NAME

       gen_udp - Interface to UDP sockets

DESCRIPTION

       The gen_udp 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} |
           {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

       socket()

              As returned by open/1,2.

EXPORTS

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

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

              Types:

                 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:

                list:
                  Received Packet is delivered as a list.

                binary:
                  Received Packet is delivered as a binary.

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

                {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.  If  Port is not set to 0 and/or {ip, ip_address()} is combined with this
                  option the fd will be bound to the given interface and  port  after  being  opened.  If  these
                  options are not given it is assumed that the fd is already bound appropriately.

                inet6:
                  Set up the socket for IPv6.

                inet:
                  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.

                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}

              If the socket is not in an active mode, data can be retrieved via the recv/2,3  calls.  Note  that
              arriving  UDP packets that are longer than the receive buffer option specifies, might 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 came. Packet is a list of bytes if the option
              list was specified. Packet is a binary if the option binary was 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.

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

              Types:

                 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}

              Types:

                 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}

              Types:

                 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

              Types:

                 Socket = socket()

              Closes a UDP socket.