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(4) 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(5)). 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(5) 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(4), attributes(5), fcntl.h(3HEAD), fcntl(2), standards(5)


April 19, 2013 ACCEPT(3SOCKET)