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man pages section 3: Library Interfaces and Headers

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Updated: Thursday, June 13, 2019
 
 

sockaddr(3HEAD)

Name

socket.h, socket, sockaddr - Internet Protocol family

Synopsis

#include <sys/socket.h>

Description

The sys/socket.h header defines the unsigned integral type sa_family_t through typedef.

The sys/socket.h header defines the sockaddr structure that includes the following members:


sa_family_t   sa_family     /* address family */
char          sa_data[]     /* socket   address (variable-length
                                data) */

libxnet Interfaces

These libxnet interfaces are available to XPG4v2 standard-conforming applications. See standards(7).

By default, and when POSIX conformance is requested by defining _XOPEN_SOURCE=500 or higher, the sys/socket.h header defines the msghdr structure to include 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 sys/socket.h header defines the cmsghdr structure to include the following members:

socklen_t  cmsg_len      /* data byte count, including hdr */
int        cmsg_level    /* originating protocol */
int        cmsg_type     /* protocol-specific type */

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 will be legal values for the level argument to the getsockopt() and setsockopt() functions. The SCM_RIGHTS type is supported for level SOL_SOCKET.

Ancillary data is also possible at the socket level. The sys/socket.h header defines the following macros for use as the cmsg_type values when cmsg_level is SOL_SOCKET.

SCM_RIGHTS

Indicates that the data array contains the access rights to be sent or received.

SCM_UCRED

Indicates that the data array contains a ucred_t to be received. The ucred_t is the credential of the sending process at the time the message was sent. This is a Sun-specific, Committed interface. See ucred_get(3C).

The IPv4 data formats generally use the same values for data passed back in cmsghdr as for setsockopt() to enable the feature. The IPv4 data formats are listed below with the associated payload for each.

IPPROTO_IP
IP_RECVDSTADDR

ipaddr_t, IP address

IPPROTO_IP
IP_RECVOPTS

variable-length IP options, up to 40 bytes

IPPROTO_IP
IP_RECVIF

uint_t, ifIndex number

IPPROTO_IP
IP_RECVSLLA

struct sockaddr_dl, link layer address

IPPROTO_IP
IP_RECVTTL

uint8_t

SOL_SOCKET
SO_RECVUCRED

ucred_tcmsghdr.cmsg_type is SCM_UCRED, not SO_RECVUCRED

The IPv6 data formats use different values for enabling the option and for passing the value back to the application. The IPv6 data formats are listed below with the associated payload for each.

IPPROTO_IPV6
IPV6_RECVPKTINFO

in_pktinfo, cmsg_type IPV6_PKTINFO

IPPROTO_IPV6
IPV6_RECVTCLASS

uint_t, cmsg_type IPV6_TCLASS

IPPROTO_IPV6
IPV6_RECVPATHMTU

ip6_mtuinfo, cmsg_type IPV6_PATHMTU

IPPROTO_IPV6
IPV6_RECVHOPLIMIT

uint_t, cmsg_type IPV6_HOPLIMIT

IPPROTO_IPV6
IPV6_RECVHOPOPTS

variable-length IPv6 options, cmsg_type IPV6_HOPOPTS

IPPROTO_IPV6
IPV6_RECVDSTOPTS

variable-length IPv6 options, cmsg_type IPV6_DSTOPTS

IPPROTO_IPV6
IPV6_RECVRTHDR

variable-length IPv6 options, cmsg_type IPV6_RTHDR

IPPROTO_IPV6
IPV6_RECVRTHDRDSTOPTS

variable-length IPv6 options, cmsg_type IPV6_DSTOPTS

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 returns 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 returns 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 returns 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.

CMSG_SPACE(len)

Given the length of an ancillary data object, CMSG_SPACE() returns the space required by the object and its cmsghdr structure, including any padding needed to satisfy alignment requirements. This macro can be used, for example, to allocate space dynamically for the ancillary data. This macro should not be used to initialize the cmsg_len member of a cmsghdr structure. Use the CMSG_LEN() macro instead.

CMSG_LEN(len)

Given the length of an ancillary data object, CMSG_LEN() returns the value to store in the cmsg_len member of the cmsghdr structure, taking into account any padding needed to satisfy alignment requirements.

The sys/socket.h header defines the linger structure that includes the following members:

int   l_onoff   /* indicates  whether  linger option is enabled */
int   l_linger  /* linger time, in seconds */

The sys/socket.h header defines the following macros:

SOCK_DGRAM

Datagram socket

SOCK_STREAM

Byte-stream socket

SOCK_SEQPACKET

Sequenced-packet socket

The sys/socket.h header defines the following macros for use as the level argument of setsockopt() and getsockopt().

SOL_SOCKET

Options to be accessed at the socket level, not the protocol level.

SOL_ROUTE

Options to be accessed at the routing socket level, not the protocol level.

The sys/socket.h header defines the following macros for use as the option_name argument of getsockopt() or setsockopt() calls:

SO_DEBUG

Debugging information is being recorded.

SO_ACCEPTCONN

Socket is accepting connections.

SO_BROADCAST

Transmission of broadcast messages is supported.

SO_REUSEADDR

Reuse of local addresses is supported.

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_SNDBUF

Send buffer size.

SO_RCVBUF

Receive buffer size.

SO_ERROR

Socket error status.

SO_TYPE

Socket type.

SO_RECVUCRED

Request the reception of user credential ancillary data. This is a Sun-specific, Committed interface. See ucred_get(3C).

SO_MAC_EXEMPT

Mandatory Access Control (MAC) exemption for unlabeled peers. This option is available only if the system is configured with Trusted Extensions.

SO_ALLZONES

Bypass zone boundaries (privileged).

SO_NOSIGPIPE

Whether SIGPIPE is send or only EPIPE is returned

The sys/socket.h header defines the following macros for use as the valid values for the msg_flags field in the msghdr structure, or the flags parameter in recvfrom(), recvmsg(), sendto(), or sendmsg() calls:

MSG_CTRUNC

Control data truncated.

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

Wait for complete message.

The sys/socket.h header defines the following macros:

AF_UNIX

UNIX domain sockets

AF_INET

Internet domain sockets

The sys/socket.h header defines the following macros:

SHUT_RD

Disables further receive operations.

SHUT_WR

Disables further send operations.

SHUT_RDWR

Disables further send and receive operations.

libsocket Interfaces

For applications that are written to use the old SunOS4.x (BSD 4.3) style sockets, __USE_SUNOS_SOCKETS__ must be defined before including sys/socket.h, as in:

cc -D__USE_SUNOS_SOCKETS__ ...
#include <sys/socket.h>

In this case, the sys/socket.h header defines the msghdr structure to include the following members rather than the POSIX standard version described above:

void           *msg_name        /* optional address */
socklen_t      msg_namelen      /* size of address */
struct iovec   *msg_iov         /* scatter/gather array */
int            msg_iovlen       /* # elements in msg_iov */
caddr_t        msg_accrights    /* access rights sent/received */
int            msg_accrightslen /*access rights buffer len */

The msg_name and msg_namelen parameters specify the destination address when the socket is unconnected The msg_name can be specified as a NULL pointer if no names are desired or required. The msg_iov and msg_iovlen parameters describe the scatter-gather locations, as described in read(2). The msg_accrights parameter specifies the buffer in which access rights sent along with the message are received. The msg_accrightslen specifies the length of the buffer.

When __USE_SUNOS_SOCKETS__ is defined before including sys/socket.h, none of the CMSG_*() macros are defined.

Attributes

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
Standard

See Also

accept(3C), bind(3C), connect(3C), getpeername(3C), getpeerucred(3C), getsockname(3C), getsockopt(3C), listen(3C), recv(3C), recvfrom(3C), recvmsg(3C), send(3C), sendmsg(3C), sendto(3C), setsockopt(3C), shutdown(3C), sockatmark(3C), socket(3C), socketpair(3C), ucred_get(3C), attributes(7), standards(7)