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Updated: Wednesday, July 27, 2022
 
 

sockaddr(3HEAD)

Name

socket.h, socket, sockaddr - sockets API header and structures

Synopsis

#include <sys/socket.h>

Description

The <sys/socket.h> header provides definitions and declarations for the sockets interfaces for inter-process and network communications. Depending on the feature test macros defined, these may be either standards-conforming or historical versions of the interfaces, as described in the following sections.

Common Interfaces

These interfaces are always available, regardless of whether __USE_SUNOS_SOCKETS__ is defined.

The <sys/socket.h> header defines the unsigned integral types sa_family_t and socklen_t through typedef.

The <sys/socket.h> header defines the sockaddr structure to hold a socket address, which includes the following members:

struct sockaddr {
    sa_family_t   sa_family;    /* address family */
    char          sa_data[];    /* socket address */
};

The <sys/socket.h> header defines the sockaddr_storage structure, which is large enough to accommodate all supported protocol-specific address structures, and 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 contains a member:

struct sockaddr {
    sa_family_t   ss_family;    /* address family */
    [...]
};

which may be used to determine what type of socket address the structure should be cast to in order to interpret the address data.

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

struct linger {
    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_RAW

Raw protocol interface

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_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 for outgoing messages

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 also defines the following macros as extensions to the standard for use as the option_name argument of getsockopt() or setsockopt() calls:

SO_ALLZONES

Bypass zone boundaries (privileged).

SO_DOMAIN

Get the domain used in the socket (get only)

SO_FLOW_NAME

Make the socket a flow filter of the specified MAC flow.

It is applicable to TCP/UDP PF_INET/PF_INET6 sockets. Requires PRIV_SYS_FLOW_CONFIG privilege.

SO_FLOW_SLA

Set per socket service level properties: priority and bandwidth limit.

It is applicable to TCP/UDP PF_INET/PF_INET6 sockets. Requires PRIV_SYS_FLOW_CONFIG privilege.

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_NOSIGPIPE

Control whether this specific socket only returns EPIPE on write when the socket is disconnected, or whether a SIGPIPE signal is also sent.

SO_PASSIVE_CONNECT

Modify connect(3C) to wait for connection request from a peer instead of initiating a connection request to it. It is applicable to TCP/SCTP PF_INET/PF_INET6 socket.

SO_PROTOTYPE

For socket in domains PF_INET and PF_INET6, get the underlying protocol number used in the socket. For socket in domain PF_ROUTE, get the address family used in the socket.

SO_RECVUCRED

Request the reception of user credential ancillary data, as described for the SCM_UCRED value of cmsg_type below. This is a Solaris-specific, Committed interface. This is only valid for sockets of type SOCK_DGRAM. See ucred_get(3C).

The <sys/socket.h> header defines the following symbolic constant for use as the maximum backlog queue length which may be specified by the backlog argument to the listen() function:

SOMAXCONN

The maximum backlog queue length.

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(), recvmmsg(), sendto(), sendmsg(), or sendmmsg() 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.

MSG_CMSG_CLOEXEC

Atomically set the FD_CLOEXEC flag on any file descriptors created via SCM_RIGHTS during recvmsg().

MSG_CMSG_CLOFORK

Atomically set the FD_CLOFORK flag on any file descriptors created via SCM_RIGHTS during recvmsg().

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

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 socket type.

The <sys/socket.h> header defines the following macros for use as the how argument to the shutdown(3C) function:

SHUT_RD

Disables further receive operations.

SHUT_WR

Disables further send operations.

SHUT_RDWR

Disables further send and receive operations.

Standard Interfaces

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

By default, when __USE_SUNOS_SOCKETS__ is not defined, 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:

struct msghdr {
    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:

struct cmsghdr {
    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 <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. The size is variable but never larger than the value returned by ucred_size(3C). This is a Solaris-specific, Committed interface. See ucred_get(3C).

The <sys/socket.h> header defines the following macros for use as the cmsg_type values when cmsg_level is IPPROTO_IP. 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.

IP_RECVDSTADDR

ipaddr_t, IP address

IP_RECVOPTS

variable-length IP options, up to 40 bytes

IP_RECVIF

uint_t, ifIndex number

IP_RECVSLLA

struct sockaddr_dl, link layer address

IP_RECVTTL

uint8_t

The <sys/socket.h> header defines the following macros for use as the cmsg_type values when cmsg_level is IPPROTO_IPV6. 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.

IPV6_RECVPKTINFO

in_pktinfo, cmsg_type IPV6_PKTINFO

IPV6_RECVTCLASS

uint_t, cmsg_type IPV6_TCLASS

IPV6_RECVPATHMTU

ip6_mtuinfo, cmsg_type IPV6_PATHMTU

IPV6_RECVHOPLIMIT

uint_t, cmsg_type IPV6_HOPLIMIT

IPV6_RECVHOPOPTS

variable-length IPv6 options, cmsg_type IPV6_HOPOPTS

IPV6_RECVDSTOPTS

variable-length IPv6 options, cmsg_type IPV6_DSTOPTS

IPV6_RECVRTHDR

variable-length IPv6 options, cmsg_type IPV6_RTHDR

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.

Historical 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), accept4(3C), bind(3C), connect(3C), getpeername(3C), getpeerucred(3C), getsockname(3C), getsockopt(3C), listen(3C), recv(3C), recvfrom(3C), recvmsg(3C), recvmmsg(3C), send(3C), sendmsg(3C), sendmmsg(3C), sendto(3C), setsockopt(3C), shutdown(3C), sockatmark(3C), socket(3C), socketpair(3C), ucred_get(3C), attributes(7), standards(7)

Gilligan, R. RFC 3493, Basic Socket Interface Extensions for IPv6. Network Working Group. February 2003. https://tools.ietf.org/html/rfc3493

History

The functions declared in this header were provided in the libsocket(3LIB) library in Solaris 2 through 11.3, and moved to the libc(3LIB) library in Solaris 11.4.

The X/Open standard-conforming interfaces were also available via the libxnet(3LIB) filter library in Solaris 2.6 through 11.3. This library became a filter on the libc(3LIB) library in Solaris 11.4.

The Historical Functionality was the default behavior when building applications on Solaris 11.3 and earlier releases, and use of the Standard Functionality on those releases required defining _XOPEN_SOURCE=500 or higher when building applications. Oracle Solaris 11.4 changed the default to the standards-conforming version, and added the requirement to define __USE_SUNOS_SOCKETS__ before including the <sys/socket.h> header to use the historical version instead.