View Source inet (kernel v10.1.2)
Access to Network protocols.
This module, together with gen_tcp
, gen_udp
and gen_sctp
provides access to the Network protocols TCP, SCTP and UDP over IP,
as well as stream and datagram protocols over the local (unix)
address domain / protocol domain.
See also ERTS User's Guide: Inet Configuration or more information about how to configure an Erlang runtime system for IP communication.
The following two Kernel configuration parameters affect the behavior of all
gen_tcp
sockets opened on an Erlang node:
inet_default_connect_options
can contain a list of default options used for all sockets created by agen_tcp:connect/2,3,4
](gen_tcp:connect/2
) call.inet_default_listen_options
can contain a list of default options used for sockets created by agen_tcp:listen/2
call.
For the gen_tcp:accept/1,2
call,
the values of the listening socket options are inherited.
Therefore there is no corresponding application variable 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}]'
Please note that the default option {active, true}
cannot be changed,
for internal implementation 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 a string "150.236.20.73"
or as a 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}}
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-device linkexfull
- Message tables fullnxdomain
- Hostname or domain name cannot be found
Summary
Types: Exported data types
Ancillary data / control messages.
A general network address.
A record describing a host; name and address.
Implementation backend selector for socket/0
.
A network address for the local
family (AF_LOCAL | AF_UNIX
)
a non-IP network address.
A socket recognized by this module and its siblings.
Types: Internal data types
Interface address description list.
A network address for the inet6
family (AF_INET6
, IPv6)
A network address for the inet
family (AF_INET
, IPv4)
Functions
Cancel a socket monitor.
Close a socket of any type.
Format an error code into a string/0
.
Get the inet
configuration.
Resolve a host to an address, in a specific addresss family.
Resolve a host to a list of addresses, in a specific address family.
Resolve (reverse) an address to a #hostent{}
record.
Resolve a hostname to a #hostent{}
record.
Resolve a hostname to a #hostent{}
record,
in a specific address family.
Get the local hostname.
Get interface names and addresses.
Get interface names and addresses, in a specific namespace.
Get one or more options for a socket.
Equivalent to getstat/2
.
Get one or more statistics options for a socket.
List network sockets.
List network sockets.
Get information about a socket.
Convert between an IPv4 address and an IPv4-mapped IPv6 address.
Test for an IP address.
Test for an IPv4 address.
Test for an IPv6 address.
Start a socket monitor.
Parse an ip_address/0
to an IPv4 or IPv6 address string.
Parse an IP address string to an ip_address/0
.
Parse (relaxed) an IPv4 address string to an ip4_address/0
.
Parse an IPv4 address string to an ip4_address/0
.
Parse (relaxed) an IPv6 address string to an ip6_address/0
.
Parse an IPv6 address string to an ip6_address/0
.
Parse an IP address string to an ip_address/0
.
Return the address of the socket's remote end.
Equivalent to peernames(Socket, 0)
.
Return the addresses of all remote ends of a socket.
Return the local port number for a socket.
Set one or more options for a socket.
Return the local address and port number for a socket.
Equivalent to socknames(Socket, 0)
.
Return all localaddresses for a socket.
Types: Exported data types
-type address_family() :: inet | inet6 | local.
Ancillary data / control messages.
Ancillary data received with a 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).
-type family_address() :: inet_address() | inet6_address() | local_address().
A general network address.
A general network address format on the form {Family, Destination}
where Family
is an atom such as local
and the format of Destination
depends on Family
. Destination
is a complete address (for example
an IP address with port number).
-type hostent() :: #hostent{h_name :: inet:hostname(), h_aliases :: [inet:hostname()], h_addrtype :: inet | inet6, h_length :: non_neg_integer(), h_addr_list :: [inet:ip_address()]}.
A record describing a host; name and address.
Corresponds to the C
: struct hostent
as returned by for example
gethostbyname(3)
.
The record is defined in the Kernel include file "inet.hrl"
.
Add the following directive to the module:
-include_lib("kernel/include/inet.hrl").
-type inet_backend() :: {inet_backend, inet | socket}.
Implementation backend selector for socket/0
.
Selects the implementation backend for [sockets](socket/0
.
The current default is inet
which uses inet_drv.c
to call
the platform's socket API. The value socket
instead uses
the socket
module and its NIF implementation.
This is a temporary option that will be ignored in a future release.
-type ip4_address() :: {0..255, 0..255, 0..255, 0..255}.
-type ip6_address() :: {0..65535, 0..65535, 0..65535, 0..65535, 0..65535, 0..65535, 0..65535, 0..65535}.
-type ip_address() :: ip4_address() | ip6_address().
A network address for the local
family (AF_LOCAL | AF_UNIX
)
This address family, also known as "Unix domain sockets" 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/0
is passed as is to the operating system,
but a string/0
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
.
-type port_number() :: 0..65535.
-type 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().
POSIX Error Code atom/0
.
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.
a non-IP network address.
Addresses besides ip_address/0
ones that are returned from
socket API functions. See in particular local_address/0
.
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 doesn't recognize.
-type socket() :: port() | module_socket().
A socket recognized by this module and its siblings.
See gen_tcp:socket/0
and gen_udp:socket/0
.
-type socket_address() :: ip_address() | any | loopback | local_address().
-type socket_getopt() :: gen_sctp:option_name() | gen_tcp:option_name() | gen_udp:option_name().
-type socket_optval() :: gen_sctp:option_value() | gen_tcp:option() | gen_udp:option() | gen_tcp:pktoptions_value().
-type socket_protocol() :: tcp | udp | sctp.
-type socket_setopt() :: gen_sctp:option() | gen_tcp:option() | gen_udp:option().
-type stat_option() ::
recv_cnt | recv_max | recv_avg | recv_oct | recv_dvi | send_cnt | send_max | send_avg |
send_oct | send_pend.
Types: Internal data types
-type 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.
A list returned from getifaddrs/0,1
for a named interface, translated from the
returned data of the POSIX API function getaddrinfo()
.
Hwaddr
is hardware dependent, for example, on Ethernet interfaces it is the
6-byte Ethernet address (MAC address (EUI-48 address)).
The tuples {addr,Addr}
, {netmask,Netmask}
, and possibly
{broadaddr,Broadaddr}
or {dstaddr,Dstaddr}
are repeated in the list
if the interface has got multiple addresses. An interface may have multiple
{flag,_}
tuples for example if it has different flags for different
address families.
Multiple {hwaddr,Hwaddr}
tuples is hard to say anything definite about,
though. The tuple {flag,Flags}
is mandatory, all others are optional.
Do not rely too much on the order of Flags
atoms or the Ifopt
tuples.
There are however some rules:
- A
{flag,_}
tuple applies to all other tuples that follow. - Immediately after
{addr,_}
follows{netmask,_}
. - Immediately thereafter may
{broadaddr,_}
follow ifbroadcast
is member ofFlags
, or{dstaddr,_}
ifpointtopoint
is member ofFlags
. Both{dstaddr,_}
and{broadaddr,_}
doesn't occur for the same{addr,_}
. - Any
{netmask,_}
,{broadaddr,_}
, or{dstaddr,_}
tuples that follow an{addr,Addr}
tuple concerns the addressAddr
.
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
andBroadaddr
values may be calculated, just as someFlags
values.
-type inet6_address() :: {inet6, {ip6_address() | any | loopback, port_number()}}.
A network address for the inet6
family (AF_INET6
, IPv6)
Warning
This address format is currently experimental and for completeness to make all address families have a
{Family, Destination}
representation.
-type inet_address() :: {inet, {ip4_address() | any | loopback, port_number()}}.
A network address for the inet
family (AF_INET
, IPv4)
Warning
This address format is currently experimental and for completeness to make all address families have a
{Family, Destination}
representation.
Types
-type ether_address() :: [0..255].
-type i_option() :: port | module | recv | sent | owner | local_address | {local_address, ShowPorts :: boolean()} | foreign_address | {foreign_address, ShowPorts :: boolean()} | state | type.
Options for selecting statistics items.
Regarding ShowPorts
, see show_ports
as described in the i/2
function,
defaults to false
.
Functions
Cancel a socket monitor.
If MRef
is a reference that the calling process obtained by calling
monitor/1
, this monitor is removed. If the monitoring is already removed,
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 couldn't be removed. Probably because the monitor has already triggered and there is a corresponding'DOWN'
message in the caller message queue.
-spec close(Socket) -> ok when Socket :: socket().
Close a socket of any type.
Format an error code into a string/0
.
Returns a diagnostic error string. For possible POSIX values and corresponding strings, see section POSIX Error Codes.
Get the inet
configuration.
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.
-spec getaddr(Host, Family) -> {ok, Address} | {error, posix()} when Host :: ip_address() | hostname(), Family :: address_family(), Address :: ip_address().
Resolve a host to an address, in a specific addresss family.
Returns the IP address for Host
as a tuple of integers.
Host
can be an IP address, a single hostname/0
,
or a fully qualified hostname/0
.
-spec getaddrs(Host, Family) -> {ok, Addresses} | {error, posix()} when Host :: ip_address() | hostname(), Family :: address_family(), Addresses :: [ip_address()].
Resolve a host to a list of addresses, in a specific address family.
Returns a list of all IP addresses for Host
.
Host
can be an IP address,
a single hostname/0
, or a fully qualified hostname/0
.
-spec gethostbyaddr(Address) -> {ok, Hostent} | {error, posix()} when Address :: string() | ip_address(), Hostent :: hostent().
Resolve (reverse) an address to a #hostent{}
record.
Returns a #hostent{}
record for the host
with the specified address.
-spec gethostbyname(Hostname) -> {ok, Hostent} | {error, posix()} when Hostname :: hostname(), Hostent :: hostent().
Resolve a hostname to a #hostent{}
record.
Returns a #hostent{}
record for the host
with the specified Hostname
.
This function uses the resolver, which is often the native (OS) resolver.
If resolver option inet6
is true
, an IPv6 address is looked up.
See ERTS User's Guide: Inet Configuration for information about the resolver configuration.
A quirk of many resolvers is that an integer string is interpreted
as an IP address. For instance, the integer string "3232235521"
and the string "192.168.0.1" are both translated
to the IP address {192,168,0,1}
.
-spec gethostbyname(Hostname, Family) -> {ok, Hostent} | {error, posix()} when Hostname :: hostname(), Family :: address_family(), Hostent :: hostent().
Resolve a hostname to a #hostent{}
record,
in a specific address family.
Returns a #hostent{}
record for the host
with the specified Hostname
, restricted to the specified address Family
.
See also gethostbyname/1
.
-spec gethostname() -> {ok, Hostname} when Hostname :: string().
Get the local hostname.
Returns the local hostname. Never fails.
-spec getifaddrs() -> {ok, [{Ifname :: string(), Ifopts :: getifaddrs_ifopts()}]} | {error, posix()}.
Get interface names and addresses.
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.
-spec getifaddrs([Option :: inet_backend() | {netns, Namespace :: file:filename_all()}] | socket()) -> {ok, [{Ifname :: string(), Ifopts :: getifaddrs_ifopts()}]} | {error, posix()}.
Get interface names and addresses, in a specific namespace.
Equivalent to getifaddrs/0
, but accepts an Option
{netns, Namespace}
that, on platforms that support the feature (Linux),
sets a network namespace for the OS call.
Also,
If the option 'inet_backend' is first in the options list,
the specified backend will be used (for 'inet', inet and
for 'socket' the equivalent net functions will be used).
See the socket option {netns, Namespace}
under setopts/2
.
-spec getopts(Socket, Options) -> {ok, OptionValues} | {error, posix()} when Socket :: socket(), Options :: [socket_getopt()], OptionValues :: [socket_optval()].
Get one or more options for a socket.
Gets all options in the list Options
from Socket
.
See setopts/2
for a list of available options. See also
the descriptions of protocol specific types referenced by
socket_optval()
.
The number of elements in the returned OptionValues
list does not necessarily
correspond to the number of options asked for. If the operating system fails to
support an option, it is left out in the returned list. An error tuple is
returned only when getting options for the socket is impossible (that is, the
socket is closed or the buffer size in a raw request is too large). This
behavior is kept for backward compatibility reasons.
A raw option request RawOptReq = {raw, Protocol, OptionNum, ValueSpec}
can be
used to get information about socket options not (explicitly) supported by the
emulator. The use of raw socket options makes the code non-portable, but allows
the Erlang programmer to take advantage of unusual features present on a
particular platform.
RawOptReq
consists of tag raw
followed by the protocol level, the option
number, and either a binary or the size, in bytes, of the buffer in which the
option value is to be stored. A binary is to be used when the underlying
getsockopt
requires input in the argument field. In this case, the binary
size shall 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 native endianness.
Asking for and inspecting raw socket options require low-level information about the current operating system and TCP stack.
Example:
Consider a Linux machine where option TCP_INFO
can be used to collect TCP
statistics for a socket. Assume you are interested in field tcpi_sacked
of
struct tcp_info
filled in when asking for TCP_INFO
. To be able to access
this information, you need to know the following:
- The numeric value of protocol level
IPPROTO_TCP
- The numeric value of option
TCP_INFO
- The size of
struct tcp_info
- The size and offset of the specific field
By inspecting the headers or writing a small C program, it is found that
IPPROTO_TCP
is 6, TCP_INFO
is 11, the structure size is 92 (bytes), the
offset of tcpi_sacked
is 28 bytes, and the value is a 32-bit integer. The
following code can be used to retrieve the value:
get_tcpi_sacked(Sock) ->
{ok,[{raw,_,_,Info}]} = inet:getopts(Sock,[{raw,6,11,92}]),
<<_:28/binary,TcpiSacked:32/native,_/binary>> = Info,
TcpiSacked.
Preferably, you would check the machine type, the operating system, and the Kernel version before executing anything similar to this code.
-spec getstat(Socket) -> {ok, OptionValues} | {error, posix()} when Socket :: socket(), OptionValues :: [{stat_option(), integer()}].
Equivalent to getstat/2
.
-spec getstat(Socket, Options) -> {ok, OptionValues} | {error, posix()} when Socket :: socket(), Options :: [stat_option()], OptionValues :: [{stat_option(), integer()}].
Get one or more statistics 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.
-spec i() -> ok.
Equivalent to i/1
for the protocols tcp
, udp
, and sctp
-spec i(show_ports | socket_protocol() | [i_option()]) -> ok.
List network sockets.
With argument Proto
equivalent to i(Proto, Options)
where Options
is a list of all atom/0
s in i_option/0
.
With argument Options
, equivalent to `i(Proto, Options)
for Proto
: tcp
, udp
, and sctp
.
With argument show_ports
(since OTP 27.0) equivalent to
`i(Proto, Options) where Option
is a list of all
options in i_option/0
with ShowPorts = true
.
-spec i(socket_protocol(), show_ports | (Options :: [i_option()])) -> ok.
List network sockets.
Lists all TCP, UDP and SCTP sockets on the terminal, those created by the Erlang runtime system as well as by the application.
The following options are available:
port
- An 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.
The Options
argument may also be (since OTP 27.0):
show_ports
- Do not translate the port numbers (of 'local_address' and 'foreign_address') to service name(s).
Get information about a socket.
Returns a term containing miscellaneous information about a socket.
-spec ipv4_mapped_ipv6_address(ip_address()) -> ip_address().
Convert between an IPv4 address and an IPv4-mapped IPv6 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 IPv6 addresses than IPv4-mapped.
-spec is_ip_address(IPAddress) -> boolean() when IPAddress :: ip_address() | term().
Test for an IP address.
Tests if the argument IPAddress
is an ip_address/0
and if so returns true
, otherwise false
.
-spec is_ipv4_address(IPv4Address) -> boolean() when IPv4Address :: ip4_address() | term().
Test for an IPv4 address.
Tests if the argument IPv4Address
is an ip4_address/0
and if so returns true
, otherwise false
.
-spec is_ipv6_address(IPv6Address) -> boolean() when IPv6Address :: ip6_address() | term().
Test for an IPv6 address.
Tests if the argument IPv6Address
is an ip6_address/0
and if so returns true
, otherwise false
.
Start a socket monitor.
If the Socket
to monitor doesn't exist or when the monitor is triggered,
a 'DOWN'
message is sent that has the following pattern:
{'DOWN', MonitorRef, Type, Object, Info}
MonitorRef
- The return value from this function.Type
- The type of socket, can be one of the followingatom/0
s:port
orsocket
.Object
- The monitored entity, the socket, which triggered the event.Info
- Either the termination reason of the socket ornosock
(theSocket
did not exist when this function was called).
Making several calls to inet:monitor/1
for the same Socket
is not an error; one monitor is created per call.
The monitor is triggered when the socket is closed in any way such as an API call, remote end close, closed by signal when owner exits, ...
-spec ntoa(IpAddress) -> Address | {error, einval} when Address :: string(), IpAddress :: ip_address().
Parse an ip_address/0
to an IPv4 or IPv6 address string.
-spec parse_address(Address) -> {ok, IPAddress} | {error, einval} when Address :: string(), IPAddress :: ip_address().
Parse an IP address string to an ip_address/0
.
Returns an ip4_address/0
or an ip6_address/0
depending
on which parsing that succeeds.
Accepts a short form IPv4 address string like parse_ipv4_address/1
.
-spec parse_ipv4_address(Address) -> {ok, IPv4Address} | {error, einval} when Address :: string(), IPv4Address :: ip4_address().
Parse (relaxed) an IPv4 address string to an ip4_address/0
.
Accepts a short form IPv4 address string (less than 4 fields)
such as "127.1"
or "0x7f000001"
.
-spec parse_ipv4strict_address(Address) -> {ok, IPv4Address} | {error, einval} when Address :: string(), IPv4Address :: ip4_address().
Parse an IPv4 address string to an ip4_address/0
.
Requires an IPv4 address string containing four fields, that is; not a short form address string.
-spec parse_ipv6_address(Address) -> {ok, IPv6Address} | {error, einval} when Address :: string(), IPv6Address :: ip6_address().
Parse (relaxed) an IPv6 address string to an ip6_address/0
.
Also accepts a (relaxed) IPv4 address string like parse_ipv4_address/1
and returns an IPv4-mapped IPv6 address.
-spec parse_ipv6strict_address(Address) -> {ok, IPv6Address} | {error, einval} when Address :: string(), IPv6Address :: ip6_address().
Parse an IPv6 address string to an ip6_address/0
.
Doesn't accept an IPv4 address string. An IPv6 address string, though,
allows an IPv4 tail like this: "::127.0.0.1"
(which is the same as "::7f00:0001"
).
-spec parse_strict_address(Address) -> {ok, IPAddress} | {error, einval} when Address :: string(), IPAddress :: ip_address().
Parse an IP address string to an ip_address/0
.
Like parse_address/1
but doesn't accept a short form IPv4 address string.
-spec peername(Socket :: socket()) -> {ok, {ip_address(), port_number()} | returned_non_ip_address()} | {error, posix()}.
Return the address of the socket's remote end.
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.
-spec peernames(Socket :: socket()) -> {ok, [{ip_address(), port_number()} | returned_non_ip_address()]} | {error, posix()}.
Equivalent to peernames(Socket, 0)
.
Notice that the behavior of this function for an SCTP one-to-many style socket is not defined by the SCTP Sockets API Extensions.
-spec peernames(Socket, Assoc) -> {ok, [{Address, Port}]} | {error, posix()} when Socket :: socket(), Assoc :: #sctp_assoc_change{state :: term(), error :: term(), outbound_streams :: term(), inbound_streams :: term(), assoc_id :: term()} | gen_sctp:assoc_id(), Address :: ip_address(), Port :: non_neg_integer().
Return the addresses of all remote ends of a socket.
Returns a list of all address/port number pairs for the remote end of an
association Assoc
of a socket.
This function can return multiple addresses for multihomed sockets, such as SCTP sockets. For other sockets it returns a one-element list.
Notice that parameter Assoc
is by the
SCTP Sockets API Extensions
defined to be ignored for one-to-one style sockets.
What the special value 0
means, is unfortunately undefined,
and hence the behavior for one-to-many style sockets.
-spec port(Socket) -> {ok, Port} | {error, any()} when Socket :: socket(), Port :: port_number().
Return the local port number for a socket.
-spec setopts(Socket, Options) -> ok | {error, posix()} when Socket :: socket(), Options :: [socket_setopt()].
Set one or more options for a socket.
Sets the list of Options
on Socket
.
The following options are available:
{active, true | false | once | N}
- If the value istrue
, 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 callinggen_tcp:recv/2,3
,gen_udp:recv/2,3
, orgen_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 is0
. 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 to0
. Once the socket's message count reaches0
, 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 messagessetopts/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 optionexit_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 ofN
appropriate for the application to provide 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 optionssndbuf
andrecbuf
, which correspond to the Kernel socket buffers. For TCP it is recommended to haveval(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 whenrecbuf
is set. However, as the size set forrecbuf
usually become larger, you are encouraged to usegetopts/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 tofalse
.{deliver, port | term}
- When{active, true}
, data is delivered on the formport
:{S, {data, [H1,..Hsz | Data]}}
orterm
:{tcp, S, [H1..Hsz | Data]}
.{dontroute, Boolean}
- Enables/disables routing bypass for outgoing messages.{exit_on_close, Boolean}
- This option is set totrue
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 usesgen_tcp:shutdown/2
to shut down the write side.{exclusiveaddruse, Boolean}
- Enables/disables exclusive address/port usage on Windows. That is, by enabling this option you can prevent other sockets from binding to the same address/port. By default this option is disabled. That is, other sockets may use the same address/port by setting{reuseaddr, true}
in combination with{reuseport, true}
unless{exclusiveaddruse, true}
has been set onSocket
. On non-Windows systems this option is silently ignored.Note
This option is currently not supported for socket created with
inet_backend = socket
{header, Size}
- This option is only meaningful if optionbinary
was specified when the socket was created. If optionheader
is specified, the firstSize
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, ifSize == 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
, andlow_watermark
.Notice that distribution sockets disable the use of
high_msgq_watermark
andlow_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
, andlow_msqg_watermark
.{ipv6_v6only, Boolean}
- Restricts the socket to use only IPv6, prohibiting any IPv4 connections. This is only applicable for IPv6 sockets (optioninet6
).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 offalse
. 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 tofalse
, 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 valuetrue
.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 allowfalse
, 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 tofalse
.{linger, {true|false, Seconds}}
- Determines the time-out, in seconds, for flushing unsent data in theclose/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
, andlow_watermark
.Notice that distribution sockets disable the use of
high_msgq_watermark
andlow_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
, andlow_msgq_watermark
.{mode, Mode :: binary | list}
- ReceivedPacket
is delivered as defined byMode
.{netns, Namespace :: file:filename_all()}
- Sets a network namespace for the socket. ParameterNamespace
is a filename defining the namespace, for example,"/var/run/netns/example"
, typically created by commandip 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
orgen_sctp:open/0,1,2
, and alsogetifaddrs/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 forsetns(2)
. However, during testing alsoCAP_SYS_PTRACE
andCAP_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 flagnosetuid
, 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 modulefile
, 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
.
- Emulator flag
{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
, orgen_sctp:open/0,1,2
.Unlike
getifaddrs/0
, Ifname is encoded a binary. In the unlikely case that a system is using non-7-bit-ASCII characters in network device names, special care has to be taken when encoding this argument.This option uses the Linux-specific socket option
SO_BINDTODEVICE
, such as in Linux kernel 2.0.30 or later, and therefore only exists when the runtime system is compiled for such an operating system.Before Linux 3.8, this socket option could be set, but could not retrieved with
getopts/2
. Since Linux 3.8, it is readable.The virtual machine also needs elevated privileges, either running as superuser or (for Linux) having capability
CAP_NET_RAW
.The primary use case for this option is to bind sockets into Linux VRF instances.
list
- ReceivedPacket
is delivered as a list.binary
- ReceivedPacket
is delivered as a binary.{nodelay, Boolean}
(TCP/IP sockets) - IfBoolean == true
, optionTCP_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 ifinet_backend =/= socket
this error will be ignored.{nopush, Boolean}
(TCP/IP sockets) - This translates toTCP_NOPUSH
on BSD and toTCP_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 togen_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 toHttpPacket
described inerlang:decode_packet/3
in ERTS. A socket in passive mode returns{ok, HttpPacket}
fromgen_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 fromhttp
/http_bin
tohttph
/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*
), optionpacket_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_ahead, Boolean}
- If set tofalse
avoids reading ahead from the OS socket layer. The default for this option istrue
which speeds up packet header parsing. Settingfalse
has a performance penalty because the packet header has to be read first, to know exactly how many bytes to read for the body, which roughly doubles the number of read operations.The use of this option is essential for example before switching to kTLS which activates OS socket layer encryption and decryption by setting special (raw) socket options. So if the Erlang socket layer has read ahead, it has read bytes that was for the OS socket layer to decrypt, which makes packet decryption derail for the connection.
Warning
For packet modes that doesn't have the packet length at a fixed location in a packet header, such as
line
orasn1
, not reading ahead can become very inefficient since sometimes the only way to accomplish this is to read one byte at the time until the length or packet end is found.{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 to5
. 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 usegetopts/2
to retrieve the size set by your operating system.{recvtclass, Boolean}
- If set totrue
activates returning the receivedTCLASS
value on platforms that implements the protocolIPPROTO_IPV6
optionIPV6_RECVTCLASS
orIPV6_2292RECVTCLASS
for the socket. The value is returned as a{tclass,TCLASS}
tuple regardless of if the platform returns anIPV6_TCLASS
or anIPV6_RECVTCLASS
CMSG value.For packet oriented sockets that supports receiving ancillary data with the payload data (
gen_udp
andgen_sctp
), theTCLASS
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 theTCLASS
value is if the platform supports thepktoptions
option.{recvtos, Boolean}
- If set totrue
activates returning the receivedTOS
value on platforms that implements the protocolIPPROTO_IP
optionIP_RECVTOS
for the socket. The value is returned as a{tos,TOS}
tuple regardless of if the platform returns anIP_TOS
or anIP_RECVTOS
CMSG value.For packet oriented sockets that supports receiving ancillary data with the payload data (
gen_udp
andgen_sctp
), theTOS
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 theTOS
value is if the platform supports thepktoptions
option.{recvttl, Boolean}
- If set totrue
activates returning the receivedTTL
value on platforms that implements the protocolIPPROTO_IP
optionIP_RECVTTL
for the socket. The value is returned as a{ttl,TTL}
tuple regardless of if the platform returns anIP_TTL
or anIP_RECVTTL
CMSG value.For packet oriented sockets that supports receiving ancillary data with the payload data (
gen_udp
andgen_sctp
), theTTL
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 theTTL
value is if the platform supports thepktoptions
option.{reuseaddr, Boolean}
- Allows or disallows reuse of local address. By default, reuse is disallowed.Note
On windows
{reuseaddr, true}
will have no effect unless also{reuseport, true}
is set. If both are set, theSO_REUSEADDR
Windows socket option will be enabled. This since settingSO_REUSEADDR
on Windows more or less has the same behavior as setting bothSO_REUSEADDR
andSO_REUSEPORT
on BSD. This behavior was introduced as of OTP 26.0.Change
Previous behavior on Windows:
- Prior to OTP 25.0, the
{reuseaddr, true}
option was silently ignored. - Between OTP 25.0 and up to the predecessor of OTP 25.2, the underlying
SO_REUSEADDR
socket option was set if{reuseaddr, true}
was set. - Between OTP 25.2 and up to the predecessor of OTP 26.0, the underlying
SO_REUSEADDR
socket option was only set on UDP sockets if{reuseaddr, true}
was set, and silently ignored on other sockets.
See also the
exclusiveaddruse
option.- Prior to OTP 25.0, the
{reuseport, Boolean}
- Allows or disallows reuse of local port which may or may not have load balancing depending on the underlying OS. By default, reuse is disallowed. See alsoreuseport_lb
.Note
On windows
{reuseport, true}
will have no effect unless also{reuseaddr, true}
is set. If both are set, theSO_REUSEADDR
Windows socket option will be enabled. This since settingSO_REUSEADDR
on Windows more or less has the same behavior as setting bothSO_REUSEADDR
andSO_REUSEPORT
on BSD. Thereuseport
option was introduced as of OTP 26.0.See also the
exclusiveaddruse
option.Note
reuseport
may or may not be the same underlying option asreuseport_lb
depending on the underlying OS. They, for example, are on Linux. When they are the same underlying option, operating on both may cause them to interact in surprising ways. For example, by enablingreuseport
and then disablingreuseport_lb
both will end up being disabled.Note
This option is currently not supported for socket created with
inet_backend = socket
{reuseport_lb, Boolean}
- Allows or disallows reuse of local port with load balancing. By default, reuse is disallowed. See alsoreuseport
.Note
reuseport_lb
may or may not be the same underlying option asreuseport
depending on the underlying OS. On Linux, for example, they are. And when they are the same underlying option, operating on both may cause them to interact in surprising ways. For example, by enablingreuseport_lb
, and then disablingreuseport
, both will end up being disabled.Note
This option is currently not supported for socket created with
inet_backend = socket
{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 (seesend_timeout_close
below). Defaults toinfinity
.{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 istrue
, which automatically closes the socket. Defaults tofalse
because of backward compatibility.{show_econnreset, Boolean}
(TCP/IP sockets) - When this option is set tofalse
, which is default, an RST received from the TCP peer is treated as a normal close (as though an FIN was sent). A caller togen_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 togen_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 togen_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 theshow_econnreset
setting from the listening socket.{sndbuf, Size}
- The minimum size of the send buffer to use for the socket. You are encouraged to usegetopts/2
, to retrieve the size set by your operating system.{priority, Integer}
- Sets theSO_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}
- SetsIP_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}
- SetsIPV6_TCLASS IP
level options on platforms where this is implemented. The behavior and allowed range varies between different systems. The option is ignored on platforms where it is not implemented. Use with caution.
In addition to these options, raw option specifications can be used. The raw
options are specified as a tuple of arity four, beginning with tag raw
,
followed by the protocol level, the option number, and the option value
specified as a binary. This corresponds to the second, third, and fourth
arguments to the setsockopt
call in the C socket API. The option value must be
coded in the native endianness of the platform and, if a structure is required,
must follow the structure alignment conventions on the specific platform.
Using raw socket options requires detailed knowledge about the current operating system and TCP stack.
Example:
This example concerns the use of raw options. Consider a Linux system where you
want to set option TCP_LINGER2
on protocol level IPPROTO_TCP
in the stack.
You know that on this particular system it defaults to 60 (seconds), but you
want to lower it to 30 for a particular socket. Option TCP_LINGER2
is not
explicitly supported by inet
, but you know that the protocol level translates
to number 6, the option number to number 8, and the value is to be specified as
a 32-bit integer. You can use this code line to set the option for the socket
named Sock
:
inet:setopts(Sock, [{raw,6,8,<<30:32/native>>}]),
As many options are silently discarded by the stack if they are specified out of
range; it can be a good idea to check that a raw option is accepted. The
following code places the value in variable TcpLinger2:
{ok,[{raw,6,8,<<TcpLinger2:32/native>>}]}=inet:getopts(Sock,[{raw,6,8,4}]),
Code such as these examples is inherently non-portable, even different versions of the same OS on the same platform can respond differently to this kind of option manipulation. Use with care.
Notice that the default options for TCP/IP sockets can be changed with the Kernel configuration parameters mentioned in the beginning of this manual page.
-spec sockname(Socket :: socket()) -> {ok, {ip_address(), port_number()} | returned_non_ip_address()} | {error, posix()}.
Return 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.
-spec socknames(Socket :: socket()) -> {ok, [{ip_address(), port_number()} | returned_non_ip_address()]} | {error, posix()}.
Equivalent to socknames(Socket, 0)
.
-spec socknames(Socket, Assoc) -> {ok, [{Address, Port}]} | {error, posix()} when Socket :: socket(), Assoc :: #sctp_assoc_change{state :: term(), error :: term(), outbound_streams :: term(), inbound_streams :: term(), assoc_id :: term()} | gen_sctp:assoc_id(), Address :: ip_address(), Port :: non_neg_integer().
Return all localaddresses for a socket.
Returns a list of all local address/port number pairs for a socket,
for the specified association Assoc
.
This function can return multiple addresses for multihomed sockets, such as SCTP sockets. For other sockets it returns a one-element list.
Notice that parameter Assoc
is by the
SCTP Sockets API Extensions
defined to be ignored for one-to-one style sockets. For one-to-many style
sockets, the special value 0
is defined to mean that the returned addresses
must be without any particular association. How different SCTP implementations
interpret this varies somewhat.