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

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

The <sys/socket.h> header shall define the sockaddr structure that includes 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. This structure 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 contain at least the following members: sa_family_t ss_family When a sockaddr_storage structure is cast as 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 sockaddr_storage structure is cast as 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 that includes 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 iovec structure shall be defined as described in <sys/uio.h> The <sys/socket.h> header shall define the cmsghdr structure that includes 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 defines the following macro 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 defines 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 that includes 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 macros, with distinct integer values: SOCK_DGRAM Datagram socket. SOCK_RAW ^{[ RS ]} Raw Protocol Interface. SOCK_SEQPACKET Sequenced-packet socket. SOCK_STREAM Byte-stream socket. The <sys/socket.h> header shall define the following macro 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 macros, with distinct integer values, for use as the option_name argument in getsockopt () or setsockopt () calls: 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 macro 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 macros, with distinct integer values, for use as the valid values for the msg_flags field in the msghdr structure, or the flags parameter in recvfrom () , recvmsg () , 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_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 macros, with distinct integer values: AF_INET Internet domain sockets for use with IPv4 addresses. AF_INET6 ^{[ IP6 ]} 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 macros, with distinct integer values: SHUT_RD Disables further receive operations. SHUT_RDWR Disables further send and receive operations. SHUT_WR Disables further send operations. 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 socket(int, int, int); int sockatmark(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 2 ³¹ -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. */ <sys/uio.h> , the System Interfaces volume of IEEE Std 1003.1-2001, accept () , bind () , connect () , getpeername () , getsockname () , getsockopt () , listen () , recv () , recvfrom () , recvmsg () , send () , sendmsg () , sendto () , setsockopt () , shutdown () , socket () , socketpair () CHANGE HISTORY First released in Issue 6. Derived from the XNS, Issue 5.2 specification. The restrict keyword is added to the prototypes for accept () , getpeername () , getsockname () , getsockopt () , and recvfrom () . End of informative text. UNIX ® is a registered Trademark of The Open Group. POSIX ® is a registered Trademark of The IEEE.