Access to TCP/IP protocols.
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 doingconnect
.inet_default_listen_options
can contain a list of default options used when issuing alisten
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#fe80,0,0,0,0,16#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}}
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
local_address() = {local, File :: binary() | string()}
This address family only works on Unix-like systems.
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
.
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
or read with the socket option
pktoptions
from a TCP socket.
The value(s) correspond to the currently active socket
options
recvtos
,
recvtclass
and
recvttl
.
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()
.
is hardware dependent,
for example, on Ethernet interfaces it is
the 6-byte Ethernet address (MAC address (EUI-48 address)).
The tuples {addr,
,
{netmask,
, and possibly
{broadaddr,
or
{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,
tuples
is hard to say anything definite about, though.
The tuple {flag,
is mandatory,
all others are optional.
Do not rely too much on the order
of
atoms
or the
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 ifbroadcast
is member of
, orFlags {dstaddr,_}
ifpointtopoint
is member of
. BothFlags {dstaddr,_}
and{broadaddr,_}
does not occur for the same{addr,_}
.Any
{netmask,_}
,{broadaddr,_}
, or{dstaddr,_}
tuples that follow an{addr,
tuple concerns the addressAddr }
.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
and
values may be calculated,
just as some
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
Functions
format_error(Reason) -> string()
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()}
Host = ip_address() | hostname()
Family = address_family()
Address = ip_address()
Returns the IP address for
as a tuple of
integers.
can be an IP address, a single
hostname, or a fully qualified hostname.
getaddrs(Host, Family) -> {ok, Addresses} | {error, posix()}
Host = ip_address() | hostname()
Family = address_family()
Addresses = [ip_address()]
Returns a list of all IP addresses for
.
can be an IP address, a single hostname, or
a fully qualified hostname.
gethostbyaddr(Address) -> {ok, Hostent} | {error, posix()}
Address = string() | ip_address()
Hostent = hostent()
Returns a hostent
record for the host with the specified
address.
gethostbyname(Hostname) -> {ok, Hostent} | {error, posix()}
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()}
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}
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.
is a Unicode string and
is a list of
interface address description tuples.
The interface address description tuples
are documented under the type of the
value.
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()}
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
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 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 system, and the Kernel version before executing anything similar to this code.
getstat(Socket) -> {ok, OptionValues} | {error, posix()}
Socket = socket()
OptionValues = [{stat_option(), integer()}]
getstat(Socket, Options) -> {ok, OptionValues} | {error, posix()}
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(
is equivalent to
getstat(
.
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_dvi
Average packet size deviation, in bytes, sent from 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.
ntoa(IpAddress) -> Address | {error, einval}
Address = string()
IpAddress = ip_address()
Parses an
ip_address()
and returns an IPv4 or IPv6 address string.
parse_address(Address) -> {ok, IPAddress} | {error, einval}
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}
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}
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}
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}
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}
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(
.
Notice that the behavior of this function for an SCTP
one-to-many style socket is not defined by the
peernames(Socket, Assoc) ->
{ok, [{Address, Port}]} | {error, posix()}
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
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
is by the
0
means, hence its behavior for one-to-many style sockets,
is unfortunately undefined.
port(Socket) -> {ok, Port} | {error, any()}
Socket = socket()
Port = port_number()
Returns the local port number for a socket.
setopts(Socket, Options) -> ok | {error, posix()}
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 disabled
.
{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
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.
{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 BERsunrm
- Sun's RPC encodingcdr
- CORBA (GIOP 1.1)fcgi
- Fast CGItpkt
- 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 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, 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 endianess 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(
.
socknames(Socket, Assoc) ->
{ok, [{Address, Port}]} | {error, posix()}
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
.
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
is by the
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 listeacces
- Permission deniedeaddrinuse
- Address already in useeaddrnotavail
- Cannot assign requested addresseadv
- Advertise erroreafnosupport
- Address family not supported by protocol familyeagain
- Resource temporarily unavailableealign
- EALIGNealready
- Operation already in progressebade
- Bad exchange descriptorebadf
- Bad file numberebadfd
- File descriptor in bad stateebadmsg
- Not a data messageebadr
- Bad request descriptorebadrpc
- Bad RPC structureebadrqc
- Bad request codeebadslt
- Invalid slotebfont
- Bad font file formatebusy
- File busyechild
- No childrenechrng
- Channel number out of rangeecomm
- Communication error on sendeconnaborted
- Software caused connection aborteconnrefused
- Connection refusedeconnreset
- Connection reset by peeredeadlk
- Resource deadlock avoidededeadlock
- Resource deadlock avoidededestaddrreq
- Destination address requirededirty
- Mounting a dirty fs without forceedom
- Math argument out of rangeedotdot
- Cross mount pointedquot
- Disk quota exceedededuppkg
- Duplicate package nameeexist
- File already existsefault
- Bad address in system call argumentefbig
- File too largeehostdown
- Host is downehostunreach
- Host is unreachableeidrm
- Identifier removedeinit
- Initialization erroreinprogress
- Operation now in progresseintr
- Interrupted system calleinval
- Invalid argumenteio
- I/O erroreisconn
- Socket is already connectedeisdir
- Illegal operation on a directoryeisnam
- Is a named fileel2hlt
- Level 2 haltedel2nsync
- Level 2 not synchronizedel3hlt
- Level 3 haltedel3rst
- Level 3 resetelbin
- ELBINelibacc
- Cannot access a needed shared libraryelibbad
- Accessing a corrupted shared libraryelibexec
- Cannot exec a shared library directlyelibmax
- Attempting to link in more shared libraries than system limitelibscn
-.lib
section ina.out
corruptedelnrng
- Link number out of rangeeloop
- Too many levels of symbolic linksemfile
- Too many open filesemlink
- Too many linksemsgsize
- Message too longemultihop
- Multihop attemptedenametoolong
- Filename too longenavail
- Unavailableenet
- ENETenetdown
- Network is downenetreset
- Network dropped connection on resetenetunreach
- Network is unreachableenfile
- File table overflowenoano
- Anode table overflowenobufs
- No buffer space availableenocsi
- No CSI structure availableenodata
- No data availableenodev
- No such deviceenoent
- No such file or directoryenoexec
- Exec format errorenolck
- No locks availableenolink
- Link has been severedenomem
- Not enough memoryenomsg
- No message of desired typeenonet
- Machine is not on the networkenopkg
- Package not installedenoprotoopt
- Bad protocol optionenospc
- No space left on deviceenosr
- Out of stream resources or not a stream deviceenosym
- Unresolved symbol nameenosys
- Function not implementedenotblk
- Block device requiredenotconn
- Socket is not connectedenotdir
- Not a directoryenotempty
- Directory not emptyenotnam
- Not a named fileenotsock
- Socket operation on non-socketenotsup
- Operation not supportedenotty
- Inappropriate device forioctl
enotuniq
- Name not unique on networkenxio
- No such device or addresseopnotsupp
- Operation not supported on socketeperm
- Not ownerepfnosupport
- Protocol family not supportedepipe
- Broken pipeeproclim
- Too many processeseprocunavail
- Bad procedure for programeprogmismatch
- Wrong program versioneprogunavail
- RPC program unavailableeproto
- Protocol erroreprotonosupport
- Protocol not supportedeprototype
- Wrong protocol type for socketerange
- Math result unrepresentableerefused
- EREFUSEDeremchg
- Remote address changederemdev
- Remote deviceeremote
- Pathname hit remote filesystemeremoteio
- Remote I/O erroreremoterelease
- EREMOTERELEASEerofs
- Read-only filesystemerpcmismatch
- Wrong RPC versionerremote
- Object is remoteeshutdown
- Cannot send after socket shutdownesocktnosupport
- Socket type not supportedespipe
- Invalid seekesrch
- No such processesrmnt
- Srmount errorestale
- Stale remote file handleesuccess
- Error 0etime
- Timer expiredetimedout
- Connection timed outetoomanyrefs
- Too many referencesetxtbsy
- Text file or pseudo-device busyeuclean
- Structure needs cleaningeunatch
- Protocol driver not attachedeusers
- Too many userseversion
- Version mismatchewouldblock
- Operation would blockexdev
- Cross-domain linkexfull
- Message tables fullnxdomain
- Hostname or domain name cannot be found