SOCKET(2) | System Calls Manual | SOCKET(2) |
socket
— create an
endpoint for communication
#include
<sys/socket.h>
int
socket
(int domain,
int type, int protocol);
socket
()
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. These families are defined in the include file ⟨sys/socket.h⟩. The currently understood formats are
PF_LOCAL Host-internal protocols, formerly called PF_UNIX, PF_UNIX Host-internal protocols, deprecated, use PF_LOCAL, PF_INET Internet version 4 protocols, PF_ROUTE Internal Routing protocol, PF_KEY Internal key-management function, PF_INET6 Internet version 6 protocols, PF_SYSTEM System domain, PF_NDRV Raw access to network device, PF_VSOCK VM Sockets protocols
The socket has the indicated type, which specifies the semantics of communication. Currently defined types are:
SOCK_STREAM SOCK_DGRAM SOCK_RAW
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). SOCK_RAW
sockets provide access to internal
network protocols and interfaces. The type SOCK_RAW
,
which is available only to the super-user.
The protocol specifies a particular protocol to be used with the socket. Normally only a single protocol exists to support a particular socket type within a given protocol family. However, it is possible that many protocols may exist, in which case a particular protocol must be specified in this manner. The protocol number to use is particular to the “communication domain” in which communication is to take place; see protocols(5).
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(2) or
connectx(2) call. Once connected,
data may be transferred using read(2) and
write(2) calls or some variant of the
send(2) and
recv(2) calls. When a session has been
completed a close(2) may be performed.
Out-of-band data may also be transmitted as described in
send(2) and received as described in
recv(2).
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 protocols optionally
keep sockets “warm” by forcing transmissions roughly every
minute in the absence of other activity. An error is then indicated if no
response can be elicited on an otherwise idle connection for a extended
period (e.g. 5 minutes). A SIGPIPE
signal is raised
if a process sends on a broken stream; this causes naive processes, which do
not handle the signal, to exit.
SOCK_DGRAM
and
SOCK_RAW
sockets allow sending of datagrams to
correspondents named in send(2) calls.
Datagrams are generally received with
recvfrom(2), 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 may also enable non-blocking
I/O and asynchronous notification of I/O events via
SIGIO
.
The operation of sockets is controlled by socket level options. These options are defined in the file ⟨sys/socket.h⟩. Setsockopt(2) and getsockopt(2) are used to set and get options, respectively.
A -1 is returned if an error occurs, otherwise the return value is a descriptor referencing the socket.
The socket
() system call fails if:
EACCES
]EAFNOSUPPORT
]EMFILE
]ENFILE
]ENOBUFS
]ENOMEM
]EPROTONOSUPPORT
]EPROTOTYPE
]If a new protocol family is defined, the socreate process is free
to return any desired error code. The socket
()
system call will pass this error code along (even if it is undefined).
#include
<sys/types.h>
#include
<sys/socket.h>
The include file
<sys/types.h>
is
necessary.
accept(2), bind(2), connect(2), connectx(2), disconnectx(2), getsockname(2), getsockopt(2), ioctl(2), listen(2), read(2), recv(2), select(2), send(2), shutdown(2), socketpair(2), write(2), getprotoent(3), inet(4), inet6(4), unix(4), compat(5)
An Introductory 4.3 BSD Interprocess Communication Tutorial, reprinted in UNIX Programmer's Supplementary Documents Volume 1.
BSD Interprocess Communication Tutorial, reprinted in UNIX Programmer's Supplementary Documents Volume 1.
The socket
() function call appeared in
4.2BSD.
March 18, 2015 | macOS 14.6 |