| gen_udp(3erl) | Erlang Module Definition | gen_udp(3erl) |
gen_udp - Interface to UDP sockets.
This module provides functions for communicating with sockets using the UDP protocol.
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:
option() =
{active, true | false | once | -32768..32767} |
{add_membership, membership()} |
{broadcast, boolean()} |
{buffer, integer() >= 0} |
{debug, boolean()} |
{deliver, port | term} |
{dontroute, boolean()} |
{drop_membership, membership()} |
{header, integer() >= 0} |
{high_msgq_watermark, integer() >= 1} |
{low_msgq_watermark, integer() >= 1} |
{mode, list | binary} |
list | binary |
{multicast_if, multicast_if()} |
{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 | debug | 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.
multicast_if() = ip_multicast_if() | ip6_multicast_if()
ip_multicast_if() = inet:ip4_address()
ip6_multicast_if() = integer()
For IPv6 this is an interface index (an integer).
membership() = ip_membership() | ip6_membership()
ip_membership() =
{MultiAddress :: inet:ip4_address(),
Interface :: inet:ip4_address()} |
{MultiAddress :: inet:ip4_address(),
Address :: inet:ip4_address(),
IfIndex :: integer()}
The tuple with size 3 is *not* supported on all platforms. 'ifindex' defaults to zero (0) on platforms that supports the 3-tuple variant.
ip6_membership() =
{MultiAddress :: inet:ip6_address(), IfIndex :: integer()}
close(Socket) -> ok
Types:
Closes a UDP socket.
controlling_process(Socket, Pid) -> ok | {error, Reason}
Types:
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:
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:
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:
Associates a UDP port number (Port) with the calling process.
The following options are available:
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).
Datagrams with a TTL of 1 are not forwarded beyond the local network. Defaults to 1.
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:
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:
Sends a packet on a connected socket (see connect/2 and connect/3).
send(Socket, Destination, Packet) -> ok | {error, Reason}
Types:
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:
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:
Sends a packet to the specified Destination with ancillary data AncData.
send(Socket, Destination, PortZero, Packet) ->
ok | {error, Reason}
Types:
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:
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.
| kernel 8.5.3 | Ericsson AB |