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NAME
gen_udp - Interface to UDP sockets.
DESCRIPTION
This module provides functions for communicating with sockets using the UDP protocol.
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.
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
open_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()
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.
connect(Socket, SockAddr) -> ok | {error, Reason}
Types:
Socket = socket()
SockAddr = socket:sockaddr_in() | socket:sockaddr_in6()
Reason = inet:posix()
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.
This means that it is not necessary to specify the destination address when sending
a datagram. That is, we can use send/2.
It also means that the socket will only received data from this address.
connect(Socket, Address, Port) -> ok | {error, Reason}
Types:
Socket = socket()
Address = inet:socket_address() | inet:hostname()
Port = inet:port_number()
Reason = inet:posix()
Connecting a UDP socket only means storing the specified (destination) socket
address, as specified by Address and Port, so that the system knows where to send
data.
This means that it is not necessary to specify the destination address when sending
a datagram. That is, we can use send/2.
It also means that the socket will only received data from this address.
open(Port) -> {ok, Socket} | {error, Reason}
open(Port, Opts) -> {ok, Socket} | {error, Reason}
Types:
Port = inet:port_number()
Opts = [inet:inet_backend() | open_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.
However, if this instead is an socket:sockaddr_in() or socket:sockaddr_in6()
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()
{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, Packet) -> ok | {error, Reason}
Types:
Socket = socket()
Packet = iodata()
Reason = not_owner | inet:posix()
Sends a packet on a connected socket (see connect/2 and connect/3).
send(Socket, Destination, Packet) -> ok | {error, Reason}
Types:
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()
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() |
socket:sockaddr_in() |
socket:sockaddr_in6()
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.