PROLOG | NAME | SYNOPSIS | DESCRIPTION | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

sys_socket.h(0P)          POSIX Programmer's Manual         sys_socket.h(0P)

PROLOG         top

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

NAME         top

       sys/socket.h — main sockets header

SYNOPSIS         top

       #include <sys/socket.h>

DESCRIPTION         top

       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 valueresult 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.1‐2008, 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 <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         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       sys_types.h(0p), sys_uio.h(0p)

       The System Interfaces volume of POSIX.1‐2008, accept(3p), bind(3p),
       connect(3p), getpeername(3p), getsockname(3p), getsockopt(3p),
       listen(3p), recv(3p), recvfrom(3p), recvmsg(3p), send(3p),
       sendmsg(3p), sendto(3p), setsockopt(3p), shutdown(3p),
       sockatmark(3p), socket(3p), socketpair(3p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                    sys_socket.h(0P)