Tribblix: manual page: accept.3socket

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/socket.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_CLOFORK
The accepted socket will have the FD_CLOFORK 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_CLOFORK
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_CLOFORK, SOCK_NONBLOCK, and SOCK_NDELAY.