[apple/xnu.git] / bsd / man / man2 / accept.2

.\"	$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/types.h>
.Fd #include <sys/socket.h>
.Ft int
.Fn accept "int s" "struct sockaddr *addr" "socklen_t *addrlen"
.Sh DESCRIPTION
The argument
.Fa s
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 .
The
.Fn accept
argument
extracts the first connection request
on the queue of pending connections, creates
a new socket with the same properties of 
.Fa 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,
.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 s
remains open.
.Pp
The argument
.Fa 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
.Fa addr
parameter is determined by the domain in which the communication
is occurring.
The 
.Fa addrlen
is a value-result parameter; it should initially contain the
amount of space pointed to by
.Fa 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
.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.  If it succeeds, it returns a non-negative
integer that is a descriptor for the accepted socket.
.Sh ERRORS
The
.Fn accept
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The descriptor is invalid.
.It Bq Er ENOTSOCK
The descriptor references a file, not a socket.
.It Bq Er EOPNOTSUPP
The referenced socket is not of type
.Dv SOCK_STREAM . 
.It Bq Er EFAULT
The
.Fa addr
parameter is not in a writable part of the
user address space.
.It Bq Er EWOULDBLOCK
The socket is marked non-blocking and no connections
are present to be accepted.
.It Bq Er EMFILE
The per-process descriptor table is full.
.It Bq Er ENFILE
The system file table is full.
.El
.Sh SEE ALSO
.Xr bind 2 ,
.Xr connect 2 ,
.Xr listen 2 ,
.Xr select 2 ,
.Xr socket 2
.Sh HISTORY
The
.Fn accept
function appeared in 
.Bx 4.2 .
Commit	Line	Data
9bccf70c A	1	.\" $NetBSD: accept.2,v 1.7 1996/01/31 20:14:42 mycroft 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 December 11, 1993
	37	.Dt ACCEPT 2
	38	.Os BSD 4.2
	39	.Sh NAME
	40	.Nm accept
	41	.Nd accept a connection on a socket
	42	.Sh SYNOPSIS
	43	.Fd #include <sys/types.h>
	44	.Fd #include <sys/socket.h>
	45	.Ft int
91447636	46	.Fn accept "int s" "struct sockaddr addr" "socklen_t addrlen"
9bccf70c A	47	.Sh DESCRIPTION
	48	The argument
	49	.Fa s
	50	is a socket that has been created with
	51	.Xr socket 2 ,
	52	bound to an address with
	53	.Xr bind 2 ,
	54	and is listening for connections after a
	55	.Xr listen 2 .
	56	The
	57	.Fn accept
	58	argument
	59	extracts the first connection request
	60	on the queue of pending connections, creates
	61	a new socket with the same properties of
	62	.Fa s
	63	and allocates a new file descriptor
	64	for the socket. If no pending connections are
	65	present on the queue, and the socket is not marked
	66	as non-blocking,
	67	.Fn accept
	68	blocks the caller until a connection is present.
	69	If the socket is marked non-blocking and no pending
	70	connections are present on the queue,
	71	.Fn accept
	72	returns an error as described below.
	73	The accepted socket
	74	may not be used
	75	to accept more connections. The original socket
	76	.Fa s
	77	remains open.
	78	.Pp
	79	The argument
	80	.Fa addr
	81	is a result parameter that is filled in with
	82	the address of the connecting entity,
	83	as known to the communications layer.
	84	The exact format of the
	85	.Fa addr
	86	parameter is determined by the domain in which the communication
	87	is occurring.
	88	The
	89	.Fa addrlen
	90	is a value-result parameter; it should initially contain the
	91	amount of space pointed to by
	92	.Fa addr ;
	93	on return it will contain the actual length (in bytes) of the
	94	address returned.
	95	This call
	96	is used with connection-based socket types, currently with
	97	.Dv SOCK_STREAM .
	98	.Pp
	99	It is possible to
	100	.Xr select 2
	101	a socket for the purposes of doing an
	102	.Fn accept
	103	by selecting it for read.
	104	.Pp
	105	For certain protocols which require an explicit confirmation,
	106	such as
	107	.Tn ISO
	108	or
	109	.Tn DATAKIT ,
	110	.Fn accept
111	can be thought of
112	as merely dequeuing the next connection
113	request and not implying confirmation.
114	Confirmation can be implied by a normal read or write on the new
115	file descriptor, and rejection can be implied by closing the
116	new socket.
117	.Pp
118	One can obtain user connection request data without confirming
119	the connection by issuing a
120	.Xr recvmsg 2
121	call with an
122	.Fa msg_iovlen
123	of 0 and a non-zero
124	.Fa msg_controllen ,
125	or by issuing a
126	.Xr getsockopt 2
127	request.
128	Similarly, one can provide user connection rejection information
129	by issuing a
130	.Xr sendmsg 2
131	call with providing only the control information,
132	or by calling
133	.Xr setsockopt 2 .
134	.Sh RETURN VALUES
135	The call returns \-1 on error. If it succeeds, it returns a non-negative
136	integer that is a descriptor for the accepted socket.
137	.Sh ERRORS
138	The
139	.Fn accept
140	will fail if:
141	.Bl -tag -width Er
142	.It Bq Er EBADF
143	The descriptor is invalid.
144	.It Bq Er ENOTSOCK
145	The descriptor references a file, not a socket.
146	.It Bq Er EOPNOTSUPP
147	The referenced socket is not of type
148	.Dv SOCK_STREAM .
149	.It Bq Er EFAULT
150	The
151	.Fa addr
152	parameter is not in a writable part of the
153	user address space.
154	.It Bq Er EWOULDBLOCK
155	The socket is marked non-blocking and no connections
156	are present to be accepted.
157	.It Bq Er EMFILE
158	The per-process descriptor table is full.
159	.It Bq Er ENFILE
160	The system file table is full.
161	.El
162	.Sh SEE ALSO
163	.Xr bind 2 ,
164	.Xr connect 2 ,
165	.Xr listen 2 ,
166	.Xr select 2 ,
167	.Xr socket 2
168	.Sh HISTORY
169	The
170	.Fn accept
171	function appeared in
172	.Bx 4.2 .