233 lines
6.1 KiB
Groff
233 lines
6.1 KiB
Groff
|
.\" $OpenBSD: accept.2,v 1.30 2022/09/11 06:38:11 jmc Exp $
|
||
|
.\" $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. 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 $Mdocdate: September 11 2022 $
|
||
|
.Dt ACCEPT 2
|
||
|
.Os
|
||
|
.Sh NAME
|
||
|
.Nm accept ,
|
||
|
.Nm accept4
|
||
|
.Nd accept a connection on a socket
|
||
|
.Sh SYNOPSIS
|
||
|
.In sys/socket.h
|
||
|
.Ft int
|
||
|
.Fn accept "int s" "struct sockaddr *addr" "socklen_t *addrlen"
|
||
|
.Ft int
|
||
|
.Fn accept4 "int s" "struct sockaddr *addr" "socklen_t *addrlen" "int flags"
|
||
|
.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
|
||
|
call extracts the first connection request on the queue of pending
|
||
|
connections, creates a new socket with the same non-blocking I/O mode as
|
||
|
.Fa s ,
|
||
|
and allocates a new file descriptor for the socket with the
|
||
|
close-on-exec flag clear.
|
||
|
.Pp
|
||
|
The
|
||
|
.Fn accept4
|
||
|
system call is similar, however the non-blocking I/O mode of the
|
||
|
new socket is determined by the
|
||
|
.Dv SOCK_NONBLOCK
|
||
|
flag in the
|
||
|
.Fa flags
|
||
|
argument and the close-on-exec flag on the new file descriptor is
|
||
|
determined by the
|
||
|
.Dv SOCK_CLOEXEC
|
||
|
flag in the
|
||
|
.Fa flags
|
||
|
argument.
|
||
|
.Pp
|
||
|
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 structure
|
||
|
.Vt sockaddr_storage
|
||
|
exists for greater portability.
|
||
|
It is large enough to hold any of the types that may be returned in the
|
||
|
.Fa addr
|
||
|
parameter.
|
||
|
.Pp
|
||
|
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.
|
||
|
If
|
||
|
.Fa addrlen
|
||
|
does not point to enough space to hold the entire socket address, the
|
||
|
result will be truncated to the initial value of
|
||
|
.Fa addrlen
|
||
|
(in bytes).
|
||
|
This call is used with connection-based socket types, currently with
|
||
|
.Dv SOCK_STREAM .
|
||
|
.Pp
|
||
|
It is possible to
|
||
|
.Xr select 2
|
||
|
or
|
||
|
.Xr poll 2
|
||
|
a socket for the purposes of doing an
|
||
|
.Fn accept
|
||
|
by selecting it for read.
|
||
|
.Sh RETURN VALUES
|
||
|
If successful,
|
||
|
.Fn accept
|
||
|
and
|
||
|
.Fn accept4
|
||
|
return a non-negative integer, the accepted socket file descriptor.
|
||
|
Otherwise, a value of \-1 is returned and
|
||
|
.Va errno
|
||
|
is set to indicate the error.
|
||
|
.Sh EXAMPLES
|
||
|
The following code uses struct
|
||
|
.Vt sockaddr_storage
|
||
|
to allocate enough space for the returned address:
|
||
|
.Bd -literal -offset indent
|
||
|
#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");
|
||
|
.Ed
|
||
|
.Sh ERRORS
|
||
|
.Fn accept
|
||
|
and
|
||
|
.Fn accept4
|
||
|
will fail if:
|
||
|
.Bl -tag -width Er
|
||
|
.It Bq Er EBADF
|
||
|
The descriptor is invalid.
|
||
|
.It Bq Er ENOTSOCK
|
||
|
The descriptor doesn't reference a socket.
|
||
|
.It Bq Er EOPNOTSUPP
|
||
|
The referenced socket is not of type
|
||
|
.Dv SOCK_STREAM .
|
||
|
.It Bq Er EINTR
|
||
|
A signal was caught before a connection arrived.
|
||
|
.It Bq Er EINVAL
|
||
|
The referenced socket is not listening for connections (that is,
|
||
|
.Xr listen 2
|
||
|
has not yet been called).
|
||
|
.It Bq Er EFAULT
|
||
|
The
|
||
|
.Fa addr
|
||
|
or
|
||
|
.Fa addrlen
|
||
|
parameter is not in a valid part of the process 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.
|
||
|
.It Bq Er ECONNABORTED
|
||
|
A connection has been aborted.
|
||
|
.El
|
||
|
.Pp
|
||
|
In addition,
|
||
|
.Fn accept4
|
||
|
will fail if
|
||
|
.Bl -tag -width Er
|
||
|
.It Bq Er EINVAL
|
||
|
.Fa flags
|
||
|
is invalid.
|
||
|
.El
|
||
|
.Sh SEE ALSO
|
||
|
.Xr bind 2 ,
|
||
|
.Xr connect 2 ,
|
||
|
.Xr listen 2 ,
|
||
|
.Xr poll 2 ,
|
||
|
.Xr select 2 ,
|
||
|
.Xr socket 2
|
||
|
.Sh STANDARDS
|
||
|
The
|
||
|
.Fn accept
|
||
|
function conforms to
|
||
|
.St -p1003.1-2008 .
|
||
|
The
|
||
|
.Fn accept4
|
||
|
function is expected to conform to a future revision of that standard.
|
||
|
.Sh HISTORY
|
||
|
The
|
||
|
.Fn accept
|
||
|
system call first appeared in
|
||
|
.Bx 4.1c
|
||
|
and
|
||
|
.Fn accept4
|
||
|
in
|
||
|
.Ox 5.7 .
|
||
|
.Sh CAVEATS
|
||
|
When
|
||
|
.Er EMFILE
|
||
|
or
|
||
|
.Er ENFILE
|
||
|
is returned,
|
||
|
new connections are neither dequeued nor discarded.
|
||
|
Thus considerable care is required in
|
||
|
.Xr select 2
|
||
|
and
|
||
|
.Xr poll 2
|
||
|
loops.
|