inet

inet(3erl)                  Erlang Module Definition                  inet(3erl)



NAME
       inet - Access to TCP/IP protocols.

DESCRIPTION
       This module provides access to TCP/IP protocols.

       See also ERTS User's Guide: Inet Configuration for more information about
       how to configure an Erlang runtime system for IP communication.

       The following two Kernel configuration parameters affect the behavior of
       all sockets opened on an Erlang node:

         * inet_default_connect_options can contain a list of default options
           used for all sockets returned when doing connect.

         * inet_default_listen_options can contain a list of default options
           used when issuing a listen call.

       When accept is issued, the values of the listening socket options are
       inherited. No such application variable is therefore needed for accept.

       Using the Kernel configuration parameters above, one can set default
       options for all TCP sockets on a node, but use this with care. Options
       such as {delay_send,true} can be specified in this way. The following is
       an example of starting an Erlang node with all sockets using delayed
       send:

       $ erl -sname test -kernel \
       inet_default_connect_options '[{delay_send,true}]' \
       inet_default_listen_options '[{delay_send,true}]'

       Notice that default option {active, true} cannot be changed, for internal
       reasons.

       Addresses as inputs to functions can be either a string or a tuple. For
       example, the IP address 150.236.20.73 can be passed to gethostbyaddr/1,
       either as string "150.236.20.73" or as tuple {150, 236, 20, 73}.

       IPv4 address examples:

       Address          ip_address()
       -------          ------------
       127.0.0.1        {127,0,0,1}
       192.168.42.2     {192,168,42,2}

       IPv6 address examples:

       Address          ip_address()
       -------          ------------
       ::1             {0,0,0,0,0,0,0,1}
       ::192.168.42.2  {0,0,0,0,0,0,(192 bsl 8) bor 168,(42 bsl 8) bor 2}
       ::FFFF:192.168.42.2
                       {0,0,0,0,0,16#FFFF,(192 bsl 8) bor 168,(42 bsl 8) bor 2}
       3ffe:b80:1f8d:2:204:acff:fe17:bf38
                       {16#3ffe,16#b80,16#1f8d,16#2,16#204,16#acff,16#fe17,16#bf38}
       fe80::204:acff:fe17:bf38
                       {16#fe80,0,0,0,0,16#204,16#acff,16#fe17,16#bf38}

       Function parse_address/1 can be useful:

       1> inet:parse_address("192.168.42.2").
       {ok,{192,168,42,2}}
       2> inet:parse_address("::FFFF:192.168.42.2").
       {ok,{0,0,0,0,0,65535,49320,10754}}

DATA TYPES
       hostent() =
           #hostent{h_name = inet:hostname(),
                    h_aliases = [inet:hostname()],
                    h_addrtype = inet | inet6,
                    h_length = integer() >= 0,
                    h_addr_list = [inet:ip_address()]}

              The record is defined in the Kernel include file "inet.hrl".

              Add the following directive to the module:

              -include_lib("kernel/include/inet.hrl").


       hostname() = atom() | string()

       ip_address() = ip4_address() | ip6_address()

       ip4_address() = {0..255, 0..255, 0..255, 0..255}

       ip6_address() =
           {0..65535,
            0..65535,
            0..65535,
            0..65535,
            0..65535,
            0..65535,
            0..65535,
            0..65535}

       port_number() = 0..65535

       family_address() =
           inet_address() | inet6_address() | local_address()

              A general address format on the form {Family, Destination} where
              Family is an atom such as local and the format of Destination
              depends on Family, and is a complete address (for example an IP
              address including port number).


       inet_address() =
           {inet, {ip4_address() | any | loopback, port_number()}}

          Warning:
              This address format is for now experimental and for completeness
              to make all address families have a {Family, Destination}
              representation.



       inet6_address() =
           {inet6, {ip6_address() | any | loopback, port_number()}}

          Warning:
              This address format is for now experimental and for completeness
              to make all address families have a {Family, Destination}
              representation.



       local_address() = {local, File :: binary() | string()}

              This address family only works on Unix-like systems.

              File is normally a file pathname in a local filesystem. It is
              limited in length by the operating system, traditionally to 108
              bytes.

              A binary() is passed as is to the operating system, but a string()
              is encoded according to the  system filename encoding mode.

              Other addresses are possible, for example Linux implements
              "Abstract Addresses". See the documentation for Unix Domain
              Sockets on your system, normally unix in manual section 7.

              In most API functions where you can use this address family the
              port number must be 0.


       socket_address() =
           ip_address() | any | loopback | local_address()

       socket_getopt() =
           gen_sctp:option_name() |
           gen_tcp:option_name() |
           gen_udp:option_name()

       socket_setopt() =
           gen_sctp:option() | gen_tcp:option() | gen_udp:option()

       returned_non_ip_address() =
           {local, binary()} | {unspec, <<>>} | {undefined, any()}

              Addresses besides ip_address() ones that are returned from socket
              API functions. See in particular local_address().  The unspec
              family corresponds to AF_UNSPEC and can occur if the other side
              has no socket address. The undefined family can only occur in the
              unlikely event of an address family that the VM does not
              recognize.


       ancillary_data() =
           [{tos, byte()} | {tclass, byte()} | {ttl, byte()}]

              Ancillary data received with the data packet, read with the socket
              option pktoptions from a TCP socket, or to set in a call to
              gen_udp:send/4 or gen_udp:send/5.

              The value(s) correspond to the currently active socket options
              recvtos, recvtclass and recvttl, or for a single send operation
              the option(s) to override the currently active socket option(s).


       getifaddrs_ifopts() =
           [Ifopt ::
                {flags,
                 Flags ::
                     [up | broadcast | loopback | pointtopoint |
                      running | multicast]} |
                {addr, Addr :: ip_address()} |
                {netmask, Netmask :: ip_address()} |
                {broadaddr, Broadaddr :: ip_address()} |
                {dstaddr, Dstaddr :: ip_address()} |
                {hwaddr, Hwaddr :: [byte()]}]

              Interface address description list returned from getifaddrs/0,1
              for a named interface, translated from the returned data of the
              POSIX API function getaddrinfo().

              Hwaddr is hardware dependent, for example, on Ethernet interfaces
              it is the 6-byte Ethernet address (MAC address (EUI-48 address)).

              The tuples {addr,Addr}, {netmask,Netmask}, and possibly
              {broadaddr,Broadaddr} or {dstaddr,Dstaddr} are repeated in the
              list if the interface has got multiple addresses. An interface may
              have multiple {flag,_} tuples for example if it has different
              flags for different address families. Multiple {hwaddr,Hwaddr}
              tuples is hard to say anything definite about, though. The tuple
              {flag,Flags} is mandatory, all others are optional.

              Do not rely too much on the order of Flags atoms or the Ifopt
              tuples. There are however some rules:

                * A {flag,_} tuple applies to all other tuples that follow.

                * Immediately after {addr,_} follows {netmask,_}.

                * Immediately thereafter may {broadaddr,_} follow if broadcast
                  is member of Flags, or {dstaddr,_} if pointtopoint is member
                  of Flags. Both {dstaddr,_} and {broadaddr,_} does not occur
                  for the same {addr,_}.

                * Any {netmask,_}, {broadaddr,_}, or {dstaddr,_} tuples that
                  follow an {addr,Addr} tuple concerns the address Addr.

              The tuple {hwaddr,_} is not returned on Solaris, as the hardware
              address historically belongs to the link layer and it is not
              returned by the Solaris API function getaddrinfo().

          Warning:
              On Windows, the data is fetched from different OS API functions,
              so the Netmask and Broadaddr values may be calculated, just as
              some Flags values.



       posix() =
           eaddrinuse | eaddrnotavail | eafnosupport | ealready |
           econnaborted | econnrefused | econnreset | edestaddrreq |
           ehostdown | ehostunreach | einprogress | eisconn | emsgsize |
           enetdown | enetunreach | enopkg | enoprotoopt | enotconn |
           enotty | enotsock | eproto | eprotonosupport | eprototype |
           esocktnosupport | etimedout | ewouldblock | exbadport |
           exbadseq |
           file:posix()

              An atom that is named from the POSIX error codes used in Unix, and
              in the runtime libraries of most C compilers. See section POSIX
              Error Codes.


       socket()

              See gen_tcp:type-socket and gen_udp:type-socket.


       address_family() = inet | inet6 | local

       socket_protocol() = tcp | udp | sctp

       stat_option() =
           recv_cnt | recv_max | recv_avg | recv_oct | recv_dvi |
           send_cnt | send_max | send_avg | send_oct | send_pend

EXPORTS
       close(Socket) -> ok

              Types:

                 Socket = socket()

              Closes a socket of any type.


       format_error(Reason) -> string()

              Types:

                 Reason = posix() | system_limit

              Returns a diagnostic error string. For possible POSIX values and
              corresponding strings, see section POSIX Error Codes.


       get_rc() ->
                 [{Par :: atom(), Val :: any()} |
                  {Par :: atom(), Val1 :: any(), Val2 :: any()}]

              Returns the state of the Inet configuration database in form of a
              list of recorded configuration parameters. For more information,
              see ERTS User's Guide: Inet Configuration.

              Only actual parameters with other than default values are
              returned, for example not directives that specify other sources
              for configuration parameters nor directives that clear parameters.


       getaddr(Host, Family) -> {ok, Address} | {error, posix()}

              Types:

                 Host = ip_address() | hostname()
                 Family = address_family()
                 Address = ip_address()

              Returns the IP address for Host as a tuple of integers. Host can
              be an IP address, a single hostname, or a fully qualified
              hostname.


       getaddrs(Host, Family) -> {ok, Addresses} | {error, posix()}

              Types:

                 Host = ip_address() | hostname()
                 Family = address_family()
                 Addresses = [ip_address()]

              Returns a list of all IP addresses for Host. Host can be an IP
              address, a single hostname, or a fully qualified hostname.


       gethostbyaddr(Address) -> {ok, Hostent} | {error, posix()}

              Types:

                 Address = string() | ip_address()
                 Hostent = hostent()

              Returns a hostent record for the host with the specified address.


       gethostbyname(Hostname) -> {ok, Hostent} | {error, posix()}

              Types:

                 Hostname = hostname()
                 Hostent = hostent()

              Returns a hostent record for the host with the specified hostname.

              If resolver option inet6 is true, an IPv6 address is looked up.


       gethostbyname(Hostname, Family) ->
                        {ok, Hostent} | {error, posix()}

              Types:

                 Hostname = hostname()
                 Family = address_family()
                 Hostent = hostent()

              Returns a hostent record for the host with the specified name,
              restricted to the specified address family.


       gethostname() -> {ok, Hostname}

              Types:

                 Hostname = string()

              Returns the local hostname. Never fails.


       getifaddrs() ->
                     {ok,
                      [{Ifname :: string(),
                        Ifopts :: getifaddrs_ifopts()}]} |
                     {error, posix()}

              Returns a list of 2-tuples containing interface names and the
              interfaces' addresses. Ifname is a Unicode string and Ifopts is a
              list of interface address description tuples.

              The interface address description tuples are documented under the
              type of the Ifopts value.


       getifaddrs(Opts) -> {ok, [{Ifname, Ifopts}]} | {error, Posix}

              Types:

                  Opts = [{netns, Namespace}]
                  Namespace =  file:filename_all()
                 Ifname = string()
                  Ifopts =  getifaddrs_ifopts()
                 Posix = posix()

              The same as getifaddrs/0 but the Option {netns, Namespace} sets a
              network namespace for the OS call, on platforms that supports that
              feature.

              See the socket option {netns, Namespace} under setopts/2.


       getopts(Socket, Options) -> {ok, OptionValues} | {error, posix()}

              Types:

                 Socket = socket()
                 Options = [socket_getopt()]
                 OptionValues = [socket_setopt() | gen_tcp:pktoptions_value()]

              Gets one or more options for a socket. For a list of available
              options, see setopts/2. See also the description for the type
              gen_tcp:pktoptions_value().

              The number of elements in the returned OptionValues list does not
              necessarily correspond to the number of options asked for. If the
              operating system fails to support an option, it is left out in the
              returned list. An error tuple is returned only when getting
              options for the socket is impossible (that is, the socket is
              closed or the buffer size in a raw request is too large). This
              behavior is kept for backward compatibility reasons.

              A raw option request RawOptReq = {raw, Protocol, OptionNum,
              ValueSpec} can be used to get information about socket options not
              (explicitly) supported by the emulator. The use of raw socket
              options makes the code non-portable, but allows the Erlang
              programmer to take advantage of unusual features present on a
              particular platform.

              RawOptReq consists of tag raw followed by the protocol level, the
              option number, and either a binary or the size, in bytes, of the
              buffer in which the option value is to be stored. A binary is to
              be used when the underlying getsockopt requires input in the
              argument field. In this case, the binary size is to correspond to
              the required buffer size of the return value. The supplied values
              in a RawOptReq correspond to the second, third, and fourth/fifth
              parameters to the getsockopt call in the C socket API. The value
              stored in the buffer is returned as a binary ValueBin, where all
              values are coded in the native endianess.

              Asking for and inspecting raw socket options require low-level
              information about the current operating system and TCP stack.

              Example:

              Consider a Linux machine where option TCP_INFO can be used to
              collect TCP statistics for a socket. Assume you are interested in
              field tcpi_sacked of struct tcp_info filled in when asking for
              TCP_INFO. To be able to access this information, you need to know
              the following:

                * The numeric value of protocol level IPPROTO_TCP

                * The numeric value of option TCP_INFO

                * The size of struct tcp_info

                * The size and offset of the specific field

              By inspecting the headers or writing a small C program, it is
              found that IPPROTO_TCP is 6, TCP_INFO is 11, the structure size is
              92 (bytes), the offset of tcpi_sacked is 28 bytes, and the value
              is a 32-bit integer. The following code can be used to retrieve
              the value:

              get_tcpi_sacked(Sock) ->
                  {ok,[{raw,_,_,Info}]} = inet:getopts(Sock,[{raw,6,11,92}]),
                  <<_:28/binary,TcpiSacked:32/native,_/binary>> = Info,
                  TcpiSacked.

              Preferably, you would check the machine type, the operating
              system, and the Kernel version before executing anything similar
              to this code.


       getstat(Socket) -> {ok, OptionValues} | {error, posix()}

       getstat(Socket, Options) -> {ok, OptionValues} | {error, posix()}

              Types:

                 Socket = socket()
                 Options = [stat_option()]
                 OptionValues = [{stat_option(), integer()}]
                 stat_option() =
                     recv_cnt | recv_max | recv_avg | recv_oct | recv_dvi |
                     send_cnt | send_max | send_avg | send_oct | send_pend

              Gets one or more statistic options for a socket.

              getstat(Socket) is equivalent to getstat(Socket, [recv_avg,
              recv_cnt, recv_dvi, recv_max, recv_oct, send_avg, send_cnt,
              send_pend, send_max, send_oct]).

              The following options are available:

                recv_avg:
                  Average size of packets, in bytes, received by the socket.

                recv_cnt:
                  Number of packets received by the socket.

                recv_dvi:
                  Average packet size deviation, in bytes, received by the
                  socket.

                recv_max:
                  Size of the largest packet, in bytes, received by the socket.

                recv_oct:
                  Number of bytes received by the socket.

                send_avg:
                  Average size of packets, in bytes, sent from the socket.

                send_cnt:
                  Number of packets sent from the socket.

                send_pend:
                  Number of bytes waiting to be sent by the socket.

                send_max:
                  Size of the largest packet, in bytes, sent from the socket.

                send_oct:
                  Number of bytes sent from the socket.


       i() -> ok

       i(Proto :: socket_protocol()) -> ok

       i(X1 :: socket_protocol(), Fs :: [atom()]) -> ok

              Lists all TCP, UDP and SCTP sockets, including those that the
              Erlang runtime system uses as well as those created by the
              application.

              The following options are available:

                port:
                  The internal index of the port.

                module:
                  The callback module of the socket.

                recv:
                  Number of bytes received by the socket.

                sent:
                  Number of bytes sent from the socket.

                owner:
                  The socket owner process.

                local_address:
                  The local address of the socket.

                foreign_address:
                  The address and port of the other end of the connection.

                state:
                  The connection state.

                type:
                  STREAM or DGRAM or SEQPACKET.


       ntoa(IpAddress) -> Address | {error, einval}

              Types:

                 Address = string()
                 IpAddress = ip_address()

              Parses an ip_address() and returns an IPv4 or IPv6 address string.


       parse_address(Address) -> {ok, IPAddress} | {error, einval}

              Types:

                 Address = string()
                 IPAddress = ip_address()

              Parses an IPv4 or IPv6 address string and returns an ip4_address()
              or ip6_address(). Accepts a shortened IPv4 address string.


       parse_ipv4_address(Address) -> {ok, IPv4Address} | {error, einval}

              Types:

                 Address = string()
                 IPv4Address = ip_address()

              Parses an IPv4 address string and returns an ip4_address().
              Accepts a shortened IPv4 address string.


       parse_ipv4strict_address(Address) ->
                                   {ok, IPv4Address} | {error, einval}

              Types:

                 Address = string()
                 IPv4Address = ip_address()

              Parses an IPv4 address string containing four fields, that is, not
              shortened, and returns an ip4_address().


       parse_ipv6_address(Address) -> {ok, IPv6Address} | {error, einval}

              Types:

                 Address = string()
                 IPv6Address = ip_address()

              Parses an IPv6 address string and returns an ip6_address(). If an
              IPv4 address string is specified, an IPv4-mapped IPv6 address is
              returned.


       parse_ipv6strict_address(Address) ->
                                   {ok, IPv6Address} | {error, einval}

              Types:

                 Address = string()
                 IPv6Address = ip_address()

              Parses an IPv6 address string and returns an ip6_address(). Does
              not accept IPv4 addresses.


       ipv4_mapped_ipv6_address(X1 :: ip_address()) -> ip_address()

              Convert an IPv4 address to an IPv4-mapped IPv6 address or the
              reverse. When converting from an IPv6 address all but the 2 low
              words are ignored so this function also works on some other types
              of addresses than IPv4-mapped.


       parse_strict_address(Address) -> {ok, IPAddress} | {error, einval}

              Types:

                 Address = string()
                 IPAddress = ip_address()

              Parses an IPv4 or IPv6 address string and returns an ip4_address()
              or ip6_address(). Does not accept a shortened IPv4 address string.


       peername(Socket :: socket()) ->
                   {ok,
                    {ip_address(), port_number()} |
                    returned_non_ip_address()} |
                   {error, posix()}

              Returns the address and port for the other end of a connection.

              Notice that for SCTP sockets, this function returns only one of
              the peer addresses of the socket. Function peernames/1,2 returns
              all.


       peernames(Socket :: socket()) ->
                    {ok,
                     [{ip_address(), port_number()} |
                      returned_non_ip_address()]} |
                    {error, posix()}

              Equivalent to peernames(Socket, 0).

              Notice that the behavior of this function for an SCTP one-to-many
              style socket is not defined by the SCTP Sockets API Extensions.


       peernames(Socket, Assoc) ->
                    {ok, [{Address, Port}]} | {error, posix()}

              Types:

                 Socket = socket()
                 Assoc = #sctp_assoc_change{} | gen_sctp:assoc_id()
                 Address = ip_address()
                 Port = integer() >= 0

              Returns a list of all address/port number pairs for the other end
              of an association Assoc of a socket.

              This function can return multiple addresses for multihomed
              sockets, such as SCTP sockets. For other sockets it returns a one-
              element list.

              Notice that parameter Assoc is by the SCTP Sockets API Extensions
              defined to be ignored for one-to-one style sockets. What the
              special value 0 means, hence its behavior for one-to-many style
              sockets, is unfortunately undefined.


       port(Socket) -> {ok, Port} | {error, any()}

              Types:

                 Socket = socket()
                 Port = port_number()

              Returns the local port number for a socket.


       setopts(Socket, Options) -> ok | {error, posix()}

              Types:

                 Socket = socket()
                 Options = [socket_setopt()]

              Sets one or more options for a socket.

              The following options are available:

                {active, true | false | once | N}:
                  If the value is true, which is the default, everything
                  received from the socket is sent as messages to the receiving
                  process.

                  If the value is false (passive mode), the process must
                  explicitly receive incoming data by calling gen_tcp:recv/2,3,
                  gen_udp:recv/2,3, or gen_sctp:recv/1,2 (depending on the type
                  of socket).


                  If the value is once ({active, once}), one data message from
                  the socket is sent to the process. To receive one more
                  message, setopts/2 must be called again with option {active,
                  once}.


                  If the value is an integer N in the range -32768 to 32767
                  (inclusive), the value is added to the socket's count of data
                  messages sent to the controlling process. A socket's default
                  message count is 0. If a negative value is specified, and its
                  magnitude is equal to or greater than the socket's current
                  message count, the socket's message count is set to 0. Once
                  the socket's message count reaches 0, either because of
                  sending received data messages to the process or by being
                  explicitly set, the process is then notified by a special
                  message, specific to the type of socket, that the socket has
                  entered passive mode. Once the socket enters passive mode, to
                  receive more messages setopts/2 must be called again to set
                  the socket back into an active mode.


                  When using {active, once} or {active, N}, the socket changes
                  behavior automatically when data is received. This can be
                  confusing in combination with connection-oriented sockets
                  (that is, gen_tcp), as a socket with {active, false} behavior
                  reports closing differently than a socket with {active, true}
                  behavior. To simplify programming, a socket where the peer
                  closed, and this is detected while in {active, false} mode,
                  still generates message {tcp_closed,Socket} when set to
                  {active, once}, {active, true}, or {active, N} mode. It is
                  therefore safe to assume that message {tcp_closed,Socket},
                  possibly followed by socket port termination (depending on
                  option exit_on_close) eventually appears when a socket changes
                  back and forth between {active, true} and {active, false}
                  mode. However, when peer closing is detected it is all up to
                  the underlying TCP/IP stack and protocol.


                  Notice that {active, true} mode provides no flow control; a
                  fast sender can easily overflow the receiver with incoming
                  messages. The same is true for {active, N} mode, while the
                  message count is greater than zero.


                  Use active mode only if your high-level protocol provides its
                  own flow control (for example, acknowledging received
                  messages) or the amount of data exchanged is small. {active,
                  false} mode, use of the {active, once} mode, or {active, N}
                  mode with values of N appropriate for the application provides
                  flow control. The other side cannot send faster than the
                  receiver can read.


                {broadcast, Boolean} (UDP sockets):
                  Enables/disables permission to send broadcasts.

                {buffer, Size}:
                  The size of the user-level buffer used by the driver. Not to
                  be confused with options sndbuf and recbuf, which correspond
                  to the Kernel socket buffers. For TCP it is recommended to
                  have val(buffer) >= val(recbuf) to avoid performance issues
                  because of unnecessary copying. For UDP the same
                  recommendation applies, but the max should not be larger than
                  the MTU of the network path. val(buffer) is automatically set
                  to the above maximum when recbuf is set. However, as the size
                  set for recbuf usually become larger, you are encouraged to
                  use getopts/2 to analyze the behavior of your operating
                  system.

                  Note that this is also the maximum amount of data that can be
                  received from a single recv call. If you are using higher than
                  normal MTU consider setting buffer higher.


                {delay_send, Boolean}:
                  Normally, when an Erlang process sends to a socket, the driver
                  tries to send the data immediately. If that fails, the driver
                  uses any means available to queue up the message to be sent
                  whenever the operating system says it can handle it. Setting
                  {delay_send, true} makes all messages queue up. The messages
                  sent to the network are then larger but fewer. The option
                  affects the scheduling of send requests versus Erlang
                  processes instead of changing any real property of the socket.
                  The option is implementation-specific. Defaults to false.

                {deliver, port | term}:
                  When {active, true}, data is delivered on the form port : {S,
                  {data, [H1,..Hsz | Data]}} or term : {tcp, S, [H1..Hsz |
                  Data]}.

                {dontroute, Boolean}:
                  Enables/disables routing bypass for outgoing messages.

                {exit_on_close, Boolean}:
                  This option is set to true by default.

                  The only reason to set it to false is if you want to continue
                  sending data to the socket after a close is detected, for
                  example, if the peer uses gen_tcp:shutdown/2 to shut down the
                  write side.


                {header, Size}:
                  This option is only meaningful if option binary was specified
                  when the socket was created. If option header is specified,
                  the first Size number bytes of data received from the socket
                  are elements of a list, and the remaining data is a binary
                  specified as the tail of the same list. For example, if Size
                  == 2, the data received matches [Byte1,Byte2|Binary].

                {high_msgq_watermark, Size}:
                  The socket message queue is set to a busy state when the
                  amount of data on the message queue reaches this limit. Notice
                  that this limit only concerns data that has not yet reached
                  the ERTS internal socket implementation. Defaults to 8 kB.

                  Senders of data to the socket are suspended if either the
                  socket message queue is busy or the socket itself is busy.


                  For more information, see options low_msgq_watermark,
                  high_watermark, and low_watermark.


                  Notice that distribution sockets disable the use of
                  high_msgq_watermark and low_msgq_watermark. Instead use the
                  distribution buffer busy limit, which is a similar feature.


                {high_watermark, Size} (TCP/IP sockets):
                  The socket is set to a busy state when the amount of data
                  queued internally by the ERTS socket implementation reaches
                  this limit. Defaults to 8 kB.

                  Senders of data to the socket are suspended if either the
                  socket message queue is busy or the socket itself is busy.


                  For more information, see options low_watermark,
                  high_msgq_watermark, and low_msqg_watermark.


                {ipv6_v6only, Boolean}:
                  Restricts the socket to use only IPv6, prohibiting any IPv4
                  connections. This is only applicable for IPv6 sockets (option
                  inet6).

                  On most platforms this option must be set on the socket before
                  associating it to an address. It is therefore only reasonable
                  to specify it when creating the socket and not to use it when
                  calling function (setopts/2) containing this description.


                  The behavior of a socket with this option set to true is the
                  only portable one. The original idea when IPv6 was new of
                  using IPv6 for all traffic is now not recommended by FreeBSD
                  (you can use {ipv6_v6only,false} to override the recommended
                  system default value), forbidden by OpenBSD (the supported
                  GENERIC kernel), and impossible on Windows (which has separate
                  IPv4 and IPv6 protocol stacks). Most Linux distros still have
                  a system default value of false. This policy shift among
                  operating systems to separate IPv6 from IPv4 traffic has
                  evolved, as it gradually proved hard and complicated to get a
                  dual stack implementation correct and secure.


                  On some platforms, the only allowed value for this option is
                  true, for example, OpenBSD and Windows. Trying to set this
                  option to false, when creating the socket, fails in this case.


                  Setting this option on platforms where it does not exist is
                  ignored. Getting this option with getopts/2 returns no value,
                  that is, the returned list does not contain an {ipv6_v6only,_}
                  tuple. On Windows, the option does not exist, but it is
                  emulated as a read-only option with value true.


                  Therefore, setting this option to true when creating a socket
                  never fails, except possibly on a platform where you have
                  customized the kernel to only allow false, which can be doable
                  (but awkward) on, for example, OpenBSD.


                  If you read back the option value using getopts/2 and get no
                  value, the option does not exist in the host operating system.
                  The behavior of both an IPv6 and an IPv4 socket listening on
                  the same port, and for an IPv6 socket getting IPv4 traffic is
                  then no longer predictable.


                {keepalive, Boolean}(TCP/IP sockets):
                  Enables/disables periodic transmission on a connected socket
                  when no other data is exchanged. If the other end does not
                  respond, the connection is considered broken and an error
                  message is sent to the controlling process. Defaults to
                  disabled.

                {linger, {true|false, Seconds}}:
                  Determines the time-out, in seconds, for flushing unsent data
                  in the close/1 socket call.

                  The first component is if linger is enabled, the second
                  component is the flushing time-out, in seconds. There are 3
                  alternatives:


                  {false, _}:
                    close/1 or shutdown/2 returns immediately, not waiting for
                    data to be flushed, with closing happening in the
                    background.

                  {true, 0}:
                    Aborts the connection when it is closed. Discards any data
                    still remaining in the send buffers and sends RST to the
                    peer.

                    This avoids TCP's TIME_WAIT state, but leaves open the
                    possibility that another "incarnation" of this connection
                    being created.


                  {true, Time} when Time > 0:
                    close/1 or shutdown/2 will not return until all queued
                    messages for the socket have been successfully sent or the
                    linger timeout (Time) has been reached.

                {low_msgq_watermark, Size}:
                  If the socket message queue is in a busy state, the socket
                  message queue is set in a not busy state when the amount of
                  data queued in the message queue falls below this limit.
                  Notice that this limit only concerns data that has not yet
                  reached the ERTS internal socket implementation. Defaults to 4
                  kB.

                  Senders that are suspended because of either a busy message
                  queue or a busy socket are resumed when the socket message
                  queue and the socket are not busy.


                  For more information, see options high_msgq_watermark,
                  high_watermark, and low_watermark.


                  Notice that distribution sockets disable the use of
                  high_msgq_watermark and low_msgq_watermark. Instead they use
                  the distribution buffer busy limit, which is a similar
                  feature.


                {low_watermark, Size} (TCP/IP sockets):
                  If the socket is in a busy state, the socket is set in a not
                  busy state when the amount of data queued internally by the
                  ERTS socket implementation falls below this limit. Defaults to
                  4 kB.

                  Senders that are suspended because of a busy message queue or
                  a busy socket are resumed when the socket message queue and
                  the socket are not busy.


                  For more information, see options high_watermark,
                  high_msgq_watermark, and low_msgq_watermark.


                {mode, Mode :: binary | list}:
                  Received Packet is delivered as defined by Mode.

                {netns, Namespace :: file:filename_all()}:
                  Sets a network namespace for the socket. Parameter Namespace
                  is a filename defining the namespace, for example,
                  "/var/run/netns/example", typically created by command ip
                  netns add example. This option must be used in a function call
                  that creates a socket, that is, gen_tcp:connect/3,4,
                  gen_tcp:listen/2, gen_udp:open/1,2 or gen_sctp:open/0,1,2, and
                  also getifaddrs/1.

                  This option uses the Linux-specific syscall setns(), such as
                  in Linux kernel 3.0 or later, and therefore only exists when
                  the runtime system is compiled for such an operating system.


                  The virtual machine also needs elevated privileges, either
                  running as superuser or (for Linux) having capability
                  CAP_SYS_ADMIN according to the documentation for setns(2).
                  However, during testing also CAP_SYS_PTRACE and
                  CAP_DAC_READ_SEARCH have proven to be necessary.


                  Example:


                setcap cap_sys_admin,cap_sys_ptrace,cap_dac_read_search+epi beam.smp

                  Notice that the filesystem containing the virtual machine
                  executable (beam.smp in the example) must be local, mounted
                  without flag nosetuid, support extended attributes, and the
                  kernel must support file capabilities. All this runs out of
                  the box on at least Ubuntu 12.04 LTS, except that SCTP sockets
                  appear to not support network namespaces.


                  Namespace is a filename and is encoded and decoded as
                  discussed in module file, with the following exceptions:


                  * Emulator flag +fnu is ignored.

                  * getopts/2 for this option returns a binary for the filename
                    if the stored filename cannot be decoded. This is only to
                    occur if you set the option using a binary that cannot be
                    decoded with the emulator's filename encoding:
                    file:native_name_encoding/0.

                {bind_to_device, Ifname :: binary()}:
                  Binds a socket to a specific network interface. This option
                  must be used in a function call that creates a socket, that
                  is, gen_tcp:connect/3,4, gen_tcp:listen/2, gen_udp:open/1,2,
                  or gen_sctp:open/0,1,2.

                  Unlike getifaddrs/0, Ifname is encoded a binary. In the
                  unlikely case that a system is using non-7-bit-ASCII
                  characters in network device names, special care has to be
                  taken when encoding this argument.


                  This option uses the Linux-specific socket option
                  SO_BINDTODEVICE, such as in Linux kernel 2.0.30 or later, and
                  therefore only exists when the runtime system is compiled for
                  such an operating system.


                  Before Linux 3.8, this socket option could be set, but could
                  not retrieved with getopts/2. Since Linux 3.8, it is readable.


                  The virtual machine also needs elevated privileges, either
                  running as superuser or (for Linux) having capability
                  CAP_NET_RAW.


                  The primary use case for this option is to bind sockets into
                  Linux VRF instances.


                list:
                  Received Packet is delivered as a list.

                binary:
                  Received Packet is delivered as a binary.

                {nodelay, Boolean}(TCP/IP sockets):
                  If Boolean == true, option TCP_NODELAY is turned on for the
                  socket, which means that also small amounts of data are sent
                  immediately.

                {nopush, Boolean}(TCP/IP sockets):
                  This translates to TCP_NOPUSH on BSD and to TCP_CORK on Linux.

                  If Boolean == true, the corresponding option is turned on for
                  the socket, which means that small amounts of data are
                  accumulated until a full MSS-worth of data is available or
                  this option is turned off.


                  Note that while TCP_NOPUSH socket option is available on OSX,
                  its semantics is very different (e.g., unsetting it does not
                  cause immediate send of accumulated data). Hence, nopush
                  option is intentionally ignored on OSX.


                {packet, PacketType}(TCP/IP sockets):
                  Defines the type of packets to use for a socket. Possible
                  values:

                  raw | 0:
                    No packaging is done.

                  1 | 2 | 4:
                    Packets consist of a header specifying the number of bytes
                    in the packet, followed by that number of bytes. The header
                    length can be one, two, or four bytes, and containing an
                    unsigned integer in big-endian byte order. Each send
                    operation generates the header, and the header is stripped
                    off on each receive operation.

                    The 4-byte header is limited to 2Gb.


                  asn1 | cdr | sunrm | fcgi | tpkt | line:
                    These packet types only have effect on receiving. When
                    sending a packet, it is the responsibility of the
                    application to supply a correct header. On receiving,
                    however, one message is sent to the controlling process for
                    each complete packet received, and, similarly, each call to
                    gen_tcp:recv/2,3 returns one complete packet. The header is
                    not stripped off.

                    The meanings of the packet types are as follows:


                    * asn1 - ASN.1 BER

                    * sunrm - Sun's RPC encoding

                    * cdr - CORBA (GIOP 1.1)

                    * fcgi - Fast CGI

                    * tpkt - TPKT format [RFC1006]

                    * line - Line mode, a packet is a line-terminated with
                      newline, lines longer than the receive buffer are
                      truncated

                  http | http_bin:
                    The Hypertext Transfer Protocol. The packets are returned
                    with the format according to HttpPacket described in
                    erlang:decode_packet/3 in ERTS. A socket in passive mode
                    returns {ok, HttpPacket} from gen_tcp:recv while an active
                    socket sends messages like {http, Socket, HttpPacket}.

                  httph | httph_bin:
                    These two types are often not needed, as the socket
                    automatically switches from http/http_bin to httph/httph_bin
                    internally after the first line is read. However, there can
                    be occasions when they are useful, such as parsing trailers
                    from chunked encoding.

                {packet_size, Integer}(TCP/IP sockets):
                  Sets the maximum allowed length of the packet body. If the
                  packet header indicates that the length of the packet is
                  longer than the maximum allowed length, the packet is
                  considered invalid. The same occurs if the packet header is
                  too large for the socket receive buffer.

                  For line-oriented protocols (line, http*), option packet_size
                  also guarantees that lines up to the indicated length are
                  accepted and not considered invalid because of internal buffer
                  limitations.


                {line_delimiter, Char}(TCP/IP sockets):
                  Sets the line delimiting character for line-oriented protocols
                  (line). Defaults to $\n.

                {raw, Protocol, OptionNum, ValueBin}:
                  See below.

                {read_packets, Integer}(UDP sockets):
                  Sets the maximum number of UDP packets to read without
                  intervention from the socket when data is available. When this
                  many packets have been read and delivered to the destination
                  process, new packets are not read until a new notification of
                  available data has arrived. Defaults to 5. If this parameter
                  is set too high, the system can become unresponsive because of
                  UDP packet flooding.

                {recbuf, Size}:
                  The minimum size of the receive buffer to use for the socket.
                  You are encouraged to use getopts/2 to retrieve the size set
                  by your operating system.

                {recvtclass, Boolean}:
                  If set to true activates returning the received TCLASS value
                  on platforms that implements the protocol IPPROTO_IPV6 option
                  IPV6_RECVTCLASS or IPV6_2292RECVTCLASS for the socket. The
                  value is returned as a {tclass,TCLASS} tuple regardless of if
                  the platform returns an IPV6_TCLASS or an IPV6_RECVTCLASS CMSG
                  value.

                  For packet oriented sockets that supports receiving ancillary
                  data with the payload data (gen_udp and gen_sctp), the TCLASS
                  value is returned in an extended return tuple contained in an
                  ancillary data  list. For stream oriented sockets (gen_tcp)
                  the only way to get the TCLASS value is if the platform
                  supports the pktoptions option.


                {recvtos, Boolean}:
                  If set to true activates returning the received TOS value on
                  platforms that implements the protocol IPPROTO_IP option
                  IP_RECVTOS for the socket. The value is returned as a
                  {tos,TOS} tuple regardless of if the platform returns an
                  IP_TOS or an IP_RECVTOS CMSG value.

                  For packet oriented sockets that supports receiving ancillary
                  data with the payload data (gen_udp and gen_sctp), the TOS
                  value is returned in an extended return tuple contained in an
                  ancillary data  list. For stream oriented sockets (gen_tcp)
                  the only way to get the TOS value is if the platform supports
                  the pktoptions option.


                {recvttl, Boolean}:
                  If set to true activates returning the received TTL value on
                  platforms that implements the protocol IPPROTO_IP option
                  IP_RECVTTL for the socket. The value is returned as a
                  {ttl,TTL} tuple regardless of if the platform returns an
                  IP_TTL or an IP_RECVTTL CMSG value.

                  For packet oriented sockets that supports receiving ancillary
                  data with the payload data (gen_udp and gen_sctp), the TTL
                  value is returned in an extended return tuple contained in an
                  ancillary data  list. For stream oriented sockets (gen_tcp)
                  the only way to get the TTL value is if the platform supports
                  the pktoptions option.


                {reuseaddr, Boolean}:
                  Allows or disallows local reuse of port numbers. By default,
                  reuse is disallowed.

                {send_timeout, Integer}:
                  Only allowed for connection-oriented sockets.

                  Specifies a longest time to wait for a send operation to be
                  accepted by the underlying TCP stack. When the limit is
                  exceeded, the send operation returns {error,timeout}. How much
                  of a packet that got sent is unknown; the socket is therefore
                  to be closed whenever a time-out has occurred (see
                  send_timeout_close below). Defaults to infinity.


                {send_timeout_close, Boolean}:
                  Only allowed for connection-oriented sockets.

                  Used together with send_timeout to specify whether the socket
                  is to be automatically closed when the send operation returns
                  {error,timeout}. The recommended setting is true, which
                  automatically closes the socket. Defaults to false because of
                  backward compatibility.


                {show_econnreset, Boolean}(TCP/IP sockets):
                  When this option is set to false, which is default, an RST
                  received from the TCP peer is treated as a normal close (as
                  though an FIN was sent). A caller to gen_tcp:recv/2 gets
                  {error, closed}. In active mode, the controlling process
                  receives a {tcp_closed, Socket} message, indicating that the
                  peer has closed the connection.

                  Setting this option to true allows you to distinguish between
                  a connection that was closed normally, and one that was
                  aborted (intentionally or unintentionally) by the TCP peer. A
                  call to gen_tcp:recv/2 returns {error, econnreset}. In active
                  mode, the controlling process receives a {tcp_error, Socket,
                  econnreset} message before the usual {tcp_closed, Socket}, as
                  is the case for any other socket error. Calls to
                  gen_tcp:send/2 also returns {error, econnreset} when it is
                  detected that a TCP peer has sent an RST.


                  A connected socket returned from gen_tcp:accept/1 inherits the
                  show_econnreset setting from the listening socket.


                {sndbuf, Size}:
                  The minimum size of the send buffer to use for the socket. You
                  are encouraged to use getopts/2, to retrieve the size set by
                  your operating system.

                {priority, Integer}:
                  Sets the SO_PRIORITY socket level option on platforms where
                  this is implemented. The behavior and allowed range varies
                  between different systems. The option is ignored on platforms
                  where it is not implemented. Use with caution.

                {tos, Integer}:
                  Sets IP_TOS IP level options on platforms where this is
                  implemented. The behavior and allowed range varies between
                  different systems. The option is ignored on platforms where it
                  is not implemented. Use with caution.

                {tclass, Integer}:
                  Sets IPV6_TCLASS IP level options on platforms where this is
                  implemented. The behavior and allowed range varies between
                  different systems. The option is ignored on platforms where it
                  is not implemented. Use with caution.

              In addition to these options, raw option specifications can be
              used. The raw options are specified as a tuple of arity four,
              beginning with tag raw, followed by the protocol level, the option
              number, and the option value specified as a binary. This
              corresponds to the second, third, and fourth arguments to the
              setsockopt call in the C socket API. The option value must be
              coded in the native endianess of the platform and, if a structure
              is required, must follow the structure alignment conventions on
              the specific platform.

              Using raw socket options requires detailed knowledge about the
              current operating system and TCP stack.

              Example:

              This example concerns the use of raw options. Consider a Linux
              system where you want to set option TCP_LINGER2 on protocol level
              IPPROTO_TCP in the stack. You know that on this particular system
              it defaults to 60 (seconds), but you want to lower it to 30 for a
              particular socket. Option TCP_LINGER2 is not explicitly supported
              by inet, but you know that the protocol level translates to number
              6, the option number to number 8, and the value is to be specified
              as a 32-bit integer. You can use this code line to set the option
              for the socket named Sock:

              inet:setopts(Sock,[{raw,6,8,<<30:32/native>>}]),

              As many options are silently discarded by the stack if they are
              specified out of range; it can be a good idea to check that a raw
              option is accepted. The following code places the value in
              variable TcpLinger2:

              {ok,[{raw,6,8,<<TcpLinger2:32/native>>}]}=inet:getopts(Sock,[{raw,6,8,4}]),

              Code such as these examples is inherently non-portable, even
              different versions of the same OS on the same platform can respond
              differently to this kind of option manipulation. Use with care.

              Notice that the default options for TCP/IP sockets can be changed
              with the Kernel configuration parameters mentioned in the
              beginning of this manual page.


       sockname(Socket :: socket()) ->
                   {ok,
                    {ip_address(), port_number()} |
                    returned_non_ip_address()} |
                   {error, posix()}

              Returns the local address and port number for a socket.

              Notice that for SCTP sockets this function returns only one of the
              socket addresses. Function socknames/1,2 returns all.


       socknames(Socket :: socket()) ->
                    {ok,
                     [{ip_address(), port_number()} |
                      returned_non_ip_address()]} |
                    {error, posix()}

              Equivalent to socknames(Socket, 0).


       socknames(Socket, Assoc) ->
                    {ok, [{Address, Port}]} | {error, posix()}

              Types:

                 Socket = socket()
                 Assoc = #sctp_assoc_change{} | gen_sctp:assoc_id()
                 Address = ip_address()
                 Port = integer() >= 0

              Returns a list of all local address/port number pairs for a socket
              for the specified association Assoc.

              This function can return multiple addresses for multihomed
              sockets, such as SCTP sockets. For other sockets it returns a one-
              element list.

              Notice that parameter Assoc is by the SCTP Sockets API Extensions
              defined to be ignored for one-to-one style sockets. For one-to-
              many style sockets, the special value 0 is defined to mean that
              the returned addresses must be without any particular association.
              How different SCTP implementations interpret this varies somewhat.


POSIX ERROR CODES
         * e2big - Too long argument list

         * eacces - Permission denied

         * eaddrinuse - Address already in use

         * eaddrnotavail - Cannot assign requested address

         * eadv - Advertise error

         * eafnosupport - Address family not supported by protocol family

         * eagain - Resource temporarily unavailable

         * ealign - EALIGN

         * ealready - Operation already in progress

         * ebade - Bad exchange descriptor

         * ebadf - Bad file number

         * ebadfd - File descriptor in bad state

         * ebadmsg - Not a data message

         * ebadr - Bad request descriptor

         * ebadrpc - Bad RPC structure

         * ebadrqc - Bad request code

         * ebadslt - Invalid slot

         * ebfont - Bad font file format

         * ebusy - File busy

         * echild - No children

         * echrng - Channel number out of range

         * ecomm - Communication error on send

         * econnaborted - Software caused connection abort

         * econnrefused - Connection refused

         * econnreset - Connection reset by peer

         * edeadlk - Resource deadlock avoided

         * edeadlock - Resource deadlock avoided

         * edestaddrreq - Destination address required

         * edirty - Mounting a dirty fs without force

         * edom - Math argument out of range

         * edotdot - Cross mount point

         * edquot - Disk quota exceeded

         * eduppkg - Duplicate package name

         * eexist - File already exists

         * efault - Bad address in system call argument

         * efbig - File too large

         * ehostdown - Host is down

         * ehostunreach - Host is unreachable

         * eidrm - Identifier removed

         * einit - Initialization error

         * einprogress - Operation now in progress

         * eintr - Interrupted system call

         * einval - Invalid argument

         * eio - I/O error

         * eisconn - Socket is already connected

         * eisdir - Illegal operation on a directory

         * eisnam - Is a named file

         * el2hlt - Level 2 halted

         * el2nsync - Level 2 not synchronized

         * el3hlt - Level 3 halted

         * el3rst - Level 3 reset

         * elbin - ELBIN

         * elibacc - Cannot access a needed shared library

         * elibbad - Accessing a corrupted shared library

         * elibexec - Cannot exec a shared library directly

         * elibmax - Attempting to link in more shared libraries than system
           limit

         * elibscn - .lib section in a.out corrupted

         * elnrng - Link number out of range

         * eloop - Too many levels of symbolic links

         * emfile - Too many open files

         * emlink - Too many links

         * emsgsize - Message too long

         * emultihop - Multihop attempted

         * enametoolong - Filename too long

         * enavail - Unavailable

         * enet - ENET

         * enetdown - Network is down

         * enetreset - Network dropped connection on reset

         * enetunreach - Network is unreachable

         * enfile - File table overflow

         * enoano - Anode table overflow

         * enobufs - No buffer space available

         * enocsi - No CSI structure available

         * enodata - No data available

         * enodev - No such device

         * enoent - No such file or directory

         * enoexec - Exec format error

         * enolck - No locks available

         * enolink - Link has been severed

         * enomem - Not enough memory

         * enomsg - No message of desired type

         * enonet - Machine is not on the network

         * enopkg - Package not installed

         * enoprotoopt - Bad protocol option

         * enospc - No space left on device

         * enosr - Out of stream resources or not a stream device

         * enosym - Unresolved symbol name

         * enosys - Function not implemented

         * enotblk - Block device required

         * enotconn - Socket is not connected

         * enotdir - Not a directory

         * enotempty - Directory not empty

         * enotnam - Not a named file

         * enotsock - Socket operation on non-socket

         * enotsup - Operation not supported

         * enotty - Inappropriate device for ioctl

         * enotuniq - Name not unique on network

         * enxio - No such device or address

         * eopnotsupp - Operation not supported on socket

         * eperm - Not owner

         * epfnosupport - Protocol family not supported

         * epipe - Broken pipe

         * eproclim - Too many processes

         * eprocunavail - Bad procedure for program

         * eprogmismatch - Wrong program version

         * eprogunavail - RPC program unavailable

         * eproto - Protocol error

         * eprotonosupport - Protocol not supported

         * eprototype - Wrong protocol type for socket

         * erange - Math result unrepresentable

         * erefused - EREFUSED

         * eremchg - Remote address changed

         * eremdev - Remote device

         * eremote - Pathname hit remote filesystem

         * eremoteio - Remote I/O error

         * eremoterelease - EREMOTERELEASE

         * erofs - Read-only filesystem

         * erpcmismatch - Wrong RPC version

         * erremote - Object is remote

         * eshutdown - Cannot send after socket shutdown

         * esocktnosupport - Socket type not supported

         * espipe - Invalid seek

         * esrch - No such process

         * esrmnt - Srmount error

         * estale - Stale remote file handle

         * esuccess - Error 0

         * etime - Timer expired

         * etimedout - Connection timed out

         * etoomanyrefs - Too many references

         * etxtbsy - Text file or pseudo-device busy

         * euclean - Structure needs cleaning

         * eunatch - Protocol driver not attached

         * eusers - Too many users

         * eversion - Version mismatch

         * ewouldblock - Operation would block

         * exdev - Cross-domain link

         * exfull - Message tables full

         * nxdomain - Hostname or domain name cannot be found

Ericsson AB                        kernel 7.0                         inet(3erl)