1.\" $NetBSD: accept.2,v 1.20 2002/02/08 01:28:16 ross Exp $ 2.\" 3.\" Copyright (c) 1983, 1990, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)accept.2 8.2 (Berkeley) 12/11/93 35.\" 36.Dd October 22, 2001 37.Dt ACCEPT 2 38.Os 39.Sh NAME 40.Nm accept 41.Nd accept a connection on a socket 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.Fd #include \*[Lt]sys/socket.h\*[Gt] 46.Ft int 47.Fn accept "int s" "struct sockaddr * restrict addr" "socklen_t * restrict addrlen" 48.Sh DESCRIPTION 49The argument 50.Fa s 51is a socket that has been created with 52.Xr socket 2 , 53bound to an address with 54.Xr bind 2 , 55and is listening for connections after a 56.Xr listen 2 . 57The 58.Fn accept 59argument 60extracts the first connection request 61on the queue of pending connections, creates 62a new socket with the same properties of 63.Fa s 64and allocates a new file descriptor 65for the socket. If no pending connections are 66present on the queue, and the socket is not marked 67as non-blocking, 68.Fn accept 69blocks the caller until a connection is present. 70If the socket is marked non-blocking and no pending 71connections are present on the queue, 72.Fn accept 73returns an error as described below. 74The accepted socket 75may not be used 76to accept more connections. The original socket 77.Fa s 78remains open. 79.Pp 80The argument 81.Fa addr 82is a result parameter that is filled in with 83the address of the connecting entity, 84as known to the communications layer. 85The exact format of the 86.Fa addr 87parameter is determined by the domain in which the communication 88is occurring. 89The 90.Fa addrlen 91is a value-result parameter; it should initially contain the 92amount of space pointed to by 93.Fa addr ; 94on return it will contain the actual length (in bytes) of the 95address returned. 96This call 97is used with connection-based socket types, currently with 98.Dv SOCK_STREAM . 99.Pp 100It is possible to 101.Xr select 2 102or 103.Xr poll 2 104a socket for the purposes of doing an 105.Fn accept 106by selecting or polling it for read. 107.Pp 108For certain protocols which require an explicit confirmation, 109such as 110.Tn ISO 111or 112.Tn DATAKIT , 113.Fn accept 114can be thought of 115as merely dequeuing the next connection 116request and not implying confirmation. 117Confirmation can be implied by a normal read or write on the new 118file descriptor, and rejection can be implied by closing the 119new socket. 120.Pp 121One can obtain user connection request data without confirming 122the connection by issuing a 123.Xr recvmsg 2 124call with an 125.Fa msg_iovlen 126of 0 and a non-zero 127.Fa msg_controllen , 128or by issuing a 129.Xr getsockopt 2 130request. 131Similarly, one can provide user connection rejection information 132by issuing a 133.Xr sendmsg 2 134call with providing only the control information, 135or by calling 136.Xr setsockopt 2 . 137.Sh RETURN VALUES 138The call returns \-1 on error. If it succeeds, it returns a non-negative 139integer that is a descriptor for the accepted socket. 140.Sh ERRORS 141The 142.Fn accept 143will fail if: 144.Bl -tag -width Er 145.It Bq Er EBADF 146The descriptor is invalid. 147.It Bq Er EINVAL 148The socket has not been set up to accept connections (using 149.Xr bind 2 150and 151.Xr listen 2 ) . 152.It Bq Er ENOTSOCK 153The descriptor references a file, not a socket. 154.It Bq Er EOPNOTSUPP 155The referenced socket is not of type 156.Dv SOCK_STREAM . 157.It Bq Er EFAULT 158The 159.Fa addr 160parameter is not in a writable part of the 161user address space. 162.It Bq Er EAGAIN 163The socket is marked non-blocking and no connections 164are present to be accepted. 165.It Bq Er EMFILE 166The per-process descriptor table is full. 167.It Bq Er ENFILE 168The system file table is full. 169.It Bq Er ECONNABORTED 170A connection has been aborted. 171.El 172.Sh SEE ALSO 173.Xr bind 2 , 174.Xr connect 2 , 175.Xr listen 2 , 176.Xr poll 2 , 177.Xr select 2 , 178.Xr socket 2 179.Sh HISTORY 180The 181.Fn accept 182function appeared in 183.Bx 4.2 . 184