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NAME

       gen_udp - Interface to UDP sockets.

DESCRIPTION

       This module provides functions for communicating with sockets using the UDP protocol.

DATA TYPES

       option() =
           {active, true | false | once | -32768..32767} |
           {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} |
           {tclass, integer() >= 0} |
           {ttl, integer() >= 0} |
           {recvtos, boolean()} |
           {recvtclass, boolean()} |
           {recvttl, boolean()} |
           {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 | tclass |
           ttl | recvtos | recvtclass | recvttl | pktoptions |
           ipv6_v6only

       socket()

              As returned by open/1,2.

EXPORTS

       close(Socket) -> ok

              Types:

                 Socket = socket()

              Closes a UDP socket.

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

              Types:

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

              Assigns  a  new  controlling  process Pid to Socket. The controlling process is the
              process that receives messages from the socket. If called by any other process than
              the  current  controlling  process,  {error, not_owner} is returned. If the process
              identified by Pid is not an  existing  local  pid,  {error,  badarg}  is  returned.
              {error, badarg} may also be returned in some cases when Socket is closed during the
              execution of this function.

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

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

              Types:

                 Port = inet:port_number()
                 Opts = [Option]
                 Option =
                     {ip, inet:socket_address()} |
                     {fd, integer() >= 0} |
                     {ifaddr, inet:socket_address()} |
                     inet:address_family() |
                     {port, inet:port_number()} |
                     {netns, file:filename_all()} |
                     {bind_to_device, binary()} |
                     option()
                 Socket = socket()
                 Reason = system_limit | inet:posix()

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

              The following options are available:

                list:
                  Received Packet is delivered as a list.

                binary:
                  Received Packet is delivered as a binary.

                {ip, Address}:
                  If the host has many network interfaces, this option  specifies  which  one  to
                  use.

                {ifaddr, Address}:
                  Same  as  {ip,  Address}.  If the host has many 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.  If  Port  is  not  set  to 0 and/or {ip,
                  ip_address()} is combined with this option, the fd is bound  to  the  specified
                  interface  and  port  after  it  is  being  opened.  If  these  options are not
                  specified, it is assumed that the fd is already bound appropriately.

                inet6:
                  Sets up the socket for IPv6.

                inet:
                  Sets up the socket for IPv4.

                local:
                  Sets up a Unix Domain Socket. See inet:local_address()

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

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

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

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

                  Datagrams with a TTL of 1 are not forwarded beyond the local network.  Defaults
                  to 1.

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

                {drop_membership, {MultiAddress, InterfaceAddress}}:
                  Leaves a multicast group.

                Opt:
                  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, if the socket is  in  an  active  mode,  the
              packets are delivered as messages to the controlling process:

              {udp, Socket, IP, InPortNo, Packet} % Without ancillary data
              {udp, Socket, IP, InPortNo, AncData, Packet} % With ancillary data

              The  message  contains  an  AncData  field  if  any  of the socket options recvtos,
              recvtclass or recvttl are active, otherwise it does not.

              If the socket is not in an active mode, data can be retrieved through the  recv/2,3
              calls.  Notice  that  arriving  UDP packets that are longer than the receive buffer
              option specifies can be truncated without warning.

              When a socket in {active, N} mode (see inet:setopts/2 for details), transitions  to
              passive ({active, false}) mode, the controlling process is notified by a message of
              the following form:

              {udp_passive, Socket}

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

              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.

       recv(Socket, Length) -> {ok, RecvData} | {error, Reason}

       recv(Socket, Length, Timeout) -> {ok, RecvData} | {error, Reason}

              Types:

                 Socket = socket()
                 Length = integer() >= 0
                 Timeout = timeout()
                 RecvData =
                     {Address, Port, Packet} | {Address, Port, AncData, Packet}
                 Address = inet:ip_address() | inet:returned_non_ip_address()
                 Port = inet:port_number()
                 AncData = inet:ancillary_data()
                 Packet = string() | binary()
                 Reason = not_owner | timeout | inet:posix()

              Receives  a  packet  from  a  socket  in  passive  mode. Optional parameter Timeout
              specifies a time-out in milliseconds. Defaults to infinity.

              If any of the socket  options  recvtos,  recvtclass  or  recvttl  are  active,  the
              RecvData tuple contains an AncData field, otherwise it does not.

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

              Types:

                 Socket = socket()
                 Destination =
                     {inet:ip_address(), inet:port_number()} |
                     inet:family_address()
                 Packet = iodata()
                 Reason = not_owner | inet:posix()

              Sends a packet to the specified Destination.

              This function is equivalent to send(Socket, Destination, [], Packet).

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

              Types:

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

              Sends a packet to the specified Host and Port.

              This clause is equivalent to send(Socket, Host, Port, [], Packet).

       send(Socket, Destination, AncData, Packet) -> ok | {error, Reason}

              Types:

                 Socket = socket()
                 Destination =
                     {inet:ip_address(), inet:port_number()} |
                     inet:family_address()
                 AncData = inet:ancillary_data()
                 Packet = iodata()
                 Reason = not_owner | inet:posix()

              Sends a packet to the specified Destination with ancillary data AncData.

          Note:
              The  ancillary  data AncData contains options that for this single message override
              the default options for the socket, an operation that may not be supported  on  all
              platforms,  and  if  so return {error, einval}. Using more than one of an ancillary
              data item type may also not be supported. AncData =:= [] is always supported.

       send(Socket, Destination, PortZero, Packet) ->
               ok | {error, Reason}

              Types:

                 Socket = socket()
                 Destination =
                     {inet:ip_address(), inet:port_number()} |
                     inet:family_address()
                 PortZero = inet:port_number()
                 Packet = iodata()
                 Reason = not_owner | inet:posix()

              Sends a packet  to  the  specified  Destination.  Since  Destination  is  complete,
              PortZero is redundant and has to be 0.

              This  is a legacy clause mostly for Destination = {local, Binary} where PortZero is
              superfluous. It is equivalent to send(Socket, Destination, [], Packet), the  clause
              right above here.

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

              Types:

                 Socket = socket()
                 Host =
                     inet:hostname() | inet:ip_address() | inet:local_address()
                 Port = inet:port_number() | atom()
                 AncData = inet:ancillary_data()
                 Packet = iodata()
                 Reason = not_owner | inet:posix()

              Sends a packet to the specified Host and Port, with ancillary data AncData.

              Argument  Host can be a hostname or a socket address, and Port can be a port number
              or a service name atom. These are resolved into a Destination and after  that  this
              function  is  equivalent  to send(Socket, Destination, AncData, Packet), read there
              about ancillary data.