require 'socket.so'

class Addrinfo
  # creates an Addrinfo object from the arguments.
  #
  # The arguments are interpreted as similar to self.
  #
  #   Addrinfo.tcp("0.0.0.0", 4649).family_addrinfo("www.ruby-lang.org", 80)
  #   #=> #<Addrinfo: 221.186.184.68:80 TCP (www.ruby-lang.org:80)>
  #
  #   Addrinfo.unix("/tmp/sock").family_addrinfo("/tmp/sock2")
  #   #=> #<Addrinfo: /tmp/sock2 SOCK_STREAM>
  #
  def family_addrinfo(*args)
    if args.empty?
      raise ArgumentError, "no address specified"
    elsif Addrinfo === args.first
      raise ArgumentError, "too many arguments" if args.length != 1
    elsif self.ip?
      raise ArgumentError, "IP address needs host and port but #{args.length} arguments given" if args.length != 2
      host, port = args
      Addrinfo.getaddrinfo(host, port, self.pfamily, self.socktype, self.protocol)[0]
    elsif self.unix?
      raise ArgumentError, "UNIX socket needs single path argument but #{args.length} arguments given" if args.length != 1
      path, = args
      Addrinfo.unix(path)
    else
      raise ArgumentError, "unexpected family"
    end
  end

  # creates a new Socket connected to the address of +local_addrinfo+.
  #
  # If no arguments are given, the address of the socket is not bound.
  #
  # If a block is given the created socket is yielded for each address.
  #
  def connect_internal(local_addrinfo) # :yields: socket
    sock = Socket.new(self.pfamily, self.socktype, self.protocol)
    begin
      sock.ipv6only! if self.ipv6?
      sock.bind local_addrinfo if local_addrinfo
      sock.connect(self)
      if block_given?
        yield sock
      else
        sock
      end
    ensure
      sock.close if !sock.closed? && (block_given? || $!)
    end
  end
  private :connect_internal

  # creates a socket connected to the address of self.
  #
  # If one or more arguments given as _local_addr_args_,
  # it is used as the local address of the socket.
  # _local_addr_args_ is given for family_addrinfo to obtain actual address.
  #
  # If no arguments given, the local address of the socket is not bound.
  #
  # If a block is given, it is called with the socket and the value of the block is returned.
  # The socket is returned otherwise.
  #
  #   Addrinfo.tcp("www.ruby-lang.org", 80).connect_from("0.0.0.0", 4649) {|s|
  #     s.print "GET / HTTP/1.0\r\nHost: www.ruby-lang.org\r\n\r\n"
  #     puts s.read
  #   }
  #
  #   # Addrinfo object can be taken for the argument.
  #   Addrinfo.tcp("www.ruby-lang.org", 80).connect_from(Addrinfo.tcp("0.0.0.0", 4649)) {|s|
  #     s.print "GET / HTTP/1.0\r\nHost: www.ruby-lang.org\r\n\r\n"
  #     puts s.read
  #   }
  #
  def connect_from(*local_addr_args, &block)
    connect_internal(family_addrinfo(*local_addr_args), &block)
  end

  # creates a socket connected to the address of self.
  #
  # If a block is given, it is called with the socket and the value of the block is returned.
  # The socket is returned otherwise.
  #
  #   Addrinfo.tcp("www.ruby-lang.org", 80).connect {|s|
  #     s.print "GET / HTTP/1.0\r\nHost: www.ruby-lang.org\r\n\r\n"
  #     puts s.read
  #   }
  #
  def connect(&block)
    connect_internal(nil, &block)
  end

  # creates a socket connected to _remote_addr_args_ and bound to self.
  #
  # If a block is given, it is called with the socket and the value of the block is returned.
  # The socket is returned otherwise.
  #
  #   Addrinfo.tcp("0.0.0.0", 4649).connect_to("www.ruby-lang.org", 80) {|s|
  #     s.print "GET / HTTP/1.0\r\nHost: www.ruby-lang.org\r\n\r\n"
  #     puts s.read
  #   }
  #
  def connect_to(*remote_addr_args, &block)
    remote_addrinfo = family_addrinfo(*remote_addr_args)
    remote_addrinfo.send(:connect_internal, self, &block)
  end

  # creates a socket bound to self.
  #
  # If a block is given, it is called with the socket and the value of the block is returned.
  # The socket is returned otherwise.
  #
  #   Addrinfo.udp("0.0.0.0", 9981).bind {|s|
  #     s.local_address.connect {|s| s.send "hello", 0 }
  #     p s.recv(10) #=> "hello"
  #   }
  #
  def bind
    sock = Socket.new(self.pfamily, self.socktype, self.protocol)
    begin
      sock.ipv6only! if self.ipv6?
      sock.setsockopt(:SOCKET, :REUSEADDR, 1)
      sock.bind(self)
      if block_given?
        yield sock
      else
        sock
      end
    ensure
      sock.close if !sock.closed? && (block_given? || $!)
    end
  end

  # creates a listening socket bound to self.
  def listen(backlog=5)
    sock = Socket.new(self.pfamily, self.socktype, self.protocol)
    begin
      sock.ipv6only! if self.ipv6?
      sock.setsockopt(:SOCKET, :REUSEADDR, 1)
      sock.bind(self)
      sock.listen(backlog)
      if block_given?
        yield sock
      else
        sock
      end
    ensure
      sock.close if !sock.closed? && (block_given? || $!)
    end
  end

  # iterates over the list of Addrinfo objects obtained by Addrinfo.getaddrinfo.
  #
  #   Addrinfo.foreach(nil, 80) {|x| p x }
  #   #=> #<Addrinfo: 127.0.0.1:80 TCP (:80)>
  #   #   #<Addrinfo: 127.0.0.1:80 UDP (:80)>
  #   #   #<Addrinfo: [::1]:80 TCP (:80)>
  #   #   #<Addrinfo: [::1]:80 UDP (:80)>
  #
  def self.foreach(nodename, service, family=nil, socktype=nil, protocol=nil, flags=nil, &block)
    Addrinfo.getaddrinfo(nodename, service, family, socktype, protocol, flags).each(&block)
  end
end

class BasicSocket < IO
  # Returns an address of the socket suitable for connect in the local machine.
  #
  # This method returns _self_.local_address, except following condition.
  #
  # - IPv4 unspecified address (0.0.0.0) is replaced by IPv4 loopback address (127.0.0.1).
  # - IPv6 unspecified address (::) is replaced by IPv6 loopback address (::1).
  #
  # If the local address is not suitable for connect, SocketError is raised.
  # IPv4 and IPv6 address which port is 0 is not suitable for connect.
  # Unix domain socket which has no path is not suitable for connect.
  #
  #   Addrinfo.tcp("0.0.0.0", 0).listen {|serv|
  #     p serv.connect_address #=> #<Addrinfo: 127.0.0.1:53660 TCP>
  #     serv.connect_address.connect {|c|
  #       s, _ = serv.accept
  #       p [c, s] #=> [#<Socket:fd 4>, #<Socket:fd 6>]
  #     }
  #   }
  #
  def connect_address
    addr = local_address
    afamily = addr.afamily
    if afamily == Socket::AF_INET
      raise SocketError, "unbound IPv4 socket" if addr.ip_port == 0
      if addr.ip_address == "0.0.0.0"
        addr = Addrinfo.new(["AF_INET", addr.ip_port, nil, "127.0.0.1"], addr.pfamily, addr.socktype, addr.protocol)
      end
    elsif defined?(Socket::AF_INET6) && afamily == Socket::AF_INET6
      raise SocketError, "unbound IPv6 socket" if addr.ip_port == 0
      if addr.ip_address == "::"
        addr = Addrinfo.new(["AF_INET6", addr.ip_port, nil, "::1"], addr.pfamily, addr.socktype, addr.protocol)
      elsif addr.ip_address == "0.0.0.0" # MacOS X 10.4 returns "a.b.c.d" for IPv4-mapped IPv6 address.
        addr = Addrinfo.new(["AF_INET6", addr.ip_port, nil, "::1"], addr.pfamily, addr.socktype, addr.protocol)
      elsif addr.ip_address == "::ffff:0.0.0.0" # MacOS X 10.6 returns "::ffff:a.b.c.d" for IPv4-mapped IPv6 address.
        addr = Addrinfo.new(["AF_INET6", addr.ip_port, nil, "::1"], addr.pfamily, addr.socktype, addr.protocol)
      end
    elsif defined?(Socket::AF_UNIX) && afamily == Socket::AF_UNIX
      raise SocketError, "unbound Unix socket" if addr.unix_path == ""
    end
    addr
  end
end

class Socket < BasicSocket
  # enable the socket option IPV6_V6ONLY if IPV6_V6ONLY is available.
  def ipv6only!
    if defined? Socket::IPV6_V6ONLY
      self.setsockopt(:IPV6, :V6ONLY, 1)
    end
  end

  # creates a new socket object connected to host:port using TCP/IP.
  #
  # If local_host:local_port is given,
  # the socket is bound to it.
  #
  # If a block is given, the block is called with the socket.
  # The value of the block is returned.
  # The socket is closed when this method returns.
  #
  # If no block is given, the socket is returned.
  #
  #   Socket.tcp("www.ruby-lang.org", 80) {|sock|
  #     sock.print "GET / HTTP/1.0\r\nHost: www.ruby-lang.org\r\n\r\n"
  #     sock.close_write
  #     puts sock.read
  #   }
  #
  def self.tcp(host, port, local_host=nil, local_port=nil) # :yield: socket
    last_error = nil
    ret = nil

    local_addr_list = nil
    if local_host != nil || local_port != nil
      local_addr_list = Addrinfo.getaddrinfo(local_host, local_port, nil, :STREAM, nil)
    end

    Addrinfo.foreach(host, port, nil, :STREAM) {|ai|
      if local_addr_list
        local_addr = local_addr_list.find {|local_ai| local_ai.afamily == ai.afamily }
        next if !local_addr
      else
        local_addr = nil
      end
      begin
        sock = local_addr ? ai.connect_from(local_addr) : ai.connect
      rescue SystemCallError
        last_error = $!
        next
      end
      ret = sock
      break
    }
    if !ret
      if last_error
        raise last_error
      else
        raise SocketError, "no appropriate local address"
      end
    end
    if block_given?
      begin
        yield ret
      ensure
        ret.close if !ret.closed?
      end
    else
      ret
    end
  end

  # :stopdoc:
  def self.ip_sockets_port0(ai_list, reuseaddr)
    begin
      sockets = []
      port = nil
      ai_list.each {|ai|
        begin
          s = Socket.new(ai.pfamily, ai.socktype, ai.protocol)
        rescue SystemCallError
          next
        end
        sockets << s
        s.ipv6only! if ai.ipv6?
        if reuseaddr
          s.setsockopt(:SOCKET, :REUSEADDR, 1)
        end
        if !port
          s.bind(ai)
          port = s.local_address.ip_port
        else
          s.bind(ai.family_addrinfo(ai.ip_address, port))
        end
      }
    rescue Errno::EADDRINUSE
      sockets.each {|s|
        s.close
      }
      retry
    end
    sockets
  ensure
    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 $! && sockets
  end
  class << self
    private :tcp_server_sockets_port0
  end
  # :startdoc:

  # creates TCP/IP server sockets for _host_ and _port_.
  # _host_ is optional.
  #
  # If no block given,
  # it returns an array of listening sockets.
  #
  # If a block is given, the block is called with the sockets.
  # The value of the block is returned.
  # The socket is closed when this method returns.
  #
  # If _port_ is 0, actual port number is choosen dynamically.
  # However all sockets in the result has same port number.
  #
  #   # tcp_server_sockets returns two sockets.
  #   sockets = Socket.tcp_server_sockets(1296)
  #   p sockets #=> [#<Socket:fd 3>, #<Socket:fd 4>]
  #
  #   # The sockets contains IPv6 and IPv4 sockets.
  #   sockets.each {|s| p s.local_address }
  #   #=> #<Addrinfo: [::]:1296 TCP>
  #   #   #<Addrinfo: 0.0.0.0:1296 TCP>
  #
  #   # IPv6 and IPv4 socket has same port number, 53114, even if it is choosen dynamically.
  #   sockets = Socket.tcp_server_sockets(0)
  #   sockets.each {|s| p s.local_address }
  #   #=> #<Addrinfo: [::]:53114 TCP>
  #   #   #<Addrinfo: 0.0.0.0:53114 TCP>
  #
  #   # The block is called with the sockets.
  #   Socket.tcp_server_sockets(0) {|sockets|
  #     p sockets #=> [#<Socket:fd 3>, #<Socket:fd 4>]
  #   }
  #
  def self.tcp_server_sockets(host=nil, port)
    if port == 0
      sockets = tcp_server_sockets_port0(host)
    else
      begin
        last_error = nil
        sockets = []
        Addrinfo.foreach(host, port, nil, :STREAM, nil, Socket::AI_PASSIVE) {|ai|
          begin
            s = ai.listen
          rescue SystemCallError
            last_error = $!
            next
          end
          sockets << s
        }
        if sockets.empty?
          raise last_error
        end
      ensure
        sockets.each {|s| s.close if !s.closed? } if $!
      end
    end
    if block_given?
      begin
        yield sockets
      ensure
        sockets.each {|s| s.close if !s.closed? }
      end
    else
      sockets
    end
  end

  # yield socket and client address for each a connection accepted via given sockets.
  #
  # The arguments are a list of sockets.
  # The individual argument should be a socket or an array of sockets.
  #
  # This method yields the block sequentially.
  # It means that the next connection is not accepted until the block returns.
  # So concurrent mechanism, thread for example, should be used to service multiple clients at a time.
  #
  def self.accept_loop(*sockets) # :yield: socket, client_addrinfo
    sockets.flatten!(1)
    if sockets.empty?
      raise ArgumentError, "no sockets"
    end
    loop {
      readable, _, _ = IO.select(sockets)
      readable.each {|r|
        begin
          sock, addr = r.accept_nonblock
        rescue IO::WaitReadable
          next
        end
        yield sock, addr
      }
    }
  end

  # creates a TCP/IP server on _port_ and calls the block for each connection accepted.
  # The block is called with a socket and a client_address as an Addrinfo object.
  #
  # If _host_ is specified, it is used with _port_ to determine the server addresses.
  #
  # The socket is *not* closed when the block returns.
  # So application should close it explicitly.
  #
  # This method calls the block sequentially.
  # It means that the next connection is not accepted until the block returns.
  # So concurrent mechanism, thread for example, should be used to service multiple clients at a time.
  #
  # Note that Addrinfo.getaddrinfo is used to determine the server socket addresses.
  # When Addrinfo.getaddrinfo returns two or more addresses,
  # IPv4 and IPv6 address for example,
  # all of them are used.
  # Socket.tcp_server_loop succeeds if one socket can be used at least.
  #
  #   # Sequential echo server.
  #   # It services only one client at a time.
  #   Socket.tcp_server_loop(16807) {|sock, client_addrinfo|
  #     begin
  #       IO.copy_stream(sock, sock)
  #     ensure
  #       sock.close
  #     end
  #   }
  #
  #   # Threaded echo server
  #   # It services multiple clients at a time.
  #   # Note that it may accept connections too much.
  #   Socket.tcp_server_loop(16807) {|sock, client_addrinfo|
  #     Thread.new {
  #       begin
  #         IO.copy_stream(sock, sock)
  #       ensure
  #         sock.close
  #       end
  #     }
  #   }
  #
  def self.tcp_server_loop(host=nil, port, &b) # :yield: socket, client_addrinfo
    tcp_server_sockets(host, port) {|sockets|
      accept_loop(sockets, &b)
    }
  end

  # :call-seq:
  #   Socket.udp_server_sockets([host, ] port)
  #
  # Creates UDP/IP sockets for a UDP server.
  #
  # If no block given, it returns an array of sockets.
  #
  # If a block is given, the block is called with the sockets.
  # The value of the block is returned.
  # The sockets are closed when this method returns.
  #
  # If _port_ is zero, some port is choosen.
  # But the choosen port is used for the all sockets.
  #
  #   # UDP/IP echo server
  #   Socket.udp_server_sockets(0) {|sockets|
  #     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 = []

    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

    sockets.each {|s|
      ai = s.local_address
      if ipv6_recvpktinfo && ai.ipv6? && ai.ip_address == "::"
        s.setsockopt(:IPV6, ipv6_recvpktinfo, 1)
      end
    }

    if block_given?
      begin
        yield sockets
      ensure
        sockets.each {|s| s.close if !s.closed? } if sockets
      end
    else
      sockets
    end
  end

  # :call-seq:
  #   Socket.udp_server_recv(sockets) {|msg, msg_src| ... }
  #
  # Receive UDP/IP packets from the given _sockets_.
  # For each packet received, the block is called.
  #
  # The block receives _msg_ and _msg_src_.
  # _msg_ is a string which is the payload of the received packet.
  # _msg_src_ is a Socket::UDPSource object which is used for reply.
  #
  # Socket.udp_server_loop can be implemented using this method as follows.
  #
  #   udp_server_sockets(host, port) {|sockets|
  #     loop {
  #       readable, _, _ = IO.select(sockets)
  #       udp_server_recv(readable) {|msg, msg_src| ... }
  #     }
  #   }
  #
  def self.udp_server_recv(sockets)
    sockets.each {|r|
      begin
        msg, sender_addrinfo, _, *controls = r.recvmsg_nonblock
      rescue IO::WaitReadable
        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_on(sockets) {|msg, msg_src| ... }
  #
  # Run UDP/IP 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, &b) # :yield: msg, msg_src
    loop {
      readable, _, _ = IO.select(sockets)
      udp_server_recv(readable, &b)
    }
  end

  # :call-seq:
  #   Socket.udp_server_loop(port) {|msg, msg_src| ... }
  #   Socket.udp_server_loop(host, port) {|msg, msg_src| ... }
  #
  # creates a UDP/IP 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/IP 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
    udp_server_sockets(host, port) {|sockets|
      udp_server_loop_on(sockets, &b)
    }
  end

  # UDP/IP address information used by Socket.udp_server_loop.
  class UDPSource
    # +remote_adress+ is an Addrinfo object.
    #
    # +local_adress+ is an Addrinfo object.
    #
    # +reply_proc+ is a Proc used to send reply back to the source.
    def initialize(remote_address, local_address, &reply_proc)
      @remote_address = remote_address
      @local_address = local_address
      @reply_proc = reply_proc
    end

    # Address of the source
    attr_reader :remote_address

    # Local address
    attr_reader :local_address

    def inspect # :nodoc:
      "\#<#{self.class}: #{@remote_address.inspect_sockaddr} to #{@local_address.inspect_sockaddr}>"
    end

    # Sends the String +msg+ to the source
    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.
  # The value of the block is returned.
  # The socket is closed when this method returns.
  #
  # If no block is given, the socket is returned.
  #
  #   # talk to /tmp/sock socket.
  #   Socket.unix("/tmp/sock") {|sock|
  #     t = Thread.new { IO.copy_stream(sock, STDOUT) }
  #     IO.copy_stream(STDIN, sock)
  #     t.join
  #   }
  #
  def self.unix(path) # :yield: socket
    addr = Addrinfo.unix(path)
    sock = addr.connect
    if block_given?
      begin
        yield sock
      ensure
        sock.close if !sock.closed?
      end
    else
      sock
    end
  end

  # creates a UNIX server socket on _path_
  #
  # If no block given, it returns a listening socket.
  #
  # If a block is given, it is called with the socket and the block value is returned.
  # When the block exits, the socket is closed and the socket file is removed.
  #
  #   socket = Socket.unix_server_socket("/tmp/s")
  #   p socket                  #=> #<Socket:fd 3>
  #   p socket.local_address    #=> #<Addrinfo: /tmp/s SOCK_STREAM>
  #
  #   Socket.unix_server_socket("/tmp/sock") {|s|
  #     p s                     #=> #<Socket:fd 3>
  #     p s.local_address       #=> # #<Addrinfo: /tmp/sock SOCK_STREAM>
  #   }
  #
  def self.unix_server_socket(path)
    if !unix_socket_abstract_name?(path)
      begin
        st = File.lstat(path)
      rescue Errno::ENOENT
      end
      if st && st.socket? && st.owned?
        File.unlink path
      end
    end
    s = Addrinfo.unix(path).listen
    if block_given?
      begin
        yield s
      ensure
        s.close if !s.closed?
        if !unix_socket_abstract_name?(path)
          File.unlink path
        end
      end
    else
      s
    end
  end

  class << self
    private

    def unix_socket_abstract_name?(path)
      /linux/ =~ RUBY_PLATFORM && /\A(\0|\z)/ =~ path
    end
  end

  # creates a UNIX socket server on _path_.
  # It calls the block for each socket accepted.
  #
  # If _host_ is specified, it is used with _port_ to determine the server ports.
  #
  # The socket is *not* closed when the block returns.
  # So application should close it.
  #
  # This method deletes the socket file pointed by _path_ at first if
  # the file is a socket file and it is owned by the user of the application.
  # This is safe only if the directory of _path_ is not changed by a malicious user.
  # So don't use /tmp/malicious-users-directory/socket.
  # Note that /tmp/socket and /tmp/your-private-directory/socket is safe assuming that /tmp has sticky bit.
  #
  #   # Sequential echo server.
  #   # It services only one client at a time.
  #   Socket.unix_server_loop("/tmp/sock") {|sock, client_addrinfo|
  #     begin
  #       IO.copy_stream(sock, sock)
  #     ensure
  #       sock.close
  #     end
  #   }
  #
  def self.unix_server_loop(path, &b) # :yield: socket, client_addrinfo
    unix_server_socket(path) {|serv|
      accept_loop(serv, &b)
    }
  end

end

