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       gen_udp - Interface to UDP sockets


       The  gen_udp  module  provides  functions  for  communicating  with  sockets using the UDP


       option() = {active, true | false | once}
                | {add_membership,
                   {inet:ip_address(), inet:ip_address()}}
                | {broadcast, boolean()}
                | {buffer, integer() >= 0}
                | {deliver, port | term}
                | {dontroute, boolean()}
                | {drop_membership,
                   {inet:ip_address(), inet:ip_address()}}
                | {header, integer() >= 0}
                | {high_msgq_watermark, integer() >= 1}
                | {low_msgq_watermark, integer() >= 1}
                | {mode, list | binary}
                | list
                | binary
                | {multicast_if, inet:ip_address()}
                | {multicast_loop, boolean()}
                | {multicast_ttl, integer() >= 0}
                | {priority, integer() >= 0}
                | {raw,
                   Protocol :: integer() >= 0,
                   OptionNum :: integer() >= 0,
                   ValueBin :: binary()}
                | {read_packets, integer() >= 0}
                | {recbuf, integer() >= 0}
                | {reuseaddr, boolean()}
                | {sndbuf, integer() >= 0}
                | {tos, integer() >= 0}
                | {ipv6_v6only, boolean()}

       option_name() = active
                     | broadcast
                     | buffer
                     | deliver
                     | dontroute
                     | header
                     | high_msgq_watermark
                     | low_msgq_watermark
                     | mode
                     | multicast_if
                     | multicast_loop
                     | multicast_ttl
                     | priority
                     | {raw,
                        Protocol :: integer() >= 0,
                        OptionNum :: integer() >= 0,
                        ValueSpec :: (ValueSize :: integer() >= 0)
                                   | (ValueBin :: binary())}
                     | read_packets
                     | recbuf
                     | reuseaddr
                     | sndbuf
                     | tos
                     | ipv6_v6only


              As returned by open/1,2.


       open(Port) -> {ok, Socket} | {error, Reason}

       open(Port, Opts) -> {ok, Socket} | {error, Reason}


                 Port = inet:port_number()
                 Opts = [Option]
                 Option = {ip, inet:ip_address()}
                        | {fd, integer() >= 0}
                        | {ifaddr, inet:ip_address()}
                        | inet:address_family()
                        | {port, inet:port_number()}
                        | option()
                 Socket = socket()
                 Reason = inet:posix()

              Associates a UDP port number (Port) with the calling process.

              The available options are:

                  Received Packet is delivered as a list.

                  Received Packet is delivered as a binary.

                {ip, ip_address()}:
                  If the host has several network interfaces, this option specifies which one  to

                {ifaddr, ip_address()}:
                  Same  as  {ip,  ip_address()}. If the host has several network interfaces, this
                  option specifies which one to use.

                {fd, integer() >= 0}:
                  If a socket has somehow been opened without using gen_udp, use this  option  to
                  pass the file descriptor for it.

                  Set up the socket for IPv6.

                  Set up the socket for IPv4.

                {udp_module, module()}:
                  Override  which  callback  module  is  used.  Defaults to inet_udp for IPv4 and
                  inet6_udp for IPv6.

                {multicast_if, Address}:
                  Set the local device for a multicast socket.

                {multicast_loop, true | false}:
                  When true sent multicast packets will be looped back to the local sockets.

                {multicast_ttl, Integer}:
                  The multicast_ttl option changes the time-to-live (TTL) for outgoing  multicast
                  datagrams in order to control the scope of the multicasts.

                  Datagrams with a TTL of 1 are not forwarded beyond the local network.
                  Default: 1

                {add_membership, {MultiAddress, InterfaceAddress}}:
                  Join a multicast group.

                {drop_membership, {MultiAddress, InterfaceAddress}}:
                  Leave multicast group.

                  See inet:setopts/2.

              The returned socket Socket is used to send packets from this port with send/4. When
              UDP packets arrive at the opened port, they are delivered as messages:

              {udp, Socket, IP, InPortNo, Packet}

              Note that arriving UDP packets that are  longer  than  the  receive  buffer  option
              specifies, might be truncated without warning.

              IP  and  InPortNo  define  the  address from which Packet came. Packet is a list of
              bytes if the option list was specified. Packet is a binary if the option binary was

              Default value for the receive buffer option is {recbuf, 8192}.

              If  Port  ==  0,  the  underlying  OS  assigns  a free UDP port, use inet:port/1 to
              retrieve it.

       send(Socket, Address, Port, Packet) -> ok | {error, Reason}


                 Socket = socket()
                 Address = inet:ip_address() | inet:hostname()
                 Port = inet:port_number()
                 Packet = iodata()
                 Reason = not_owner | inet:posix()

              Sends a packet to the specified address and  port.  The  Address  argument  can  be
              either a hostname, or an IP address.

       recv(Socket, Length) ->
               {ok, {Address, Port, Packet}} | {error, Reason}

       recv(Socket, Length, Timeout) ->
               {ok, {Address, Port, Packet}} | {error, Reason}


                 Socket = socket()
                 Length = integer() >= 0
                 Timeout = timeout()
                 Address = inet:ip_address()
                 Port = inet:port_number()
                 Packet = string() | binary()
                 Reason = not_owner | inet:posix()

              This function receives a packet from a socket in passive mode.

              The  optional  Timeout  parameter  specifies a timeout in milliseconds. The default
              value is infinity.

       controlling_process(Socket, Pid) -> ok | {error, Reason}


                 Socket = socket()
                 Pid = pid()
                 Reason = closed | not_owner | inet:posix()

              Assigns a new controlling process Pid to Socket. The  controlling  process  is  the
              process  which  receives  messages  from the socket. If called by any other process
              than the current controlling process, {error, not_owner} is returned.

       close(Socket) -> ok


                 Socket = socket()

              Closes a UDP socket.