.\" $NetBSD: accept.2,v 1.7 1996/01/31 20:14:42 mycroft Exp $ .\" .\" Copyright (c) 1983, 1990, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)accept.2 8.2 (Berkeley) 12/11/93 .\" .Dd December 11, 1993 .Dt ACCEPT 2 .Os BSD 4.2 .Sh NAME .Nm accept .Nd accept a connection on a socket .Sh SYNOPSIS .Fd #include <sys/socket.h> .Ft int .Fo accept .Fa "int socket" .Fa "struct sockaddr *restrict address" .Fa "socklen_t *restrict address_len" .Fc .Sh DESCRIPTION The argument .Fa socket is a socket that has been created with .Xr socket 2 , bound to an address with .Xr bind 2 , and is listening for connections after a .Xr listen 2 . .Fn accept extracts the first connection request on the queue of pending connections, creates a new socket with the same properties of .Fa socket , 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, .Fn 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, .Fn accept returns an error as described below. The accepted socket may not be used to accept more connections. The original socket .Fa socket, remains open. .Pp The argument .Fa address 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 .Fa address parameter is determined by the domain in which the communication is occurring. The .Fa address_len is a value-result parameter; it should initially contain the amount of space pointed to by .Fa address ; 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 .Dv SOCK_STREAM . .Pp It is possible to .Xr select 2 a socket for the purposes of doing an .Fn accept by selecting it for read. .Pp For certain protocols which require an explicit confirmation, such as .Tn ISO or .Tn DATAKIT , .Fn 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. .Pp One can obtain user connection request data without confirming the connection by issuing a .Xr recvmsg 2 call with an .Fa msg_iovlen of 0 and a non-zero .Fa msg_controllen , or by issuing a .Xr getsockopt 2 request. Similarly, one can provide user connection rejection information by issuing a .Xr sendmsg 2 call with providing only the control information, or by calling .Xr setsockopt 2 . .Sh RETURN VALUES The call returns \-1 on error and the global variable .Va errno is set to indicate the error. If it succeeds, it returns a non-negative integer that is a descriptor for the accepted socket. .Sh ERRORS The .Fn accept system call will fail if: .Bl -tag -width Er .\" ========== .It Bq Er EBADF .Fa socket is not a valid file descriptor. .\" ========== .It Bq Er ECONNABORTED The connection to .Fa socket has been aborted. .\" ========== .It Bq Er EFAULT The .Fa address parameter is not in a writable part of the user address space. .\" ========== .It Bq Er EINTR The .Fn accept system call was terminated by a signal. .\" ========== .It Bq Er EINVAL .Fa socket is unwilling to accept connections. .\" ========== .It Bq Er EMFILE The per-process descriptor table is full. .\" ========== .It Bq Er ENFILE The system file table is full. .\" ========== .It Bq Er ENOMEM Insufficient memory was available to complete the operation. .\" ========== .It Bq Er ENOTSOCK .Fa socket references a file type other than a socket. .\" ========== .It Bq Er EOPNOTSUPP .Fa socket is not of type .Dv SOCK_STREAM and thus does not accept connections. .\" ========== .It Bq Er EWOULDBLOCK .Fa socket is marked as non-blocking and no connections are present to be accepted. .El .Sh LEGACY SYNOPSIS .Fd #include <sys/types.h> .Fd #include <sys/socket.h> .Pp The include file .In sys/types.h is necessary. .Sh SEE ALSO .Xr bind 2 , .Xr connect 2 , .Xr listen 2 , .Xr select 2 , .Xr socket 2 , .Xr compat 5 .Sh HISTORY The .Fn accept function appeared in .Bx 4.2 .