DragonFly On-Line Manual Pages

ACCEPT(2)                DragonFly System Calls Manual               ACCEPT(2)

NAME
     accept, accept4 -- accept a connection on a socket

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>

     int
     accept(int s, struct sockaddr *addr, socklen_t *addrlen);

     int
     accept4(int s, struct sockaddr * restrict addr,
         socklen_t * restrict addrlen, int flags);

DESCRIPTION
     The argument 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() system call extracts the first connection
     request on the queue of pending connections, creates a new socket, and
     allocates a new file descriptor for the socket which inherits the state
     of the O_NONBLOCK and O_ASYNC properties, socket buffer settings, socket
     options, and the destination of SIGIO and SIGURG signals from the
     original socket s.

     The accept4() system call is similar, but the O_NONBLOCK property of the
     new socket is instead determined by the SOCK_NONBLOCK flag in the flags
     argument, the O_ASYNC property is cleared, the signal destination is
     cleared and the close-on-exec flag on the new file descriptor can be set
     via the SOCK_CLOEXEC flag in the flags argument.

     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.  To ensure that the returned
     address fits, *addr should have a size of at least sizeof(struct
     sockaddr_storage).  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.  These
     system calls are used with connection-based socket types, currently with
     SOCK_STREAM and SOCK_SEQPACKET.

     It is possible to select(2) a socket for the purposes of doing an
     accept() by selecting it for read.

     For certain protocols which require an explicit confirmation, such as ISO
     or DATAKIT, accept() can be thought of as merely dequeueing 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.

     For some applications, performance may be enhanced by using an
     accept_filter(9) to pre-process incoming connections.

RETURN VALUES
     These calls returns -1 on error.  If they succeed, they return a non-
     negative integer that is a descriptor for the accepted socket.

ERRORS
     The accept() and accept4() system calls will fail if:

     [EBADF]            The descriptor is invalid.

     [EINTR]            The accept() operation was interrupted.

     [EMFILE]           The per-process descriptor table is full.

     [ENFILE]           The system file table is full.

     [ENOTSOCK]         The descriptor references a file, not a socket.

     [EINVAL]           listen(2) has not been called on the socket
                        descriptor.

     [EFAULT]           The addr parameter is not in a writable part of the
                        user address space.

     [EWOULDBLOCK]      The socket is marked non-blocking and no connections
                        are present to be accepted.

     [ECONNABORTED]     A connection arrived, but it was closed while waiting
                        on the listen queue.

     The accept4() system call will also fail if:

     [EINVAL]           The flags argument is invalid.

SEE ALSO
     bind(2), connect(2), getpeername(2), listen(2), select(2), socket(2),
     accept_filter(9)

HISTORY
     The accept() system call appeared in 4.2BSD.

     The accept4() system call appeared in DragonFly 4.3.

DragonFly 4.3                  October 29, 2015                  DragonFly 4.3