gen_udp(3)

NAME
gen_udp - Interface to UDP sockets.

DESCRIPTION

This module provides functions for communicating over UDP protocol sockets.

NOTE: Functions that create sockets can take an optional option; {inet_backend, Backend} that, if specified, has to be the first option. This selects the implementation backend towards the platform's socket API. This is a temporary option that will be ignored in a future release. The default is Backend = inet that selects the traditional inet_drv.c driver. The other choice is Backend = socket that selects the new socket module and its NIF implementation. The system default can be changed when the node is started with the application kernel's configuration variable inet_backend. For gen_udp with inet_backend = socket we have tried to be as "compatible" as possible which has sometimes been impossible. Here is a list of cases when the behaviour of inet-backend inet (default) and socket are different:

    • The option read_packets is currently ignored.

    • Windows require sockets (domain = inet | inet6) to be bound. Currently all sockets created on Windows with inet_backend = socket will be bound. If the user does not provide an address, gen_udp will try to 'figure out' an address itself.

DATA TYPES

ip6_membership() :: {MultiAddress :: inet:ip6_address(), IfIndex :: integer()}.
ip6_multicast_if() :: integer().

    IPv6 this multicast interface index (an integer).
ip_membership() :: {MultiAddress :: inet:ip4_address(), Interface :: inet:ip4_address()} | {MultiAddress :: inet:ip4_address(), Address :: inet:ip4_address(), IfIndex :: integer()}.

    IP multicast membership.

    The 3-tuple form isn't supported on all platforms. 'ifindex' defaults to zero (0) on platforms that supports the 3-tuple variant.
ip_multicast_if() :: inet:ip4_address().
membership() :: ip_membership() | ip6_membership().
multicast_if() :: ip_multicast_if() | ip6_multicast_if().
open_option() :: {ip, inet:socket_address()} | {fd, non_neg_integer()} | {ifaddr, socket:sockaddr_in() | socket:sockaddr_in6() | inet:socket_address()} | inet:address_family() | {port, inet:port_number()} | {netns, file:filename_all()} | {bind_to_device, binary()} | option().
option() :: {active, true | false | once | -32768..32767} | {add_membership, membership()} | {broadcast, boolean()} | {buffer, non_neg_integer()} | {debug, boolean()} | {deliver, port | term} | {dontroute, boolean()} | {drop_membership, membership()} | {exclusiveaddruse, boolean()} | {header, non_neg_integer()} | {high_msgq_watermark, pos_integer()} | {low_msgq_watermark, pos_integer()} | {mode, list | binary} | list | binary | {multicast_if, multicast_if()} | {multicast_loop, boolean()} | {multicast_ttl, non_neg_integer()} | {priority, non_neg_integer()} | {raw, Protocol :: non_neg_integer(), OptionNum :: non_neg_integer(), ValueBin :: binary()} | {read_packets, non_neg_integer()} | {recbuf, non_neg_integer()} | {reuseaddr, boolean()} | {reuseport, boolean()} | {reuseport_lb, boolean()} | {sndbuf, non_neg_integer()} | {tos, non_neg_integer()} | {tclass, non_neg_integer()} | {ttl, non_neg_integer()} | {recvtos, boolean()} | {recvtclass, boolean()} | {recvttl, boolean()} | {ipv6_v6only, boolean()}.
option_name() :: active | broadcast | buffer | debug | deliver | dontroute | exclusiveaddruse | header | high_msgq_watermark | low_msgq_watermark | mode | multicast_if | multicast_loop | multicast_ttl | priority | {raw, Protocol :: non_neg_integer(), OptionNum :: non_neg_integer(), ValueSpec :: (ValueSize :: non_neg_integer()) | (ValueBin :: binary())} | read_packets | recbuf | reuseaddr | reuseport | reuseport_lb | sndbuf | tos | tclass | ttl | recvtos | recvtclass | recvttl | pktoptions | ipv6_v6only.
socket() :: inet:socket().

    A socket as returned by open/1,2.

FUNCTIONS

close(Socket) -> ok when Socket :: socket().

    Closes a UDP socket.
connect(Socket, SockAddr) -> ok | {error, Reason} when Socket :: socket(), SockAddr :: socket:sockaddr_in() | socket:sockaddr_in6(), Reason :: inet:posix().

    Connect a UDP socket.

    Connecting a UDP socket only means storing the specified (destination) socket address, as specified by SockAddr, so that the system knows where to send data.

    When the socket is "connected" it is not necessary to specify the destination address when sending a datagram. That is; send/2 may be used.

    It also means that the socket will only receive data from the connected address. Other messages are discarded on arrival by the OS protocol stack.
connect(Socket, Address, Port) -> ok | {error, Reason} when Socket :: socket(), Address :: inet:socket_address() | inet:hostname(), Port :: inet:port_number(), Reason :: inet:posix().

    Connect a UDP socket.

    See connect/2.

    With this function the destination is specified with separate Address and Port arguments where Address may be an IP address or a host name.
controlling_process(Socket, Pid) -> ok | {error, Reason} when Socket :: socket(), Pid :: pid(), Reason :: closed | not_owner | badarg | inet:posix().

    Change the controlling process (owner) of a socket.

    Assigns a new controlling process Pid to Socket. The controlling process is the process that the socket sends messages to. If this function is called from 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/0, {error, badarg} is returned. {error, badarg} may also be returned in some cases when Socket is closed during the execution of this function.

    If the socket is in active mode, this function will transfer any messages from the socket in the mailbox of the caller to the new controlling process.

    If any other process is interacting with the socket during the transfer, it may not work correctly and messages may remain in the caller's mailbox. For instance, changing the sockets active mode during the transfer could cause this.
open(Port, Opts) -> {ok, Socket} | {error, Reason} when Port :: inet:port_number(), Opts :: [inet:inet_backend() | open_option()], Socket :: socket(), Reason :: system_limit | inet:posix().

    Open a UDP socket.

    The created socket is bound to the UDP port number Port. If Port == 0, the underlying OS assigns a free (ephemeral) UDP port; use inet:port/1 to retrieve it.

    The process that calls this function becomes the Socket's controlling process (socket owner).

    UDP socket options list
        Received Packet is delivered as a list.
    binary
        Received Packet is delivered as a binary.
    {ip, Address}
        If the local host has many IP addresses, this option specifies which one to use.
    {ifaddr, Address}
        Same as {ip, Address}.

        However, if this instead is a socket:sockaddr_in/0 or socket:sockaddr_in6/0 this takes precedence over any value previously set with the ip options. If the ip option comes after the ifaddr option, it may be used to update its corresponding field of the ifaddr option (the addr field).
    {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/0
    {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.
    option/0
        See inet:setopts/2.

    UDP packets are sent with this socket using send(Socket, ...). When UDP packets arrive to the Socket's UDP port, and the socket is in an active mode, the packets are delivered as messages to the controlling process (socket owner):

        {udp, Socket, PeerIP, PeerPort, Packet} % Without ancillary data
        {udp, Socket, PeerIP, PeerPort, AncData, Packet} % With ancillary data

    PeerIP and PeerPort are the address from which Packet was sent. Packet is a list of bytes ([byte/0] if option list is active and a binary/0 if option binaryis active (they are mutually exclusive).

    The message contains an AncData field only if any of the socket options recvtos, recvtclass or recvttl are active.

    When a socket in {active, N} mode (see inet:setopts/2 for details), transitions to passive ({active, false}) mode (N counts down to 0), the controlling process is notified by a message on this form:

        {udp_passive, Socket}

    If the OS protocol stack reports an error for the socket, the following message is sent to the controlling process:

        {udp_error, Socket, Reason}

    Reason is mostly a POSIX Error Code.

    If the socket is in passive mode (not in an active mode), received data can be retrieved with therecv/2,3](recv/2) calls. Note that incoming UDP packets that are longer than the receive buffer option specifies can be truncated without warning.

    The default value for the receive buffer option is {recbuf, 9216}.
recv(Socket, Length, Timeout) -> {ok, RecvData} | {error, Reason} when Socket :: socket(), Length :: non_neg_integer(), 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().

    Receive a packet from a socket in passive mode.

    Timeout specifies a time-out in milliseconds.

    If any of the socket options recvtos, recvtclass or recvttl are active, the RecvData tuple contains an AncData field, otherwise it doesn't.
send(Socket, Packet) -> ok | {error, Reason} when Socket :: socket(), Packet :: iodata(), Reason :: not_owner | inet:posix().

    Send a packet on a connected UDP socket.

    To connect a UDP socket, use connect/2 or connect/3.
send(Socket, Destination, Packet) -> ok | {error, Reason} when Socket :: socket(), Destination :: {inet:ip_address(), inet:port_number()} | inet:family_address() | socket:sockaddr_in() | socket:sockaddr_in6(), Packet :: iodata(), Reason :: not_owner | inet:posix().

    Equivalent to send(Socket, Destination, [], Packet).
send(Socket, Host, Port, Packet) -> ok | {error, Reason} when Socket :: socket(), Host :: inet:hostname() | inet:ip_address(), Port :: inet:port_number() | atom(), Packet :: iodata(), Reason :: not_owner | inet:posix(); (Socket, Destination, AncData, Packet) -> ok | {error, Reason} when Socket :: socket(), Destination :: {inet:ip_address(), inet:port_number()} | inet:family_address() | socket:sockaddr_in() | socket:sockaddr_in6(), AncData :: inet:ancillary_data(), Packet :: iodata(), Reason :: not_owner | inet:posix(); (Socket, Destination, PortZero, Packet) -> ok | {error, Reason} when Socket :: socket(), Destination :: {inet:ip_address(), inet:port_number()} | inet:family_address(), PortZero :: inet:port_number(), Packet :: iodata(), Reason :: not_owner | inet:posix().

    Send a UDP packet to the specified destination.

    With arguments Host and Port

    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 to a Destination and then this function is equivalent to send(Socket, Destination, [], Packet) just below.

    With arguments Destination and AncData (since OTP 22.1)

    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.

    With arguments Destination and PortZero (since OTP 22.1)

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

    This is a legacy clause mostly for Destination = {local, Binary} where PortZero is superfluous. Equivalent to send(Socket, Destination, [], Packet), right above here.
send(Socket, Host, Port, AncData, Packet) -> ok | {error, Reason} when 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().

    Send a packet to the specified destination, with ancillary data.

    Equivalent to send(Socket, Host, Port, Packet) regarding Host and Port and also equivalent to send(Socket, Destination, AncData, Packet) regarding the ancillary data: AncData.