1.\" Copyright (c) 1983, 1990, 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)accept.2 6.6 (Berkeley) 4/29/91 33.\" 34.Dd April 29, 1991 35.Dt ACCEPT 2 36.Os BSD 4.2 37.Sh NAME 38.Nm accept 39.Nd accept a connection on a socket 40.Sh SYNOPSIS 41.Fd #include <sys/types.h> 42.Fd #include <sys/socket.h> 43.Ft int 44.Fn accept "int s" "struct sockaddr *addr" "int *addrlen" 45.Sh DESCRIPTION 46The argument 47.Fa s 48is a socket that has been created with 49.Xr socket 2 , 50bound to an address with 51.Xr bind 2 , 52and is listening for connections after a 53.Xr listen 2 . 54The 55.Fn accept 56argument 57extracts the first connection request 58on the queue of pending connections, creates 59a new socket with the same properties of 60.Fa s 61and allocates a new file descriptor 62for the socket. If no pending connections are 63present on the queue, and the socket is not marked 64as non-blocking, 65.Fn accept 66blocks the caller until a connection is present. 67If the socket is marked non-blocking and no pending 68connections are present on the queue, 69.Fn accept 70returns an error as described below. 71The accepted socket 72may not be used 73to accept more connections. The original socket 74.Fa s 75remains open. 76.Pp 77The argument 78.Fa addr 79is a result parameter that is filled in with 80the address of the connecting entity, 81as known to the communications layer. 82The exact format of the 83.Fa addr 84parameter is determined by the domain in which the communication 85is occurring. 86The 87.Fa addrlen 88is a value-result parameter; it should initially contain the 89amount of space pointed to by 90.Fa addr ; 91on return it will contain the actual length (in bytes) of the 92address returned. 93This call 94is used with connection-based socket types, currently with 95.Dv SOCK_STREAM . 96.Pp 97It is possible to 98.Xr select 2 99a socket for the purposes of doing an 100.Fn accept 101by selecting it for read. 102.Pp 103For certain protocols which require an explicit confirmation, 104such as 105.Tn ISO 106or 107.Tn DATAKIT , 108.Fn accept 109can be thought of 110as merely dequeueing the next connection 111request and not implying confirmation. 112Confirmation can be implied by a normal read or write on the new 113file desciptor, and rejection can be implied by closing the 114new socket. 115.Pp 116One can obtain user connection request data without confirming 117the connection by issuing a 118.Xr recvmsg 2 119call with an 120.Fa msg_iovlen 121of 0 and a non-zero 122.Fa msg_controllen , 123or by issuing a 124.Xr getsockopt 2 125request. 126Similarly, one can provide user connection rejection information 127by issuing a 128.Xr sendmsg 2 129call with providing only the control information, 130or by calling 131.Xr setsockopt 2 . 132.Sh RETURN VALUES 133The call returns \-1 on error. If it succeeds, it returns a non-negative 134integer that is a descriptor for the accepted socket. 135.Sh ERRORS 136The 137.Fn accept 138will fail if: 139.Bl -tag -width EWOULDBLOCK 140.It Bq Er EBADF 141The descriptor is invalid. 142.It Bq Er ENOTSOCK 143The descriptor references a file, not a socket. 144.It Bq Er EOPNOTSUPP 145The referenced socket is not of type 146.Dv SOCK_STREAM . 147.It Bq Er EFAULT 148The 149.Fa addr 150parameter is not in a writable part of the 151user address space. 152.It Bq Er EWOULDBLOCK 153The socket is marked non-blocking and no connections 154are present to be accepted. 155.El 156.Sh SEE ALSO 157.Xr bind 2 , 158.Xr connect 2 , 159.Xr listen 2 , 160.Xr select 2 , 161.Xr socket 2 162.Sh HISTORY 163The 164.Nm 165function appeared in 166.Bx 4.2 . 167