inet - Access to TCP/IP protocols.
Please see following description for synopsis
inet(3) Erlang Module Definition inet(3)
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 inter-
nal 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
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).
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} repre-
sentation.
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} repre-
sentation.
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()
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).
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 inter-
faces it is the 6-byte Ethernet address (MAC address (EUI-48
address)).
The tuples {addr,Addr}, {netmask,Netmask}, and possibly {broad-
addr,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.
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
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 mon-
itor 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 informa-
tion, 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 parame-
ters.
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 host-
name.
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 host-
name.
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_setopt() | gen_tcp:pktoptions_value()]
Gets one or more options for a socket. For a list of available
options, see setopts/2. See also the description for the type
gen_tcp:pktoptions_value().
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 rea-
sons.
A raw option request RawOptReq = {raw, Protocol, OptionNum, Val-
ueSpec} 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 pro-
grammer to take advantage of unusual features present on a par-
ticular 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 corre-
spond to the required buffer size of the return value. The sup-
plied 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 Val-
ueBin, where all values are coded in the native endianess.
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 sys-
tem, 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 containg 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 pat-
tern:
{'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 cre-
ation).
Making several calls to inet:monitor/1 for the same Socket is
not an error; it results in as many independent monitoring
instances.
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 = ip_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 = ip_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 = ip_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 = ip_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 Exten-
sions.
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 sock-
ets, such as SCTP sockets. For other sockets it returns a one-
element list.
Notice that parameter Assoc is by the SCTP Sockets API Exten-
sions 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 receiv-
ing 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 mes-
sage, 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 speci-
fied, 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} behav-
ior 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 termi-
nation (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 pro-
vides 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 recommenda-
tion 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 con-
tinue 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 speci-
fied when the socket was created. If option header is speci-
fied, 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 sepa-
rate 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 compli-
cated 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 sys-
tem. The behavior of both an IPv6 and an IPv4 socket listen-
ing 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 com-
ponent 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 back-
ground.
{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 fea-
ture.
{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 sock-
ets appear to not support network namespaces.
Namespace is a filename and is encoded and decoded as dis-
cussed in module file, with the following exceptions:
* Emulator flag +fnu is ignored.
* getopts/2 for this option returns a binary for the file-
name 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 charac-
ters in network device names, special care has to be taken
when encoding this argument.
This option uses the Linux-specific socket option SO_BIND-
TODEVICE, 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 read-
able.
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 contain-
ing 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 applica-
tion 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 trun-
cated
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 auto-
matically 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 con-
sidered 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 proto-
cols (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 desti-
nation process, new packets are not read until a new notifi-
cation of available data has arrived. Defaults to 5. If this
parameter is set too high, the system can become unrespon-
sive 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 ancil-
lary data with the payload data (gen_udp and gen_sctp), the
TCLASS value is returned in an extended return tuple con-
tained 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 ancil-
lary 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 plat-
form 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 ancil-
lary 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 plat-
form supports the pktoptions option.
{reuseaddr, Boolean}:
Allows or disallows local reuse of port numbers. By default,
reuse is disallowed.
{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, econnre-
set} 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 plat-
forms 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 endianess of the platform and, if a struc-
ture is required, must follow the structure alignment conven-
tions 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 trans-
lates 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 sock-
ets, such as SCTP sockets. For other sockets it returns a one-
element list.
Notice that parameter Assoc is by the SCTP Sockets API Exten-
sions 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
Ericsson AB kernel 8.2 inet(3)