accept - accept a connection on a socket
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);
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().
The accept() function returns −1 on error. If it succeeds,
it returns a non-negative integer that is a descriptor for the accepted
socket.
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.
See attributes(7) for descriptions of the following attributes:
ATTRIBUTE
TYPE |
ATTRIBUTE VALUE |
MT-Level |
Safe |
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)