accept(2) - NetBSD Manual Pages

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ACCEPT(2)                 NetBSD Programmer's Manual                 ACCEPT(2)


NAME

     accept - 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);


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() argument extracts the first connection request
     on the queue of pending connections, creates a new socket with the same
     properties of 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 ad-
     dress 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 pa-
     rameter; it should initially contain the amount of space pointed to by
     addr; on return it will contain the actual length (in bytes) of the ad-
     dress returned.  This call is used with connection-based socket types,
     currently with SOCK_STREAM.

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

     For certain protocols which require an explicit confirmation, such as ISO
     or DATAKIT, accept() can be thought of as merely dequeuing the next con-
     nection request and not implying confirmation.  Confirmation can be im-
     plied 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 con-
     nection 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 with providing only the control information, or by call-
     ing setsockopt(2).


RETURN VALUES

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


ERRORS

     The accept() will fail if:

     [EBADF]       The descriptor is invalid.

     [EINVAL]      The socket has not been set up to accept connections (using
                   bind(2) and listen(2)).

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

     [EOPNOTSUPP]  The referenced socket is not of type SOCK_STREAM.

     [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.

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

     [ENFILE]      The system file table is full.


SEE ALSO

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


HISTORY

     The accept() function appeared in 4.2BSD.

NetBSD 1.5                     December 11, 1993                             2