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ACCEPT(2)                 FreeBSD System Calls Manual                ACCEPT(2)

     accept - accept a connection on a socket

     Standard C Library (libc, -lc)

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

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

     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() call extracts the first connection request on
     the queue of pending connections, creates a new socket with the same
     properties as s, and allocates a new file descriptor 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 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.  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.  This call is used with connection-based socket types,
     currently with SOCK_STREAM.

     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.

     One can obtain user connection request data without confirming the
     connection by issuing a recvmsg(2) call with an msg_iovlen of 0 and a
     non-zero msg_controllen, or by issuing a getsockopt(2) request.
     Similarly, one can provide user connection rejection information by
     issuing a sendmsg(2) call providing only the control information, or by
     calling setsockopt(2).

     The call returns -1 on error.  If it succeeds, it returns a non-negative
     integer that is a descriptor for the accepted socket.

     The accept() 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

     [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.

     bind(2), connect(2), getpeername(2), listen(2), select(2), socket(2)

     The accept() function appeared in 4.2BSD.

FreeBSD 11.0-PRERELEASE        December 11, 1993       FreeBSD 11.0-PRERELEASE


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