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NAME
inet - Access to TCP/IP Protocols
DESCRIPTION
Provides access to TCP/IP protocols.
See also ERTS User's Guide, Inet configuration for more information on how to configure an
Erlang runtime system for IP communication.
Two Kernel configuration parameters affect the behaviour of all sockets opened on an
Erlang node: inet_default_connect_options can contain a list of default options used for
all sockets returned when doing connect, and inet_default_listen_options can contain a
list of default options used when issuing a listen call. When accept is issued, the values
of the listensocket options are inherited, why no such application variable is needed for
accept.
Using the Kernel configuration parameters mentioned above, one can set default options for
all TCP sockets on a node. This should be used with care, but options like
{delay_send,true} might be specified in this way. An example of starting an Erlang node
with all sockets using delayed send could look like this:
$ erl -sname test -kernel \
inet_default_connect_options '[{delay_send,true}]' \
inet_default_listen_options '[{delay_send,true}]'
Note that the default option {active, true} currently cannot be changed, for internal
reasons.
Addresses as inputs to functions can be either a string or a tuple. For instance, the IP
address 150.236.20.73 can be passed to gethostbyaddr/1 either as the string
"150.236.20.73" or as the 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
{16#FFFF,0,0,0,0,0,(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}
A function that may be useful is parse_address/1:
1> inet:parse_address("192.168.42.2").
{ok,{192,168,42,2}}
2> inet:parse_address("FFFF::192.168.42.2").
{ok,{65535,0,0,0,0,0,49320,10754}}
DATA TYPES
hostent() =
#hostent{h_name = undefined | inet:hostname(),
h_aliases = [inet:hostname()],
h_addrtype = undefined | inet | inet6,
h_length = undefined | 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
posix() = exbadport | exbadseq | file:posix()
An atom which is named from the Posix error codes used in Unix, and in the runtime
libraries of most C compilers. See POSIX Error Codes.
socket()
See gen_tcp(3erl) and gen_udp(3erl).
address_family() = inet | inet6
EXPORTS
close(Socket) -> ok
Types:
Socket = socket()
Closes a socket of any type.
get_rc() -> [{Par :: any(), Val :: any()}]
Returns the state of the Inet configuration database in form of a list of recorded
configuration parameters. (See the ERTS User's Guide, Inet configuration, for more
information). Only parameters with other than default values are returned.
format_error(Reason) -> string()
Types:
Reason = posix() | system_limit
Returns a diagnostic error string. See the section below for possible Posix values
and the corresponding strings.
getaddr(Host, Family) -> {ok, Address} | {error, posix()}
Types:
Host = ip_address() | hostname()
Family = address_family()
Address = ip_address()
Returns the IP-address for Host as a tuple of integers. Host can be an IP-address,
a single hostname or a fully qualified hostname.
getaddrs(Host, Family) -> {ok, Addresses} | {error, posix()}
Types:
Host = ip_address() | hostname()
Family = address_family()
Addresses = [ip_address()]
Returns a list of all IP-addresses for Host. Host can be an IP-address, a single
hostname or a fully qualified hostname.
gethostbyaddr(Address) -> {ok, Hostent} | {error, posix()}
Types:
Address = string() | ip_address()
Hostent = hostent()
Returns a hostent record given an address.
gethostbyname(Hostname) -> {ok, Hostent} | {error, posix()}
Types:
Hostname = hostname()
Hostent = hostent()
Returns a hostent record given a hostname.
gethostbyname(Hostname, Family) ->
{ok, Hostent} | {error, posix()}
Types:
Hostname = hostname()
Family = address_family()
Hostent = hostent()
Returns a hostent record given a hostname, restricted to the given address family.
gethostname() -> {ok, Hostname}
Types:
Hostname = string()
Returns the local hostname. Will never fail.
getifaddrs() -> {ok, Iflist} | {error, posix()}
Types:
Iflist = [{Ifname, [Ifopt]}]
Ifname = string()
Ifopt = {flag, [Flag]}
| {addr, Addr}
| {netmask, Netmask}
| {broadaddr, Broadaddr}
| {dstaddr, Dstaddr}
| {hwaddr, Hwaddr}
Flag = up
| broadcast
| loopback
| pointtopoint
| running
| multicast
Addr = Netmask = Broadaddr = Dstaddr = ip_address()
Hwaddr = [byte()]
Returns a list of 2-tuples containing interface names and the interface's
addresses. Ifname is a Unicode string. Hwaddr is hardware dependent, e.g on
Ethernet interfaces it is the 6-byte Ethernet address (MAC address (EUI-48
address)).
The {addr,Addr}, {netmask,_} and {broadaddr,_} tuples are repeated in the result
list iff the interface has multiple addresses. If you come across an interface that
has multiple {flag,_} or {hwaddr,_} tuples you have a really strange interface or
possibly a bug in this function. The {flag,_} tuple is mandatory, all other
optional.
Do not rely too much on the order of Flag atoms or Ifopt tuples. There are some
rules, though:
*
Immediately after {addr,_} follows {netmask,_}
*
Immediately thereafter follows {broadaddr,_} if the broadcast flag is not set
and the pointtopoint flag is set.
*
Any {netmask,_}, {broadaddr,_} or {dstaddr,_} tuples that follow an {addr,_}
tuple concerns that address.
The {hwaddr,_} tuple is not returned on Solaris since the hardware address
historically belongs to the link layer and only the superuser can read such
addresses.
On Windows, the data is fetched from quite different OS API functions, so the
Netmask and Broadaddr values may be calculated, just as some Flag values. You have
been warned. Report flagrant bugs.
getopts(Socket, Options) -> {ok, OptionValues} | {error, posix()}
Types:
Socket = socket()
Options = [socket_getopt()]
OptionValues = [socket_setopt()]
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()
Gets one or more options for a socket. See setopts/2 for a list of available
options.
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 simply left out in the returned list. An error tuple is
only returned when getting options for the socket is impossible (i.e. 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 the current platform.
The RawOptReq consists of the 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 should be used when the underlying getsockopt
requires input in the argument field, in which case the size of the binary should
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.
As an example, consider a Linux machine where the TCP_INFO option could be used to
collect TCP statistics for a socket. Lets say we're interested in the tcpi_sacked
field of the struct tcp_info filled in when asking for TCP_INFO. To be able to
access this information, we need to know both the numeric value of the protocol
level IPPROTO_TCP, the numeric value of the option TCP_INFO, the size of the struct
tcp_info and the size and offset of the specific field. By inspecting the headers
or writing a small C program, we found IPPROTO_TCP to be 6, TCP_INFO to be 11, the
structure size to be 92 (bytes), the offset of tcpi_sacked to be 28 bytes and the
actual value to be a 32 bit integer. We could use the following code 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 OS and the kernel version prior
to executing anything similar to the code above.
getstat(Socket) -> {ok, OptionValues} | {error, posix()}
getstat(Socket, Options) -> {ok, OptionValues} | {error, posix()}
Types:
Socket = socket()
Options = [stat_option()]
OptionValues = [{stat_option(), integer()}]
stat_option() = recv_cnt
| recv_max
| recv_avg
| recv_oct
| recv_dvi
| send_cnt
| send_max
| send_avg
| send_oct
| send_pend
Gets one or more statistic options for a socket.
getstat(Socket) is equivalent to getstat(Socket, [recv_avg, recv_cnt, recv_dvi,
recv_max, recv_oct, send_avg, send_cnt, send_dvi, send_max, send_oct]).
The following options are available:
recv_avg:
Average size of packets in bytes received to the socket.
recv_cnt:
Number of packets received to the socket.
recv_dvi:
Average packet size deviation in bytes received to the socket.
recv_max:
The size of the largest packet in bytes received to the socket.
recv_oct:
Number of bytes received to 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 received sent from the socket.
send_max:
The size of the largest packet in bytes sent from the socket.
send_oct:
Number of bytes sent from the socket.
ntoa(IpAddress) -> {ok, Address} | {error, einval}
Types:
Address = string()
IpAddress = ip_address()
Parses an ip_address() and returns an IPv4 or IPv6 address string.
parse_ipv4_address(Address) -> {ok, IPv4Address} | {error, einval}
Types:
Address = string()
IPv4Address = ip_address()
Parses an IPv4 address string and returns an ip4_address(). Accepts a shortened
IPv4 shortened address string.
parse_ipv4strict_address(Address) ->
{ok, IPv4Address} | {error, einval}
Types:
Address = string()
IPv4Address = ip_address()
Parses an IPv4 address string containing four fields, i.e not shortened, and
returns an ip4_address().
parse_ipv6_address(Address) -> {ok, IPv6Address} | {error, einval}
Types:
Address = string()
IPv6Address = ip_address()
Parses an IPv6 address string and returns an ip6_address(). If an IPv4 address
string is passed, an IPv4-mapped IPv6 address is returned.
parse_ipv6strict_address(Address) ->
{ok, IPv6Address} | {error, einval}
Types:
Address = string()
IPv6Address = ip_address()
Parses an IPv6 address string and returns an ip6_address(). Does not accept IPv4
adresses.
parse_address(Address) -> {ok, IPAddress} | {error, einval}
Types:
Address = string()
IPAddress = ip_address()
Parses an IPv4 or IPv6 address string and returns an ip4_address() or
ip6_address(). Accepts a shortened IPv4 address string.
parse_strict_address(Address) -> {ok, IPAddress} | {error, einval}
Types:
Address = string()
IPAddress = ip_address()
Parses an IPv4 or IPv6 address string and returns an ip4_address() or
ip6_address(). Does not accept a shortened IPv4 address string.
peername(Socket) -> {ok, {Address, Port}} | {error, posix()}
Types:
Socket = socket()
Address = ip_address()
Port = integer() >= 0
Returns the address and port for the other end of a connection.
Note that for SCTP sockets this function only returns one of the socket's peer
addresses. The function peernames/1,2 returns all.
peernames(Socket) -> {ok, [{Address, Port}]} | {error, posix()}
Types:
Socket = socket()
Address = ip_address()
Port = integer() >= 0
Equivalent to peernames(Socket, 0). Note that this function's behaviour for an SCTP
one-to-many style socket is not defined by the SCTP Sockets API Extensions.
peernames(Socket, Assoc) ->
{ok, [{Address, Port}]} | {error, posix()}
Types:
Socket = socket()
Assoc = #sctp_assoc_change{} | gen_sctp:assoc_id()
Address = ip_address()
Port = integer() >= 0
Returns a list of all address/port number pairs for the other end of a socket's
association Assoc.
This function can return multiple addresses for multihomed sockets such as SCTP
sockets. For other sockets it returns a one element list.
Note that the Assoc parameter is by the SCTP Sockets API Extensions defined to be
ignored for one-to-one style sockets. What the special value 0 means hence its
behaviour for one-to-many style sockets is unfortunately not defined.
port(Socket) -> {ok, Port} | {error, any()}
Types:
Socket = socket()
Port = port_number()
Returns the local port number for a socket.
sockname(Socket) -> {ok, {Address, Port}} | {error, posix()}
Types:
Socket = socket()
Address = ip_address()
Port = integer() >= 0
Returns the local address and port number for a socket.
Note that for SCTP sockets this function only returns one of the socket addresses.
The function socknames/1,2 returns all.
socknames(Socket) -> {ok, [{Address, Port}]} | {error, posix()}
Types:
Socket = socket()
Address = ip_address()
Port = integer() >= 0
Equivalent to socknames(Socket, 0).
socknames(Socket, Assoc) ->
{ok, [{Address, Port}]} | {error, posix()}
Types:
Socket = socket()
Assoc = #sctp_assoc_change{} | gen_sctp:assoc_id()
Address = ip_address()
Port = integer() >= 0
Returns a list of all local address/port number pairs for a socket for the given
association Assoc.
This function can return multiple addresses for multihomed sockets such as SCTP
sockets. For other sockets it returns a one element list.
Note that the Assoc parameter 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 shall be without regard to
any particular association. How different SCTP implementations interprets this
varies somewhat.
setopts(Socket, Options) -> ok | {error, posix()}
Types:
Socket = socket()
Options = [socket_setopt()]
socket_setopt() = gen_sctp:option()
| gen_tcp:option()
| gen_udp:option()
Sets one or more options for a socket. The following options are available:
{active, true | false | once}:
If the value is true, which is the default, everything received from the socket
will be 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 or gen_udp:recv/2,3 (depending on the type of socket).
If the value is once ({active, once}), one data message from the socket will be
sent to the process. To receive one more message, setopts/2 must be called
again with the {active, once} option.
When using {active, once}, the socket changes behaviour automatically when data
is received. This can sometimes be confusing in combination with connection
oriented sockets (i.e. gen_tcp) as a socket with {active, false} behaviour
reports closing differently than a socket with {active, true} behaviour. To
make programming easier, a socket where the peer closed and this was detected
while in {active, false} mode, will still generate the message
{tcp_closed,Socket} when set to {active, once} or {active, true} mode. It is
therefore safe to assume that the message {tcp_closed,Socket}, possibly
followed by socket port termination (depending on the exit_on_close option)
will eventually appear when a socket changes back and forth between {active,
true} and {active, false} mode. However, when peer closing is detected is all
up to the underlying TCP/IP stack and protocol.
Note that {active,true} mode provides no flow control; a fast sender could
easily overflow the receiver with incoming messages. Use active mode only if
your high-level protocol provides its own flow control (for instance,
acknowledging received messages) or the amount of data exchanged is small.
{active,false} mode or use of the {active, once} mode provides flow control;
the other side will not be able send faster than the receiver can read.
{broadcast, Boolean}(UDP sockets):
Enable/disable permission to send broadcasts.
{buffer, Size}:
Determines the size of the user-level software buffer used by the driver. Not
to be confused with sndbuf and recbuf options which correspond to the kernel
socket buffers. It is recommended to have val(buffer) >=
max(val(sndbuf),val(recbuf)). In fact, the val(buffer) is automatically set to
the above maximum when sndbuf or recbuf values are set.
{delay_send, Boolean}:
Normally, when an Erlang process sends to a socket, the driver will try to
immediately send the data. If that fails, the driver will use any means
available to queue up the message to be sent whenever the operating system says
it can handle it. Setting {delay_send, true} will make all messages queue up.
This makes the messages actually sent onto the network be larger but fewer. The
option actually affects the scheduling of send requests versus Erlang processes
instead of changing any real property of the socket. Needless to say it is an
implementation specific option. Default is false.
{deliver, port | term}:
When {active, true} delivers data on the forms port : {S, {data, [H1,..Hsz |
Data]}} or term : {tcp, S, [H1..Hsz | Data]}.
{dontroute, Boolean}:
Enable/disable routing bypass for outgoing messages.
{exit_on_close, Boolean}:
By default this option is set to true.
The only reason to set it to false is if you want to continue sending data to
the socket after a close has been detected, for instance if the peer has used
gen_tcp:shutdown/2 to shutdown the write side.
{header, Size}:
This option is only meaningful if the binary option was specified when the
socket was created. If the header option is specified, the first Size number
bytes of data received from the socket will be elements of a list, and the rest
of the data will be a binary given as the tail of the same list. If for example
Size == 2, the data received will match [Byte1,Byte2|Binary].
{high_msgq_watermark, Size}:
The socket message queue will be set into a busy state when the amount of data
queued on the message queue reaches this limit. Note that this limit only
concerns data that have not yet reached the ERTS internal socket
implementation. Default value used is 8 kB.
Senders of data to the socket will be suspended if either the socket message
queue is busy, or the socket itself is busy.
For more information see the low_msgq_watermark, high_watermark, and
low_watermark options.
Note that distribution sockets will disable the use of high_msgq_watermark and
low_msgq_watermark, and will instead use the distribution buffer busy limit
which is a similar feature.
{high_watermark, Size} (TCP/IP sockets):
The socket will be set into a busy state when the amount of data queued
internally by the ERTS socket implementation reaches this limit. Default value
used is 8 kB.
Senders of data to the socket will be suspended if either the socket message
queue is busy, or the socket itself is busy.
For more information see the low_watermark, high_msgq_watermark, and
low_msqg_watermark options.
{ipv6_v6only, Boolean}:
Restricts the socket to only use IPv6, prohibiting any IPv4 connections. This
is only applicable for IPv6 sockets (option inet6).
On most platforms this option has to be set on the socket before associating it
to an address. Therefore it is only reasonable to give it when creating the
socket and not to use it when calling the function (setopts/2) containing this
description.
The behaviour of a socket with this socket option set to true is becoming 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 (that has separate IPv4 and
IPv6 protocol stacks). Most Linux distros still have a system default value of
false. This policy shift among operating systems towards separating IPv6 from
IPv4 traffic has evolved since 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, e.g. OpenBSD
and Windows. Trying to set this option to false when creating the socket will
in this case fail.
Setting this option on platforms where it does not exist is ignored and getting
this option with getopts/2 returns no value i.e the returned list will not
contain an {ipv6_v6only,_} tuple. On Windows the option acually does not exist,
but it is emulated as being a read-only option with the value true.
So it boils down to that setting this option to true when creating a socket
will never fail except possibly (at the time of this writing) on a platform
where you have customized the kernel to only allow false, which might be doable
(but weird) on e.g. OpenBSD.
If you read back the option value using getopts/2 and get no value the option
does not exist in the host OS and all bets are off regarding the behaviour of
both an IPv6 and an IPv4 socket listening on the same port as well as for an
IPv6 socket getting IPv4 traffic.
{keepalive, Boolean}(TCP/IP sockets):
Enables/disables periodic transmission on a connected socket, when no other
data is being exchanged. If the other end does not respond, the connection is
considered broken and an error message will be sent to the controlling process.
Default disabled.
{linger, {true|false, Seconds}}:
Determines the timeout in seconds for flushing unsent data in the close/1
socket call. If the 1st component of the value tuple is false, the 2nd one is
ignored, which means that close/1 returns immediately not waiting for data to
be flushed. Otherwise, the 2nd component is the flushing time-out in seconds.
{low_msgq_watermark, Size}:
If the socket message queue is in a busy state, the socket message queue will
be set in a not busy state when the amount of data queued in the message queue
falls below this limit. Note that this limit only concerns data that have not
yet reached the ERTS internal socket implementation. Default value used is 4
kB.
Senders that have been suspended due to either a busy message queue or a busy
socket, will be resumed when neither the socket message queue, nor the socket
are busy.
For more information see the high_msgq_watermark, high_watermark, and
low_watermark options.
Note that distribution sockets will disable the use of high_msgq_watermark and
low_msgq_watermark, and will instead 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 will be set in a not busy state
when the amount of data queued internally by the ERTS socket implementation
falls below this limit. Default value used is 4 kB.
Senders that have been suspended due to either a busy message queue or a busy
socket, will be resumed when neither the socket message queue, nor the socket
are busy.
For more information see the high_watermark, high_msgq_watermark, and
low_msgq_watermark options.
{mode, Mode :: binary | list}:
Received Packet is delivered as defined by Mode.
{netns, Namespace :: file:filename_all()}:
Set a network namespace for the socket. The Namespace parameter is a filename
defining the namespace for example "/var/run/netns/example" typically created
by the command ip netns add example. This option must be used in a function
call that creates a socket i.e gen_tcp:connect/3,4, gen_tcp:listen/2,
gen_udp:open/1,2 or gen_sctp:open/0-2.
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 has been compiled
for such an operating system.
The virtual machine also needs elevated privileges either running as superuser
or (for Linux) having the capability CAP_SYS_ADMIN according to the
documentation for setns(2). However, during testing also CAP_SYS_PTRACE and
CAP_DAC_READ_SEARCH has proven to be necessary. Example:
setcap cap_sys_admin,cap_sys_ptrace,cap_dac_read_search+epi beam.smp
The Namespace is a file name and is encoded and decoded as discussed in file
except that the emulator flag +fnu is ignored and getopts/2 for this option
will return a binary for the filename if the stored filename can not be
decoded, which should only happen if you set the option using a binary that can
not be decoded with the emulator's filename encoding:
file:native_name_encoding/0.
list:
Received Packet is delivered as a list.
binary:
Received Packet is delivered as a binary.
{nodelay, Boolean}(TCP/IP sockets):
If Boolean == true, the TCP_NODELAY option is turned on for the socket, which
means that even small amounts of data will be sent immediately.
{packet, PacketType}(TCP/IP sockets):
Defines the type of packets to use for a socket. The following values are
valid:
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 length of header can be one, two, or
four bytes; containing an unsigned integer in big-endian byte order. Each
send operation will generate the header, and the header will be stripped off
on each receive operation.
In current implementation 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, there will be one message sent to the controlling process
for each complete packet received, and, similarly, each call to
gen_tcp:recv/2,3 returns one complete packet. The header is not stripped off.
The meanings of the packet types are as follows:
asn1 - ASN.1 BER,
sunrm - Sun's RPC encoding,
cdr - CORBA (GIOP 1.1),
fcgi - Fast CGI,
tpkt - TPKT format [RFC1006],
line - Line mode, a packet is a line terminated with newline, lines longer
than the receive buffer are truncated.
http | http_bin:
The Hypertext Transfer Protocol. The packets are returned with the format
according to HttpPacket described in erlang:decode_packet/3. A socket in
passive mode will return {ok, HttpPacket} from gen_tcp:recv while an active
socket will send messages like {http, Socket, HttpPacket}.
httph | httph_bin:
These two types are often not needed as the socket will automatically switch
from http/http_bin to httph/httph_bin internally after the first line has
been read. There might be occasions however when they are useful, such as
parsing trailers from chunked encoding.
{packet_size, Integer}(TCP/IP sockets):
Sets the max allowed length of the packet body. If the packet header indicates
that the length of the packet is longer than the max allowed length, the packet
is considered invalid. The same happens if the packet header is too big 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
due to internal buffer limitations.
{priority, Priority}:
Set the protocol-defined priority for all packets to be sent on this socket.
{raw, Protocol, OptionNum, ValueBin}:
See below.
{read_packets, Integer}(UDP sockets):
Sets the max 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. The default is 5, and if this parameter is set too
high the system can become unresponsive due to UDP packet flooding.
{recbuf, Size}:
Gives the size of the receive buffer to use for the socket.
{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 will
return {error,timeout}. How much of a packet that actually got sent is unknown,
why the socket should be closed whenever a timeout has occurred (see
send_timeout_close). Default is infinity.
{send_timeout_close, Boolean}:
Only allowed for connection oriented sockets.
Used together with send_timeout to specify whether the socket will be
automatically closed when the send operation returns {error,timeout}. The
recommended setting is true which will automatically close the socket. Default
is false due to backward compatibility.
{sndbuf, Size}:
Gives the size of the send buffer to use for the socket.
{priority, Integer}:
Sets the SO_PRIORITY socket level option on platforms where this is
implemented. The behaviour and allowed range varies on different systems. The
option is ignored on platforms where the option is not implemented. Use with
caution.
{tos, Integer}:
Sets IP_TOS IP level options on platforms where this is implemented. The
behaviour and allowed range varies on different systems. The option is ignored
on platforms where the option is not implemented. Use with caution.
In addition to the options mentioned above, raw option specifications can be used.
The raw options are specified as a tuple of arity four, beginning with the tag raw,
followed by the protocol level, the option number and the actual option value
specified as a binary. This corresponds to the second, third and fourth argument to
the setsockopt call in the C socket API. The option value needs to be coded in the
native endianess of the platform and, if a structure is required, needs to follow
the struct alignment conventions on the specific platform.
Using raw socket options require detailed knowledge about the current operating
system and TCP stack.
As an example of the usage of raw options, consider a Linux system where you want
to set the TCP_LINGER2 option on the IPPROTO_TCP protocol level in the stack. You
know that on this particular system it defaults to 60 (seconds), but you would like
to lower it to 30 for a particular socket. The TCP_LINGER2 option is not explicitly
supported by inet, but you know that the protocol level translates to the number 6,
the option number to the number 8 and the value is to be given as a 32 bit integer.
You can use this line of code 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 given out of range,
it could be a good idea to check that a raw option really got accepted. This code
places the value in the variable TcpLinger2:
{ok,[{raw,6,8,<<TcpLinger2:32/native>>}]}=inet:getopts(Sock,[{raw,6,8,4}]),
Code such as the examples above is inherently non portable, even different versions
of the same OS on the same platform may respond differently to this kind of option
manipulation. Use with care.
Note that the default options for TCP/IP sockets can be changed with the Kernel
configuration parameters mentioned in the beginning of this document.
POSIX ERROR CODES
* e2big - argument list too long
* eacces - permission denied
* eaddrinuse - address already in use
* eaddrnotavail - cannot assign requested address
* eadv - advertise error
* eafnosupport - address family not supported by protocol family
* eagain - resource temporarily unavailable
* ealign - EALIGN
* ealready - operation already in progress
* ebade - bad exchange descriptor
* ebadf - bad file number
* ebadfd - file descriptor in bad state
* ebadmsg - not a data message
* ebadr - bad request descriptor
* ebadrpc - RPC structure is bad
* ebadrqc - bad request code
* ebadslt - invalid slot
* ebfont - bad font file format
* ebusy - file busy
* echild - no children
* echrng - channel number out of range
* ecomm - communication error on send
* econnaborted - software caused connection abort
* econnrefused - connection refused
* econnreset - connection reset by peer
* edeadlk - resource deadlock avoided
* edeadlock - resource deadlock avoided
* edestaddrreq - destination address required
* edirty - mounting a dirty fs w/o force
* edom - math argument out of range
* edotdot - cross mount point
* edquot - disk quota exceeded
* eduppkg - duplicate package name
* eexist - file already exists
* efault - bad address in system call argument
* efbig - file too large
* ehostdown - host is down
* ehostunreach - host is unreachable
* eidrm - identifier removed
* einit - initialization error
* einprogress - operation now in progress
* eintr - interrupted system call
* einval - invalid argument
* eio - I/O error
* eisconn - socket is already connected
* eisdir - illegal operation on a directory
* eisnam - is a named file
* el2hlt - level 2 halted
* el2nsync - level 2 not synchronized
* el3hlt - level 3 halted
* el3rst - level 3 reset
* elbin - ELBIN
* elibacc - cannot access a needed shared library
* elibbad - accessing a corrupted shared library
* elibexec - cannot exec a shared library directly
* elibmax - attempting to link in more shared libraries than system limit
* elibscn - .lib section in a.out corrupted
* elnrng - link number out of range
* eloop - too many levels of symbolic links
* emfile - too many open files
* emlink - too many links
* emsgsize - message too long
* emultihop - multihop attempted
* enametoolong - file name too long
* enavail - not available
* enet - ENET
* enetdown - network is down
* enetreset - network dropped connection on reset
* enetunreach - network is unreachable
* enfile - file table overflow
* enoano - anode table overflow
* enobufs - no buffer space available
* enocsi - no CSI structure available
* enodata - no data available
* enodev - no such device
* enoent - no such file or directory
* enoexec - exec format error
* enolck - no locks available
* enolink - link has be severed
* enomem - not enough memory
* enomsg - no message of desired type
* enonet - machine is not on the network
* enopkg - package not installed
* enoprotoopt - bad protocol option
* enospc - no space left on device
* enosr - out of stream resources or not a stream device
* enosym - unresolved symbol name
* enosys - function not implemented
* enotblk - block device required
* enotconn - socket is not connected
* enotdir - not a directory
* enotempty - directory not empty
* enotnam - not a named file
* enotsock - socket operation on non-socket
* enotsup - operation not supported
* enotty - inappropriate device for ioctl
* enotuniq - name not unique on network
* enxio - no such device or address
* eopnotsupp - operation not supported on socket
* eperm - not owner
* epfnosupport - protocol family not supported
* epipe - broken pipe
* eproclim - too many processes
* eprocunavail - bad procedure for program
* eprogmismatch - program version wrong
* eprogunavail - RPC program not available
* eproto - protocol error
* eprotonosupport - protocol not supported
* eprototype - protocol wrong type for socket
* erange - math result unrepresentable
* erefused - EREFUSED
* eremchg - remote address changed
* eremdev - remote device
* eremote - pathname hit remote file system
* eremoteio - remote i/o error
* eremoterelease - EREMOTERELEASE
* erofs - read-only file system
* erpcmismatch - RPC version is wrong
* erremote - object is remote
* eshutdown - cannot send after socket shutdown
* esocktnosupport - socket type not supported
* espipe - invalid seek
* esrch - no such process
* esrmnt - srmount error
* estale - stale remote file handle
* esuccess - Error 0
* etime - timer expired
* etimedout - connection timed out
* etoomanyrefs - too many references
* etxtbsy - text file or pseudo-device busy
* euclean - structure needs cleaning
* eunatch - protocol driver not attached
* eusers - too many users
* eversion - version mismatch
* ewouldblock - operation would block
* exdev - cross-domain link
* exfull - message tables full
* nxdomain - the hostname or domain name could not be found