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



PROLOG
       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.

NAME
       sys/socket.h -- main sockets header

SYNOPSIS
       #include <sys/socket.h>

DESCRIPTION
       The <sys/socket.h> header shall define the socklen_t type, which is an
       integer type of width of at least 32 bits; see APPLICATION USAGE.

       The <sys/socket.h> header shall define the sa_family_t unsigned integer
       type.

       The <sys/socket.h> header shall define the sockaddr 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 sockaddr structure is used to define a socket address which is used
       in the bind(), connect(), getpeername(), getsockname(), recvfrom(), and
       sendto() functions.

       The <sys/socket.h> header shall define the sockaddr_storage 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 sockaddr_storage structure shall include at least the following
       members:


           sa_family_t   ss_family

       When a pointer to a sockaddr_storage structure is cast as a pointer to
       a sockaddr structure, the ss__family field of the sockaddr_storage
       structure shall map onto the sa__family field of the sockaddr structure.
       When a pointer to a sockaddr_storage structure is cast as a pointer to
       a protocol-specific address structure, the ss__family field shall map
       onto a field of that structure that is of type sa_family_t and that
       identifies the protocol's address family.

       The <sys/socket.h> header shall define the msghdr 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 msg__iov.
           void          *msg_control     Ancillary data; see below.
           socklen_t      msg_controllen  Ancillary data buffer len.
           int            msg_flags       Flags on received message.

       The msghdr structure is used to minimize the number of directly
       supplied parameters to the recvmsg() and sendmsg() functions. This
       structure is used as a value-result parameter in the recvmsg() function
       and value only for the sendmsg() function.

       The <sys/socket.h> header shall define the iovec structure as described
       in <sys/uio.h>.

       The <sys/socket.h> header shall define the cmsghdr structure, which
       shall include at least the following members:


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

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

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

       The values for cmsg__level shall be legal values for the level argument
       to the getsockopt() and setsockopt() functions. The system
       documentation shall specify the cmsg__type definitions for the supported
       protocols.

       Ancillary data is also possible at the socket level. The <sys/socket.h>
       header shall define the following symbolic constant for use as the
       cmsg__type value when cmsg__level is SOL_SOCKET:

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

       The <sys/socket.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(cmsg)
             If the argument is a pointer to a cmsghdr structure, this macro
             shall return an unsigned character pointer to the data array
             associated with the cmsghdr structure.

       CMSG_NXTHDR(mhdr,cmsg)
             If the first argument is a pointer to a msghdr structure and the
             second argument is a pointer to a cmsghdr structure in the
             ancillary data pointed to by the msg__control field of that msghdr
             structure, this macro shall return a pointer to the next cmsghdr
             structure, or a null pointer if this structure is the last
             cmsghdr in the ancillary data.

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

       The <sys/socket.h> header shall define the linger 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 <sys/socket.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 <sys/socket.h> header shall define the following symbolic constant
       for use as the level argument of setsockopt() and getsockopt().

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

       The <sys/socket.h> header shall define the following symbolic constants
       with distinct values for use as the option__name argument in
       getsockopt() or setsockopt() calls (see the System Interfaces volume of
       POSIX.1-2017, Section 2.10.16, Use of Options):

       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 <sys/socket.h> header shall define the following symbolic constant
       for use as the maximum backlog queue length which may be specified by
       the backlog field of the listen() function:

       SOMAXCONN     The maximum backlog queue length.

       The <sys/socket.h> header shall define the following symbolic constants
       with distinct values for use as the valid values for the msg__flags
       field in the msghdr structure, or the flags parameter in recv(),
       recvfrom(), recvmsg(), send(), sendmsg(), or sendto() 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 <sys/socket.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 <sys/socket.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 <sys/socket.h> header shall define the size_t and ssize_t types as
       described in <sys/types.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 <sys/socket.h> may also make visible all symbols from
       <sys/uio.h>.

       The following sections are informative.

APPLICATION USAGE
       To forestall portability problems, it is recommended that applications
       not use values larger than 231 -1 for the socklen_t type.

       The sockaddr_storage 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
       getpeername(), 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 __ss__align following __ss__pad1
       is used to force a 64-bit alignment which covers proper alignment good
       enough for needs of at least sockaddr_in6 (IPv6) and sockaddr_in (IPv4)
       address data structures. The size of padding field __ss__pad1 depends on
       the chosen alignment boundary. The size of padding field __ss__pad2
       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. */
           };

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       <sys_types.h>, <sys_uio.h>

       The System Interfaces volume of POSIX.1-2017, accept(), bind(),
       connect(), getpeername(), getsockname(), getsockopt(), listen(),
       recv(), recvfrom(), recvmsg(), send(), sendmsg(), sendto(),
       setsockopt(), shutdown(), sockatmark(), socket(), socketpair()

COPYRIGHT
       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)
