socket(3)

NAME
socket - Socket interface.

DESCRIPTION

This module provides an API for network sockets. Functions are provided to create, delete and manipulate the sockets as well as sending and receiving data on them.

The intent is that it shall be as "close as possible" to the OS level socket interface. The only significant additions are that some of the functions, e.g. recv/3, have a time-out argument, and that recv/* for a stream socket iterates until the requested amount of data has been received.

    Note

    Asynchronous Calls

    Some functions feature asynchronous calls. This is achieved by setting the Timeout argument to nowait or to a Handle :: reference/0. See the respective function's type specification. This module has two different implementations of asynchronous calls. One on the Unix family of operating systems: select - based on the standard socket interface's select(3)/poll(3) calls, and one on Windows: completion - based on asynchronous I/O Completion Ports. The difference shows in the return values and message formats because they have slightly different semantics.

    The completion and select Return Values

    For instance, the call recv(Socket, 0, nowait), when there is no data available for reading, will, depending on the operating system, return one of:

        • {completion, CompletionInfo}

        • {select, SelectInfo} Where CompletionInfo is {completion_info, _, CompletionHandle} and SelectInfo is {select_info, _, SelectHandle}. Both the CompletionHandle and the SelectHandle are of type reference/0. When the operation can continue, a completion message containing the CompletionHandle or a select message containing the SelectHandle is sent to the calling process. On select systems, recv/2,3,4 may also return:

        • {select, {SelectInfo, Data} This may happen for sockets of type stream when Length > 1 since the OS may split a data stream at any point and deliver just the first part of the requested data. For the next recv/2,3,4 call; the Length to receive will probably have to be adjusted due to the already delivered data in this return value. On select systems, when the {otp, select_read} option is true, the asynchronous recv/3,4, recvfrom/3,4, and recvmsg/3,4,5 functions may also return:

        • {select_read, {SelectInfo, Data} This indicates that the receive operation was completed; all requested data has been delivered, and that the calling process will get a select message when there is data available for the next receive operation.

        The completion and select Messages

        The completion message has the format:

        • {'$socket', Socket, completion, {CompletionHandle, CompletionStatus}} The select message has the format:

        • {'$socket', Socket, select, SelectHandle} When a completion message is received (which contains the result of the operation), it means that the operation has been completed and CompletionStatus is the return value for the operation, which is what the function that initiated the operation could have returned, with the nowait argument, except for the completion and select return values. When a select message is received, it only means that the operation may now continue, by retrying the operation (which may return a new {select, _} value). Some operations are retried by repeating the same function call, and some have a dedicated function variant to be used for the retry. See the respective function's documentation.

        Operation Queuing on select Systems

        On select systems, all other processes are locked out until the current process has completed the operation as in a continuation call has returned a value indicating success or failure (not a select or select_read return). Other processes are queued and get a select return which makes them wait for their turn. Note that receiving data from parallel processes is only suitable for some protocols. For a stream socket it is in general a recipe for disaster.

        Cancelling an operation

        An operation that is in progress (not completed) may be canceled using cancel/2 both on completion and select systems. Cancelling an operation ensures that there is no completion, select, nor abort message in the inbox after the cancel/2 call.

        Using a Handle

        If creating a reference/0 with make_ref() and using that as the Timeout | Handle argument, the same Handle will then be the SelectHandle in the returned select_info/0 and the received select message, or be the CompletionHandle in the returned completion_info/0 and the received completion message. The compiler may then optimize a following receive statement to only scan the messages that arrive after the reference/0 is created. If the message queue is large this is a big optimization. It is not possible to have more than one operation in progress with the same reference/0.

        Repeating an Operation on a select Systems

        Onselect systems, if a call would be repeated before the select message has been received it replaces the operation in progress:

              {select, {select_info, Handle}} = socket:accept(LSock, nowait),
              {ok, Socket} = socket:accept(LSock, 1000),
              :

        Above, Handle is no longer valid once the second accept/2, call has been made (the first call is automatically canceled). After the second accept/2 call returns, the accept operation has completed. Note that there is a race here; there is no way to know if the call is repeated before the select message is sent since it may have been sent just before the repeated call. So now there might be a select message containing Handle in the inbox.

        The abort Message

        Another message the user must be prepared for (when using nowait | Handle) is the abort message:

        • {'$socket', Socket, abort, Info} This message indicates that the operation in progress has been aborted. For instance, if the socket has been closed by another process; Info will be {Handle, closed}.

NOTE: Support for IPv6 has been implemented but not fully tested.

This module was introduced in OTP 22.0, as experimental code.

    • In OTP 22.1, the nowait argument was added for many functions, and the cancel/2 and info/1 functions were also added.

    • In OTP 22.3, the number_of/0 function was added.

    • In OTP 23.0, the functions is_supported/1,2 and the open/1,2 functions with an FD argument were added.

    • In OTP 23.1, the use_registry/1 function was added.

    • In OTP 24.0, the select_handle/0 argument was added for many functions, the cancel/1, cancel_monitor/1, getopt/3 with tuple options, getopt_native/3, info/0, monitor/1, open/3 with an option list, many variants of the recv/*, recvfrom/*, recvmsg/*, send/*, sendmsg/*, the sendto/* functions, the sendfile/* functions, and the setopt/3, setopt_native/3 functions, were added.

    • In OTP 24.1, the i/* functions were added.

    • In OTP 24.2, the ioctl/* functions were added.

    • In OTP 26.0, the completion_handle/0 argument was added for many functions, and the cancel/2 function with completion_info/0 argument was added. That is: support for Windows asynchronous I/O Completion Ports was added. The Unix-ish flavored (select handle) API features could be considered no longer experimental.

    • In OTP 27.0, the Windows flavored (completion handle) API features could be considered no longer experimental.

    • In OTP 29.0, (experimental) complete support for SCTP was added (functionally feature compatible with inet). Not (yet) supported for FreeBSD.

  Examples

    client(SAddr, SPort) ->
       {ok, Sock} = socket:open(inet, stream, tcp),
       ok = socket:connect(Sock, #{family => inet,
                                   addr   => SAddr,
                                   port   => SPort}),
       Msg = <<"hello">>,
       ok = socket:send(Sock, Msg),
       ok = socket:shutdown(Sock, write),
       {ok, Msg} = socket:recv(Sock),
       ok = socket:close(Sock).
    server(Addr, Port) ->
       {ok, LSock} = socket:open(inet, stream, tcp),
       ok = socket:bind(LSock, #{family => inet,
                                 port   => Port,
                                 addr   => Addr}),
       ok = socket:listen(LSock),
       {ok, Sock} = socket:accept(LSock),
       {ok, Msg} = socket:recv(Sock),
       ok = socket:send(Sock, Msg),
       ok = socket:close(Sock),
       ok = socket:close(LSock).

DATA TYPES

cmsg() :: cmsg_recv() | cmsg_send().

    Control messages (ancillary messages).
cmsg_recv() :: #{level := socket, type := timestamp, data := binary(), value => timeval()} | #{level := socket, type := timestampns, data := binary(), value => timespec()} | #{level := socket, type := rights, data := binary()} | #{level := socket, type := credentials, data := binary()} | #{level := ip, type := tos, data := binary(), value => ip_tos()} | #{level := ip, type := recvtos, data := binary(), value := ip_tos()} | #{level := ip, type := ttl, data := binary(), value => integer()} | #{level := ip, type := recvttl, data := binary(), value := integer()} | #{level := ip, type := pktinfo, data := binary(), value => ip_pktinfo()} | #{level := ip, type := origdstaddr, data := binary(), value => sockaddr_recv()} | #{level := ip, type := recverr, data := binary(), value => extended_err()} | #{level := ipv6, type := hoplimit, data := binary(), value => integer()} | #{level := ipv6, type := pktinfo, data := binary(), value => ipv6_pktinfo()} | #{level := ipv6, type := recverr, data := binary(), value => extended_err()} | #{level := ipv6, type := tclass, data := binary(), value => integer()}.

    Control messages (ancillary messages) returned by recvmsg/1,2,3,5.

    A control message has got a data field with a native (binary) value for the message data, and may also have a decoded value field if this socket library successfully decoded the data.
cmsg_send() :: #{level := sctp, type := sndrcv, value := sctp_snd_rcv_info()} | #{level := socket, type := timestamp, data => native_value(), value => timeval()} | #{level := socket, type := rights, data := native_value()} | #{level := socket, type := credentials, data := native_value()} | #{level := ip, type := tos, data => native_value(), value => iptos_value()} | #{level := ip, type := ttl, data => native_value(), value => integer()} | #{level := ip, type := hoplimit, data => native_value(), value => integer()} | #{level := ipv6, type := tclass, data => native_value(), value => integer()}.

    Control messages (ancillary messages) accepted by sendmsg/2,3,4.

    A control message may for some message types have a value field with a symbolic value, or a data field with a native value, that has to be binary compatible what is defined in the platform's header files.
completion_handle() :: reference().

    Completion operation handle.

    A reference/0 that uniquely identifies the (completion) operation, contained in the returned completion_info/0.
completion_info() :: {completion_info, CompletionTag :: completion_tag(), CompletionHandle :: completion_handle()}.

    Completion operation info.

    Returned by an operation that requires the caller to wait for a completion message containing the CompletionHandle and the result of the operation; the CompletionStatus.
completion_tag() :: accept | connect | recv | recvfrom | recvmsg | recvmmsg | send | sendv | sendto | sendmsg | sendmmsg | sendfile.

    Completion operation tag.

    A tag that describes the ongoing (completion) operation (= function name), contained in the returned completion_info/0.
domain() :: inet | inet6 | local | unspec.

    Protocol domain a.k.a address family.

    A lowercase atom/0 representing a protocol domain on the platform named AF_* (or PF_*). For example inet corresponds to AF_INET.

    is_supported(ipv6) tells if the IPv6 protocol, protocol domain inet6, is supported.

    is_supported(local) tells if the protocol domain local is supported.

    supports/0 reports both values, but also many more, with a single call.
ee_origin() :: none | local | icmp | icmp6.
eei() :: #{info := econnreset | econnaborted | netname_deleted | too_many_cmds | atom(), raw_info := term()}.

    Extended Error Information.

    A term containing additional (error) information if the socket NIF has been configured to produce it.
extended_err() :: #{error := posix(), origin := icmp, type := dest_unreach, code := icmp_dest_unreach() | 0..255, info := 0..4294967295, data := 0..4294967295, offender := sockaddr_recv()} | #{error := posix(), origin := icmp, type := time_exceeded | 0..255, code := 0..255, info := 0..4294967295, data := 0..4294967295, offender := sockaddr_recv()} | #{error := posix(), origin := icmp6, type := dest_unreach, code := icmpv6_dest_unreach() | 0..255, info := 0..4294967295, data := 0..4294967295, offender := sockaddr_recv()} | #{error := posix(), origin := icmp6, type := pkt_toobig | time_exceeded | 0..255, code := 0..255, info := 0..4294967295, data := 0..4294967295, offender := sockaddr_recv()} | #{error := posix(), origin := ee_origin() | 0..255, type := 0..255, code := 0..255, info := 0..4294967295, data := 0..4294967295, offender := sockaddr_recv()}.
hatype() :: netrom | eether | ether | ax25 | pronet | chaos | ieee802 | arcnet | appletlk | dlci | atm | metricom | ieee1394 | eui64 | infiniband | tunnel | tunnel6 | loopback | localtlk | none | void | non_neg_integer().
icmp_dest_unreach() :: net_unreach | host_unreach | port_unreach | frag_needed | net_unknown | host_unknown.
icmpv6_dest_unreach() :: noroute | adm_prohibited | not_neighbour | addr_unreach | port_unreach | policy_fail | reject_route.
in6_addr() :: {0..65535, 0..65535, 0..65535, 0..65535, 0..65535, 0..65535, 0..65535, 0..65535}.
in6_flow_info() :: 0..1048575.
in6_scope_id() :: 0..4294967295.
in_addr() :: {0..255, 0..255, 0..255, 0..255}.
info() :: #{counters := #{atom() := non_neg_integer()}, iov_max := non_neg_integer(), use_registry := boolean(), io_backend := #{name := atom()}, load_nif_result := undefined | ok | {error, term()}}.

    Platform dependent information items.

    The value of iov_max is the value of the IOV_MAX constant in the system headers, which is the largest allowed I/O vector. See also sendmsg/4 regarding the iov key of msg_send/0. The smallest allowed IOV_MAX value according to POSIX is 16, but check your platform documentation to be sure.

    About the use_registry key, see use_registry/1 and the otp_socket_option/0 with the same name.
info_keys() :: [domain | type | protocol | fd | owner | local_address | remote_address | recv | sent | state].

    Information element designators for the i/1 and i/2 functions.
interface_type() :: other | hdh1822 | x25ddh | x25 | ether | ppp | loop | ipv4 | ipv6 | '6to4' | gif | faith | stf | bridge | cellular | non_neg_integer().

    The interface type (of the datalink). We only translate a few values to atoms, the rest are left as (unsigned) integer values.
invalid() :: {invalid, What :: term()}.
ioctl_device_flag() :: up | broadcast | debug | loopback | pointopoint | notrailers | knowsepoch | running | noarp | promisc | allmulti | master | oactive | slave | simplex | link0 | link1 | link2 | multicast | portsel | automedia | cantconfig | ppromisc | dynamic | monitor | staticarp | dying | renaming | nogroup | lower_up | dormant | echo.
ioctl_device_map() :: #{mem_start := non_neg_integer(), mem_end := non_neg_integer(), base_addr := non_neg_integer(), irq := non_neg_integer(), dma := non_neg_integer(), port := non_neg_integer()}.
ip_mreq() :: #{multiaddr := in_addr(), interface := in_addr()}.

    C: struct ip_mreq

    Corresponds to the C struct ip_mreq for managing multicast groups.
ip_mreq_source() :: #{multiaddr := in_addr(), interface := in_addr(), sourceaddr := in_addr()}.

    C: struct ip_mreq_source

    Corresponds to the C struct ip_mreq_source for managing multicast groups.
ip_msfilter() :: #{multiaddr := in_addr(), interface := in_addr(), mode := include | exclude, slist := [in_addr()]}.

    C: struct ip_msfilter

    Corresponds to the C struct ip_msfilter for managing multicast source filtering (RFC 3376).
ip_pktinfo() :: #{ifindex := non_neg_integer(), spec_dst := in_addr(), addr := in_addr()}.

    C: struct ip_pktinfo
ip_pmtudisc() :: want | dont | do | probe.

    C: IP_PMTUDISC_* values. => Lowercase atom/0 values corresponding to the C library constants IP_PMTUDISC_*. Some constant(s) may be unsupported by the platform.
ip_tos() :: #{native := iptos_native(), tos := iptos_tos(), dscp := iptos_dscp() | non_neg_integer()}.

    C: IPTOS_* values.

    Note that since there are two different representations of TOS; according to RFC 1349 ("classic TOS") and RFC 2474 (DSCP), we have three different value representations for tos: native (the raw unencoded value of the TOS octet), tos (classic), and dscp.

    When sending or setting (the ip tos option), the user can choose between the three different (value) representations. When reading, the value is represented as a map with all three representations, since 'socket' does not know which one is expected. Its then up to the user pick the one they want.

    An integer dscp value is a DSCP field value that is not known from the IANA registry (see iptos_dscp/0).
iptos_dscp() :: cs0 | le | cs1 | af11 | af12 | af13 | cs2 | af21 | af22 | af23 | cs3 | af31 | af32 | af33 | cs4 | af41 | af42 | af43 | cs5 | voice_admit | nqb | ef | cs6 | cs7.

    These symbolic DSCP values are according to IANA's [Differentiated Services Field Codepoints registry] (https://www.iana.org/assignments/dscp-registry/dscp-registry.xhtml).
iptos_native() :: non_neg_integer().
iptos_tos() :: #{precedence := iptos_tos_prec() | non_neg_integer(), tos := iptos_tos_value() | non_neg_integer()}.

    Lowercase atom/0 values corresponding to the C library constants IPTOS_*. The atoms are named like The C library names, but to avoid platform depencendy, the set of names and values follow RFC 1349, not the C library header files.

    An integer value is a field value that is not named in the RFC.
iptos_tos_prec() :: netcontrol | internetcontrol | critical_ecp | flashoverride | flash | immediate | priority | routine.
iptos_tos_value() :: default | lowdelay | throughput | reliability | mincost.
iptos_value() :: iptos_tos() | iptos_dscp() | iptos_native().
ipv6_hops() :: default | 0..255.

    IPv6 hop limit value.

    The value default is only valid to set and is translated to the C value -1, meaning the route default.
ipv6_mreq() :: #{multiaddr := in6_addr(), interface := non_neg_integer()}.

    C: struct ipv6_mreq

    Corresponds to the C struct ipv6_mreq for managing multicast groups. See also RFC 2553.
ipv6_pktinfo() :: #{addr := in6_addr(), ifindex := integer()}.

    C: struct in6_pktinfo
ipv6_pmtudisc() :: want | dont | do | probe.

    C: IPV6_PMTUDISC_* values

    Lowercase atom/0 values corresponding to the C library constants IPV6_PMTUDISC_*. Some constant(s) may be unsupported by the platform.
level() :: socket | protocol().

    Protocol level.

    A lowercase atom/0 OS protocol level, that is: socket or a protocol/0 name.

    socket is the SOL_SOCKET protocol level in the OS header files, with options named SO_* .
linger() :: #{onoff := boolean(), linger := non_neg_integer()}.

    C: struct linger

    Corresponds to the C struct linger for managing the socket option {socket, linger}.
msg() :: msg_send() | msg_recv().

    C: struct msghdr
msg_data_recv() :: #{addr => sockaddr_recv(), iov := erlang:iovec(), ctrl := [cmsg_recv() | #{level := level() | integer(), type := integer(), data := binary()}], flags := [msg_flag() | integer()]}.

    Message returned by recvmsg/1,2,3,5.

    Corresponds to a C struct msghdr, see your platform documentation for recvmsg(2). addr
        Optional peer address, used on unconnected sockets. Corresponds to msg_name and msg_namelen fields of a struct msghdr. If NULL the map key is not present.
    iov
        Data as a list of binaries. The msg_iov and msg_iovlen fields of a struct msghdr.
    ctrl
        A possibly empty list of control messages (CMSG). Corresponds to the msg_control and msg_controllen fields of a struct msghdr.
    flags
        Message flags. Corresponds to the msg_flags field of a struct msghdr. Unknown flags, if any, are returned in one integer/0, last in the containing list.
msg_flag() :: cmsg_cloexec | confirm | ctrunc | dontroute | eor | errqueue | more | oob | peek | trunc.

    Platform dependent message flags.

    Translates to/from message flag constants on the platform. These flags are lowercase while the constants are uppercase with prefix MSG_; for example oob translates to MSG_OOB.

    Some flags are only used for sending, some only for receiving, some in received control messages, and some for several of these. Not all flags are supported on all platforms. See the platform's documentation, supports(msg_flags), and is_supported(msg_flags, MsgFlag).
msg_notification_recv() :: #{addr => sockaddr_recv(), notification := sctp_notification(), ctrl := [#{level := level() | integer(), type := integer(), data := binary()}], flags := [notification | [msg_flag() | integer()]]}.

    Notifications can be received on a SCTP socket (type = seqpacket and protocol = sctp).
msg_recv() :: msg_data_recv() | msg_notification_recv().

    Message returned by recvmsg/1,2,3,5.
msg_send() :: #{addr => sockaddr(), iov := erlang:iovec(), ctrl => [cmsg_send() | #{level := level() | integer(), type := integer(), data := binary()}]}.

    Message sent by sendmsg/2,3,4.

    Corresponds to a C struct msghdr, see your platform documentation for sendmsg(2). addr
        Optional peer address, used on unconnected sockets. Corresponds to msg_name and msg_namelen fields of a struct msghdr. If not used they are set to NULL, 0.
    iov
        Mandatory data as a list of binaries. The msg_iov and msg_iovlen fields of a struct msghdr.
    ctrl
        Optional list of control messages (CMSG). Corresponds to the msg_control and msg_controllen fields of a struct msghdr. If not used they are set to NULL, 0.

    The msg_flags field of the struct msghdr is set to 0.
native_value() :: integer() | boolean() | binary().
otp_socket_option() :: debug | iow | controlling_process | rcvbuf | rcvctrlbuf | sndctrlbuf | select_read | meta | use_registry | fd | domain.

    Protocol level otp socket option.

    Socket options for the otp pseudo protocol level, that is: {otp, Name} options.

    This protocol level is the Erlang/OTP's socket implementation layer, hence above all OS protocol levels. debug
        boolean/0 - Activate debug logging.
    iow
        boolean/0 - Inform On Wrap of statistics counters.
    controlling_process
        pid/0 - The socket "owner". Only the current controlling process can set this option.
    rcvbuf
        BufSize :: (default | integer()>0) | {N :: integer()>0, BufSize :: (default | integer()>0)} - Receive buffer size.

        The value default is only valid to set.

        N specifies the number of read attempts to do in a tight loop before assuming no more data is pending.

        This is the allocation size for the receive buffer used when calling the OS protocol stack's receive API, when no specific size (size 0) is requested. When the receive function returns the receive buffer is reallocated to the actually received size. If the data is copied or shrunk in place is up to the allocator, and can to some extent be configured in the Erlang VM.

        The similar socket option; {socket,rcvbuf} is a related option for the OS' protocol stack that on Unix corresponds to SOL_SOCKET,SO_RCVBUF.
    rcvctrlbuf
        BufSize :: (default | integer()>0) - Allocation size for the ancillary data buffer used when calling the OS protocol stack's receive API.

        The value default is only valid to set.
    sndctrlbuf
        BufSize :: (default | integer()>0) - Allocation size for the ancillary data buffer used when calling the OS protocol stack's sendmsg API.

        The value default is only valid to set.

        It is the user's responsibility to set a buffer size that has room for the encoded ancillary data in the message to send.

        See sendmsg and also the ctrl field of the msg_send/0 type.
    select_read
        boolean/0 - On select implementations, see Asynchronous Calls, automatically activate select after a completed read.

        Instead of {ok, Data} the receive operation returns {select_read, {SelectInfo, Data}}, and the calling process can wait for a select message containing SelectInfo when there is data available again.

        Setting this option locks out other processes from receiving any data since the current process continues its operation, so it effectively disables receive operation queuing.
    fd
        integer/0 - Only valid to get. The OS protocol levels' socket descriptor. Functions open/1,2 can be used to create a socket according to this module from an existing OS socket descriptor.
    use_registry
        boolean/0 - Only valid to get. The value is set when the socket is created with open/2 or open/4.

    Options not described here are intentionally undocumented and for Erlang/OTP internal use only.
packet_type() :: host | broadcast | multicast | otherhost | outgoing | loopback | user | kernel | fastroute | non_neg_integer().
port_number() :: 0..65535.
posix() :: inet:posix().

    Posix error codes.

    Local alias for inet:posix/0, a set of atom/0s.
protocol() :: atom().

    Protocol name.

    A lowercase atom/0 representing an OS protocol name. To be used for example in socket_option/0 in control messages.

    They have the following names in the OS header files: ip
        IPPROTO_IP a.k.a SOL_IP with options named IP_*.
    ipv6
        IPPROTO_IPV6 a.k.a SOL_IPV6 with options named IPV6_*.
    tcp
        IPPROTO_TCP with options named TCP_*.
    mptcp
        IPPROTO_MPTCP with a few options named MPTCP_*. Most TCP_* options apply which is the purpose of Multi-Path TCP.
    udp
        IPPROTO_UDP with options named UDP_*.
    sctp
        IPPROTO_SCTP with options named SCTP_*.

    There are many other possible protocols, but the ones above are those for which this socket library implements socket options and/or control messages.

    All protocols known to the OS are enumerated when the Erlang VM is started, through the C library call getprotoent(). See the OS man page for protocols(5). Those in the list above are valid if supported by the platform, even if they aren't enumerated.

    The calls is_supported(ipv6) , is_supported(sctp) and is_supported(mptcp) can be used to find out if the protocols ipv6, sctp and mptcp are supported on the platform as in; appropriate header file and libraries exist.

    The call is_supported(protocols, Protocol) can only be used to find out if the platform knows the protocol number for a named Protocol.

    See open/2,3,4
sctp_adapt_event() :: #{type := adaptation_event, flags := uint16(), adaption_ind := uint32(), assoc_id := sctp_assoc_id()}.

    A peer has sent a Adaptation Layer Indication parameter.

    C: struct sctp_adaptation_event
sctp_assoc_change() :: #{type := assoc_change, flags := integer(), state := sctp_assoc_change_state(), error := sctp_operation_error(), outbound_streams := integer(), inbound_streams := integer(), assoc_id := sctp_assoc_id()}.

    An SCTP association has either begun or ended.

    C: struct sctp_assoc_change
sctp_assoc_change_state() :: comm_up | comm_lost | restart | shutdown_comp | cant_str_assoc | integer().
sctp_assoc_id() :: integer().

    C: sctp_assoc_t
sctp_assoc_reset_event() :: #{type := assoc_reset, flags := [denied | failed], assoc_id := sctp_assoc_id(), local_tsn := uint32(), remote_tsn := uint32()}.

    C: struct sctp_assoc_reset_event
sctp_assoc_stats() :: #{assoc_id := sctp_assoc_id(), max_rto_addr := sockaddr(), max_rto := uint64(), in_sacks := uint64(), out_sacks := uint64(), in_packets := uint64(), out_packets := uint64(), rtx_chunks := uint64(), out_of_seq_tsns := uint64(), in_dup_chunks := uint64(), gap_ack_recv := uint64(), in_unordered_chunks := uint64(), out_unordered_chunks := uint64(), in_ordered_chunks := uint64(), out_ordered_chunks := uint64(), in_ctrl_chunks := uint64(), out_ctrl_chunks := uint64()}.

    C: struct sctp_assoc_stats.
sctp_assocparams() :: #{assoc_id := sctp_assoc_id(), asocmaxrxt := uint16(), number_peer_destinations := uint16(), peer_rwnd := uint32(), local_rwnd := uint32(), cookie_life := uint32()}.

    C: struct sctp_assocparams
sctp_authkey() :: #{type := authkey, flags := uint16(), keynumber := uint16(), altkeynumber := uint16(), indication := uint32(), assoc_id := sctp_assoc_id()}.

    When a receiver is using authentication, info about new keys and errors are provided in this notification.

    C: struct sctp_authkey_event
sctp_event_subscribe() :: #{data_io := boolean(), association := boolean(), address := boolean(), send_failure := boolean(), peer_error := boolean(), shutdown := boolean(), partial_delivery := boolean(), adaptation_layer => boolean(), sender_dry => boolean(), stream_reset => boolean(), assoc_reset => boolean(), stream_change => boolean()}.

    C: struct sctp_event_subscribe.

    Not all fields are implemented on all platforms; unimplemented fields are ignored, but implemented fields are mandatory. Note that the '_event' suffixes have been stripped from the C struct field names, for convenience.
sctp_initmsg() :: #{num_ostreams := uint16(), max_instreams := uint16(), max_attempts := uint16(), max_init_timeo := uint16()}.

    C: struct sctp_initmsg.
sctp_notification() :: sctp_assoc_change() | sctp_paddr_change() | sctp_send_failed() | sctp_remote_error() | sctp_shutdown_event() | sctp_adapt_event() | sctp_pdapi_event() | sctp_authkey() | sctp_sender_dry() | sctp_stream_reset_event() | sctp_assoc_reset_event() | sctp_stream_change_event() | sctp_send_failed_event() | sctp_notification_generic().

    All possible notification types. All of them has at least two fields: 'type' and 'flags' ('flags' are not allways used).

    C: union sctp_notification
sctp_notification_generic() :: #{type := uint16(), flags := uint16()}.

    C: union sctp_notification

    This is intended as a fallback type for any notification we have not yet implemented.
sctp_operation_error() :: unknown | bad_sid | missing_parm | stale_cookie | no_resources | bad_addr | unrec_chunk | bad_mandparm | unrec_parm | no_usr_data | cookie_shut | restart_new_addrs | user_abort | delete_lastaddr | resource_shortage | delete_srcaddr | auth_err | pos_integer().

    These error codes are (currently) defined in RFC 4960, and named as Operation Errors.
sctp_paddr_change() :: #{type := peer_addr_change, flags := pos_integer(), addr := socket:sockaddr(), state := sctp_peer_addr_change_state(), error := pos_integer(), assoc_id := sctp_assoc_id()}.

    A destination address on a multi-homed peer has encountered a change.

    C: struct sctp_paddr_change
sctp_pap_flag() :: enable_heartbeats | disable_heartbeats | send_heartbeat_immediately | enable_pmtu_discovery | disable_pmtu_discovery | enable_sack | disable_sack | set_heartbeat_delay_to_zero | ipv6_flowlabel | dscp.

    C: enum sctp_spp_flags.
sctp_pap_flags() :: integer() | [sctp_pap_flag()].

    There are three pairs of flags that cannot be both be set (maybe obviously) at the same time:

        • enable_heartbeats and disable_heartbeats

        • enable_pmtu_discovery and disable_pmtu_discovery

        • enable_sack and disable_sack
sctp_pdapi_event() :: #{type := partial_delivery_event, flags := uint16(), indication := uint16(), assoc_id := sctp_assoc_id(), stream => uint32(), seq => uint32()}.

    A receiver is engaged in a partial delivery.

    Note that not all fields are available on all platforms. The stream and/or seq fields may not be present.

    C: struct sctp_pdapi_event
sctp_peer_addr_change_state() :: addr_available | addr_unreachable | addr_removed | addr_added | addr_made_prim | addr_confirmed | addr_potentially_failed | integer().
sctp_peer_address_info() :: #{assoc_id := sctp_assoc_id(), address := sockaddr(), state := sctp_peer_address_state(), cwnd := uint32(), srtt := uint32(), rto := uint32(), mtu := uint32()}.

    C: struct sctp_paddrinfo.
sctp_peer_address_parameters() :: #{assoc_id := sctp_assoc_id(), addr := sockaddr(), heatbeat_interval := uint32(), path_max_rxt := uint16(), path_mtu => uint32(), sack_delay => uint32(), flags => sctp_pap_flags(), ipv6_flowlabel => uint32(), dscp => uint8()}.

    C: struct sctp_paddrparams.
sctp_peer_address_state() :: inactive | potentially_failed | active | unconfirmed | unknown.

    C: enum sctp_spinfo_state.
sctp_remote_error() :: #{type := remote_error, flags := uint16(), error := sctp_operation_error(), assoc_id := sctp_assoc_id(), remote_causes := [integer()]}.

    A remote peer may send an operational error message to its peer.

    C: struct sctp_remote_error
sctp_rtoinfo() :: #{assoc_id := sctp_assoc_id(), initial := uint32(), max := uint32(), min := uint32()}.

    C: struct sctp_rtoinfo.
sctp_send_failed() :: #{type := send_failed, flags := uint16(), error := uint32(), info := sctp_snd_rcv_info(), assoc_id := sctp_assoc_id(), data := binary()}.

    SCTP cannot deliver a message.

    C: struct sctp_send_failed

    Deprecated.
sctp_send_failed_event() :: #{type := send_failed_event, flags := [data_unsent | data_sent], error := uint32(), info := sctp_snd_info(), assoc_id := sctp_assoc_id(), data := binary()}.

    SCTP cannot deliver a message.

    C: struct sctp_send_failed_event
sctp_sender_dry() :: #{type := sender_dry, flags := uint16(), assoc_id := sctp_assoc_id()}.

    The SCTP stack has no more user data to send or retransmit.

    C: struct sctp_sender_dry_event
sctp_set_adaptation_layer_ind() :: #{ind := uint32()}.

    C: struct sctp_setadaptation.
sctp_set_peer_primary_address() :: #{assoc_id := sctp_assoc_id(), addr := sockaddr()}.

    C: struct sctp_setpeerprim.
sctp_set_primary_address() :: #{assoc_id := sctp_assoc_id(), addr := sockaddr()}.

    C: struct sctp_prim.
sctp_setadaption() :: #{adaption_ind := uint32()}.

    C: struct sctp_setadaption
sctp_shutdown_event() :: #{type := shutdown_event, flags := uint16(), assoc_id := sctp_assoc_id()}.

    A peer has sent a SHUTDOWN.

    C: struct sctp_shutdown_event
sctp_snd_info() :: #{sid := uint16(), flags := uint16(), ppid := uint16(), context := uint32(), assic_id := sctp_assoc_id()}.

    C: struct sctp_sndinfo
sctp_snd_rcv_info() :: #{stream := uint16(), ssn => uint16(), flags => sctp_snd_rcv_info_flags(), ppid => uint32(), context => uint32(), time_to_live => uint32(), tsn => uint32(), cum_tsn => uint32(), assoc_id := sctp_assoc_id()}.

    SCTP options for sendmsg() and SCTP header information about a received message through recvmsg().

    When sending, only the stream and assoc_id fields needs to be assigned. When receiving all values will be assigned.

    C: struct sctp_sndrcvinfo
sctp_snd_rcv_info_flags() :: [unordered | addr_over | abort | eof].
sctp_status() :: #{assoc_id := sctp_assoc_id(), state := sctp_peer_address_state(), rwnd := uint32(), unacked_data := uint16(), pending_data := uint16(), in_streams := uint16(), out_streams := uint16(), fragmentation_point := uint32(), primary := sctp_peer_address_info()}.

    C: struct sctp_status.
sctp_stream_change_event() :: #{type := stream_change, flags := [denied | failed], assoc_id := sctp_assoc_id(), inbound_streams := uint16(), outbound_streams := uint16()}.

    C: struct sctp_stream_change_event
sctp_stream_reset_event() :: #{type := stream_reset, flags := [incoming_ssn | outgoing_ssn | denied | failed], assoc_id := sctp_assoc_id(), stream_list := [uint16()]}.

    C: struct sctp_stream_reset_event
select_handle() :: reference().

    Select operation handle.

    A reference/0 that uniquely identifies the (select) operation, contained in the returned select_info/0.
select_info() :: {select_info, SelectTag :: select_tag(), SelectHandle :: select_handle()}.

    Select operation info.

    Returned by an operation that requires the caller to wait for a select message containing the SelectHandle.

    On select systems, if the option {otp, select_read} is set, {select_read, {select_info(), _}} is returned instead of {ok, _} to indicate that a new asynchronous receive operation has been initiated and the caller should wait for a select message containing the SelectHandle.
select_tag() :: accept | connect | recv | recvfrom | recvmsg | recvmmsg | send | sendv | sendto | sendmsg | sendmmsg | sendfile | {recv | recvfrom | recvmsg | recvmmsg | send | sendv | sendto | sendmsg | sendmmsg | sendfile, ContData :: term()}.

    Select operation tag.

    A tag that describes the (select) operation (= function name), contained in the returned select_info/0.
sockaddr() :: sockaddr_in() | sockaddr_in6() | sockaddr_un() | sockaddr_ll() | sockaddr_dl() | sockaddr_unspec() | sockaddr_native().
sockaddr_dl() :: #{family := link, index := non_neg_integer(), type := interface_type(), nlen := non_neg_integer(), alen := non_neg_integer(), slen := non_neg_integer(), data := binary()}.

    C: struct sockaddr_dl

    Link level address (PF_LINK) on BSD:s.
sockaddr_in() :: #{family := inet, port := port_number(), addr := any | broadcast | loopback | in_addr()}.

    C: struct sockaddr_in

    Domain inet (IPv4) address.
sockaddr_in6() :: #{family := inet6, port := port_number(), addr := any | loopback | in6_addr(), flowinfo := in6_flow_info(), scope_id := in6_scope_id()}.

    C: struct sockaddr_in6

    Domain inet6 (IPv6) address.
sockaddr_ll() :: #{family := packet, protocol := non_neg_integer(), ifindex := integer(), pkttype := packet_type(), hatype := hatype(), addr := binary()}.

    C: struct sockaddr_ll

    Domain packet, type raw (link level) address.
sockaddr_native() :: #{family := integer(), addr := binary()}.

    C: struct sockaddr

    In C, a struct sockaddr with the integer value of sa_family in the map/0 key family, and the content of sa_data in the map/0 key addr.
sockaddr_recv() :: sockaddr() | binary().
sockaddr_un() :: #{family := local, path := binary() | string()}.

    C: struct sockaddr_un.

    A Unix Domain socket address, a.k.a local address (AF_LOCAL).

    The path element will always be a binary when returned from this module. When supplied to an API function in this module it may be a string/0, which will be encoded into a binary according to the native file name encoding on the platform.

    A terminating zero character will be appended before the address path is given to the OS, and the terminating zero will be stripped before giving the address path to the caller.

    Linux's non-portable abstract socket address extension is handled by not doing any terminating zero processing in either direction, if the first byte of the address is zero.
sockaddr_unspec() :: #{family := unspec, addr := binary()}.

    C: struct sockaddr of AF_UNSPEC

    In C, a struct sockaddr with sa_family = AF_UNSPEC and the content of sa_data in the map/0 key addr.
socket() :: {'$socket', socket_handle()}.

    A socket, according to this module.

    Created and returned by open/1,2,3,4 and accept/1,2.
socket_counters() :: #{read_byte := non_neg_integer(), read_fails := non_neg_integer(), read_pkg := non_neg_integer(), read_pkg_max := non_neg_integer(), read_tries := non_neg_integer(), read_waits := non_neg_integer(), write_byte := non_neg_integer(), write_fails := non_neg_integer(), write_pkg := non_neg_integer(), write_pkg_max := non_neg_integer(), write_tries := non_neg_integer(), write_waits := non_neg_integer(), sendfile => non_neg_integer(), sendfile_byte => non_neg_integer(), sendfile_fails => non_neg_integer(), sendfile_max => non_neg_integer(), sendfile_pkg => non_neg_integer(), sendfile_pkg_max => non_neg_integer(), sendfile_tries => non_neg_integer(), sendfile_waits => non_neg_integer(), acc_success := non_neg_integer(), acc_fails := non_neg_integer(), acc_tries := non_neg_integer(), acc_waits := non_neg_integer()}.

    A map/0 of Name := Counter associations.
-opaque socket_handle()

    Opaque socket handle unique for the socket.
socket_info() :: #{domain := domain() | integer(), type := type() | integer(), protocol := protocol() | integer(), owner := pid(), ctype := normal | fromfd | {fromfd, integer()}, counters := socket_counters(), num_readers := non_neg_integer(), num_writers := non_neg_integer(), num_acceptors := non_neg_integer(), writable := boolean(), readable := boolean(), rstates := [atom()], wstates := [atom()]}.
socket_option() :: {Level :: socket, Opt :: acceptconn | acceptfilter | bindtodevice | broadcast | bsp_state | busy_poll | debug | domain | dontroute | error | exclusiveaddruse | keepalive | linger | mark | maxdg | max_msg_size | oobinline | passcred | peek_off | peercred | priority | protocol | rcvbuf | rcvbufforce | rcvlowat | rcvtimeo | reuseaddr | reuseport | rxq_ovfl | setfib | sndbuf | sndbufforce | sndlowat | sndtimeo | timestamp | timestampns | type} | {Level :: ip, Opt :: add_membership | add_source_membership | block_source | dontfrag | drop_membership | drop_source_membership | freebind | hdrincl | minttl | msfilter | mtu | mtu_discover | multicast_all | multicast_if | multicast_loop | multicast_ttl | nodefrag | options | pktinfo | recvdstaddr | recverr | recvif | recvopts | recvorigdstaddr | recvtos | recvttl | retopts | router_alert | sndsrcaddr | tos | transparent | ttl | unblock_source} | {Level :: ipv6, Opt :: addrform | add_membership | authhdr | auth_level | checksum | drop_membership | dstopts | esp_trans_level | esp_network_level | faith | flowinfo | hopopts | ipcomp_level | join_group | leave_group | mtu | mtu_discover | multicast_hops | multicast_if | multicast_loop | portrange | pktoptions | recverr | recvhoplimit | hoplimit | recvpktinfo | pktinfo | recvtclass | router_alert | rthdr | tclass | unicast_hops | use_min_mtu | v6only} | {Level :: tcp, Opt :: congestion | cork | info | keepcnt | keepidle | keepintvl | maxseg | md5sig | nodelay | noopt | nopush | syncnt | user_timeout} | {Level :: udp, Opt :: cork} | {Level :: sctp, Opt :: adaption_layer | associnfo | auth_active_key | auth_asconf | auth_chunk | auth_key | auth_delete_key | autoclose | context | default_send_param | delayed_ack_time | disable_fragments | hmac_ident | events | explicit_eor | fragment_interleave | get_peer_addr_info | initmsg | i_want_mapped_v4_addr | local_auth_chunks | maxseg | maxburst | nodelay | partial_delivery_point | peer_addr_params | peer_auth_chunks | primary_addr | reset_streams | rtoinfo | set_peer_primary_addr | status | use_ext_recvinfo}.

    Socket option.

    Socket options of the form {Level, Opt} where the OS protocol Level = level/0 and Opt is a socket option on that protocol level.

    The OS name for an options is, except where otherwise noted, the Opt atom, in capitals, with prefix according to level/0.

    NOTE: The IPv6 option pktoptions is a special (barf) case. It is intended for backward compatibility usage only. Do not use this option.

    NOTE: See the OS documentation for every socket option.

    An option below that has the value type boolean/0 will translate the value false to a C int with value 0, and the value true to !!0 (not (not false)).

    An option with value type integer/0 will be translated to a C int that may have a restricted range, for example byte: 0..255. See the OS documentation.

    The calls supports(options), supports(options, Level) and is_supported(options, {Level, Opt}) can be used to find out which socket options that are supported by the platform.

    Options for protocol level socket: {socket, acceptconn}
        Value = boolean()
    {socket, bindtodevice}
        Value = string()
    {socket, broadcast}
        Value = boolean()
    {socket, debug}
        Value = integer()
    {socket, domain}
        Value = domain/0

        Only valid to get.

        The socket's protocol domain. Does not work on for instance FreeBSD.
    {socket, dontroute}
        Value = boolean()
    {socket, keepalive}
        Value = boolean()
    {socket, linger}
        Value = abort | linger/0

        The value abort is shorthand for #{onoff => true, linger => 0}, and only valid to set.
    {socket, oobinline}
        Value = boolean()
    {socket, passcred}
        Value = boolean()
    {socket, peek_off}
        Value = integer()

        Currently disabled due to a possible infinite loop when calling recv/1-4 with peek in Flags.
    {socket, priority}
        Value = integer()
    {socket, protocol}
        Value = protocol/0

        Only valid to get.

        The socket's protocol. Does not work on for instance Darwin.
    {socket, rcvbuf}
        Value = integer()
    {socket, rcvlowat}
        Value = integer()
    {socket, rcvtimeo}
        Value = timeval/0

        This option is unsupported per default; OTP has to be explicitly built with the --enable-esock-rcvsndtimeo configure option for this to be available.

        Since our implementation uses non-blocking sockets, it is unknown if and how this option works, or even if it may cause malfunction. Therefore, we do not recommend setting this option.

        Instead, use the Timeout argument to, for instance, the recv/3 function.
    {socket, reuseaddr}
        Value = boolean()
    {socket, reuseport}
        Value = boolean()
    {socket, sndbuf}
        Value = integer()
    {socket, sndlowat}
        Value = integer()
    {socket, sndtimeo}
        Value = timeval/0

        This option is unsupported per default; OTP has to be explicitly built with the --enable-esock-rcvsndtimeo configure option for this to be available.

        Since our implementation uses non-blocking sockets, it is unknown if and how this option works, or even if it may cause malfunction. Therefore, we do not recommend setting this option.

        Instead, use the Timeout argument to, for instance, the send/3 function.
    {socket, timestamp}
        Value = boolean()

        Enable or disable the SO_TIMESTAMP socket option. When enabled, the socket will receive timestamps in control messages for received packets.
    {socket, timestampns}
        Value = boolean()

        Enable or disable the SO_TIMESTAMPNS socket option. When enabled, the socket will receive nanosecond-precision timestamps in control messages for received packets.
    {socket, type}
        Value = type/0

        Only valid to get.

        The socket's type.

    Options for protocol level ip: {ip, add_membership}
        Value = ip_mreq/0

        Only valid to set.
    {ip, add_source_membership}
        Value = ip_mreq_source/0

        Only valid to set.
    {ip, block_source}
        Value = ip_mreq_source/0

        Only valid to set.
    {ip, drop_membership}
        Value = ip_mreq/0

        Only valid to set.
    {ip, drop_source_membership}
        Value = ip_mreq_source/0

        Only valid to set.
    {ip, freebind}
        Value = boolean()
    {ip, hdrincl}
        Value = boolean()
    {ip, minttl}
        Value = integer()
    {ip, msfilter}
        Value = null | ip_msfilter/0

        Only valid to set.

        The value null passes a NULL pointer and size 0 to the C library call.
    {ip, mtu}
        Value = integer()

        Only valid to get.
    {ip, mtu_discover}
        Value = ip_pmtudisc() | integer()

        An integer/0 value according to the platform's header files.
    {ip, multicast_all}
        Value = boolean()
    {ip, multicast_if}
        Value = any | in_addr/0
    {ip, multicast_loop}
        Value = boolean()
    {ip, multicast_ttl}
        Value = integer()
    {ip, nodefrag}
        Value = boolean()
    {ip, pktinfo}
        Value = boolean()
    {ip, recvdstaddr}
        Value = boolean()
    {ip, recverr}
        Value = boolean()

        Enable extended reliable error message passing.

        Warning! When this option is enabled, error messages may arrive on the socket's error queue, which should be read using the message flag errqueue, and using recvmsg/1,2,3,4,5 to get all error information in the message's ctrl field as a control message #{level := ip, type := recverr}.

        A working strategy should be to first poll the error queue using recvmsg/2,3,4 with Timeout =:= 0 and Flags containing errqueue (ignore the return value {error, timeout}) before reading the actual data to ensure that the error queue gets cleared. And read the data using one of the nowait | select_handle() recv functions: recv/3,4, recvfrom/3,4 or recvmsg/3,4,5. Otherwise you might accidentally cause a busy loop in and out of 'select' for the socket.
    {ip, recvif}
        Value = boolean()
    {ip, recvopts}
        Value = boolean()
    {ip, recvorigdstaddr}
        Value = boolean()
    {ip, recvtos}
        Value = boolean()
    {ip, recvttl}
        Value = boolean()
    {ip, retopts}
        Value = boolean()
    {ip, router_alert}
        Value = integer()
    {ip, sendsrcaddr}
        Value = boolean()
    {ip, tos}
        Value = iptos_value() | ip_tos()

        When sending/setting the value is according to iptos_value/0. When reading/getting the value is according to ip_tos/0.
    {ip, transparent}
        Value = boolean()
    {ip, ttl}
        Value = integer()
    {ip, unblock_source}
        Value = ip_mreq_source/0

        Only valid to set.

    Options for protocol level ipv6: {ipv6, addrform}
        Value = domain/0

        As far as we know the only valid value is inet and it is only allowed for an IPv6 socket that is connected and bound to an IPv4-mapped IPv6 address.
    {ipv6, add_membership}
        Value = ipv6_mreq/0

        Only valid to set.
    {ipv6, authhdr}
        Value = boolean()
    {ipv6, drop_membership}
        Value = ipv6_mreq/0

        Only valid to set.
    {ipv6, dstopts}
        Value = boolean()
    {ipv6, flowinfo}
        Value = boolean()
    {ipv6, hoplimit}
        Value = boolean()
    {ipv6, hopopts}
        Value = boolean()
    {ipv6, mtu}
        Value = integer()
    {ipv6, mtu_discover}
        Value = ipv6_pmtudisc() | integer()

        An integer/0 value is according to the platform's header files.
    {ipv6, multicast_hops}
        Value = ipv6_hops/0
    {ipv6, multicast_if}
        Value = integer()
    {ipv6, multicast_loop}
        Value = boolean()
    {ipv6, recverr}
        Value = boolean()

        Warning! See the socket option {ip, recverr} regarding the socket's error queue. The same warning applies for this option.
    {ipv6, recvhoplimit}
        Value = boolean()
    {ipv6, recvpktinfo}
        Value = boolean()
    {ipv6, recvtclass}
        Value = boolean()
    {ipv6, router_alert}
        Value = integer()
    {ipv6, rthdr}
        Value = boolean()
    {ipv6, tclass}
        Value = boolean()
    {ipv6, unicast_hops}
        Value = ipv6_hops/0
    {ipv6, v6only}
        Value = boolean()

    Options for protocol level sctp. See also RFC 6458. {sctp, associnfo}
        Value = sctp_assocparams/0
    {sctp, autoclose}
        Value = integer()
    {sctp, disable_fragments}
        Value = boolean()
    {sctp, events}
        Value = sctp_event_subscribe/0

        Only valid to set.
    {sctp, initmsg}
        Value = sctp_initmsg/0
    {sctp, maxseg}
        Value = integer()
    {sctp, nodelay}
        Value = boolean()
    {sctp, rtoinfo}
        Value = sctp_rtoinfo/0
    {sctp, get_peer_addr_info}
        Value = sctp_peer_address_info/0

        Only valid for get. Also, requires an OptValue (containing sctp_assoc_id/0 and sockaddr/0) specifying the peer. See getopt/3 for more info.
    {sctp, status}
        Value = sctp_status/0

        Only valid for get. Also, requires an OptValue (containing sctp_assoc_id/0) specifying the association. See getopt/3 for more info.

    Options for protocol level tcp: {tcp, congestion}
        Value = string()
    {tcp, cork}
        Value = boolean()
    {tcp, keepcnt}
        Value = integer()
    {tcp, keepidle}
        Value = integer()
    {tcp, keepintvl}
        Value = integer()
    {tcp, maxseg}
        Value = integer()
    {tcp, nodelay}
        Value = boolean()
    {tcp, nopush}
        Value = boolean()
    {tcp, user_timeout}
        Value = non_neg_integer()

    Options for protocol level udp: {udp, cork}
        Value = boolean()
timespec() :: #{sec := integer(), nsec := integer()}.

    C: struct timespec

    Corresponds to the C struct timespec. The field sec holds seconds, and nsec nanoseconds.
timeval() :: #{sec := integer(), usec := integer()}.

    C: struct timeval

    Corresponds to the C struct timeval. The field sec holds seconds, and usec microseconds.
type() :: stream | dgram | raw | rdm | seqpacket.

    Protocol type.

    A lowercase atom/0 representing a protocol type on the platform named SOCK_*. For example stream corresponds to SOCK_STREAM.
uint16() :: 0..65535.
uint32() :: 0..4294967295.
uint64() :: 0..18446744073709551615.
uint8() :: 0..255.

FUNCTIONS

accept(ListenSocket) -> Result when Result :: {ok, Socket} | {error, Reason}, ListenSocket :: socket(), Socket :: socket(), Reason :: dynamic().

    Equivalent to accept(ListenSocket, infinity).
accept(ListenSocket, Timeout :: infinity) -> {ok, Socket} | {error, Reason} when ListenSocket :: socket(), Socket :: socket(), Reason :: posix() | closed | invalid() | {create_accept_socket, posix()} | {add_socket, posix()} | {update_accept_context, posix()}; (ListenSocket, Timeout :: non_neg_integer()) -> {ok, Socket} | {error, Reason} when ListenSocket :: socket(), Socket :: socket(), Reason :: posix() | closed | invalid() | timeout | {create_accept_socket, posix()} | {add_socket, posix()} | {update_accept_context, posix()}; (ListenSocket, nowait | (Handle :: select_handle() | completion_handle())) -> {ok, Socket} | {select, SelectInfo} | {completion, CompletionInfo} | {error, Reason} when ListenSocket :: socket(), Socket :: socket(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid() | {create_accept_socket, posix()} | {add_accept_socket, posix()} | {update_accept_context, posix()}.

    Accept a connection on a listening socket.

    ListenSocket has to be of a connection oriented type (types stream or seqpacket, see open/1), and set to listen (see listen/1).

    If the Timeout argument is infinity; accepts the first pending incoming connection for the listen socket or wait for one to arrive, and return the new connection socket.

    If the Timeout argument is a time-out value (non_neg_integer/0); returns {error, timeout} if no connection has arrived after Timeout milliseconds.

    If the Handle argument nowait (since OTP 22.1), starts an asynchronous call if the operation couldn't be completed immediately.

    If the Handle argument is a select_handle/0, (since OTP 24.0), or on Windows, the equivalent completion_handle/0 (since OTP 26.0), starts an asynchronous call like for nowait.

    The possible values for CompletionStatus in the completion message are: {ok, NewSocket}
        Success; A connection has been accepted.
    {error, Reason}
        An error occured and no connection was established.

    See the note Asynchronous Calls at the start of this module reference manual page.
bind(Socket, Addr) -> ok | {error, Reason} when Socket :: socket(), Addr :: sockaddr() | any | broadcast | loopback, Reason :: posix() | closed | invalid().

    Bind a name to a socket.

    When a socket is created (with open), it has no address assigned to it. bind assigns the address specified by the Addr argument.

    The rules used for name binding vary between domains.

    If you bind a socket to an address in for example the inet or inet6 address families, with an ephemeral port number (0), and want to know which port that was chosen, you can find out using something like: {ok, #{port := Port}} =socket:sockname(Socket)
bind(Socket, Addrs, Action) -> ok | {error, Reason} when Socket :: socket(), Addrs :: [sockaddr_in()] | [sockaddr_in() | sockaddr_in6()], Action :: add | remove, Reason :: posix() | closed.

    Bind a list of socket addreses to a socket.

    When a socket is created (with open), it has no address assigned to it. This bind assigns the address specified by the Addr argument.

    Calling this function is only valid if the socket is type = seqpacket and protocol = sctp.

    If the domain is inet, then all addresses must be IPv4. If the domain is inet6, the addresses can be either IPv4 or IPv6.
cancel(Socket, SelectInfo | CompletionInfo) -> ok | {error, Reason} when Socket :: socket(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: closed | invalid().

    Cancel an asynchronous call in progress.

    Call this function to cancel an asynchronous call in progress, that is; it returned a value containing a completion_info/0 or select_info/0.

    See the note Asynchronous Calls at the start of this module reference manual page.

    If another process tries an operation of the same basic type (accept/1 | send/2 | recv/2) it will be enqueued and notified through a select or completion message when the current operation and all enqueued before it has been completed. If the current operation is canceled by this function it is treated as a completed operation; the process first in queue is notified.

    If SelectInfo | CompletionInfo does not match an operation in progress for the calling process, this function returns {error, {invalid, SelectInfo | CompletionInfo}}.
cancel_monitor(MRef :: reference()) -> boolean().

    Cancel a socket monitor.

    If MRef is a reference that the calling process obtained by calling monitor/1, this monitor is removed. If there is no such monitor for the calling process (or MRef doesn't correspond to a monitor), nothing happens.

    The returned value is one of the following: true
        The monitor was found and removed. In this case, no 'DOWN' message corresponding to this monitor has been delivered and will not be delivered.
    false
        The monitor was not found so it couldn't be removed. This might be because the monitor has already triggered and there is a 'DOWN' message from this monitor in the caller message queue.
close(Socket) -> ok | {error, Reason} when Socket :: socket(), Reason :: posix() | closed | timeout.

    Close a socket.

    NOTE: Note that for Protocol = tcp (see open/3), although TCP guarantees that when the other side sees the stream close all data that we sent before closing has been delivered, there is no way for us to know that the other side got all data and the stream close. All kinds of network and OS issues may obliterate that. To get such a guarantee we need to implement an in-band acknowledge protocol on the connection, or we can use the shutdown function to signal that no more data will be sent and then wait for the other end to close the socket. Then we will see our read side getting a socket close. In this way we implement a small acknowledge protocol using shutdown/2. The other side cannot know that we ever saw the socket close, but in a client/server scenario that is often not relevant.
connect(Socket :: socket()) -> ok | {error, Reason} when Reason :: posix() | closed | invalid().

    Finalize a connect/3 operation.

    See the note Asynchronous Calls at the start of this module reference manual page.

    On select systems this function finalizes a connection setup on a socket, after receiving a select message {'$socket', Socket, select, SelectHandle}, and returns whether the connection setup was successful or not.

    Instead of calling this function, for backwards compatibility, it is allowed to call connect/2,3 again, but that incurs more overhead since the connect address and time-out argument are processed in vain.

    The call that completes the connect operation, the second call, cannot return a select return value.
connect(Socket :: socket(), SockAddr :: sockaddr() | [SockAddr :: term()]) -> ok | {error, Reason :: dynamic()}.

    Equivalent to connect(Socket, SockAddr, infinity) or connect(Socket, SockAddrs, undefined, infinity).
connect(Socket, SockAddrs, TimeoutOrHandle) -> {ok, AssocId} | {error, Reason} when Socket :: socket(), SockAddrs :: [sockaddr_in()] | [sockaddr_in6()], TimeoutOrHandle :: infinity | Timeout | nowait | Handle, Timeout :: non_neg_integer(), Handle :: select_handle(), AssocId :: sctp_assoc_id(), Reason :: posix() | closed | invalid() | already; (Socket, SockAddr, Timeout :: infinity) -> ok | {error, Reason} when Socket :: socket(), SockAddr :: sockaddr(), Reason :: posix() | closed | invalid() | already | not_bound | {add_socket, posix()} | {update_connect_context, posix()}; (Socket, SockAddr, Timeout :: non_neg_integer()) -> ok | {error, Reason} when Socket :: socket(), SockAddr :: sockaddr(), Reason :: posix() | closed | invalid() | already | not_bound | timeout | {add_socket, posix()} | {update_connect_context, posix()}; (Socket, SockAddr, nowait | Handle) -> ok | {select, SelectInfo} | {completion, CompletionInfo} | {error, Reason} when Socket :: socket(), SockAddr :: sockaddr(), Handle :: select_handle() | completion_handle(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid() | already | not_bound | {add_socket, posix()} | {update_connect_context, posix()}.

    Connect the socket to the given address(s).

    This function connects the socket to the address(s) specified by the SockAddr|SockAddrs argument.

    If a connection attempt is already in progress (by another process), {error, already} is returned.

    NOTE: On Windows the socket has to be bound.

    If the time-out argument (argument 3) is infinity it is up to the OS implementation to decide when the connection attempt failed and then what to return; probably {error, etimedout}. The OS time-out may be very long.

    If the time-out argument (argument 3) is a time-out value (non_neg_integer/0); return {error, timeout} if the connection hasn't been established within Timeout milliseconds.

    NOTE: Note that when this call has returned {error, timeout} the connection state of the socket is uncertain since the platform's network stack may complete the connection at any time, up to some platform specific time-out. Repeating a connection attempt towards the same address would be ok, but towards a different address could end up with a connection to either address. The safe play is to close the socket and start over. Also note that this applies to cancelling a nowait connect call described below.

    If the time-out argument (argument 2) is nowait (since OTP 22.1), start an asynchronous call if the operation couldn't be completed immediately.

    If the time-out argument (argument 2) is a Handle :: select_handle/0, (since OTP 24.0), or on Windows, the equivalent Handle :: completion_handle/0 (since OTP 26.0), start an asynchronous call like for nowait.

    See the note Asynchronous Calls at the start of this module reference manual page.

    After receiving a select message; call connect/1 to complete the operation.

    If cancelling the operation with cancel/2 see the note above about connection time-out.

    The possible values for CompletionStatus in the completion message are: ok
        Complete success; A connection has been established.
    {error, Reason}
        An error occured and no connection was established.

    NOTE: Note that calling with a list of socket addresses only works for SCTP sockets (type = seqpacket). And that the family of all addresses in the list is either IPv4 (inet) or IPv6 (inet6).
getopt(socket(), SocketOption :: {Level :: otp, Opt :: otp_socket_option()}) -> {ok, Value :: term()} | {error, invalid() | closed}; (socket(), SocketOption :: socket_option()) -> {ok, Value :: term()} | {error, posix() | invalid() | closed}.

    Get the value of a socket option.

    Gets the value of an OS protocol level socket option, or from the otp pseudo protocol level, which is this module's implementation level above the OS protocol levels.

    See the type otp_socket_option() for a description of the otp protocol level.

    See the type socket_option/0 for which OS protocol level options that this implementation knows about, how they are related to OS option names, and if there are known peculiarities with any of them.

    What options that are valid depends on the OS, and on the kind of socket (domain/0,type/0 and protocol/0). See the type socket_option() and the socket options chapter in the User's Guide for more info.

    NOTE: Not all options are valid, nor possible to get, on all platforms. That is, even if this socket implementation support an option; it doesn't mean that the underlying OS does.
getopt(Socket :: socket(), SocketOption :: {sctp, get_peer_addr_info}, OptValue :: #{assoc_id := sctp_assoc_id(), addr := sockaddr()}) -> {ok, Value :: sctp_peer_address_info()} | {error, posix() | invalid() | closed}; (Socket :: socket(), SocketOption :: {sctp, status}, OptValue :: #{assoc_id := sctp_assoc_id()}) -> {ok, Value :: sctp_status()} | {error, posix() | invalid() | closed}; (Socket :: socket(), Level :: level(), Opt :: term()) -> {ok, Value :: term()} | {error, posix() | invalid() | closed}.

    Get a socket option, with a specifier (extra input) OptValue.

    This function is used when the option takes an input 'value' argument. We only support this for a limited set of options: {sctp, get_peer_addr_info} and {sctp, status}.

    Some uses of this function is for backwards compatibility reasons.

    For instance, getopt(Socket, Level, Opt) is equivalent to getopt(Socket, {Level, Opt}), or as a special case if Opt = {NativeOpt :: integer/0, ValueSpec} equivalent to getopt_native(Socket, {Level, NativeOpt}, ValueSpec).

    Use getopt/2 or getopt_native/3 instead to handle the option level and name as a single term, and to make the difference between known options and native options clear.
getopt_native(socket(), SocketOption :: socket_option() | {Level :: level() | (NativeLevel :: integer()), NativeOpt :: integer()}, ValueType :: integer) -> {ok, Value :: integer()} | {error, posix() | invalid() | closed}; (socket(), SocketOption :: socket_option() | {Level :: level() | (NativeLevel :: integer()), NativeOpt :: integer()}, ValueType :: boolean) -> {ok, Value :: boolean()} | {error, posix() | invalid() | closed}; (socket(), SocketOption :: socket_option() | {Level :: level() | (NativeLevel :: integer()), NativeOpt :: integer()}, ValueSize :: non_neg_integer()) -> {ok, Value :: binary()} | {error, posix() | invalid() | closed}; (socket(), SocketOption :: socket_option() | {Level :: level() | (NativeLevel :: integer()), NativeOpt :: integer()}, ValueSpec :: binary()) -> {ok, Value :: binary()} | {error, posix() | invalid() | closed}.

    Get a "native" socket option.

    Gets a socket option that may be unknown to our implementation, or that has a type not compatible with our implementation, that is; in "native mode".

    The socket option may be specified with an ordinary socket_option() tuple, with a known Level = level() and an integer NativeOpt, or with both an integer NativeLevel and NativeOpt.

    How to decode the option value has to be specified either with ValueType, by specifying the ValueSize for a binary/0 that will contain the fetched option value, or by specifying a binary/0 ValueSpec that will be copied to a buffer for the getsockopt() call to write the value in which will be returned as a new binary/0.

    If ValueType is integer a C type (int) will be fetched, if it is boolean a C type (int) will be fetched and converted into a boolean/0 according to the C implementation's notion about true and false.

    If an option is valid depends both on the platform and on what kind of socket it is (domain/0, type/0 and protocol/0).

    The integer values for NativeLevel and NativeOpt as well as the Value encoding has to be deduced from the header files for the running system.
i() -> ok.

    Print information to the erlang shell in table format for all sockets.

    The information printed for each socket is specified by the default set of info_keys/0 (all keys).

    The sockets that are printed are all sockets created by this socket module's implementation.
i(InfoKeys :: info_keys()) -> ok; (Domain :: inet | inet6 | local) -> ok; (Proto :: sctp | tcp | udp) -> ok; (Type :: dgram | seqpacket | stream) -> ok.

    Print information to the erlang shell in table format for all sockets.

    If the argument is a list of info_keys/0, print the specified information for all sockets. See i/0.

    Otherwise the same as i/2 with the same first argument and the default information (see i/0).
i(Domain :: inet | inet6 | local, InfoKeys) -> ok when InfoKeys :: info_keys(); (Proto :: sctp | tcp | udp, InfoKeys) -> ok when InfoKeys :: info_keys(); (Type :: dgram | seqpacket | stream, InfoKeys) -> ok when InfoKeys :: info_keys().

    Print information to the erlang shell in table format for a selection of sockets.

    The argument InfoKeys specifies which information is printed for each socket.

    If the first argument is Domain print information for all sockets of that specific domain/0.

    If the first argument is Proto print information for all sockets of that specific protocol/0.

    If the first argument is Type print information for all sockets of that specific type/0.
info() -> info().

    Get miscellaneous information about this socket library.

    The function returns a map with each information item as a key-value pair.

    NOTE: In order to ensure data integrity, mutexes are taken when needed. So, don't call this function often.
info(Socket) -> socket_info() when Socket :: socket().

    Get miscellaneous info about a socket.

    The function returns a map with each information item as a key-value pair reflecting the "current" state of the socket (such as counter values).

    NOTE: In order to ensure data integrity, mutexes are taken when needed. So, don't call this function often.
ioctl(Socket, GetRequest :: gifconf) -> {ok, IFConf :: [#{name := string, addr := sockaddr()}]} | {error, Reason} when Socket :: socket(), Reason :: posix() | closed; (Socket, GetRequest :: nread | nwrite | nspace) -> {ok, NumBytes :: non_neg_integer()} | {error, Reason} when Socket :: socket(), Reason :: posix() | closed; (Socket, GetRequest :: atmark) -> {ok, Available :: boolean()} | {error, Reason} when Socket :: socket(), Reason :: posix() | closed; (Socket, GetRequest :: tcp_info) -> {ok, Info :: map()} | {error, Reason} when Socket :: socket(), Reason :: posix() | closed.

    Set socket (device) parameters.

    This function retrieves a specific parameter, according to the GetRequest argument. gifconf
        Get a list of interface (transport layer) addresses.

        Result; a list of map/0s, one for each interface, with its name and address.
    nread
        Get the number of bytes immediately available for reading (since OTP 26.1).

        Result; the number of bytes, integer/0.
    nwrite
        Get the number of bytes in the send queue (since OTP 26.1).

        Result; the number of bytes, integer/0.
    nspace
        Get the free space in the send queue (since OTP 26.1).

        Result; the number of bytes, integer/0.
    atmark
        Test if there is OOB (out-of-bound) data waiting to be read (since OTP 26.1).

        Result; a boolean/0.
    tcp_info
        Get miscellaneous TCP related information for a connected socket (since OTP 26.1).

        Result; a map/0 with information items as key-value pairs.

    NOTE: Not all requests are supported by all platforms. To see if a ioctl request is supported on the current platform:

        	    Request = nread,
        	    true = socket:is_supported(ioctl_requests, Request),
        	    :
ioctl(Socket, GetRequest, NameOrIndex) -> {ok, Result} | {error, Reason} when Socket :: socket(), GetRequest :: gifname | gifindex | gifaddr | gifdstaddr | gifbrdaddr | gifnetmask | gifhwaddr | genaddr | gifmtu | giftxqlen | gifflags | tcp_info, NameOrIndex :: string() | integer(), Result :: dynamic(), Reason :: posix() | closed; (Socket, SetRequest, Value) -> ok | {error, Reason} when Socket :: socket(), SetRequest :: rcvall, Value :: off | on | iplevel, Reason :: posix() | closed; (Socket, SetRequest, Value) -> ok | {error, Reason} when Socket :: socket(), SetRequest :: rcvall_igmpmcast | rcvall_mcast, Value :: off | on, Reason :: posix() | closed.

    Get or set socket (device) parameters.

    This function retrieves a specific parameter, according to one of the following GetRequest arguments. The third argument is the (lookup) "key", identifying the interface, for most requests the name of the interface as a string/0. Also, see the note above. gifname
        Get the name of the interface with the specified index ( integer/0).

        Result; the name of the interface, string/0.
    gifindex
        Get the index of the interface with the specified name.

        Result; the interface index, integer/0.
    gifaddr
        Get the address of the interface with the specified name.

        Result; the address of the interface, sockaddr/0.
    gifdstaddr
        Get the destination address of the point-to-point interface with the specified name.

        Result; the destination address of the interface, sockaddr/0.
    gifbrdaddr
        Get the broadcast address of the interface with the specified name.

        Result; broadcast address of the interface, sockaddr/0.
    gifnetmask
        Get the network mask of the interface with the specified name.

        Result; the network mask of the interface, sockaddr/0.
    gifhwaddr | genaddr
        Get the hardware address for the interface with the specified name.

        Result; the hardware address of the interface, sockaddr/0 | binary/0. The family field contains the 'ARPHRD' device type (or an integer).
    gifmtu
        Get the MTU (Maximum Transfer Unit) for the interface with the specified name.

        Result; MTU of the interface, integer/0.
    giftxqlen
        Get the transmit queue length of the interface with the specified name.

        Result; transmit queue length of the interface, integer/0.
    gifflags
        Get the active flag word of the interface with the specified name.

        Result; the active flag word of the interface, is a list of ioctl_device_flag/0 | integer( ).

    With the following SetRequest argument this function sets the Value for the request parameter (since OTP 26.1). rcvall
        Enables (or disables) a socket to receive all IPv4 or IPv6 packages passing through a network interface.

        The Socket has to be one of: An IPv4 socket
            Created with the address domain inet, socket type raw and protocol ip.
        An IPv6 socket
            Created with the address domain inet6, socket type raw and protocol ipv6.

        The socket must also be bound to an (explicit) local IPv4 or IPv6 interface (any isn't allowed).

        Setting this IOCTL requires elevated privileges.

    With the following SetRequest arguments this function sets the Value for the request parameter (since OTP 26.1). rcvall_igmpmcall
        Enables (or disables) a socket to receive IGMP multicast IP traffic, without receiving any other IP traffic.

        The socket has to be created with the address domain inet, socket type raw and protocol igmp.

        The socket must also be bound to an (explicit) local interface (any isn't allowed).

        The receive buffer must be sufficiently large.

        Setting this IOCTL requires elevated privileges.
    rcvall_mcall
        Enables (or disables) a socket to receive all multicast IP traffic (as in; all IP packets destined for IP addresses in the range 224.0.0.0 to 239.255.255.255).

        The socket has to be created with the address domain inet, socket type raw and protocol udp.

        The socket must also be bound to an (explicit) local interface (any isn't allowed), And bound to port 0.

        The receive buffer must be sufficiently large.

        Setting this IOCTL requires elevated privileges.
ioctl(Socket, SetRequest, Name, Value) -> ok | {error, Reason} when Socket :: socket(), SetRequest :: sifflags | sifaddr | sifdstaddr | sifbrdaddr | sifnetmask | sifhwaddr | sifmtu | siftxqlen, Name :: string(), Value :: dynamic(), Reason :: posix() | closed.

    Set socket (device) parameters.

    This function sets a specific parameter, according to the SetRequest argument. The Name argument is the name of the interface, and the Value argument is the value to set.

    These operations require elevated privileges. sifflags
        Set the the active flag word, #{Flag => boolean()}, of the interface with the specified name.

        Each flag to be changed should be added to the value map/0, with the value true if the Flag should be set and false if the flag should be cleared.
    sifaddr
        Set the address, sockaddr/0, of the interface with the specified name.
    sifdstaddr
        Set the destination address, sockaddr/0, of a point-to-point interface with the specified name.
    sifbrdaddr
        Set the broadcast address, sockaddr/0, of the interface with the specified name.
    sifnetmask
        Set the network mask, sockaddr/0, of the interface with the specified name.
    sifhwaddr
        Set the hardware address, sockaddr/0, of the interface with the specified name.
    sifmtu
        Set the MTU (Maximum Transfer Unit), integer/0, for the interface with the specified name.
    siftxqlen
        Set the transmit queue length, integer/0, of the interface with the specified name.
is_supported(Key1 :: term()) -> boolean().

    Check if a socket feature is supported.

    Returns true if supports/0 has a {Key1, true} tuple or a {Key1, list()} tuple in its returned list, otherwise false (also for unknown keys).

    Example:

        true = socket:is_supported(local),
is_supported(Key1 :: term(), Key2 :: term()) -> boolean().

    Check if a socket feature is supported.

    Returns true if supports(Key1) has a {Key2, true} tuple in its returned list, otherwise false (also for unknown keys).

    Example:

        true = socket:is_supported(msg_flags, errqueue),
listen(Socket :: socket()) -> ok | {error, Reason :: posix() | closed}.

    Make a socket listen for connections.

    Equivalent to listen(Socket, Backlog) with a default value for Backlog (currently 5).
listen(Socket, IsServer) -> ok | {error, Reason} when Socket :: socket(), IsServer :: boolean(), Reason :: posix() | closed; (Socket, Backlog) -> ok | {error, Reason} when Socket :: socket(), Backlog :: pos_integer(), Reason :: posix() | closed.

    Make a socket listen for connections.

    The IsServer clauses are intended to be used for SCTP sockets. The Backlog argument states the length of the queue for incoming not yet accepted connections. Exactly how that number is interpreted is up to the OS' protocol stack, but the resulting effective queue length will most probably be perceived as at least that long.

    NOTE: On Windows the socket has to be bound.
monitor(Socket :: socket()) -> MonitorRef :: reference().

    Start a socket monitor.

    If the Socket doesn't exist or when later the monitor is triggered, a 'DOWN' message is sent to the process that called monitor/1 with the following pattern:

        	    {'DOWN', MonitorRef, socket, Socket, Info}

    Info is the termination reason of the socket or nosock if Socket did not exist when the monitor was started.

    Making several calls to socket:monitor/1 for the same Socket is not an error; each call creates an independent monitor instance.
number_of() -> non_neg_integer().

    Return the number of active sockets.
open(FD :: integer()) -> dynamic().

    Equivalent to open(FD, #{}).
open(FD, Opts) -> {ok, Socket} | {error, Reason} when FD :: integer(), Opts :: #{domain => domain() | integer(), type => type() | integer(), protocol => default | protocol() | integer(), dup => boolean(), debug => boolean(), use_registry => boolean()}, Socket :: socket(), Reason :: posix() | domain | type | protocol; (Domain, Type) -> {ok, Socket} | {error, Reason} when Domain :: domain(), Type :: type() | integer(), Socket :: socket(), Reason :: posix() | protocol.

    Create a socket.

    With arguments Domain and Type

    Equivalent to open(Domain, Type, default, #{}).

    With arguments FD and Opts (since OTP 23.0)

    Creates an endpoint for communication (socket) based on an already existing file descriptor that must be a socket. This function attempts to retrieve the file descriptor's domain, type and protocol from the system. This is however not possible on all platforms; in that case they should be specified in Opts.

    The Opts argument can provide extra information: domain
        The file descriptor's communication domain. See also

        open/2,3,4.
    type
        The file descriptor's socket type.

        See also open/2,3,4.
    protocol
        The file descriptor's protocol. The atom default is equivalent to the integer protocol number 0 which means the default protocol for a given domain and type.

        If the protocol can not be retrieved from the platform for the socket, and protocol is not specified, the default protocol is used, which may or may not be correct.

        See also open/2,3,4.
    dup
        If false don't duplicate the provided file descriptor.

        Defaults to true; do duplicate the file descriptor.
    debug
        If true enable socket debug logging.

        Defaults to false; don't enable socket debug logging.
    use_registry
        Enable or disable use of the socket registry for this socket. This overrides the global setting.

        Defaults to the global setting, see use_registry/1.

    NOTE: This function should be used with care! On some platforms it is necessary to provide domain, type and protocol since they cannot be retrieved from the platform. On some platforms it is not easy to get hold of a file descriptor to use in this function.
open(Domain, Type, Opts | Protocol) -> {ok, Socket} | {error, Reason} when Domain :: domain() | integer(), Type :: type() | integer(), Opts :: map(), Protocol :: default | protocol() | integer(), Socket :: socket(), Reason :: posix() | protocol.

    Create a socket.

    With arguments Domain, Type and Protocol

    Equivalent to open(Domain, Type, Protocol, #{}).

    With arguments Domain, Type and Opts (since OTP 24.0)

    Equivalent to open(Domain, Type, default, #{}).
open(Domain, Type, Protocol, Opts) -> {ok, Socket} | {error, Reason} when Domain :: domain() | integer(), Type :: type() | integer(), Protocol :: default | protocol() | integer(), Opts :: #{netns => string(), debug => boolean(), use_registry => boolean()}, Socket :: socket(), Reason :: posix() | protocol.

    Create a socket.

    Creates an endpoint for communication (socket).

    Domain and Type may be integer/0s, as defined in the platform's header files. The same goes for Protocol as defined in the platform's services(5) database. See also the OS man page for the library call socket(2).

    NOTE: For some combinations of Domain and Type the platform has got a default protocol that can be selected with Protocol = default, and the platform may allow or require selecting the default protocol, or a specific protocol. Examples: socket:open(inet, stream, tcp)
        It is common that for protocol domain and type inet,stream it is allowed to select the tcp protocol although that mostly is the default.
    socket:open(local, dgram)
        It is common that for the protocol domain local it is mandatory to not select a protocol, that is; to select the default protocol.

    The Opts argument is intended for "other" options. The supported option(s) are described below: netns: string()
        Used to set the network namespace during the open call. Only supported on Linux.
    debug: boolean()
        Enable or disable debug logging.

        Defaults to false.
    use_registry: boolean()
        Enable or disable use of the socket registry for this socket. This overrides the global value.

        Defaults to the global value, see use_registry/1.
peeloff(Socket, AssocId) -> {ok, NewSock} | {ok, NewSock, InheritErrs} | {error, Reason} when Socket :: socket(), AssocId :: sctp_assoc_id(), NewSock :: socket(), InheritErrs :: [{SockOpt, get | set, Reason}], SockOpt :: socket_option(), Reason :: posix() | closed.

    Branch off an association into a separate socket.

    Equivalent to peeloff(Socket, AssocId, [])
peeloff(Socket, AssocId, InheritOpts) -> {ok, NewSock} | {ok, NewSock, InheritErrs} | {error, Reason} when Socket :: socket(), AssocId :: sctp_assoc_id(), InheritOpts :: [socket_option()], NewSock :: socket(), InheritErrs :: [{SockOpt, get | set, Reason}], SockOpt :: socket_option(), Reason :: posix() | closed.

    Branch off an association into a separate socket.

    Create a new one-to-one socket from an existing one-to-many socket. The specified InheritOpts will be inherited by the new socket (get from existing socket and then set on the new socket).

    If the peeloff operation is successful but some (or all) of the InheritOpts failed to transfer to the new socket, {'ok', NewSock, InheritErrs} is returned. It is then up to the caller to decide if this is acceptable.
peername(Socket :: socket()) -> {ok, SockAddr} | {error, Reason} when SockAddr :: sockaddr_recv(), Reason :: posix() | closed.

    Return the remote address of a socket.

    Returns the address of the connected peer, that is, the remote end of the socket.
peernames(Socket :: socket(), AssocId :: sctp_assoc_id()) -> {ok, [SockAddr]} | {error, Reason} when SockAddr :: sockaddr_recv(), Reason :: posix() | closed.

    Return the remote (peer) address(s) of an association of a socket.

    If the socket is IPv4 then all returned addresess will be IPv4. If the socket is IPv6, then the returned addresess can be a mix of IPv4 and IPv6.

    For a one-to-many socket, AssocId specifies the association. For a one-to-one socket, AssocId is ignored.

    The behaviour if AssocId is 0 (zero), is undefined for one-to-many sockets.
recv(Socket :: socket()) -> dynamic().

    Equivalent to recv(Socket, 0, [], infinity).
recv(Socket :: socket(), Flags :: [msg_flag() | integer()]) -> dynamic(); (Socket :: socket(), Length :: non_neg_integer()) -> dynamic().

    Receive data on a connected socket.

    With argument Length; equivalent to recv(Socket, Length, [], infinity).

    With argument Flags; equivalent to recv(Socket, 0, Flags, infinity) (since OTP 24.0).
recv(Socket, Flags, TimeoutOrHandle) -> dynamic() when Socket :: socket(), Flags :: [msg_flag() | integer()], TimeoutOrHandle :: timeout() | nowait | select_handle() | completion_handle(); (Socket :: socket(), Length :: non_neg_integer(), Flags :: [msg_flag() | integer()]) -> dynamic(); (Socket :: socket(), Length :: non_neg_integer(), TimeoutOrHandle) -> dynamic() when TimeoutOrHandle :: timeout() | nowait | select_handle() | completion_handle().

    Receive data on a connected socket.

    With arguments Length and Flags; equivalent to recv(Socket, Length, Flags, infinity).

    With arguments Length and TimeoutOrHandle; equivalent to recv(Socket, Length, [], TimeoutOrHandle). TimeoutOrHandle :: nowait has been allowed since OTP 22.1. TimeoutOrHandle :: Handle has been allowed since OTP 24.0.

    With arguments Flags and TimeoutOrHandle; equivalent to recv(Socket, 0, Flags, TimeoutOrHandle) (since OTP 24.0).
recv(Socket, Length, Flags, Timeout :: infinity) -> {ok, Data} | {error, Reason} | {error, {Reason, Data}} when Socket :: socket(), Length :: non_neg_integer(), Flags :: [msg_flag() | integer()], Data :: binary(), Reason :: posix() | closed | invalid(); (Socket, Length, Flags, Timeout :: non_neg_integer()) -> {ok, Data} | {error, Reason} | {error, {Reason, Data}} when Socket :: socket(), Length :: non_neg_integer(), Flags :: [msg_flag() | integer()], Data :: binary(), Reason :: posix() | closed | invalid() | timeout; (Socket, Length, Flags, nowait | Handle) -> {ok, Data} | {select, SelectInfo} | {select, {SelectInfo, Data}} | {select_read, {SelectInfo, Data}} | {completion, CompletionInfo} | {error, Reason} when Socket :: socket(), Length :: non_neg_integer(), Flags :: [msg_flag() | integer()], Handle :: select_handle() | completion_handle(), Data :: binary(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid().

    Receive data on a connected socket.

    The argument Length specifies the size of the receive buffer. Packet oriented sockets truncate the packet if the size is too small.

    If Length == 0; a default buffer size is used, which can be set by socket:setopt(Socket, {otp,recvbuf}, BufSz).

    For a socket of type stream, when a Timeout argument is used, the operation iterates until Length bytes has been received, or the operation times out. If Length == 0 all readily available data is returned.

    On a select system, when the default receive buffer size option {otp,recvbuf} special value {N,BufSize} is used, N limits how many BufSize buffers that may be received in a tight loop before the receive operation returns. The option value {1,BufSize} is equivalent to just specifying a size value BufSize.

    The message Flags may be symbolic msg_flag/0s and/or integer/0s as in the platform's appropriate header files. The values of all symbolic flags and integers are or:ed together.

    When there is a socket error this function returns {error, Reason}, or if some data arrived before the error; {error, {Reason, Data}} (can only happen for a socket of type stream).

    If the Timeout argument is infinity; waits for the data to arrive. For a socket of type stream this call won't return until all requested data can be delivered, or if "all available" was requested when the first data chunk arrives, or if the OS reports an error for the operation.

    If the Timeout argument is a time-out value (non_neg_integer/0); return {error, timeout} if no data has arrived after Timeout milliseconds, or {error, {timeout, Data}} if some but not enough data has been received on a socket of type stream with Length > 0. It can also return directly with {ok, Data} (type dgram).

    Timeout = 0 only polls the OS receive call and doesn't engage the Asynchronous Calls mechanisms. If no data is immediately available {error, timeout} is returned. On a socket of type stream, {error, {timeout, Data}} is returned if there is an insufficient amount of data immediately available.

    If the Handle argument is nowait (since OTP 22.1), starts an asynchronous call if the operation couldn't be completed immediately.

    If the Handle argument is a select_handle/0, (since OTP 24.0), or on Windows, the equivalent completion_handle/0 (since OTP 26.0), starts an asynchronous call like for nowait.

    See the note Asynchronous Calls at the start of this module reference manual page.

    The possible values for CompletionStatus in the completion message are: {ok, Data}
        Complete success; All requested data was read.
    {more, Data}
        Partial success; Some, but not all, data was read.
    {error, Reason}
        An error occured and no data was read.

    On select systems, for a socket of type stream, if Length > 0 and there is some but not enough data available, this function will return {select, {SelectInfo, Data}} with partial Data. A repeated call to complete the operation may need an updated Length argument.

    On select systems, if the option {otp, select_read} is set, {select_read, {SelectInfo, Data}} is returned instead of {ok, Data} and a new asynchronous receive operation has been initiated, which can be seen as an automatic nowait call whenever a receive operation is completed.
recvfrom(Socket :: socket()) -> dynamic().

    Equivalent to recvfrom(Socket, 0, [], infinity).
recvfrom(Socket :: socket(), Flags :: list()) -> dynamic(); (Socket :: socket(), BufSz :: non_neg_integer()) -> dynamic().

    Receive a message on a socket.

    With argument BufSz; equivalent to recvfrom(Socket, BufSz, [], infinity).

    With argument Flags; equivalent to recvfrom(Socket, 0, Flags, infinity) (since OTP 24.0).
recvfrom(Socket :: socket(), Flags :: [msg_flag() | integer()], TimeoutOrHandle :: dynamic()) -> dynamic(); (Socket :: socket(), BufSz :: non_neg_integer(), Flags :: [msg_flag() | integer()]) -> dynamic(); (Socket :: socket(), BufSz :: non_neg_integer(), TimeoutOrHandle) -> dynamic() when TimeoutOrHandle :: timeout() | nowait | select_handle() | completion_handle().

    Receive a message on a socket.

    With arguments BufSz and Flags; equivalent to recvfrom(Socket, BufSz, Flags, infinity).

    With arguments BufSz and TimeoutOrHandle; equivalent to recvfrom(Socket, BufSz, [], TimeoutOrHandle).

    With arguments Flags and TimeoutOrHandle; equivalent to recvfrom(Socket, 0, Flags, TimeoutOrHandle)

    TimeoutOrHandle :: 'nowait' has been allowed since OTP 22.1.

    TimeoutOrHandle :: Handle has been allowed since OTP 24.0.
recvfrom(Socket, BufSz, Flags, Timeout :: infinity) -> {ok, {Source, Data}} | {error, Reason} when Socket :: socket(), BufSz :: non_neg_integer(), Flags :: [msg_flag() | integer()], Source :: sockaddr_recv(), Data :: binary(), Reason :: posix() | closed | invalid(); (Socket, BufSz, Flags, Timeout :: non_neg_integer()) -> {ok, {Source, Data}} | {error, Reason} when Socket :: socket(), BufSz :: non_neg_integer(), Flags :: [msg_flag() | integer()], Source :: sockaddr_recv(), Data :: binary(), Reason :: posix() | closed | invalid() | timeout; (Socket, BufSz, Flags, nowait | Handle) -> {ok, {Source, Data}} | {select, SelectInfo} | {select_read, {SelectInfo, {Source, Data}}} | {completion, CompletionInfo} | {error, Reason} when Socket :: socket(), BufSz :: non_neg_integer(), Flags :: [msg_flag() | integer()], Handle :: select_handle() | completion_handle(), Source :: sockaddr_recv(), Data :: binary(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid().

    Receive a message on a socket.

    This function is intended primarily for sockets that are not connection oriented such as type dgram or seqpacket where messages may arrive from different source addresses.

    Argument BufSz specifies the number of bytes for the receive buffer. If the buffer size is too small, the message will be truncated.

    If BufSz is 0, a default buffer size is used, which can be set by socket:setopt(Socket, {otp,recvbuf}, BufSz).

    If there is no known appropriate buffer size, it may be possible to use the receive message flag peek. When this flag is used, the message is not "consumed" from the underlying buffers, so another recvfrom/1,2,3,4 call is needed, possibly with an adjusted buffer size.

    The message Flags may be symbolic msg_flag/0s and/or integer/0s, as in the platform's appropriate header files. The values of all symbolic flags and integers are or:ed together.

    If the Timeout argument is infinity; waits for a message to arrive, or for a socket error.

    If the Timeout argument is a time-out value (non_neg_integer/0); returns {error, timeout} if no message has arrived after Timeout milliseconds.

    Timeout = 0 only polls the OS receive call and doesn't engage the Asynchronous Calls mechanisms. If no message is immediately available {error, timeout} is returned.

    If the Handle argument is nowait (since OTP 22.1), starts an asynchronous call if the operation couldn't be completed immediately.

    If the 'Handle' argument is a select_handle/0, (since OTP 24.0), or on Windows, the equivalent completion_handle/0 (since OTP 26.0), starts an asynchronous call like for nowait.

    See the note Asynchronous Calls at the start of this module reference manual page.

    The possible values for CompletionStatus in the completion message are: {ok, {Source, Data}}
        Success.
    {error, Reason}
        An error occured and no data was read.
recvmmsg(Socket, VLen, BufSz, CtrlSz, Flags, Timeout :: infinity) -> {ok, Msgs} | {error, Reason} when Socket :: socket(), VLen :: non_neg_integer(), BufSz :: non_neg_integer(), CtrlSz :: non_neg_integer(), Flags :: [msg_flag() | integer()], Msgs :: [msg_recv()], Reason :: posix() | closed | invalid(); (Socket, VLen, BufSz, CtrlSz, Flags, Timeout :: non_neg_integer()) -> {ok, Msgs} | {error, Reason} when Socket :: socket(), VLen :: non_neg_integer(), BufSz :: non_neg_integer(), CtrlSz :: non_neg_integer(), Flags :: [msg_flag() | integer()], Msgs :: [msg_recv()], Reason :: posix() | closed | invalid() | timeout; (Socket, VLen, BufSz, CtrlSz, Flags, nowait | Handle) -> {ok, Msgs} | {select, SelectInfo} | {select_read, {SelectInfo, Msgs}} | {completion, CompletionInfo} | {error, Reason} when Socket :: socket(), VLen :: non_neg_integer(), BufSz :: non_neg_integer(), CtrlSz :: non_neg_integer(), Handle :: select_handle() | completion_handle(), Flags :: [msg_flag() | integer()], Msgs :: [msg_recv()], SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid().

    Receive multiple messages on a socket.

    This function is equivalent to calling recvmsg/5 multiple times, but uses the platform's recvmmsg syscall for better performance when receiving multiple datagrams.

    NOTE: This function is only available on Linux and BSD systems (not macOS/Darwin or Windows). On unsupported platforms, it will return {error, notsup}.

    Arguments: VLen
        Maximum number of messages to receive (must be >= 1).
    BufSz
        Buffer size for each message (0 uses default).
    CtrlSz
        Control message buffer size for each message (0 uses default).
    Flags
        Receive flags (same as recvmsg/5).
    Timeout
        Timeout or nowait or infinity.

    Returns a list of message maps, one per received message. The list length indicates how many messages were actually received.
recvmsg(Socket :: socket()) -> dynamic().

    Equivalent to recvmsg(Socket, 0, 0, [], infinity).
recvmsg(Socket :: socket(), Flags :: list()) -> dynamic(); (Socket :: socket(), TimeoutOrHandle) -> dynamic() when TimeoutOrHandle :: timeout() | nowait | Handle, Handle :: select_handle() | completion_handle().

    Receive a message on a socket.

    With argument Flags; equivalent to recvmsg(Socket, 0, 0, Flags, infinity).

    With argument TimeoutOrHandle; equivalent to recvmsg(Socket, 0, 0, [], TimeoutOrHandle).

    TimeoutOrHandle :: nowait has been allowed since OTP 22.1.

    TimeoutOrHandle :: Handle has been allowed since OTP 24.0.
recvmsg(Socket :: dynamic(), Flags :: list(), TimeoutOrHandle :: dynamic()) -> dynamic(); (Socket :: dynamic(), BufSz :: integer(), CtrlSz :: integer()) -> dynamic().

    Receive a message on a socket.

    With arguments Flags; equivalent to recvmsg(Socket, 0, 0, Flags, infinity).

    With argument TimeoutOrHandle; equivalent to recvmsg(Socket, 0, 0, [], TimeoutOrHandle).

    TimeoutOrHandle :: nowait has been allowed since OTP 22.1.

    TimeoutOrHandle :: Handle has been allowed since OTP 24.0.
recvmsg(Socket :: socket(), BufSz :: non_neg_integer(), CtrlSz :: non_neg_integer(), TimeoutOrHandle :: dynamic()) -> dynamic().

    Equivalent to recvmsg(Socket, BufSz, CtrlSz, [], TimeoutOrHandle).
recvmsg(Socket, BufSz, CtrlSz, Flags, Timeout :: infinity) -> {ok, Msg} | {error, Reason} when Socket :: socket(), BufSz :: non_neg_integer(), CtrlSz :: non_neg_integer(), Flags :: [msg_flag() | integer()], Msg :: msg_recv(), Reason :: posix() | closed | invalid(); (Socket, BufSz, CtrlSz, Flags, Timeout :: non_neg_integer()) -> {ok, Msg} | {error, Reason} when Socket :: socket(), BufSz :: non_neg_integer(), CtrlSz :: non_neg_integer(), Flags :: [msg_flag() | integer()], Msg :: msg_recv(), Reason :: posix() | closed | invalid() | timeout; (Socket, BufSz, CtrlSz, Flags, nowait | Handle) -> {ok, Msg} | {select, SelectInfo} | {select_read, {SelectInfo, Msg}} | {completion, CompletionInfo} | {error, Reason} when Socket :: socket(), BufSz :: non_neg_integer(), CtrlSz :: non_neg_integer(), Handle :: select_handle() | completion_handle(), Flags :: [msg_flag() | integer()], Msg :: msg_recv(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid().

    Receive a message on a socket.

    This function receives a data message with control messages as well as its source address.

    Arguments BufSz and CtrlSz specifies the number of bytes for the receive buffer and the control message buffer. If the buffer size(s) is(are) too small, the message and/or control message list will be truncated.

    If BufSz is 0, a default buffer size is used, which can be set by socket:setopt(Socket, {otp,recvbuf}, BufSz). The same applies to CtrlSz and socket:setopt(Socket, {otp,recvctrlbuf}, CtrlSz).

    If there is no known appropriate buffer size, it may be possible to use the receive message flag peek. When this flag is used, the message is not "consumed" from the underlying buffers, so another recvfrom/1,2,3,4 call is needed, possibly with an adjusted buffer size.

    The message Flags may be symbolic msg_flag/0s and/or integer/0s, as in the platform's appropriate header files. The values of all symbolic flags and integers are or:ed together.

    If the Timeout argument is infinity; waits for the message to arrive, or for a socket error.

    If the Timeout argument is a time-out value (non_neg_integer/0); return {error, timeout} if no message has arrived after Timeout milliseconds.

    Timeout = 0 only polls the OS receive call and doesn't engage the Asynchronous Calls mechanisms. If no message is immediately available {error, timeout} is returned.

    If the Handle argument is nowait (since OTP 22.1), starts an asynchronous call if the operation couldn't be completed immediately.

    If the 'Handle' argument is a select_handle/0, (since OTP 24.0), or on Windows, the equivalent completion_handle/0 (since OTP 26.0), starts an asynchronous call like for nowait.

    See the note Asynchronous Calls at the start of this module reference manual page.

    The possible values for CompletionStatus in the completion message are: {ok, Msg}
        Success.
    {error, Reason}
        An error occured and no data was read.
rest_iov(Written, IOV) -> RestIOV when Written :: non_neg_integer(), IOV :: erlang:iovec(), RestIOV :: erlang:iovec().

    Calculate the rest I/O vector after a partially successful sendv (CompletionStatus was {ok, Written}).
send(Socket, Data) -> Result when Socket :: socket(), Data :: iodata(), Result :: ok | {ok, RestData :: binary()} | {select, SelectInfo :: dynamic()} | {completion, CompletionInfo :: dynamic()} | {error, Reason :: dynamic()}.

    Equivalent to send(Socket, Data, [], infinity).
send(Socket :: term(), Data :: term(), Cont :: tuple()) -> _; (Socket :: term(), Data :: term(), Flags :: list()) -> _; (Socket :: term(), Data :: term(), Timeout :: timeout()) -> _.

    Send data on a connected socket.

    With argument Timeout; equivalent to send(Socket, Data, [], Timeout).

    With argument Flags; equivalent to send(Socket, Data, Flags, infinity).

    With argument Cont; equivalent to send(Socket, Data, Cont, infinity) (since OTP 24.0).
send(Socket, Data, Flags | Cont, Timeout :: infinity) -> ok | {ok, RestData} | {error, Reason} | {error, {Reason, RestData}} when Socket :: socket(), Data :: iodata(), Flags :: [msg_flag() | integer()], Cont :: select_info(), RestData :: binary(), Reason :: posix() | closed | invalid() | netname_deleted | too_many_cmds | eei(); (Socket, Data, Flags | Cont, Timeout :: non_neg_integer()) -> ok | {ok, RestData} | {error, Reason | timeout} | {error, {Reason | timeout, RestData}} when Socket :: socket(), Data :: iodata(), Flags :: [msg_flag() | integer()], Cont :: select_info(), RestData :: binary(), Reason :: posix() | closed | invalid() | netname_deleted | too_many_cmds | eei(); (Socket, Data, Flags | Cont, nowait | Handle) -> ok | {ok, RestData} | {select, SelectInfo} | {select, {SelectInfo, RestData}} | {completion, CompletionInfo} | {error, Reason} when Socket :: socket(), Data :: iodata(), Flags :: [msg_flag() | integer()], Cont :: select_info(), Handle :: select_handle() | completion_handle(), RestData :: binary(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid() | netname_deleted | too_many_cmds | eei().

    Send data on a connected socket.

    The message Flags may be symbolic msg_flag/0s and/or integer/0s as in the platform's appropriate header files. The values of all symbolic flags and integers are or:ed together.

    The Data, if it is not a binary/0, is copied into one before calling the platform network API, because a single buffer is required. A returned RestData is a sub binary of it.

    The return value indicates the result from the platform's network layer: ok
        All data was accepted by the OS for delivery
    {ok, RestData}
        Some but not all data was accepted, but no error was reported (partially successful send). RestData is the tail of Data that wasn't accepted.

        This cannot happen for a socket of type stream where such a partially successful send is retried until the data is either accepted for delivery or there is an error.

        For a socket of type dgram this should probably also not happen since a message that cannot be passed atomically should render an error.

        It is nevertheless possible for the platform's network layer to return this, surely more possible for a socket of type seqpacket.
    {error, Reason}
        An error has been reported and no data was accepted for delivery. Reason :: posix/0 is what the platform's network layer reported. closed means that this socket library was informed that the socket was closed, and invalid/0 means that this socket library found an argument to be invalid.
    {error, {Reason, RestData}}
        An error was reported but before that some data was accepted for delivery. RestData is the tail of Data that wasn't accepted. See {error, Reason} above.

        This can only happen for a socket of type stream when a partially successful send is retried until there is an error.

    If the Timeout argument is infinity; wait for the OS to complete the send operation (take responsibility for the data), or return an error.

    If the Timeout argument is a time-out value (non_neg_integer/0); return {error, timeout} if no data has been sent within Timeout millisecond, or {error, {timeout, RestData}} if some data was sent (accepted by the OS for delivery). RestData is the tail of the data that hasn't been sent.

    If the Handle argument is nowait (since OTP 22.1), starts an asynchronous call if the operation couldn't be completed immediately.

    If the Handle argument is a select_handle/0, (since OTP 24.0), or on Windows, the equivalent completion_handle/0 (since OTP 26.0), starts an asynchronous call like for nowait.

    See the note Asynchronous Calls at the start of this module reference manual page.

    The possible values for CompletionStatus in the completion message are: ok
        Complete success; The data was written in its entirety.
    {ok, Written}
        Partial success; Some but not all data was written, but no error was reported. Written is the number of bytes that was written.
    {error, Reason}
        An error occured and no data was sent.

    If the function is called with a Cont argument, that is; the SelectInfo from the previous send/3,4 call; the send is continued with preprocessed send parameters in the SelectInfo. Using this argument variant avoids for example having to validate and encode message flags in every call but the first.
sendfile(Socket, FileHandle | Continuation) -> dynamic() when Socket :: socket(), FileHandle :: file:fd(), Continuation :: select_info().

    Send a file on a socket.

    Equivalent to sendfile(Socket, FileHandle_or_Continuation, 0, 0, infinity).
sendfile(Socket, FileHandle | Continuation, Timeout | Handle) -> dynamic() when Socket :: socket(), FileHandle :: file:fd(), Continuation :: select_info(), Timeout :: infinity | non_neg_integer(), Handle :: nowait | select_handle().

    Send a file on a socket.

    Equivalent to sendfile(Socket, FileHandle_or_Continuation, 0, 0, Timeout_or_Handle).
sendfile(Socket, FileHandle | Continuation, Offset, Count) -> dynamic() when Socket :: socket(), FileHandle :: file:fd(), Continuation :: select_info(), Offset :: integer(), Count :: non_neg_integer().

    Send a file on a socket.

    Equivalent to sendfile(Socket, FileHandle_or_Continuation, Offset, Count, infinity).
sendfile(Socket, FileHandle | Continuation, Offset, Count, Timeout :: infinity) -> {ok, BytesSent} | {error, Reason} | {error, {Reason, BytesSent}} when Socket :: socket(), FileHandle :: file:fd(), Continuation :: select_info(), Offset :: integer(), Count :: non_neg_integer(), BytesSent :: non_neg_integer(), Reason :: posix() | closed | invalid(); (Socket, FileHandle | Continuation, Offset, Count, Timeout :: non_neg_integer()) -> {ok, BytesSent} | {error, Reason} | {error, {Reason, BytesSent}} when Socket :: socket(), FileHandle :: file:fd(), Continuation :: select_info(), Offset :: integer(), Count :: non_neg_integer(), BytesSent :: non_neg_integer(), Reason :: posix() | closed | invalid() | timeout; (Socket, FileHandle | Continuation, Offset, Count, nowait | (SelectHandle :: select_handle())) -> {ok, BytesSent} | {select, SelectInfo} | {select, {SelectInfo, BytesSent}} | {error, Reason} when Socket :: socket(), FileHandle :: file:fd(), Continuation :: select_info(), Offset :: integer(), Count :: non_neg_integer(), BytesSent :: non_neg_integer(), SelectInfo :: select_info(), Reason :: posix() | closed | invalid().

    Send a file on a socket.

    NOTE: This function unsupported on Windows.

    The FileHandle argument must refer to an open raw file as described in file:open/2.

    The Offset argument is the file offset to start reading from. The default offset is 0.

    The Count argument is the number of bytes to transfer from FileHandle to Socket. If Count = 0 (the default) the transfer stops at the end of file.

    The return value indicates the result from the platform's network layer: {ok, BytesSent}
        The transfer completed successfully after BytesSent bytes of data.
    {error, Reason}
        An error has been reported and no data was transferred. Reason :: posix/0 is what the platform's network layer reported. closed means that this socket library was informed that the socket was closed, and invalid/0 means that this socket library found an argument to be invalid.
    {error, {Reason, BytesSent}}
        An error has been reported but before that some data was transferred. See {error, Reason} and {ok, BytesSent} above.

    If the Timeout argument is infinity; wait for the OS to complete the send operation (take responsibility for the data), or return an error.

    If the Timeout argument is a time-out value (non_neg_integer/0); return {error, timeout} if no data has been sent within Timeout millisecond, or {error, {timeout, BytesSent}} if some but not all data was sent (accepted by the OS for delivery).

    If the Handle argument is nowait, starts an asynchronous call if the operation couldn't be completed immediately.

    If the Handle argument is a select_handle/0, starts an asynchronous call like for nowait.

    See the note Asynchronous Calls at the start of this module reference manual page.

    After receiving a select message; call sendfile/2,3,4,5 with SelectInfo as the Continuation argument, to complete the operation.

    If the function is called with a Continuation argument, that is; the SelectInfo from the previous sendfile/5 call; the transfer is continued with preprocessed parameters in the SelectInfo.

    The Offset and maybe Count arguments will probably need to be updated between continuation calls.
sendmmsg(Socket, Msgs, Flags, Timeout :: infinity) -> ok | {ok, Rest} | {error, Reason} when Socket :: socket(), Msgs :: [msg_send()], Flags :: [msg_flag() | integer()], Rest :: [erlang:iovec()], Reason :: posix() | closed | invalid(); (Socket, Msgs, Flags, Timeout :: non_neg_integer()) -> ok | {ok, Rest} | {error, Reason | timeout} when Socket :: socket(), Msgs :: [msg_send()], Flags :: [msg_flag() | integer()], Rest :: [erlang:iovec()], Reason :: posix() | closed | invalid(); (Socket, Msgs, Flags, nowait | Handle) -> ok | {ok, Rest} | {select_write, {SelectInfo, SentCount}} | {select, SelectInfo} | {completion, CompletionInfo} | {error, Reason} when Socket :: socket(), Msgs :: [msg_send()], Flags :: [msg_flag() | integer()], Handle :: select_handle() | completion_handle(), Rest :: [erlang:iovec()], SentCount :: non_neg_integer(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid().

    Send multiple messages on a socket.

    This function is equivalent to calling sendmsg/4 multiple times, but uses the platform's sendmmsg syscall for better performance when sending multiple datagrams.

    NOTE: This function is only available on Linux and BSD systems (not macOS/Darwin or Windows). On unsupported platforms, it will return {error, notsup}.

    On success, returns either:

        • ok – when all messages were sent in full (or there were zero messages).

        • {ok, Rest} – when one or more messages had a partial write. Rest is a list with one element per message that was not fully sent, in message order. Each element is the remaining data for that message in the same form as sendmsg/4's rest data (erlang:iovec/0), so you can retry with sendmsg for each.

    On error returns {error, Reason}.
sendmsg(Socket, Msg) -> Result when Socket :: socket(), Msg :: msg_send() | erlang:iovec(), Result :: dynamic().

    Equivalent to sendmsg(Socket, Msg, [], infinity).
sendmsg(Socket :: socket(), Msg :: msg_send(), Flags :: list()) -> dynamic(); (Socket :: socket(), Data :: msg_send() | erlang:iovec(), Cont :: select_info()) -> dynamic(); (Socket :: socket(), Msg :: msg_send(), Timeout :: infinity) -> dynamic().

    Send data and control messages on a socket.

    With arguments Msg and Timeout; equivalent to sendmsg(Socket, Msg, [], Timeout).

    With arguments Msg and Flags; equivalent to sendmsg(Socket, Msg, Flags, infinity).

    With arguments Data and Cont; equivalent to sendmsg(Socket, Data, Cont, infinity) since OTP 24.0.
sendmsg(Socket, Msg, Flags, Timeout :: infinity) -> ok | {ok, RestData} | {error, Reason} | {error, {Reason, RestData}} when Socket :: socket(), Msg :: msg_send(), Flags :: [msg_flag() | integer()], RestData :: erlang:iovec(), Reason :: posix() | closed | invalid(); (Socket, Msg, Flags, Timeout :: non_neg_integer()) -> ok | {ok, RestData} | {error, Reason | timeout} | {error, {Reason | timeout, RestData}} when Socket :: socket(), Msg :: msg_send(), Flags :: [msg_flag() | integer()], RestData :: erlang:iovec(), Reason :: posix() | closed | invalid(); (Socket, Msg, Flags, nowait | Handle) -> ok | {ok, RestData} | {select, SelectInfo} | {select, {SelectInfo, RestData}} | {completion, CompletionInfo} | {error, Reason} | {error, {Reason, RestData}} when Socket :: socket(), Msg :: msg_send(), Flags :: [msg_flag() | integer()], Handle :: select_handle() | completion_handle(), RestData :: erlang:iovec(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid(); (Socket, Data, Cont, Timeout :: infinity) -> ok | {ok, RestData} | {error, Reason} | {error, {Reason, RestData}} when Socket :: socket(), Data :: msg_send() | erlang:iovec(), Cont :: select_info(), RestData :: erlang:iovec(), Reason :: posix() | closed | invalid(); (Socket, Data, Cont, Timeout :: non_neg_integer()) -> ok | {ok, RestData} | {error, Reason | timeout} | {error, {Reason | timeout, RestData}} when Socket :: socket(), Data :: msg_send() | erlang:iovec(), Cont :: select_info(), RestData :: erlang:iovec(), Reason :: posix() | closed | invalid(); (Socket, Data, Cont, nowait | Handle) -> ok | {ok, RestData} | {select, SelectInfo} | {select, {SelectInfo, RestData}} | {completion, CompletionInfo} | {error, Reason} | {error, {Reason, RestData}} when Socket :: socket(), Data :: msg_send() | erlang:iovec(), Cont :: select_info(), Handle :: select_handle(), RestData :: erlang:iovec(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid().

    Send data and control messages on a socket.

    The argument Msg is a map that contains the data to be sent under the key iov as anerlang:iovec/0 (list of binary/0). It may also contain the destination address under the key addr, which is mandatory if the socket isn't connected. If the socket is connected it is best to not have an addr key since the platform may regard that as an error (or ignore it). Under the key ctrl there may be a list of protocol and platform dependent control messages (a.k.a ancillary data, a.k.a control information) to send.

    The message data is given to the platform's network layer as an I/O vector without copying the content. If the number of elements in the I/O vector is larger than allowed on the platform (reported in the iov_max field from info/0), on a socket of type stream the send is iterated over all elements, but for other socket types the call fails.

    See send/4 for a description of the Flags argument and the return values.

    NOTE: On Windows, this function can only be used with datagram and raw sockets.

    If the Timeout argument is infinity; wait for the OS to complete the send operation (take responsibility for the data), or return an error.

    If the Timeout argument is a time-out value (non_neg_integer/0); return {error, timeout} if no data has been sent within Timeout millisecond, or {error, {timeout, RestData}} if some data was sent (accepted by the OS for delivery). RestData is the tail of the data that hasn't been sent.

    If the Handle argument is nowait (since OTP 22.1), starts an asynchronous call if the operation couldn't be completed immediately.

    If the Handle argument is a select_handle/0, (since OTP 24.0), or on Windows, the equivalent completion_handle/0 (since OTP 26.0), starts an asynchronous call like for nowait.

    See the note Asynchronous Calls at the start of this module reference manual page.

    The possible values for CompletionStatus in the completion message are: ok
        Complete success; The data was written in its entirety.
    {ok, Written}
        Partial success; Some but not all data was written, but no error was reported. Written is the number of bytes that was written.
    {error, Reason}
        An error occured and no data was sent.

    After receiving a select message; call sendmsg/3,4 with SelectInfo as the Cont argument, to complete the operation.

    With the arguments Data and Cont, continues the send operation. Cont should be the SelectInfo returned from the previous sendmsg/2,3,4 call.

    Data can be a Msg map/0 where only the key iov is used, or an erlang:iovec/0.
sendto(Socket :: socket(), Data :: iodata(), Cont | Dest) -> Result when Cont :: select_info(), Dest :: sockaddr(), Result :: ok | {ok, RestData} | {error, Reason} | {error, {Reason, RestData}}, RestData :: binary(), Reason :: posix() | closed | invalid().

    Send data on a socket.

    With argument Dest; equivalent to sendto(Socket, Data, Dest, [], infinity).

    With argument Cont; equivalent to sendto(Socket, Data, Cont, infinity) since OTP 24.0.
sendto(Socket :: socket(), Data :: iodata(), Dest :: sockaddr(), Flags :: [msg_flag() | integer()]) -> dynamic(); (Socket :: socket(), Data :: iodata(), Cont :: select_info(), Timeout :: timeout() | nowait | (Handle :: select_handle())) -> dynamic(); (Socket :: socket(), Data :: iodata(), Dest :: sockaddr(), Timeout :: timeout() | nowait | (Handle :: select_handle() | completion_handle())) -> dynamic().

    Send data on a socket.

    With arguments Dest and TimeoutOrHandle; equivalent to sendto(Socket, Data, Dest, [], TimeoutOrHandle).

    With arguments Dest and Flags; equivalent to sendto(Socket, Data, Dest, Flags, infinity).

    With arguments Cont and TimeoutOrHandle; Cont must be the SelectInfo from the previous sendto/3,4,5 call and the send is continued with preprocessed send parameters in the SelectInfo. Using this argument variant avoids for example having o validate and encode message flags in every call but the first. (Since OTP 24.0)

    See the last argument (argument 5) of sendto/5 for an explanation of TimeoutOrHandle.
sendto(Socket, Data, Dest, Flags, Timeout :: infinity) -> ok | {ok, RestData} | {error, Reason} | {error, {Reason, RestData}} when Socket :: socket(), Data :: iodata(), Dest :: sockaddr(), Flags :: [msg_flag() | integer()], RestData :: binary(), Reason :: posix() | closed | invalid(); (Socket, Data, Dest, Flags, Timeout :: non_neg_integer()) -> ok | {ok, RestData} | {error, Reason | timeout} | {error, {Reason | timeout, RestData}} when Socket :: socket(), Data :: iodata(), Dest :: sockaddr(), Flags :: [msg_flag() | integer()], RestData :: binary(), Reason :: posix() | closed | invalid(); (Socket, Data, Dest, Flags, nowait | Handle) -> ok | {ok, RestData} | {select, SelectInfo} | {select, {SelectInfo, RestData}} | {completion, CompletionInfo} | {error, Reason} when Socket :: socket(), Data :: iodata(), Dest :: sockaddr(), Flags :: [msg_flag() | integer()], Handle :: select_handle() | completion_handle(), RestData :: binary(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid().

    Send data on a socket.

    The To argument is the destination address where to send the data. For a connected socket this argument is still passed to the OS call that may ignore the address or return an error.

    See send/4 for a description of the Flags and Data arguments, and the return values.

    If the Timeout argument is infinity; wait for the OS to complete the send operation (take responsibility for the data), or return an error.

    If the Timeout argument is a time-out value (non_neg_integer/0); return {error, timeout} if no data has been sent within Timeout millisecond, or {error, {timeout, RestData}} if some data was sent (accepted by the OS for delivery). RestData is the tail of the data that hasn't been sent.

    If the Handle argument is nowait (since OTP 22.1), starts an asynchronous call if the operation couldn't be completed immediately.

    If the Handle argument is a select_handle/0, (since OTP 24.0), or on Windows, the equivalent completion_handle/0 (since OTP 26.0), starts an asynchronous call like for nowait.

    See the note Asynchronous Calls at the start of this module reference manual page.

    The possible values for CompletionStatus in the completion message are: ok
        Complete success; The data was written in its entirety.
    {ok, Written}
        Partial success; Some but not all data was written, but no error was reported. Written is the number of bytes that was written.
    {error, Reason}
        An error occured and no data was sent.

    After receiving a select message; call sendto/3,4 with SelectInfo as the Cont argument, to complete the operation.
sendv(Socket, IOV, Timeout :: infinity) -> ok | {ok, RestIOV} | {error, Reason} | {error, {Reason, RestIOV}} when Socket :: socket(), IOV :: erlang:iovec(), RestIOV :: erlang:iovec(), Reason :: posix() | closed | invalid(); (Socket, IOV, Timeout :: non_neg_integer()) -> ok | {ok, RestIOV} | {error, Reason} | {error, {Reason, RestIOV}} when Socket :: socket(), IOV :: erlang:iovec(), RestIOV :: erlang:iovec(), Reason :: posix() | closed | invalid() | timeout; (Socket, IOV, nowait | Handle) -> ok | {ok, RestIOV} | {select, SelectInfo} | {select, {SelectInfo, RestIOV}} | {completion, CompletionInfo} | {completion, {CompletionInfo, RestIOV}} | {error, Reason} | {error, {Reason, RestIOV}} when Socket :: socket(), IOV :: erlang:iovec(), Handle :: select_handle() | completion_handle(), RestIOV :: erlang:iovec(), SelectInfo :: select_info(), CompletionInfo :: completion_info(), Reason :: posix() | closed | invalid(); (Socket, IOV, Cont) -> ok | {ok, RestIOV} | {error, Reason} | {error, {Reason, RestIOV}} when Socket :: socket(), IOV :: erlang:iovec(), Cont :: select_info(), RestIOV :: erlang:iovec(), Reason :: posix() | closed | invalid().

    Send erlang:iovec/0 data on a connected socket.

    See sendmsg/4 about how the IOV data is handled towards the platform's network layer.

    The return value indicates the result from the platform's network layer: ok
        All data has been accepted by the OS for delivery.
    {ok, RestIOV}
        Some but not all data was accepted, but no error was reported (partially successful send). RestIOV is the tail of IOV that wasn't accepted.
    {error, Reason}
        An error has been reported and no data was accepted for delivery. Reason :: posix/0 is what the platform's network layer reported. closed means that this socket library was informed that the socket was closed, and invalid/0 means that this socket library found an argument to be invalid.
    {error, {Reason, RestIOV}}
        - An error was reported but before that some data was accepted for delivery. RestIOV is the tail of IOV that wasn't accepted. See {error, Reason} above.

    If the Timeout argument is infinity; wait for the OS to complete the send operation (take responsibility for the data), or return an error.

    If the Timeout argument is a time-out value (non_neg_integer/0); return {error, timeout} if no data has been sent within Timeout millisecond, or {error, {timeout, RestIOV}} if some data was sent (accepted by the OS for delivery). RestIOV is the tail of the data that hasn't been sent.

    If the Handle argument is nowait, starts an asynchronous call if the operation couldn't be completed immediately.

    If the Handle argument is a select_handle/0, or on Windows, the equivalent completion_handle/0, starts an asynchronous call like for nowait.

    See the note Asynchronous Calls at the start of this module reference manual page.

    The possible values for CompletionStatus in the completion message are: ok
        Complete success; The I/O vector was written in its entirety.
    {ok, Written}
        Partial success; Some but not all data was written, but no error was reported. Written is the number of bytes that was written. rest_iov(Written, IOV) can be used to calculate the rest I/O vector (from the original IOV).
    {error, Reason}
        An error occured and no data was sent.

    With the argument Cont, equivalent to sendv(Socket, IOV, Cont, infinity).
sendv(Socket, IOV, Cont, Timeout :: infinity) -> ok | {ok, RestIOV} | {error, Reason} | {error, {Reason, RestIOV}} when Socket :: socket(), IOV :: erlang:iovec(), Cont :: select_info(), RestIOV :: erlang:iovec(), Reason :: posix() | closed | invalid(); (Socket, IOV, Cont, Timeout :: non_neg_integer()) -> ok | {ok, RestIOV} | {error, Reason} | {error, {Reason | RestIOV}} when Socket :: socket(), IOV :: erlang:iovec(), Cont :: select_info(), RestIOV :: erlang:iovec(), Reason :: posix() | closed | invalid() | timeout; (Socket, IOV, Cont, nowait | SelectHandle) -> ok | {ok, RestIOV} | {select, SelectInfo} | {select, {SelectInfo, RestIOV}} | {error, Reason} | {error, {Reason, RestIOV}} when Socket :: socket(), IOV :: erlang:iovec(), Cont :: select_info(), SelectHandle :: select_handle(), RestIOV :: erlang:iovec(), SelectInfo :: select_info(), Reason :: posix() | closed | invalid().

    Send data on a connected socket, continuation.

    Continues sending data on a connected socket. Cont is the SelectInfo returned from the previous sendv/2,3 call. IOV should be the rest data that wasn't sent.

    See asynchronous calls about continuing unfinished calls.

    See sendv/3 about the return values.
setopt(Socket, SocketOption, Value) -> ok | {error, invalid() | closed} when Socket :: socket(), SocketOption :: {Level :: otp, Opt :: otp_socket_option()}, Value :: dynamic(); (Socket, SocketOption, Value) -> ok | {error, posix() | invalid() | closed} when Socket :: socket(), SocketOption :: socket_option(), Value :: dynamic().

    Set a socket option.

    Set an OS protocol level option, or an otp pseudo protocol level option. The latter level is this module's implementation level above the OS protocol levels.

    See the type otp_socket_option() for a description of the otp protocol level.

    See the type socket_option/0 for which OS protocol level options that this implementation knows about, how they are related to OS option names, and if there are known peculiarities with any of them.

    What options that are valid depends on the OS, and on the kind of socket (domain/0,type/0 and protocol/0). See the type socket_option() and the socket options chapter in the User's Guide for more info.

    NOTE: Not all options are valid, nor possible to set, on all platforms. That is, even if this socket implementation support an option; it doesn't mean that the underlying OS does.
setopt(socket(), Level :: term(), Opt :: term(), Value :: term()) -> _.

    Set a socket option (backwards compatibility function).

    Equivalent to setopt(Socket, {Level, Opt}, Value), or as a special case if Opt = NativeOpt :: integer/0 and Value = binary/0 equivalent to setopt_native(Socket, {Level, NativeOpt}, ValueSpec).

    Use setopt/3 or setopt_native/3 instead to handle the option level and name as a single term, and to make the difference between known options and native options clear.
setopt_native(Socket, Option, Value) -> ok | {error, posix() | invalid() | closed} when Socket :: socket(), Option :: socket_option() | {Level, NativeOpt} | {NativeLevel, NativeOpt}, Value :: native_value(), Level :: level(), NativeLevel :: integer(), NativeOpt :: integer().

    Set a "native" socket option.

    Sets a socket option that may be unknown to our implementation, or that has a type not compatible with our implementation, that is; in "native mode".

    If Value is an integer/0 it will be used as a C type (int), if it is a boolean/0 it will be used as a C type (int) with the C implementations values for false or true, and if it is a binary/0 its content and size will be used as the option value.

    The socket option may be specified with an ordinary socket_option/0 tuple, with a symbolic Level as {Level :: level/0, NativeOpt :: integer/0}, or with integers for both NativeLevel and NativeOpt as {NativeLevel :: integer/0, NativeOpt :: integer/0}.

    If an option is valid depends both on the platform and on what kind of socket it is (domain/0, type/0 and protocol/0).

    The integer values for NativeLevel and NativeOpt as well as the Value encoding has to be deduced from the header files for the running system.
shutdown(Socket, How) -> ok | {error, Reason} when Socket :: socket(), How :: read | write | read_write, Reason :: posix() | closed.

    Shut down all or part of a full-duplex connection.
sockname(Socket :: socket()) -> {ok, SockAddr} | {error, Reason} when SockAddr :: sockaddr_recv(), Reason :: posix() | closed.

    Get the socket's address.

    Returns the address to which the socket is currently bound. If the bind address had the wildcard port 0, the address returned by this function contains the ephemeral port selected by the OS.
socknames(Socket :: socket(), AssocId :: sctp_assoc_id()) -> {ok, [SockAddr]} | {error, Reason} when SockAddr :: sockaddr_recv(), Reason :: posix() | closed.

    Get the socket's address.

    Returns all the locally bound addresses to which the socket is currently bound.

    If the socket is IPv4 then all returned addresess will be IPv4. If the socket is IPv6, then the returned addresess can be a mix of IPv4 and IPv6.

    For a one-to-many socket, AssocId specifies the association. For a one-to-one socket, AssocId is ignored.

    If AssocId is 0 (zero), then the returned addresses are without any particular association.
supports() -> [{Key1 :: term(), boolean() | [{Key2 :: term(), boolean() | [{Key3 :: term(), boolean()}]}]}].

    Retrieve information about what socket features the module and the platform supports.

    Returns a list of, in no particular order, {Key1, supports(Key1)} tuples for every Key1 described in supports/1, and {Key, boolean()} tuples for each of the following keys: sctp
        SCTP support
    ipv6
        IPv6 support
    local
        Unix Domain sockets support ( AF_UNIX | AF_LOCAL)
    netns
        Network Namespaces support (Linux, setns(2))
    sendfile
        Sendfile support ( sendfile(2))
supports(Key1 :: term()) -> [{Key2 :: term(), boolean() | [{Key3 :: term(), boolean()}]}].

    Retrieve information about what socket features the module and the platform supports.

    If Key1 = msg_flags returns a list of {Flag, boolean()} tuples for every Flag in msg_flag/0 with the boolean/0 indicating if the flag is supported on this platform.

    If Key1 = protocols returns a list of {Name, boolean()} tuples for every Name inprotocol/0 with the boolean/0 indicating if the protocol is supported on this platform.

    If Key1 = options returns a list of {SocketOption, boolean()} tuples for every SocketOption in socket_option/0 with the boolean/0 indicating if the socket option is supported on this platform.

    There is no particular order of any of the returned lists.

    For other values of Key1 returns []. Note that in future versions of this module or on different platforms, there might be more supported keys.
supports(Key1 :: term(), Key2 :: term()) -> [{Key3 :: term(), boolean()}].

    Retrieve information about what socket features the module and the platform supports.

    If Key1 = options, for a Key2 in level/0 returns a list of {Opt, boolean()} tuples for all known socket options Opt on that Level = Key2 with the boolean/0 indicating if the socket option is supported on this platform. See setopt/3 and getopt/2.

    There is no particular order of any of the returned lists.

    For other values of Key1 or Key2 returns []. Note that in future versions of this module or on different platforms, there might be more supported keys.
use_registry(D :: boolean()) -> ok.

    Set the global use_registry option default value.

    Globally change if the socket registry is to be used or not. Note that its still possible to override this explicitly when creating an individual sockets, see open/2,3,4 for more info (the Opts :: map/0).
which_sockets() -> [socket()].

    Return a list of all known sockets.

    Equivalent to which_sockets(fun (_) -> true end).
which_sockets(FilterRule) -> [socket()] when FilterRule :: inet | inet6 | local | stream | dgram | seqpacket | sctp | tcp | udp | pid() | fun((socket_info()) -> boolean()).

    Return a filtered list of known sockets.

    There are several predefined FilterRules and one general: inet | inet6
        Only the sockets with matching domain/0 are returned.
    stream | dgram | seqpacket
        Only the sockets with matching type/0 are returned.
    sctp | tcp | udp
        Only the sockets with matching protocol/0 are returned.
    pid/0
        Only the sockets with matching Controlling Process are returned. See the OTP socket option controlling_process.
    fun((socket_info()) -> boolean())
        The general filter rule. A fun that takes the socket info and returns a boolean/0 indicating if the socket should be returned or not.