_port0): extracted from tcp_server_sockets_port0.
+	  (Socket::UDPSource): new class.
+
 Tue Feb 10 21:14:43 2009  Tanaka Akira  <akr@fsij.org>
 
 	* ext/socket/socket.c (sockaddr_obj): fill pfamily.
diff --git a/ext/socket/lib/socket.rb b/ext/socket/lib/socket.rb
index 3e26c9d6c2..ff5fb088da 100644
--- a/ext/socket/lib/socket.rb
+++ b/ext/socket/lib/socket.rb
@@ -226,8 +226,7 @@ class Socket
     end
   end
 
-  def self.tcp_server_sockets_port0(host)
-    ai_list = Addrinfo.getaddrinfo(host, 0, nil, :STREAM, nil, Socket::AI_PASSIVE)
+  def self.ip_sockets_port0(ai_list, reuseaddr)
     begin
       sockets = []
       port = nil
@@ -239,14 +238,15 @@ class Socket
         end
         sockets << s
         s.ipv6only! if ai.ipv6?
-        s.setsockopt(:SOCKET, :REUSEADDR, 1)
+        if reuseaddr
+          s.setsockopt(:SOCKET, :REUSEADDR, 1)
+        end
         if !port
           s.bind(ai)
           port = s.local_address.ip_port
         else
-          s.bind(Addrinfo.tcp(ai.ip_address, port))
+          s.bind(ai.family_addrinfo(ai.ip_address, port))
         end
-        s.listen(5)
       }
     rescue Errno::EADDRINUSE
       sockets.each {|s|
@@ -256,11 +256,21 @@ class Socket
     end
     sockets
   ensure
-    if $!
-      sockets.each {|s|
-        s.close if !s.closed?
-      }
-    end
+    sockets.each {|s| s.close if !s.closed? } if $!
+  end
+  class << self
+    private :ip_sockets_port0
+  end
+
+  def self.tcp_server_sockets_port0(host)
+    ai_list = Addrinfo.getaddrinfo(host, 0, nil, :STREAM, nil, Socket::AI_PASSIVE)
+    sockets = ip_sockets_port0(ai_list, true)
+    sockets.each {|s|
+      s.listen(5)
+    }
+    sockets
+  ensure
+    sockets.each {|s| s.close if !s.closed? } if $!
   end
   class << self
     private :tcp_server_sockets_port0
@@ -395,6 +405,163 @@ class Socket
     end
   end
 
+  # :call-seq:
+  #   Socket.udp_server_sockets([host, ] port)
+  #
+  # Creates UDP sockets for a UDP server.
+  # It returns an array of sockets.
+  #
+  # If _port_ is zero, some port is choosen.
+  # But the choosen port is used for the all sockets.
+  #
+  #   # UDP echo server
+  #   sockets = Socket.udp_server_sockets(0)
+  #   p sockets.first.local_address.ip_port     #=> 32963
+  #   Socket.udp_server_loop_on(sockets) {|msg, msg_src|
+  #     msg_src.reply msg
+  #   }
+  #
+  def self.udp_server_sockets(host=nil, port)
+    last_error = nil
+    sockets = []
+    addr_hash = {}
+
+    ipv6_recvpktinfo = nil
+    if defined? Socket::AncillaryData
+      if defined? Socket::IPV6_RECVPKTINFO # RFC 3542
+        ipv6_recvpktinfo = Socket::IPV6_RECVPKTINFO
+      elsif defined? Socket::IPV6_PKTINFO # RFC 2292
+        ipv6_recvpktinfo = Socket::IPV6_PKTINFO
+      end
+    end
+
+    local_addrs = Socket.ip_address_list
+
+    ip_list = []
+    Addrinfo.foreach(host, port, nil, :DGRAM, nil, Socket::AI_PASSIVE) {|ai|
+      if ai.ipv4? && ai.ip_address == "0.0.0.0"
+        local_addrs.each {|a|
+          next if !a.ipv4?
+          ip_list << Addrinfo.new(a.to_sockaddr, :INET, :DGRAM, 0);
+        }
+      elsif ai.ipv6? && ai.ip_address == "::" && !ipv6_recvpktinfo
+        local_addrs.each {|a|
+          next if !a.ipv6?
+          ip_list << Addrinfo.new(a.to_sockaddr, :INET6, :DGRAM, 0);
+        }
+      else
+        ip_list << ai
+      end
+    }
+
+    if port == 0
+      sockets = ip_sockets_port0(ip_list, false)
+    else
+      ip_list.each {|ip|
+        ai = Addrinfo.udp(ip.ip_address, port)
+        begin
+          s = ai.bind
+        rescue SystemCallError
+          last_error = $!
+          next
+        end
+        sockets << s
+      }
+      if sockets.empty?
+        raise last_error
+      end
+    end
+
+    pktinfo_sockets = {}
+    sockets.each {|s|
+      ai = s.local_address
+      if ipv6_recvpktinfo && ai.ipv6? && ai.ip_address == "::"
+        s.setsockopt(:IPV6, ipv6_recvpktinfo, 1)
+        pktinfo_sockets[s] = true
+      end
+    }
+
+    sockets
+  end
+
+  # :call-seq:
+  #   Socket.udp_server_loop_on(sockets) {|msg, msg_src| ... }
+  #
+  # Run UDP server loop on the given sockets.
+  #
+  # The return value of Socket.udp_server_sockets is appropriate for the argument.
+  #
+  # It calls the block for each message received.
+  #
+  def self.udp_server_loop_on(sockets) # :yield: msg, msg_src
+    loop {
+      readable, _, _ = IO.select(sockets)
+      readable.each {|r|
+        begin
+          msg, sender_addrinfo, rflags, *controls = r.recvmsg_nonblock
+        rescue Errno::EWOULDBLOCK
+          next
+        end
+        ai = r.local_address
+        if ai.ipv6? and pktinfo = controls.find {|c| c.cmsg_is?(:IPV6, :PKTINFO) }
+          ai = Addrinfo.udp(pktinfo.ipv6_pktinfo_addr.ip_address, ai.ip_port)
+          yield msg, UDPSource.new(sender_addrinfo, ai) {|reply_msg|
+            r.sendmsg reply_msg, 0, sender_addrinfo, pktinfo
+          }
+        else
+          yield msg, UDPSource.new(sender_addrinfo, ai) {|reply_msg|
+            r.send reply_msg, 0, sender_addrinfo
+          }
+        end
+      }
+    }
+  end
+
+  # :call-seq:
+  #   Socket.udp_server_loop(port) {|msg, msg_src| ... }
+  #   Socket.udp_server_loop(host, port) {|msg, msg_src| ... }
+  #
+  # creates a UDP server on _port_ and calls the block for each message arrived.
+  # The block is called with the message and its source information.
+  #
+  # This method allocates sockets internally using _port_.
+  # If _host_ is specified, it is used conjunction with _port_ to determine the server addresses.
+  #
+  # The _msg_ is a string.
+  #
+  # The _msg_src_ is a Socket::UDPSource object.
+  # It is used for reply.
+  #
+  #   # UDP echo server.
+  #   Socket.udp_server_loop(9261) {|msg, msg_src|
+  #     msg_src.reply msg
+  #   }
+  #
+  def self.udp_server_loop(host=nil, port, &b) # :yield: message, message_source
+    sockets = udp_server_sockets(host, port)
+    udp_server_loop_on(sockets, &b)
+  ensure
+    sockets.each {|s| s.close if !s.closed? } if sockets
+  end
+
+  # UDP address information used by Socket.udp_server_loop.
+  class UDPSource
+    def initialize(remote_address, local_address, &reply_proc)
+      @remote_address = remote_address
+      @local_address = local_address
+      @reply_proc = reply_proc
+    end
+    attr_reader :remote_address, :local_address
+
+    def inspect
+      "\#<#{self.class}: #{@sender.inspect_sockaddr} to #{@receiver.inspect_sockaddr}>"
+    end
+
+    def reply(msg)
+      @reply_proc.call msg
+    end
+  end
+
   # creates a new socket connected to path using UNIX socket socket.
   #
   # If a block is given, the block is called with the socket.
diff --git a/test/socket/test_socket.rb b/test/socket/test_socket.rb
index cb54540249..5b2b7b41d7 100644
--- a/test/socket/test_socket.rb
+++ b/test/socket/test_socket.rb
@@ -225,4 +225,38 @@ class TestSocket < Test::Unit::TestCase
 
   end
 
+  def test_udp_server
+    begin
+      ip_addrs = Socket.ip_address_list
+    rescue NotImplementedError
+    end
+
+    sockets = Socket.udp_server_sockets(0)
+    port = sockets.first.local_address.ip_port
+
+    th = Thread.new {
+      Socket.udp_server_loop_on(sockets) {|msg, msg_src|
+        break if msg == "exit"
+        rmsg = Marshal.dump([msg, msg_src.remote_address, msg_src.local_address])
+        msg_src.reply rmsg
+      }
+    }
+
+    ip_addrs.each {|ai|
+      Addrinfo.udp(ai.ip_address, port).connect {|s|
+        msg1 = "<<<#{ai.inspect}>>>"
+        s.sendmsg msg1
+        msg2, addr = s.recvmsg
+        msg2, remote_address, local_address = Marshal.load(msg2)
+        assert_equal(msg1, msg2)
+        assert_equal(ai.ip_address, addr.ip_address)
+      }
+    }
+  ensure
+    if th
+      Addrinfo.udp("127.0.0.1", port).connect {|s| s.sendmsg "exit" }
+      th.join
+    end
+  end
+
 end if defined?(Socket)