ACCEPT
Section: Linux Programmer's Manual (2)
Updated: 24 July 1993
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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 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)
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 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 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 connections 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)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUES
-
- ERRORS
-
- HISTORY
-
- SEE ALSO
-
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