accept
Hurricane Electric Internet Services
NAME
accept - accept a connection on a socket
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int accept(int s, struct sockaddr *addr, int *addrlen);
DESCRIPTION
The argument s is a socket that has been created with
socket(2), bound to an address with bind(2), and is lis-
tening 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 descrip-
tor for the socket. If no pending connections are present
on the queue, and the socket is not marked as non-block-
ing, accept blocks the caller until a connection is pre-
sent. 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 param-
eter is determined by the domain in which the communica-
tion is occurring. The addrlen is a value-result parame-
ter; 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 confirma-
tion, 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 con-
firming 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 pro-
vide user connection rejection information by issuing a
sendmsg(2) call with providing only the control informa-
tion, or by calling 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
EBADF The descriptor is invalid.
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 connec-
tions are present to be accepted.
HISTORY
The accept function appeared in BSD 4.2.
SEE ALSO
bind(2), connect(2), listen(2), select(2), socket(2)
Hurricane Electric Internet Services
Copyright (C) 1998
Hurricane Electric.
All Rights Reserved.