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.
