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NAME
inet - Access to TCP/IP protocols.
DESCRIPTION
This module provides access to TCP/IP protocols.
See also ERTS User's Guide: Inet Configuration for more information about how to configure
an Erlang runtime system for IP communication.
The following two Kernel configuration parameters affect the behavior of all sockets
opened on an Erlang node:
* inet_default_connect_options can contain a list of default options used for all
sockets returned when doing connect.
* inet_default_listen_options can contain a list of default options used when issuing a
listen call.
When accept is issued, the values of the listening socket options are inherited. No such
application variable is therefore needed for accept.
Using the Kernel configuration parameters above, one can set default options for all TCP
sockets on a node, but use this with care. Options such as {delay_send,true} can be
specified in this way. The following is an example of starting an Erlang node with all
sockets using delayed send:
$ erl -sname test -kernel \
inet_default_connect_options '[{delay_send,true}]' \
inet_default_listen_options '[{delay_send,true}]'
Notice that default option {active, true} cannot be changed, for internal reasons.
Addresses as inputs to functions can be either a string or a tuple. For example, the IP
address 150.236.20.73 can be passed to gethostbyaddr/1, either as string "150.236.20.73"
or as tuple {150, 236, 20, 73}.
IPv4 address examples:
Address ip_address()
------- ------------
127.0.0.1 {127,0,0,1}
192.168.42.2 {192,168,42,2}
IPv6 address examples:
Address ip_address()
------- ------------
::1 {0,0,0,0,0,0,0,1}
::192.168.42.2 {0,0,0,0,0,0,(192 bsl 8) bor 168,(42 bsl 8) bor 2}
::FFFF:192.168.42.2
{0,0,0,0,0,16#FFFF,(192 bsl 8) bor 168,(42 bsl 8) bor 2}
3ffe:b80:1f8d:2:204:acff:fe17:bf38
{16#3ffe,16#b80,16#1f8d,16#2,16#204,16#acff,16#fe17,16#bf38}
fe80::204:acff:fe17:bf38
{16#fe80,0,0,0,16#204,16#acff,16#fe17,16#bf38}
Function parse_address/1 can be useful:
1> inet:parse_address("192.168.42.2").
{ok,{192,168,42,2}}
2> inet:parse_address("::FFFF:192.168.42.2").
{ok,{0,0,0,0,0,65535,49320,10754}}
DATA TYPES
Exported data types
hostent() =
#hostent{h_name = inet:hostname(),
h_aliases = [inet:hostname()],
h_addrtype = inet | inet6,
h_length = integer() >= 0,
h_addr_list = [inet:ip_address()]}
The record is defined in the Kernel include file "inet.hrl".
Add the following directive to the module:
-include_lib("kernel/include/inet.hrl").
hostname() = atom() | string()
ip_address() = ip4_address() | ip6_address()
ip4_address() = {0..255, 0..255, 0..255, 0..255}
ip6_address() =
{0..65535,
0..65535,
0..65535,
0..65535,
0..65535,
0..65535,
0..65535,
0..65535}
port_number() = 0..65535
family_address() =
inet_address() | inet6_address() | local_address()
A general address format on the form {Family, Destination} where Family is an atom
such as local and the format of Destination depends on Family, and is a complete
address (for example an IP address including port number).
local_address() = {local, File :: binary() | string()}
This address family only works on Unix-like systems.
File is normally a file pathname in a local filesystem. It is limited in length by
the operating system, traditionally to 108 bytes.
A binary() is passed as is to the operating system, but a string() is encoded
according to the system filename encoding mode.
Other addresses are possible, for example Linux implements "Abstract Addresses".
See the documentation for Unix Domain Sockets on your system, normally unix in
manual section 7.
In most API functions where you can use this address family the port number must be
0.
inet_backend() = {inet_backend, inet | socket}
Select the implementation backend for sockets. The current default is inet which at
the bottom uses inet_drv.c to call the platform's socket API. The value socket
instead at the bottom uses the socket module and its NIF implementation.
This is a temporary option that will be ignored in a future release.
socket_address() =
ip_address() | any | loopback | local_address()
socket_getopt() =
gen_sctp:option_name() |
gen_tcp:option_name() |
gen_udp:option_name()
socket_setopt() =
gen_sctp:option() | gen_tcp:option() | gen_udp:option()
socket_optval() =
gen_sctp:option_value() |
gen_tcp:option() |
gen_udp:option() |
gen_tcp:pktoptions_value()
returned_non_ip_address() =
{local, binary()} | {unspec, <<>>} | {undefined, any()}
Addresses besides ip_address() ones that are returned from socket API functions.
See in particular local_address(). The unspec family corresponds to AF_UNSPEC and
can occur if the other side has no socket address. The undefined family can only
occur in the unlikely event of an address family that the VM does not recognize.
ancillary_data() =
[{tos, byte()} | {tclass, byte()} | {ttl, byte()}]
Ancillary data received with the data packet, read with the socket option
pktoptions from a TCP socket, or to set in a call to gen_udp:send/4 or
gen_udp:send/5.
The value(s) correspond to the currently active socket options recvtos, recvtclass
and recvttl, or for a single send operation the option(s) to override the currently
active socket option(s).
posix() =
eaddrinuse | eaddrnotavail | eafnosupport | ealready |
econnaborted | econnrefused | econnreset | edestaddrreq |
ehostdown | ehostunreach | einprogress | eisconn | emsgsize |
enetdown | enetunreach | enopkg | enoprotoopt | enotconn |
enotty | enotsock | eproto | eprotonosupport | eprototype |
esocktnosupport | etimedout | ewouldblock | exbadport |
exbadseq |
file:posix()
An atom that is named from the POSIX error codes used in Unix, and in the runtime
libraries of most C compilers. See section POSIX Error Codes.
socket()
See gen_tcp:type-socket and gen_udp:type-socket.
address_family() = inet | inet6 | local
socket_protocol() = tcp | udp | sctp
stat_option() =
recv_cnt | recv_max | recv_avg | recv_oct | recv_dvi |
send_cnt | send_max | send_avg | send_oct | send_pend
DATA TYPES
Internal data types
inet_address() =
{inet, {ip4_address() | any | loopback, port_number()}}
Warning:
This address format is for now experimental and for completeness to make all
address families have a {Family, Destination} representation.
inet6_address() =
{inet6, {ip6_address() | any | loopback, port_number()}}
Warning:
This address format is for now experimental and for completeness to make all
address families have a {Family, Destination} representation.
getifaddrs_ifopts() =
[Ifopt ::
{flags,
Flags ::
[up | broadcast | loopback | pointtopoint |
running | multicast]} |
{addr, Addr :: ip_address()} |
{netmask, Netmask :: ip_address()} |
{broadaddr, Broadaddr :: ip_address()} |
{dstaddr, Dstaddr :: ip_address()} |
{hwaddr, Hwaddr :: [byte()]}]
Interface address description list returned from getifaddrs/0,1 for a named
interface, translated from the returned data of the POSIX API function
getaddrinfo().
Hwaddr is hardware dependent, for example, on Ethernet interfaces it is the 6-byte
Ethernet address (MAC address (EUI-48 address)).
The tuples {addr,Addr}, {netmask,Netmask}, and possibly {broadaddr,Broadaddr} or
{dstaddr,Dstaddr} are repeated in the list if the interface has got multiple
addresses. An interface may have multiple {flag,_} tuples for example if it has
different flags for different address families. Multiple {hwaddr,Hwaddr} tuples is
hard to say anything definite about, though. The tuple {flag,Flags} is mandatory,
all others are optional.
Do not rely too much on the order of Flags atoms or the Ifopt tuples. There are
however some rules:
* A {flag,_} tuple applies to all other tuples that follow.
* Immediately after {addr,_} follows {netmask,_}.
* Immediately thereafter may {broadaddr,_} follow if broadcast is member of
Flags, or {dstaddr,_} if pointtopoint is member of Flags. Both {dstaddr,_} and
{broadaddr,_} does not occur for the same {addr,_}.
* Any {netmask,_}, {broadaddr,_}, or {dstaddr,_} tuples that follow an
{addr,Addr} tuple concerns the address Addr.
The tuple {hwaddr,_} is not returned on Solaris, as the hardware address
historically belongs to the link layer and it is not returned by the Solaris API
function getaddrinfo().
Warning:
On Windows, the data is fetched from different OS API functions, so the Netmask and
Broadaddr values may be calculated, just as some Flags values.
EXPORTS
close(Socket) -> ok
Types:
Socket = socket()
Closes a socket of any type.
cancel_monitor(MRef) -> boolean()
Types:
MRef = reference()
If MRef is a reference that the calling process obtained by calling monitor/1, this
monitor is turned off. If the monitoring is already turned off, nothing happens.
The returned value is one of the following:
true:
The monitor was found and removed. In this case, no 'DOWN' message
corresponding to this monitor has been delivered and will not be delivered.
false:
The monitor was not found and could not be removed. This probably because a
'DOWN' message corresponding to this monitor has already been placed in the
caller message queue.
Failure: It is an error if MRef refers to a monitor started by another process.
format_error(Reason) -> string()
Types:
Reason = posix() | system_limit
Returns a diagnostic error string. For possible POSIX values and corresponding
strings, see section POSIX Error Codes.
get_rc() ->
[{Par :: atom(), Val :: any()} |
{Par :: atom(), Val1 :: any(), Val2 :: any()}]
Returns the state of the Inet configuration database in form of a list of recorded
configuration parameters. For more information, see ERTS User's Guide: Inet
Configuration.
Only actual parameters with other than default values are returned, for example not
directives that specify other sources for configuration parameters nor directives
that clear parameters.
getaddr(Host, Family) -> {ok, Address} | {error, posix()}
Types:
Host = ip_address() | hostname()
Family = address_family()
Address = ip_address()
Returns the IP address for Host as a tuple of integers. Host can be an IP address,
a single hostname, or a fully qualified hostname.
getaddrs(Host, Family) -> {ok, Addresses} | {error, posix()}
Types:
Host = ip_address() | hostname()
Family = address_family()
Addresses = [ip_address()]
Returns a list of all IP addresses for Host. Host can be an IP address, a single
hostname, or a fully qualified hostname.
gethostbyaddr(Address) -> {ok, Hostent} | {error, posix()}
Types:
Address = string() | ip_address()
Hostent = hostent()
Returns a hostent record for the host with the specified address.
gethostbyname(Hostname) -> {ok, Hostent} | {error, posix()}
Types:
Hostname = hostname()
Hostent = hostent()
Returns a hostent record for the host with the specified hostname.
If resolver option inet6 is true, an IPv6 address is looked up.
gethostbyname(Hostname, Family) ->
{ok, Hostent} | {error, posix()}
Types:
Hostname = hostname()
Family = address_family()
Hostent = hostent()
Returns a hostent record for the host with the specified name, restricted to the
specified address family.
gethostname() -> {ok, Hostname}
Types:
Hostname = string()
Returns the local hostname. Never fails.
getifaddrs() ->
{ok,
[{Ifname :: string(),
Ifopts :: getifaddrs_ifopts()}]} |
{error, posix()}
Returns a list of 2-tuples containing interface names and the interfaces'
addresses. Ifname is a Unicode string and Ifopts is a list of interface address
description tuples.
The interface address description tuples are documented under the type of the
Ifopts value.
getifaddrs(Opts) -> {ok, [{Ifname, Ifopts}]} | {error, Posix}
Types:
Opts = [{netns, Namespace}]
Namespace = file:filename_all()
Ifname = string()
Ifopts = getifaddrs_ifopts()
Posix = posix()
The same as getifaddrs/0 but the Option {netns, Namespace} sets a network namespace
for the OS call, on platforms that supports that feature.
See the socket option {netns, Namespace} under setopts/2.
getopts(Socket, Options) -> {ok, OptionValues} | {error, posix()}
Types:
Socket = socket()
Options = [socket_getopt()]
OptionValues = [socket_optval()]
Gets one or more options for a socket. For a list of available inet options, see
setopts/2. See also the descriptions for the protocol specific types referenced by
socket_optval().
The number of elements in the returned OptionValues list does not necessarily
correspond to the number of options asked for. If the operating system fails to
support an option, it is left out in the returned list. An error tuple is returned
only when getting options for the socket is impossible (that is, the socket is
closed or the buffer size in a raw request is too large). This behavior is kept for
backward compatibility reasons.
A raw option request RawOptReq = {raw, Protocol, OptionNum, ValueSpec} can be used
to get information about socket options not (explicitly) supported by the emulator.
The use of raw socket options makes the code non-portable, but allows the Erlang
programmer to take advantage of unusual features present on a particular platform.
RawOptReq consists of tag raw followed by the protocol level, the option number,
and either a binary or the size, in bytes, of the buffer in which the option value
is to be stored. A binary is to be used when the underlying getsockopt requires
input in the argument field. In this case, the binary size is to correspond to the
required buffer size of the return value. The supplied values in a RawOptReq
correspond to the second, third, and fourth/fifth parameters to the getsockopt call
in the C socket API. The value stored in the buffer is returned as a binary
ValueBin, where all values are coded in the native endianness.
Asking for and inspecting raw socket options require low-level information about
the current operating system and TCP stack.
Example:
Consider a Linux machine where option TCP_INFO can be used to collect TCP
statistics for a socket. Assume you are interested in field tcpi_sacked of struct
tcp_info filled in when asking for TCP_INFO. To be able to access this information,
you need to know the following:
* The numeric value of protocol level IPPROTO_TCP
* The numeric value of option TCP_INFO
* The size of struct tcp_info
* The size and offset of the specific field
By inspecting the headers or writing a small C program, it is found that
IPPROTO_TCP is 6, TCP_INFO is 11, the structure size is 92 (bytes), the offset of
tcpi_sacked is 28 bytes, and the value is a 32-bit integer. The following code can
be used to retrieve the value:
get_tcpi_sacked(Sock) ->
{ok,[{raw,_,_,Info}]} = inet:getopts(Sock,[{raw,6,11,92}]),
<<_:28/binary,TcpiSacked:32/native,_/binary>> = Info,
TcpiSacked.
Preferably, you would check the machine type, the operating system, and the Kernel
version before executing anything similar to this code.
getstat(Socket) -> {ok, OptionValues} | {error, posix()}
getstat(Socket, Options) -> {ok, OptionValues} | {error, posix()}
Types:
Socket = socket()
Options = [stat_option()]
OptionValues = [{stat_option(), integer()}]
stat_option() =
recv_cnt | recv_max | recv_avg | recv_oct | recv_dvi |
send_cnt | send_max | send_avg | send_oct | send_pend
Gets one or more statistic options for a socket.
getstat(Socket) is equivalent to getstat(Socket, [recv_avg, recv_cnt, recv_dvi,
recv_max, recv_oct, send_avg, send_cnt, send_pend, send_max, send_oct]).
The following options are available:
recv_avg:
Average size of packets, in bytes, received by the socket.
recv_cnt:
Number of packets received by the socket.
recv_dvi:
Average packet size deviation, in bytes, received by the socket.
recv_max:
Size of the largest packet, in bytes, received by the socket.
recv_oct:
Number of bytes received by the socket.
send_avg:
Average size of packets, in bytes, sent from the socket.
send_cnt:
Number of packets sent from the socket.
send_pend:
Number of bytes waiting to be sent by the socket.
send_max:
Size of the largest packet, in bytes, sent from the socket.
send_oct:
Number of bytes sent from the socket.
i() -> ok
i(Proto :: socket_protocol()) -> ok
i(X1 :: socket_protocol(), Fs :: [atom()]) -> ok
Lists all TCP, UDP and SCTP sockets, including those that the Erlang runtime system
uses as well as those created by the application.
The following options are available:
port:
The internal index of the port.
module:
The callback module of the socket.
recv:
Number of bytes received by the socket.
sent:
Number of bytes sent from the socket.
owner:
The socket owner process.
local_address:
The local address of the socket.
foreign_address:
The address and port of the other end of the connection.
state:
The connection state.
type:
STREAM or DGRAM or SEQPACKET.
info(Socket) -> Info
Types:
Socket = socket()
Info = term()
Produces a term containing miscellaneous information about a socket.
monitor(Socket) -> reference()
Types:
Socket = socket()
Start monitor the socket Socket.
If the monitored socket does not exist or when the monitor is triggered, a 'DOWN'
message is sent that has the following pattern:
{'DOWN', MonitorRef, Type, Object, Info}
MonitorRef:
The identity of the socket.
Type:
The type of socket, can be one of the following atoms: port or socket.
Object:
The monitored entity, the socket, which triggered the event.
Info:
Either the termination reason of the socket or nosock (socket Socket did not
exist at the time of monitor creation).
Making several calls to inet:monitor/1 for the same Socket is not an error; it
results in as many independent monitoring instances.
is_ip_address(IPAddress) -> boolean()
Types:
IPAddress = ip_address() | term()
Tests if IPAddress is an ip_address() and returns true if so, otherwise false.
is_ipv4_address(IPv4Address) -> boolean()
Types:
IPv4Address = ip4_address() | term()
Tests if IPAddress is an ip4_address() and returns true if so, otherwise false.
is_ipv6_address(IPv6Address) -> boolean()
Types:
IPv6Address = ip6_address() | term()
Tests if IPAddress is an ip6_address() and returns true if so, otherwise false.
ntoa(IpAddress) -> Address | {error, einval}
Types:
Address = string()
IpAddress = ip_address()
Parses an ip_address() and returns an IPv4 or IPv6 address string.
parse_address(Address) -> {ok, IPAddress} | {error, einval}
Types:
Address = string()
IPAddress = ip_address()
Parses an IPv4 or IPv6 address string and returns an ip4_address() or
ip6_address(). Accepts a shortened IPv4 address string.
parse_ipv4_address(Address) -> {ok, IPv4Address} | {error, einval}
Types:
Address = string()
IPv4Address = ip4_address()
Parses an IPv4 address string and returns an ip4_address(). Accepts a shortened
IPv4 address string.
parse_ipv4strict_address(Address) ->
{ok, IPv4Address} | {error, einval}
Types:
Address = string()
IPv4Address = ip4_address()
Parses an IPv4 address string containing four fields, that is, not shortened, and
returns an ip4_address().
parse_ipv6_address(Address) -> {ok, IPv6Address} | {error, einval}
Types:
Address = string()
IPv6Address = ip6_address()
Parses an IPv6 address string and returns an ip6_address(). If an IPv4 address
string is specified, an IPv4-mapped IPv6 address is returned.
parse_ipv6strict_address(Address) ->
{ok, IPv6Address} | {error, einval}
Types:
Address = string()
IPv6Address = ip6_address()
Parses an IPv6 address string and returns an ip6_address(). Does not accept IPv4
addresses.
ipv4_mapped_ipv6_address(X1 :: ip_address()) -> ip_address()
Convert an IPv4 address to an IPv4-mapped IPv6 address or the reverse. When
converting from an IPv6 address all but the 2 low words are ignored so this
function also works on some other types of addresses than IPv4-mapped.
parse_strict_address(Address) -> {ok, IPAddress} | {error, einval}
Types:
Address = string()
IPAddress = ip_address()
Parses an IPv4 or IPv6 address string and returns an ip4_address() or
ip6_address(). Does not accept a shortened IPv4 address string.
peername(Socket :: socket()) ->
{ok,
{ip_address(), port_number()} |
returned_non_ip_address()} |
{error, posix()}
Returns the address and port for the other end of a connection.
Notice that for SCTP sockets, this function returns only one of the peer addresses
of the socket. Function peernames/1,2 returns all.
peernames(Socket :: socket()) ->
{ok,
[{ip_address(), port_number()} |
returned_non_ip_address()]} |
{error, posix()}
Equivalent to peernames(Socket, 0).
Notice that the behavior of this function for an SCTP one-to-many style socket is
not defined by the SCTP Sockets API Extensions.
peernames(Socket, Assoc) ->
{ok, [{Address, Port}]} | {error, posix()}
Types:
Socket = socket()
Assoc = #sctp_assoc_change{} | gen_sctp:assoc_id()
Address = ip_address()
Port = integer() >= 0
Returns a list of all address/port number pairs for the other end of an association
Assoc of a socket.
This function can return multiple addresses for multihomed sockets, such as SCTP
sockets. For other sockets it returns a one-element list.
Notice that parameter Assoc is by the SCTP Sockets API Extensions defined to be
ignored for one-to-one style sockets. What the special value 0 means, hence its
behavior for one-to-many style sockets, is unfortunately undefined.
port(Socket) -> {ok, Port} | {error, any()}
Types:
Socket = socket()
Port = port_number()
Returns the local port number for a socket.
setopts(Socket, Options) -> ok | {error, posix()}
Types:
Socket = socket()
Options = [socket_setopt()]
Sets one or more options for a socket.
The following options are available:
{active, true | false | once | N}:
If the value is true, which is the default, everything received from the socket
is sent as messages to the receiving process.
If the value is false (passive mode), the process must explicitly receive
incoming data by calling gen_tcp:recv/2,3, gen_udp:recv/2,3, or
gen_sctp:recv/1,2 (depending on the type of socket).
If the value is once ({active, once}), one data message from the socket is sent
to the process. To receive one more message, setopts/2 must be called again
with option {active, once}.
If the value is an integer N in the range -32768 to 32767 (inclusive), the
value is added to the socket's count of data messages sent to the controlling
process. A socket's default message count is 0. If a negative value is
specified, and its magnitude is equal to or greater than the socket's current
message count, the socket's message count is set to 0. Once the socket's
message count reaches 0, either because of sending received data messages to
the process or by being explicitly set, the process is then notified by a
special message, specific to the type of socket, that the socket has entered
passive mode. Once the socket enters passive mode, to receive more messages
setopts/2 must be called again to set the socket back into an active mode.
When using {active, once} or {active, N}, the socket changes behavior
automatically when data is received. This can be confusing in combination with
connection-oriented sockets (that is, gen_tcp), as a socket with {active,
false} behavior reports closing differently than a socket with {active, true}
behavior. To simplify programming, a socket where the peer closed, and this is
detected while in {active, false} mode, still generates message
{tcp_closed,Socket} when set to {active, once}, {active, true}, or {active, N}
mode. It is therefore safe to assume that message {tcp_closed,Socket}, possibly
followed by socket port termination (depending on option exit_on_close)
eventually appears when a socket changes back and forth between {active, true}
and {active, false} mode. However, when peer closing is detected it is all up
to the underlying TCP/IP stack and protocol.
Notice that {active, true} mode provides no flow control; a fast sender can
easily overflow the receiver with incoming messages. The same is true for
{active, N} mode, while the message count is greater than zero.
Use active mode only if your high-level protocol provides its own flow control
(for example, acknowledging received messages) or the amount of data exchanged
is small. {active, false} mode, use of the {active, once} mode, or {active, N}
mode with values of N appropriate for the application provides flow control.
The other side cannot send faster than the receiver can read.
{broadcast, Boolean} (UDP sockets):
Enables/disables permission to send broadcasts.
{buffer, Size}:
The size of the user-level buffer used by the driver. Not to be confused with
options sndbuf and recbuf, which correspond to the Kernel socket buffers. For
TCP it is recommended to have val(buffer) >= val(recbuf) to avoid performance
issues because of unnecessary copying. For UDP the same recommendation applies,
but the max should not be larger than the MTU of the network path. val(buffer)
is automatically set to the above maximum when recbuf is set. However, as the
size set for recbuf usually become larger, you are encouraged to use getopts/2
to analyze the behavior of your operating system.
Note that this is also the maximum amount of data that can be received from a
single recv call. If you are using higher than normal MTU consider setting
buffer higher.
{delay_send, Boolean}:
Normally, when an Erlang process sends to a socket, the driver tries to send
the data immediately. If that fails, the driver uses any means available to
queue up the message to be sent whenever the operating system says it can
handle it. Setting {delay_send, true} makes all messages queue up. The messages
sent to the network are then larger but fewer. The option affects the
scheduling of send requests versus Erlang processes instead of changing any
real property of the socket. The option is implementation-specific. Defaults to
false.
{deliver, port | term}:
When {active, true}, data is delivered on the form port : {S, {data, [H1,..Hsz
| Data]}} or term : {tcp, S, [H1..Hsz | Data]}.
{dontroute, Boolean}:
Enables/disables routing bypass for outgoing messages.
{exit_on_close, Boolean}:
This option is set to true by default.
The only reason to set it to false is if you want to continue sending data to
the socket after a close is detected, for example, if the peer uses
gen_tcp:shutdown/2 to shut down the write side.
{header, Size}:
This option is only meaningful if option binary was specified when the socket
was created. If option header is specified, the first Size number bytes of data
received from the socket are elements of a list, and the remaining data is a
binary specified as the tail of the same list. For example, if Size == 2, the
data received matches [Byte1,Byte2|Binary].
{high_msgq_watermark, Size}:
The socket message queue is set to a busy state when the amount of data on the
message queue reaches this limit. Notice that this limit only concerns data
that has not yet reached the ERTS internal socket implementation. Defaults to 8
kB.
Senders of data to the socket are suspended if either the socket message queue
is busy or the socket itself is busy.
For more information, see options low_msgq_watermark, high_watermark, and
low_watermark.
Notice that distribution sockets disable the use of high_msgq_watermark and
low_msgq_watermark. Instead use the distribution buffer busy limit, which is a
similar feature.
{high_watermark, Size} (TCP/IP sockets):
The socket is set to a busy state when the amount of data queued internally by
the ERTS socket implementation reaches this limit. Defaults to 8 kB.
Senders of data to the socket are suspended if either the socket message queue
is busy or the socket itself is busy.
For more information, see options low_watermark, high_msgq_watermark, and
low_msqg_watermark.
{ipv6_v6only, Boolean}:
Restricts the socket to use only IPv6, prohibiting any IPv4 connections. This
is only applicable for IPv6 sockets (option inet6).
On most platforms this option must be set on the socket before associating it
to an address. It is therefore only reasonable to specify it when creating the
socket and not to use it when calling function (setopts/2) containing this
description.
The behavior of a socket with this option set to true is the only portable one.
The original idea when IPv6 was new of using IPv6 for all traffic is now not
recommended by FreeBSD (you can use {ipv6_v6only,false} to override the
recommended system default value), forbidden by OpenBSD (the supported GENERIC
kernel), and impossible on Windows (which has separate IPv4 and IPv6 protocol
stacks). Most Linux distros still have a system default value of false. This
policy shift among operating systems to separate IPv6 from IPv4 traffic has
evolved, as it gradually proved hard and complicated to get a dual stack
implementation correct and secure.
On some platforms, the only allowed value for this option is true, for example,
OpenBSD and Windows. Trying to set this option to false, when creating the
socket, fails in this case.
Setting this option on platforms where it does not exist is ignored. Getting
this option with getopts/2 returns no value, that is, the returned list does
not contain an {ipv6_v6only,_} tuple. On Windows, the option does not exist,
but it is emulated as a read-only option with value true.
Therefore, setting this option to true when creating a socket never fails,
except possibly on a platform where you have customized the kernel to only
allow false, which can be doable (but awkward) on, for example, OpenBSD.
If you read back the option value using getopts/2 and get no value, the option
does not exist in the host operating system. The behavior of both an IPv6 and
an IPv4 socket listening on the same port, and for an IPv6 socket getting IPv4
traffic is then no longer predictable.
{keepalive, Boolean}(TCP/IP sockets):
Enables/disables periodic transmission on a connected socket when no other data
is exchanged. If the other end does not respond, the connection is considered
broken and an error message is sent to the controlling process. Defaults to
false.
{linger, {true|false, Seconds}}:
Determines the time-out, in seconds, for flushing unsent data in the close/1
socket call.
The first component is if linger is enabled, the second component is the
flushing time-out, in seconds. There are 3 alternatives:
{false, _}:
close/1 or shutdown/2 returns immediately, not waiting for data to be
flushed, with closing happening in the background.
{true, 0}:
Aborts the connection when it is closed. Discards any data still remaining in
the send buffers and sends RST to the peer.
This avoids TCP's TIME_WAIT state, but leaves open the possibility that
another "incarnation" of this connection being created.
{true, Time} when Time > 0:
close/1 or shutdown/2 will not return until all queued messages for the
socket have been successfully sent or the linger timeout (Time) has been
reached.
{low_msgq_watermark, Size}:
If the socket message queue is in a busy state, the socket message queue is set
in a not busy state when the amount of data queued in the message queue falls
below this limit. Notice that this limit only concerns data that has not yet
reached the ERTS internal socket implementation. Defaults to 4 kB.
Senders that are suspended because of either a busy message queue or a busy
socket are resumed when the socket message queue and the socket are not busy.
For more information, see options high_msgq_watermark, high_watermark, and
low_watermark.
Notice that distribution sockets disable the use of high_msgq_watermark and
low_msgq_watermark. Instead they use the distribution buffer busy limit, which
is a similar feature.
{low_watermark, Size} (TCP/IP sockets):
If the socket is in a busy state, the socket is set in a not busy state when
the amount of data queued internally by the ERTS socket implementation falls
below this limit. Defaults to 4 kB.
Senders that are suspended because of a busy message queue or a busy socket are
resumed when the socket message queue and the socket are not busy.
For more information, see options high_watermark, high_msgq_watermark, and
low_msgq_watermark.
{mode, Mode :: binary | list}:
Received Packet is delivered as defined by Mode.
{netns, Namespace :: file:filename_all()}:
Sets a network namespace for the socket. Parameter Namespace is a filename
defining the namespace, for example, "/var/run/netns/example", typically
created by command ip netns add example. This option must be used in a function
call that creates a socket, that is, gen_tcp:connect/3,4, gen_tcp:listen/2,
gen_udp:open/1,2 or gen_sctp:open/0,1,2, and also getifaddrs/1.
This option uses the Linux-specific syscall setns(), such as in Linux kernel
3.0 or later, and therefore only exists when the runtime system is compiled for
such an operating system.
The virtual machine also needs elevated privileges, either running as superuser
or (for Linux) having capability CAP_SYS_ADMIN according to the documentation
for setns(2). However, during testing also CAP_SYS_PTRACE and
CAP_DAC_READ_SEARCH have proven to be necessary.
Example:
setcap cap_sys_admin,cap_sys_ptrace,cap_dac_read_search+epi beam.smp
Notice that the filesystem containing the virtual machine executable (beam.smp
in the example) must be local, mounted without flag nosetuid, support extended
attributes, and the kernel must support file capabilities. All this runs out of
the box on at least Ubuntu 12.04 LTS, except that SCTP sockets appear to not
support network namespaces.
Namespace is a filename and is encoded and decoded as discussed in module file,
with the following exceptions:
* Emulator flag +fnu is ignored.
* getopts/2 for this option returns a binary for the filename if the stored
filename cannot be decoded. This is only to occur if you set the option using
a binary that cannot be decoded with the emulator's filename encoding:
file:native_name_encoding/0.
{bind_to_device, Ifname :: binary()}:
Binds a socket to a specific network interface. This option must be used in a
function call that creates a socket, that is, gen_tcp:connect/3,4,
gen_tcp:listen/2, gen_udp:open/1,2, or gen_sctp:open/0,1,2.
Unlike getifaddrs/0, Ifname is encoded a binary. In the unlikely case that a
system is using non-7-bit-ASCII characters in network device names, special
care has to be taken when encoding this argument.
This option uses the Linux-specific socket option SO_BINDTODEVICE, such as in
Linux kernel 2.0.30 or later, and therefore only exists when the runtime system
is compiled for such an operating system.
Before Linux 3.8, this socket option could be set, but could not retrieved with
getopts/2. Since Linux 3.8, it is readable.
The virtual machine also needs elevated privileges, either running as superuser
or (for Linux) having capability CAP_NET_RAW.
The primary use case for this option is to bind sockets into Linux VRF
instances.
list:
Received Packet is delivered as a list.
binary:
Received Packet is delivered as a binary.
{nodelay, Boolean}(TCP/IP sockets):
If Boolean == true, option TCP_NODELAY is turned on for the socket, which means
that also small amounts of data are sent immediately.
This option is not supported for domain = local, but if inet_backend =/= socket
this error will be ignored.
{nopush, Boolean}(TCP/IP sockets):
This translates to TCP_NOPUSH on BSD and to TCP_CORK on Linux.
If Boolean == true, the corresponding option is turned on for the socket, which
means that small amounts of data are accumulated until a full MSS-worth of data
is available or this option is turned off.
Note that while TCP_NOPUSH socket option is available on OSX, its semantics is
very different (e.g., unsetting it does not cause immediate send of accumulated
data). Hence, nopush option is intentionally ignored on OSX.
{packet, PacketType}(TCP/IP sockets):
Defines the type of packets to use for a socket. Possible values:
raw | 0:
No packaging is done.
1 | 2 | 4:
Packets consist of a header specifying the number of bytes in the packet,
followed by that number of bytes. The header length can be one, two, or four
bytes, and containing an unsigned integer in big-endian byte order. Each send
operation generates the header, and the header is stripped off on each
receive operation.
The 4-byte header is limited to 2Gb.
asn1 | cdr | sunrm | fcgi | tpkt | line:
These packet types only have effect on receiving. When sending a packet, it
is the responsibility of the application to supply a correct header. On
receiving, however, one message is sent to the controlling process for each
complete packet received, and, similarly, each call to gen_tcp:recv/2,3
returns one complete packet. The header is not stripped off.
The meanings of the packet types are as follows:
* asn1 - ASN.1 BER
* sunrm - Sun's RPC encoding
* cdr - CORBA (GIOP 1.1)
* fcgi - Fast CGI
* tpkt - TPKT format [RFC1006]
* line - Line mode, a packet is a line-terminated with newline, lines longer
than the receive buffer are truncated
http | http_bin:
The Hypertext Transfer Protocol. The packets are returned with the format
according to HttpPacket described in erlang:decode_packet/3 in ERTS. A socket
in passive mode returns {ok, HttpPacket} from gen_tcp:recv while an active
socket sends messages like {http, Socket, HttpPacket}.
httph | httph_bin:
These two types are often not needed, as the socket automatically switches
from http/http_bin to httph/httph_bin internally after the first line is
read. However, there can be occasions when they are useful, such as parsing
trailers from chunked encoding.
{packet_size, Integer}(TCP/IP sockets):
Sets the maximum allowed length of the packet body. If the packet header
indicates that the length of the packet is longer than the maximum allowed
length, the packet is considered invalid. The same occurs if the packet header
is too large for the socket receive buffer.
For line-oriented protocols (line, http*), option packet_size also guarantees
that lines up to the indicated length are accepted and not considered invalid
because of internal buffer limitations.
{line_delimiter, Char}(TCP/IP sockets):
Sets the line delimiting character for line-oriented protocols (line). Defaults
to $\n.
{raw, Protocol, OptionNum, ValueBin}:
See below.
{read_packets, Integer}(UDP sockets):
Sets the maximum number of UDP packets to read without intervention from the
socket when data is available. When this many packets have been read and
delivered to the destination process, new packets are not read until a new
notification of available data has arrived. Defaults to 5. If this parameter is
set too high, the system can become unresponsive because of UDP packet
flooding.
{recbuf, Size}:
The minimum size of the receive buffer to use for the socket. You are
encouraged to use getopts/2 to retrieve the size set by your operating system.
{recvtclass, Boolean}:
If set to true activates returning the received TCLASS value on platforms that
implements the protocol IPPROTO_IPV6 option IPV6_RECVTCLASS or
IPV6_2292RECVTCLASS for the socket. The value is returned as a {tclass,TCLASS}
tuple regardless of if the platform returns an IPV6_TCLASS or an
IPV6_RECVTCLASS CMSG value.
For packet oriented sockets that supports receiving ancillary data with the
payload data (gen_udp and gen_sctp), the TCLASS value is returned in an
extended return tuple contained in an ancillary data list. For stream
oriented sockets (gen_tcp) the only way to get the TCLASS value is if the
platform supports the pktoptions option.
{recvtos, Boolean}:
If set to true activates returning the received TOS value on platforms that
implements the protocol IPPROTO_IP option IP_RECVTOS for the socket. The value
is returned as a {tos,TOS} tuple regardless of if the platform returns an
IP_TOS or an IP_RECVTOS CMSG value.
For packet oriented sockets that supports receiving ancillary data with the
payload data (gen_udp and gen_sctp), the TOS value is returned in an extended
return tuple contained in an ancillary data list. For stream oriented sockets
(gen_tcp) the only way to get the TOS value is if the platform supports the
pktoptions option.
{recvttl, Boolean}:
If set to true activates returning the received TTL value on platforms that
implements the protocol IPPROTO_IP option IP_RECVTTL for the socket. The value
is returned as a {ttl,TTL} tuple regardless of if the platform returns an
IP_TTL or an IP_RECVTTL CMSG value.
For packet oriented sockets that supports receiving ancillary data with the
payload data (gen_udp and gen_sctp), the TTL value is returned in an extended
return tuple contained in an ancillary data list. For stream oriented sockets
(gen_tcp) the only way to get the TTL value is if the platform supports the
pktoptions option.
{reuseaddr, Boolean}:
Allows or disallows local reuse of address. By default, reuse is disallowed.
Note:
On Windows this option will be ignored unless Socket is an UDP socket. This since
the behavior of reuseaddr is very different on Windows compared to other system.
{send_timeout, Integer}:
Only allowed for connection-oriented sockets.
Specifies a longest time to wait for a send operation to be accepted by the
underlying TCP stack. When the limit is exceeded, the send operation returns
{error,timeout}. How much of a packet that got sent is unknown; the socket is
therefore to be closed whenever a time-out has occurred (see send_timeout_close
below). Defaults to infinity.
{send_timeout_close, Boolean}:
Only allowed for connection-oriented sockets.
Used together with send_timeout to specify whether the socket is to be
automatically closed when the send operation returns {error,timeout}. The
recommended setting is true, which automatically closes the socket. Defaults to
false because of backward compatibility.
{show_econnreset, Boolean} (TCP/IP sockets) :
When this option is set to false, which is default, an RST received from the
TCP peer is treated as a normal close (as though an FIN was sent). A caller to
gen_tcp:recv/2 gets {error, closed}. In active mode, the controlling process
receives a {tcp_closed, Socket} message, indicating that the peer has closed
the connection.
Setting this option to true allows you to distinguish between a connection that
was closed normally, and one that was aborted (intentionally or
unintentionally) by the TCP peer. A call to gen_tcp:recv/2 returns {error,
econnreset}. In active mode, the controlling process receives a {tcp_error,
Socket, econnreset} message before the usual {tcp_closed, Socket}, as is the
case for any other socket error. Calls to gen_tcp:send/2 also returns {error,
econnreset} when it is detected that a TCP peer has sent an RST.
A connected socket returned from gen_tcp:accept/1 inherits the show_econnreset
setting from the listening socket.
{sndbuf, Size}:
The minimum size of the send buffer to use for the socket. You are encouraged
to use getopts/2, to retrieve the size set by your operating system.
{priority, Integer}:
Sets the SO_PRIORITY socket level option on platforms where this is
implemented. The behavior and allowed range varies between different systems.
The option is ignored on platforms where it is not implemented. Use with
caution.
{tos, Integer}:
Sets IP_TOS IP level options on platforms where this is implemented. The
behavior and allowed range varies between different systems. The option is
ignored on platforms where it is not implemented. Use with caution.
{tclass, Integer}:
Sets IPV6_TCLASS IP level options on platforms where this is implemented. The
behavior and allowed range varies between different systems. The option is
ignored on platforms where it is not implemented. Use with caution.
In addition to these options, raw option specifications can be used. The raw
options are specified as a tuple of arity four, beginning with tag raw, followed by
the protocol level, the option number, and the option value specified as a binary.
This corresponds to the second, third, and fourth arguments to the setsockopt call
in the C socket API. The option value must be coded in the native endianness of the
platform and, if a structure is required, must follow the structure alignment
conventions on the specific platform.
Using raw socket options requires detailed knowledge about the current operating
system and TCP stack.
Example:
This example concerns the use of raw options. Consider a Linux system where you
want to set option TCP_LINGER2 on protocol level IPPROTO_TCP in the stack. You know
that on this particular system it defaults to 60 (seconds), but you want to lower
it to 30 for a particular socket. Option TCP_LINGER2 is not explicitly supported by
inet, but you know that the protocol level translates to number 6, the option
number to number 8, and the value is to be specified as a 32-bit integer. You can
use this code line to set the option for the socket named Sock:
inet:setopts(Sock,[{raw,6,8,<<30:32/native>>}]),
As many options are silently discarded by the stack if they are specified out of
range; it can be a good idea to check that a raw option is accepted. The following
code places the value in variable TcpLinger2:
{ok,[{raw,6,8,<<TcpLinger2:32/native>>}]}=inet:getopts(Sock,[{raw,6,8,4}]),
Code such as these examples is inherently non-portable, even different versions of
the same OS on the same platform can respond differently to this kind of option
manipulation. Use with care.
Notice that the default options for TCP/IP sockets can be changed with the Kernel
configuration parameters mentioned in the beginning of this manual page.
sockname(Socket :: socket()) ->
{ok,
{ip_address(), port_number()} |
returned_non_ip_address()} |
{error, posix()}
Returns the local address and port number for a socket.
Notice that for SCTP sockets this function returns only one of the socket
addresses. Function socknames/1,2 returns all.
socknames(Socket :: socket()) ->
{ok,
[{ip_address(), port_number()} |
returned_non_ip_address()]} |
{error, posix()}
Equivalent to socknames(Socket, 0).
socknames(Socket, Assoc) ->
{ok, [{Address, Port}]} | {error, posix()}
Types:
Socket = socket()
Assoc = #sctp_assoc_change{} | gen_sctp:assoc_id()
Address = ip_address()
Port = integer() >= 0
Returns a list of all local address/port number pairs for a socket for the
specified association Assoc.
This function can return multiple addresses for multihomed sockets, such as SCTP
sockets. For other sockets it returns a one-element list.
Notice that parameter Assoc is by the SCTP Sockets API Extensions defined to be
ignored for one-to-one style sockets. For one-to-many style sockets, the special
value 0 is defined to mean that the returned addresses must be without any
particular association. How different SCTP implementations interpret this varies
somewhat.
POSIX ERROR CODES
* e2big - Too long argument list
* eacces - Permission denied
* eaddrinuse - Address already in use
* eaddrnotavail - Cannot assign requested address
* eadv - Advertise error
* eafnosupport - Address family not supported by protocol family
* eagain - Resource temporarily unavailable
* ealign - EALIGN
* ealready - Operation already in progress
* ebade - Bad exchange descriptor
* ebadf - Bad file number
* ebadfd - File descriptor in bad state
* ebadmsg - Not a data message
* ebadr - Bad request descriptor
* ebadrpc - Bad RPC structure
* ebadrqc - Bad request code
* ebadslt - Invalid slot
* ebfont - Bad font file format
* ebusy - File busy
* echild - No children
* echrng - Channel number out of range
* ecomm - Communication error on send
* econnaborted - Software caused connection abort
* econnrefused - Connection refused
* econnreset - Connection reset by peer
* edeadlk - Resource deadlock avoided
* edeadlock - Resource deadlock avoided
* edestaddrreq - Destination address required
* edirty - Mounting a dirty fs without force
* edom - Math argument out of range
* edotdot - Cross mount point
* edquot - Disk quota exceeded
* eduppkg - Duplicate package name
* eexist - File already exists
* efault - Bad address in system call argument
* efbig - File too large
* ehostdown - Host is down
* ehostunreach - Host is unreachable
* eidrm - Identifier removed
* einit - Initialization error
* einprogress - Operation now in progress
* eintr - Interrupted system call
* einval - Invalid argument
* eio - I/O error
* eisconn - Socket is already connected
* eisdir - Illegal operation on a directory
* eisnam - Is a named file
* el2hlt - Level 2 halted
* el2nsync - Level 2 not synchronized
* el3hlt - Level 3 halted
* el3rst - Level 3 reset
* elbin - ELBIN
* elibacc - Cannot access a needed shared library
* elibbad - Accessing a corrupted shared library
* elibexec - Cannot exec a shared library directly
* elibmax - Attempting to link in more shared libraries than system limit
* elibscn - .lib section in a.out corrupted
* elnrng - Link number out of range
* eloop - Too many levels of symbolic links
* emfile - Too many open files
* emlink - Too many links
* emsgsize - Message too long
* emultihop - Multihop attempted
* enametoolong - Filename too long
* enavail - Unavailable
* enet - ENET
* enetdown - Network is down
* enetreset - Network dropped connection on reset
* enetunreach - Network is unreachable
* enfile - File table overflow
* enoano - Anode table overflow
* enobufs - No buffer space available
* enocsi - No CSI structure available
* enodata - No data available
* enodev - No such device
* enoent - No such file or directory
* enoexec - Exec format error
* enolck - No locks available
* enolink - Link has been severed
* enomem - Not enough memory
* enomsg - No message of desired type
* enonet - Machine is not on the network
* enopkg - Package not installed
* enoprotoopt - Bad protocol option
* enospc - No space left on device
* enosr - Out of stream resources or not a stream device
* enosym - Unresolved symbol name
* enosys - Function not implemented
* enotblk - Block device required
* enotconn - Socket is not connected
* enotdir - Not a directory
* enotempty - Directory not empty
* enotnam - Not a named file
* enotsock - Socket operation on non-socket
* enotsup - Operation not supported
* enotty - Inappropriate device for ioctl
* enotuniq - Name not unique on network
* enxio - No such device or address
* eopnotsupp - Operation not supported on socket
* eperm - Not owner
* epfnosupport - Protocol family not supported
* epipe - Broken pipe
* eproclim - Too many processes
* eprocunavail - Bad procedure for program
* eprogmismatch - Wrong program version
* eprogunavail - RPC program unavailable
* eproto - Protocol error
* eprotonosupport - Protocol not supported
* eprototype - Wrong protocol type for socket
* erange - Math result unrepresentable
* erefused - EREFUSED
* eremchg - Remote address changed
* eremdev - Remote device
* eremote - Pathname hit remote filesystem
* eremoteio - Remote I/O error
* eremoterelease - EREMOTERELEASE
* erofs - Read-only filesystem
* erpcmismatch - Wrong RPC version
* erremote - Object is remote
* eshutdown - Cannot send after socket shutdown
* esocktnosupport - Socket type not supported
* espipe - Invalid seek
* esrch - No such process
* esrmnt - Srmount error
* estale - Stale remote file handle
* esuccess - Error 0
* etime - Timer expired
* etimedout - Connection timed out
* etoomanyrefs - Too many references
* etxtbsy - Text file or pseudo-device busy
* euclean - Structure needs cleaning
* eunatch - Protocol driver not attached
* eusers - Too many users
* eversion - Version mismatch
* ewouldblock - Operation would block
* exdev - Cross-domain link
* exfull - Message tables full
* nxdomain - Hostname or domain name cannot be found