sys_socket.h(0p) — Linux manual page

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.1‐2017, 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         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.1‐2017, 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 1003.1-2017, 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(0P)

Pages that refer to this page: netdb.h(0p)netinet_in.h(0p)netinet_tcp.h(0p)sys_un.h(0p)unistd.h(0p)accept(3p)bind(3p)connect(3p)freeaddrinfo(3p)getnameinfo(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)