socket(3SOCKET) Sockets Library Functions socket(3SOCKET)NAMEsocket - create an endpoint for communication
SYNOPSIS
cc [ flag ... ] file ... -lsocket-lnsl [ library ... ]
#include <sys/types.h>
#include <sys/socket.h>
int socket(int domain, int type, int protocol);
DESCRIPTION
The socket() function creates an endpoint for communication and returns
a descriptor.
The domain parameter specifies a communications domain within which
communication will take place; this selects the protocol family which
should be used. The protocol family generally is the same as the
address family for the addresses supplied in later operations on the
socket. These families are defined in the include file <sys/socket.h>.
There must be an entry in the netconfig(4) file for at least each pro‐
tocol family and type required. If protocol has been specified, but no
exact match for the tuplet family, type, protocol is found, then the
first entry containing the specified family and type with zero for pro‐
tocol will be used. The currently understood formats are:
PF_UNIX UNIX system internal protocols
PF_INET Internet Protocol Version 4 (IPv4)
PF_INET6 Internet Protocol Version 6 (IPv6)
PF_NCA Network Cache and Accelerator (NCA) protocols
The socket has the indicated type, which specifies the communication
semantics. Currently defined types are:
SOCK_STREAM
SOCK_DGRAM
SOCK_RAW
SOCK_SEQPACKET
SOCK_RDM
A SOCK_STREAM type provides sequenced, reliable, two-way connection-
based byte streams. An out-of-band data transmission mechanism may be
supported. A SOCK_DGRAM socket supports datagrams (connectionless,
unreliable messages of a fixed (typically small) maximum length). A
SOCK_SEQPACKET socket may provide a sequenced, reliable, two-way con‐
nection-based data transmission path for datagrams of fixed maximum
length; a consumer may be required to read an entire packet with each
read system call. This facility is protocol specific, and presently not
implemented for any protocol family. SOCK_RAW sockets provide access to
internal network interfaces. The types SOCK_RAW, which is available
only to a user with the net_rawaccess privilege, and SOCK_RDM, for
which no implementation currently exists, are not described here.
The protocol parameter specifies a particular protocol to be used with
the socket. Normally only a single protocol exists to support a partic‐
ular socket type within a given protocol family. However, multiple pro‐
tocols may exist, in which case a particular protocol must be specified
in this manner. The protocol number to use is particular to the "commu‐
nication domain" in which communication is to take place. If a protocol
is specified by the caller, then it will be packaged into a socket
level option request and sent to the underlying protocol layers.
Sockets of type SOCK_STREAM are full-duplex byte streams, similar to
pipes. A stream socket must be in a connected state before any data may
be sent or received on it. A connection to another socket is created
with a connect(3SOCKET) call. Once connected, data may be transferred
using read(2) and write(2) calls or some variant of the send(3SOCKET)
and recv(3SOCKET) calls. When a session has been completed, a close(2)
may be performed. Out-of-band data may also be transmitted as described
on the send(3SOCKET) manual page and received as described on the
recv(3SOCKET) manual page.
The communications protocols used to implement a SOCK_STREAM insure
that data is not lost or duplicated. If a piece of data for which the
peer protocol has buffer space cannot be successfully transmitted
within a reasonable length of time, then the connection is considered
broken and calls will indicate an error with −1 returns and with
ETIMEDOUT as the specific code in the global variable errno. The proto‐
cols optionally keep sockets "warm" by forcing transmissions roughly
every minute in the absence of other activity. An error is then indi‐
cated if no response can be elicited on an otherwise idle connection
for a extended period (for instance 5 minutes). A SIGPIPE signal is
raised if a thread sends on a broken stream; this causes naive pro‐
cesses, which do not handle the signal, to exit.
SOCK_SEQPACKET sockets employ the same system calls as SOCK_STREAM
sockets. The only difference is that read(2) calls will return only
the amount of data requested, and any remaining in the arriving packet
will be discarded.
SOCK_DGRAM and SOCK_RAW sockets allow datagrams to be sent to corre‐
spondents named in sendto(3SOCKET) calls. Datagrams are generally
received with recvfrom(3SOCKET), which returns the next datagram with
its return address.
An fcntl(2) call can be used to specify a process group to receive a
SIGURG signal when the out-of-band data arrives. It can also enable
non-blocking I/O.
The operation of sockets is controlled by socket level options. These
options are defined in the file <sys/socket.h>. setsockopt(3SOCKET) and
getsockopt(3SOCKET) are used to set and get options, respectively.
RETURN VALUES
Upon successful completion, a descriptor referencing the socket is
returned. Otherwise, -1 is returned and errno is set to indicate the
error.
ERRORS
The socket() function will fail if:
EACCES Permission to create a socket of the specified type
or protocol is denied.
EAFNOSUPPORT The specified address family is not supported by the
protocol family.
EMFILE The per-process descriptor table is full.
ENOMEM Insufficient user memory is available.
ENOSR There were insufficient STREAMS resources available
to complete the operation.
EPFNOSUPPORT The specified protocol family is not supported.
EPROTONOSUPPORT The protocol type is not supported by the address
family.
EPROTOTYPE The socket type is not supported by the protocol.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOnca(1), close(2), fcntl(2), ioctl(2), read(2), write(2),
accept(3SOCKET), bind(3SOCKET), connect(3SOCKET), getsockname(3SOCKET),
getsockopt(3SOCKET), in.h(3HEAD),listen(3SOCKET), recv(3SOCKET), set‐
sockopt(3SOCKET), send(3SOCKET), shutdown(3SOCKET), socket.h(3HEAD),
socketpair(3SOCKET), attributes(5)SunOS 5.10 28 Aug 2007 socket(3SOCKET)
