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Version 5.1

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Interface to UDP sockets.


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


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} |
     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 |
     Protocol :: integer() >= 0,
     OptionNum :: integer() >= 0,
     ValueSpec ::
         (ValueSize :: integer() >= 0) | (ValueBin :: binary())} |
    read_packets |
    recbuf |
    reuseaddr |
    sndbuf |
    tos |


As returned by open/1,2.


close(Socket) -> ok


Socket = socket()

Closes a UDP socket.

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 that receives messages from the socket. If called by any other process than the current controlling process, {error, not_owner} is returned.

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


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

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

The following options are available:


Received Packet is delivered as a list.


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.


Sets up the socket for IPv6.


Sets up the socket for IPv4.


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.


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 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, {Address, Port, Packet}} | {error, Reason}

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


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

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

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


Socket = socket()
Packet = iodata()
Reason = not_owner | inet:posix()

Sends a packet to the specified address and port. Argument Address can be a hostname or a socket address.