ACCEPT(3SOCKET) Sockets Library Functions ACCEPT(3SOCKET)
NAME
accept - accept a connection on a socket
SYNOPSIS
cc [
flag ... ]
file ...
-lsocket -lnsl [
library ... ]
#include <sys/types.h>
#include <sys/socket.h>
int accept(
int s,
struct sockaddr *addr,
socklen_t *addrlen);
int accept4(
int s,
struct sockaddr *addr,
socklen_t *addrlen,
int flags);
DESCRIPTION
The argument
s is a socket that has been created with
socket(3SOCKET) and
bound to an address with
bind(3SOCKET), and that is listening for
connections after a call to
listen(3SOCKET). The
accept() function
extracts the first connection on the queue of pending connections,
creates a new socket with the properties of
s, and allocates a new file
descriptor,
ns, 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 as non-
blocking and no pending connections are present on the queue,
accept() returns an error as described below. The
accept() function uses the
netconfig(5) file to determine the
STREAMS device file name associated
with
s. This is the device on which the connect indication will be
accepted. The accepted socket,
ns, is used to read and write data to and
from the socket that connected to
ns. It is not used to accept more
connections. The original socket (
s) remains open for accepting further
connections.
The argument
addr is a result parameter that is filled in with the
address of the connecting entity as it is known to the communications
layer. The exact format of the
addr parameter is determined by the
domain in which the communication occurs.
The argument
addrlen is a value-result parameter. Initially, it contains
the amount of space pointed to by
addr; on return it contains the length
in bytes of the address returned.
The
accept() function is used with connection-based socket types,
currently with
SOCK_STREAM.
The
accept4() function allows flags that control the behavior of a
successfully accepted socket. If
flags is 0,
accept4() acts identically
to
accept(). Values for
flags are constructed by a bitwise-inclusive-OR
of flags from the following list, defined in <sys/socketvar.h>.
SOCK_CLOEXEC The accepted socket will have the FD_CLOEXEC flag set as if
fcntl() was called on it. This flag is set before the socket
is passed to the caller thus avoiding the race condition
between
accept() and
fcntl(). See,
O_CLOEXEC in
open(2) for
more details.
SOCK_NDELAY The accepted socket will have the
O_NDELAY flag set as if
fcntl() was called on it. This sets the socket into non-
blocking mode. See
O_NDELAY in
fcntl.h(3HEAD) for more
details.
SOCK_NONBLOCK The accepted socket will have the
O_NONBLOCK flag set as if
fcntl() was called on it. This sets the socket into non-
blocking mode (POSIX; see
standards(7)). See
O_NONBLOCK in
fcntl.h(3HEAD) for more details.
It is possible to
select(3C) or
poll(2) a socket for the purpose of an
accept() by selecting or polling it for a read. However, this will only
indicate when a connect indication is pending; it is still necessary to
call
accept().
RETURN VALUES
The
accept() function returns
-1 on error. If it succeeds, it returns a
non-negative integer that is a descriptor for the accepted socket.
ERRORS
accept() and
accept4() will fail if:
EBADF The descriptor is invalid.
ECONNABORTED The remote side aborted the connection before the
accept() operation completed.
EFAULT The
addr parameter or the
addrlen parameter is invalid.
EINTR The
accept() attempt was interrupted by the delivery of a
signal.
EMFILE The per-process descriptor table is full.
ENODEV The protocol family and type corresponding to
s could
not be found in the
netconfig file.
ENOMEM There was insufficient user memory available to complete
the operation.
ENOSR There were insufficient
STREAMS resources available to
complete the operation.
ENOTSOCK The descriptor does not reference a socket.
EOPNOTSUPP The referenced socket is not of type
SOCK_STREAM.
EPROTO A protocol error has occurred; for example, the
STREAMS protocol stack has not been initialized or the connection
has already been released.
EWOULDBLOCK The socket is marked as non-blocking and no connections
are present to be accepted.
Additionally,
accept4() will fail if:
EINVAL The
flags value is invalid. The
flags argument can only
be the bitwise inclusive-OR of
SOCK_CLOEXEC,
SOCK_NONBLOCK, and
SOCK_NDELAY.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|MT-Level | Safe |
+---------------+-----------------+
SEE ALSO
poll(2),
bind(3SOCKET),
connect(3SOCKET),
listen(3SOCKET),
sockaddr(3SOCKET),
select(3C),
socket.h(3HEAD),
socket(3SOCKET),
netconfig(5),
attributes(7),
fcntl.h(3HEAD),
fcntl(2),
standards(7) April 19, 2013
ACCEPT(3SOCKET)