int
accept(
int s
, struct sockaddr * restrict addr
, socklen_t * restrict addrlen
)
s
is a socket that has been created with
socket(2),
bound to an address with
bind(2),
and is listening for connections after a
listen(2).
The
accept(
)
argument
extracts the first connection request on the queue of pending
connections, creates a new socket with the same properties of
s
and allocates a new file descriptor
for the socket.
If no pending connections are
present on the queue, and the socket is not marked
as non-blocking,
accept(
)
blocks the caller until a connection is present.
If the socket is marked non-blocking and no pending
connections are present on the queue,
accept(
)
returns an error as described below.
The accepted socket
may not be used
to accept more connections.
The original socket
s
remains open.
The argument
addr
is a result parameter that is filled in with
the address of the connecting entity,
as known to the communications layer.
The exact format of the
addr
parameter is determined by the domain in which the communication
is occurring.
The
addrlen
is a value-result parameter; it should initially contain the
amount of space pointed to by
addr
;
on return it will contain the actual length (in bytes) of the
address returned.
This call
is used with connection-based socket types, currently with
SOCK_STREAM
.
It is possible to
select(2)
or
poll(2)
a socket for the purposes of doing an
accept()
by selecting or polling it for read.
For certain protocols which require an explicit confirmation,
such as
ISO
or
DATAKIT,
accept()
can be thought of
as merely dequeuing the next connection
request and not implying confirmation.
Confirmation can be implied by a normal read or write on the new
file descriptor, and rejection can be implied by closing the
new socket.
One can obtain user connection request data without confirming
the connection by issuing a
recvmsg(2)
call with an
msg_iovlen
of 0 and a non-zero
msg_controllen
,
or by issuing a
getsockopt(2)
request.
Similarly, one can provide user connection rejection information
by issuing a
sendmsg(2)
call with providing only the control information,
or by calling
setsockopt(2).
)
will fail if:
EAGAIN
]
EBADF
]
ECONNABORTED
]
EFAULT
]
addr
parameter is not in a writable part of the
user address space.
EINTR
]
)
call has been interrupted by a signal.
EINVAL
]
EMFILE
]
ENFILE
]
ENOTSOCK
]
EOPNOTSUPP
]
SOCK_STREAM
.
)
function appeared in
4.2BSD.