NAME    [Toc]    [Back]

     accept - accept a connection on a socket

SYNOPSIS    [Toc]    [Back]

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

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

DESCRIPTION    [Toc]    [Back]

     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 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) or poll(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 dequeuing
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 nonzero
 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).

RETURN VALUES    [Toc]    [Back]

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

ERRORS    [Toc]    [Back]

     The accept() will fail if:

     [EBADF]       The descriptor is invalid.

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

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

     [EINVAL]      The referenced socket  is  not  listening  for
connections
                   (that  is, listen(2) has not yet been called).

     [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.

     [ECONNABORTED]
                   A connection has been aborted.

SEE ALSO    [Toc]    [Back]

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

HISTORY    [Toc]    [Back]

     The accept() function appeared in 4.2BSD.

OpenBSD      3.6                        February     15,     1999