sys_socket.h(3)            POSIX Programmer's Manual           sys_socket.h(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       sys/socket.h -- main sockets header

SSYYNNOOPPSSIISS
       #include <sys/socket.h>

DDEESSCCRRIIPPTTIIOONN
       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the ssoocckklleenn__tt type, which is an
       integer type of width of at least 32 bits; see APPLICATION USAGE.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the ssaa__ffaammiillyy__tt unsigned integer
       type.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the ssoocckkaaddddrr structure, which
       shall include at least the following members:


           sa_family_t  sa_family  Address family.
           char         sa_data[]  Socket address (variable-length data).

       The ssoocckkaaddddrr structure is used to define a socket address which is used
       in the _b_i_n_d(), _c_o_n_n_e_c_t(), _g_e_t_p_e_e_r_n_a_m_e(), _g_e_t_s_o_c_k_n_a_m_e(), _r_e_c_v_f_r_o_m(), and
       _s_e_n_d_t_o() functions.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the ssoocckkaaddddrr__ssttoorraaggee structure,
       which shall be:

        *  Large enough to accommodate all supported protocol-specific address
           structures

        *  Aligned at an appropriate boundary so that pointers to it can be
           cast as pointers to protocol-specific address structures and used
           to access the fields of those structures without alignment problems

       The ssoocckkaaddddrr__ssttoorraaggee structure shall include at least the following
       members:


           sa_family_t   ss_family

       When a pointer to a ssoocckkaaddddrr__ssttoorraaggee structure is cast as a pointer to
       a ssoocckkaaddddrr structure, the _s_s___f_a_m_i_l_y field of the ssoocckkaaddddrr__ssttoorraaggee
       structure shall map onto the _s_a___f_a_m_i_l_y field of the ssoocckkaaddddrr structure.
       When a pointer to a ssoocckkaaddddrr__ssttoorraaggee structure is cast as a pointer to
       a protocol-specific address structure, the _s_s___f_a_m_i_l_y field shall map
       onto a field of that structure that is of type ssaa__ffaammiillyy__tt and that
       identifies the protocol's address family.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the mmssgghhddrr structure, which
       shall include at least the following members:


           void          *msg_name        Optional address.
           socklen_t      msg_namelen     Size of address.
           struct iovec  *msg_iov         Scatter/gather array.
           int            msg_iovlen      Members in _m_s_g___i_o_v.
           void          *msg_control     Ancillary data; see below.
           socklen_t      msg_controllen  Ancillary data buffer _l_e_n.
           int            msg_flags       Flags on received message.

       The mmssgghhddrr structure is used to minimize the number of directly
       supplied parameters to the _r_e_c_v_m_s_g() and _s_e_n_d_m_s_g() functions. This
       structure is used as a _v_a_l_u_e-_r_e_s_u_l_t parameter in the _r_e_c_v_m_s_g() function
       and _v_a_l_u_e only for the _s_e_n_d_m_s_g() function.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the iioovveecc structure as described
       in _<_s_y_s_/_u_i_o_._h_>.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the ccmmssgghhddrr structure, which
       shall include at least the following members:


           socklen_t  cmsg_len    Data byte count, including the ccmmssgghhddrr.
           int        cmsg_level  Originating protocol.
           int        cmsg_type   Protocol-specific type.

       The ccmmssgghhddrr structure is used for storage of ancillary data object
       information.

       Ancillary data consists of a sequence of pairs, each consisting of a
       ccmmssgghhddrr structure followed by a data array. The data array contains the
       ancillary data message, and the ccmmssgghhddrr structure contains descriptive
       information that allows an application to correctly parse the data.

       The values for _c_m_s_g___l_e_v_e_l shall be legal values for the _l_e_v_e_l argument
       to the _g_e_t_s_o_c_k_o_p_t() and _s_e_t_s_o_c_k_o_p_t() functions. The system
       documentation shall specify the _c_m_s_g___t_y_p_e definitions for the supported
       protocols.

       Ancillary data is also possible at the socket level. The _<_s_y_s_/_s_o_c_k_e_t_._h_>
       header shall define the following symbolic constant for use as the
       _c_m_s_g___t_y_p_e value when _c_m_s_g___l_e_v_e_l is SOL_SOCKET:

       SCM_RIGHTS    Indicates that the data array contains the access rights
                     to be sent or received.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the following macros to gain
       access to the data arrays in the ancillary data associated with a
       message header:

       CMSG_DATA(_c_m_s_g)
             If the argument is a pointer to a ccmmssgghhddrr structure, this macro
             shall return an unsigned character pointer to the data array
             associated with the ccmmssgghhddrr structure.

       CMSG_NXTHDR(_m_h_d_r_,_c_m_s_g)
             If the first argument is a pointer to a mmssgghhddrr structure and the
             second argument is a pointer to a ccmmssgghhddrr structure in the
             ancillary data pointed to by the _m_s_g___c_o_n_t_r_o_l field of that mmssgghhddrr
             structure, this macro shall return a pointer to the next ccmmssgghhddrr
             structure, or a null pointer if this structure is the last
             ccmmssgghhddrr in the ancillary data.

       CMSG_FIRSTHDR(_m_h_d_r)
             If the argument is a pointer to a mmssgghhddrr structure, this macro
             shall return a pointer to the first ccmmssgghhddrr structure in the
             ancillary data associated with this mmssgghhddrr structure, or a null
             pointer if there is no ancillary data associated with the mmssgghhddrr
             structure.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the lliinnggeerr structure, which
       shall include at least the following members:


           int  l_onoff   Indicates whether linger option is enabled.
           int  l_linger  Linger time, in seconds.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the following symbolic constants
       with distinct values:

       SOCK_DGRAM    Datagram socket.

       SOCK_RAW      Raw Protocol Interface.

       SOCK_SEQPACKET
                     Sequenced-packet socket.

       SOCK_STREAM   Byte-stream socket.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the following symbolic constant
       for use as the _l_e_v_e_l argument of _s_e_t_s_o_c_k_o_p_t() and _g_e_t_s_o_c_k_o_p_t().

       SOL_SOCKET    Options to be accessed at socket level, not protocol
                     level.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the following symbolic constants
       with distinct values for use as the _o_p_t_i_o_n___n_a_m_e argument in
       _g_e_t_s_o_c_k_o_p_t() or _s_e_t_s_o_c_k_o_p_t() calls (see the System Interfaces volume of
       POSIX.1-2017, _S_e_c_t_i_o_n _2_._1_0_._1_6, _U_s_e _o_f _O_p_t_i_o_n_s):

       SO_ACCEPTCONN Socket is accepting connections.

       SO_BROADCAST  Transmission of broadcast messages is supported.

       SO_DEBUG      Debugging information is being recorded.

       SO_DONTROUTE  Bypass normal routing.

       SO_ERROR      Socket error status.

       SO_KEEPALIVE  Connections are kept alive with periodic messages.

       SO_LINGER     Socket lingers on close.

       SO_OOBINLINE  Out-of-band data is transmitted in line.

       SO_RCVBUF     Receive buffer size.

       SO_RCVLOWAT   Receive ``low water mark''.

       SO_RCVTIMEO   Receive timeout.

       SO_REUSEADDR  Reuse of local addresses is supported.

       SO_SNDBUF     Send buffer size.

       SO_SNDLOWAT   Send ``low water mark''.

       SO_SNDTIMEO   Send timeout.

       SO_TYPE       Socket type.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the following symbolic constant
       for use as the maximum _b_a_c_k_l_o_g queue length which may be specified by
       the _b_a_c_k_l_o_g field of the _l_i_s_t_e_n() function:

       SOMAXCONN     The maximum _b_a_c_k_l_o_g queue length.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the following symbolic constants
       with distinct values for use as the valid values for the _m_s_g___f_l_a_g_s
       field in the mmssgghhddrr structure, or the _f_l_a_g_s parameter in _r_e_c_v(),
       _r_e_c_v_f_r_o_m(), _r_e_c_v_m_s_g(), _s_e_n_d(), _s_e_n_d_m_s_g(), or _s_e_n_d_t_o() calls:

       MSG_CTRUNC    Control data truncated.

       MSG_DONTROUTE Send without using routing tables.

       MSG_EOR       Terminates a record (if supported by the protocol).

       MSG_OOB       Out-of-band data.

       MSG_NOSIGNAL  No SIGPIPE generated when an attempt to send is made on a
                     stream-oriented socket that is no longer connected.

       MSG_PEEK      Leave received data in queue.

       MSG_TRUNC     Normal data truncated.

       MSG_WAITALL   Attempt to fill the read buffer.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the following symbolic constants
       with distinct values:

       AF_INET       Internet domain sockets for use with IPv4 addresses.

       AF_INET6      Internet domain sockets for use with IPv6 addresses.

       AF_UNIX       UNIX domain sockets.

       AF_UNSPEC     Unspecified.

       The value of AF_UNSPEC shall be 0.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the following symbolic constants
       with distinct values:

       SHUT_RD       Disables further receive operations.

       SHUT_RDWR     Disables further send and receive operations.

       SHUT_WR       Disables further send operations.

       The _<_s_y_s_/_s_o_c_k_e_t_._h_> header shall define the ssiizzee__tt and ssssiizzee__tt types as
       described in _<_s_y_s_/_t_y_p_e_s_._h_>.

       The following shall be declared as functions and may also be defined as
       macros. Function prototypes shall be provided.


           int     accept(int, struct sockaddr *restrict, socklen_t *restrict);
           int     bind(int, const struct sockaddr *, socklen_t);
           int     connect(int, const struct sockaddr *, socklen_t);
           int     getpeername(int, struct sockaddr *restrict, socklen_t *restrict);
           int     getsockname(int, struct sockaddr *restrict, socklen_t *restrict);
           int     getsockopt(int, int, int, void *restrict, socklen_t *restrict);
           int     listen(int, int);
           ssize_t recv(int, void *, size_t, int);
           ssize_t recvfrom(int, void *restrict, size_t, int,
                   struct sockaddr *restrict, socklen_t *restrict);
           ssize_t recvmsg(int, struct msghdr *, int);
           ssize_t send(int, const void *, size_t, int);
           ssize_t sendmsg(int, const struct msghdr *, int);
           ssize_t sendto(int, const void *, size_t, int, const struct sockaddr *,
                   socklen_t);
           int     setsockopt(int, int, int, const void *, socklen_t);
           int     shutdown(int, int);
           int     sockatmark(int);
           int     socket(int, int, int);
           int     socketpair(int, int, int, int [2]);

       Inclusion of _<_s_y_s_/_s_o_c_k_e_t_._h_> may also make visible all symbols from
       _<_s_y_s_/_u_i_o_._h_>.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       To forestall portability problems, it is recommended that applications
       not use values larger than 231 -1 for the ssoocckklleenn__tt type.

       The ssoocckkaaddddrr__ssttoorraaggee structure solves the problem of declaring storage
       for automatic variables which is both large enough and aligned enough
       for storing the socket address data structure of any family. For
       example, code with a file descriptor and without the context of the
       address family can pass a pointer to a variable of this type, where a
       pointer to a socket address structure is expected in calls such as
       _g_e_t_p_e_e_r_n_a_m_e(), and determine the address family by accessing the
       received content after the call.

       The example below illustrates a data structure which aligns on a 64-bit
       boundary. An implementation-defined field ___s_s___a_l_i_g_n following ___s_s___p_a_d_1
       is used to force a 64-bit alignment which covers proper alignment good
       enough for needs of at least ssoocckkaaddddrr__iinn66 (IPv6) and ssoocckkaaddddrr__iinn (IPv4)
       address data structures. The size of padding field ___s_s___p_a_d_1 depends on
       the chosen alignment boundary. The size of padding field ___s_s___p_a_d_2
       depends on the value of overall size chosen for the total size of the
       structure. This size and alignment are represented in the above example
       by implementation-defined (not required) constants _SS_MAXSIZE (chosen
       value 128) and _SS_ALIGNMENT (with chosen value 8). Constants
       _SS_PAD1SIZE (derived value 6) and _SS_PAD2SIZE (derived value 112) are
       also for illustration and not required. The implementation-defined
       definitions and structure field names above start with an <underscore>
       to denote implementation private name space. Portable code is not
       expected to access or reference those fields or constants.


           /*
            *  Desired design of maximum size and alignment.
            */
           #define _SS_MAXSIZE 128
               /* Implementation-defined maximum size. */
           #define _SS_ALIGNSIZE (sizeof(int64_t))
               /* Implementation-defined desired alignment. */

           /*
            *  Definitions used for sockaddr_storage structure paddings design.
            */
           #define _SS_PAD1SIZE (_SS_ALIGNSIZE - sizeof(sa_family_t))
           #define _SS_PAD2SIZE (_SS_MAXSIZE - (sizeof(sa_family_t)+ \
                                 _SS_PAD1SIZE + _SS_ALIGNSIZE))
           struct sockaddr_storage {
               sa_family_t  ss_family;  /* Address family. */
           /*
            *  Following fields are implementation-defined.
            */
               char _ss_pad1[_SS_PAD1SIZE];
                   /* 6-byte pad; this is to make implementation-defined
                      pad up to alignment field that follows explicit in
                      the data structure. */
               int64_t _ss_align;  /* Field to force desired structure
                                      storage alignment. */
               char _ss_pad2[_SS_PAD2SIZE];
                   /* 112-byte pad to achieve desired size,
                      _SS_MAXSIZE value minus size of ss_family
                      __ss_pad1, __ss_align fields is 112. */
           };

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       <<ssyyss__ttyyppeess..hh>>, <<ssyyss__uuiioo..hh>>

       The System Interfaces volume of POSIX.1-2017, _a_c_c_e_p_t(), _b_i_n_d(),
       _c_o_n_n_e_c_t(), _g_e_t_p_e_e_r_n_a_m_e(), _g_e_t_s_o_c_k_n_a_m_e(), _g_e_t_s_o_c_k_o_p_t(), _l_i_s_t_e_n(),
       _r_e_c_v(), _r_e_c_v_f_r_o_m(), _r_e_c_v_m_s_g(), _s_e_n_d(), _s_e_n_d_m_s_g(), _s_e_n_d_t_o(),
       _s_e_t_s_o_c_k_o_p_t(), _s_h_u_t_d_o_w_n(), _s_o_c_k_a_t_m_a_r_k(), _s_o_c_k_e_t(), _s_o_c_k_e_t_p_a_i_r()

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                      sys_socket.h(3)
