#include <sys/socket.h>
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:
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:
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:
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:
The <sys/socket.h> header shall define the following symbolic constant for use as the level argument of setsockopt() and getsockopt().
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):
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:
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:
The <sys/socket.h> header shall define the following symbolic constants with distinct values:
The value of AF_UNSPEC shall be 0.
The <sys/socket.h> header shall define the following symbolic constants with distinct values:
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.
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. */
};
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()
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 .