ACCEPT(2) BSD Programmer's Manual ACCEPT(2)NAMEaccept - accept a connection on a socket
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() call extracts the first connection request on the
queue of pending connections, creates a new socket with the same proper-
ties 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 ori-
ginal 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 structure sockaddr_storage exists for
greater portability. It is large enough to hold any of the types that may
be returned in the addr parameter. 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 re-
turned. 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, 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 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 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.
EXAMPLES
The following code uses struct sockaddr_storage to allocate enough space
for the returned address:
#include <sys/types.h>
#include <sys/socket.h>
struct sockaddr_storage addr;
socklen_t len = sizeof(addr);
int retcode;
retcode = accept(s, (struct sockaddr *)&addr, &len);
if (retcode == -1)
err(1, "accept");
ERRORS
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 or addrlen parameter is not in a valid part of the
process 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 ALSObind(2), connect(2), listen(2), poll(2), select(2), socket(2)HISTORY
The accept() function appeared in 4.2BSD.
MirOS BSD #10-current February 15, 1999 1
