.\" Copyright (c) 2002 William C. Fenner.  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.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE 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.
.\"
.\" $FreeBSD: src/lib/libc/net/sockatmark.3,v 1.4 2002/12/19 09:40:22 ru Exp $
.\"
.Dd October 13, 2002
.Dt SOCKATMARK 3
.Os
.Sh NAME
.Nm sockatmark
.Nd determine whether the read pointer is at the OOB mark
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/socket.h
.Ft int
.Fn sockatmark "int s"
.Sh DESCRIPTION
To find out if the read pointer is currently pointing at
the mark in the data stream, the
.Fn sockatmark
function is provided.
If
.Fn sockatmark
returns 1, the next read will return data
after the mark.
Otherwise (assuming out of band data has arrived),
the next read will provide data sent by the client prior
to transmission of the out of band signal.
The routine used
in the remote login process to flush output on receipt of an
interrupt or quit signal is shown below.
It reads the normal data up to the mark (to discard it),
then reads the out-of-band byte.
.Bd -literal -offset indent
#include <sys/socket.h>
\&...
void
oob(void)
{
	int out = FWRITE, mark;
	char waste[BUFSIZ];

	/* flush local terminal output */
	ioctl(1, TIOCFLUSH, (char *)&out);
	for (;;) {
		if ((mark = sockatmark(rem)) < 0) {
			perror("sockatmark");
			break;
		}
		if (mark)
			break;
		read(rem, waste, sizeof (waste));
	}
	if (recv(rem, &mark, 1, MSG_OOB) < 0) {
		perror("recv");
		...
	}
	...
}
.Ed
.Sh RETURN VALUES
Upon successful completion, the
.Fn sockatmark
function returns the value 1 if the read pointer is pointing at
the OOB mark, 0 if it is not.
Otherwise the value \-1 is returned
and the global variable
.Va errno
is set to
indicate the error.
.Sh ERRORS
The
.Fn sockatmark
call fails if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa s
argument
is not a valid descriptor.
.It Bq Er ENOTTY
The
.Fa s
argument
is a descriptor for a file, not a socket.
.El
.Sh SEE ALSO
.Xr recv 2 ,
.Xr send 2
.Sh HISTORY
The
.Fn sockatmark
function was introduced by
.St -p1003.1-2001 ,
to standardize the historical
.Dv SIOCATMARK
.Xr ioctl 2 .
The
.Er ENOTTY
error instead of the usual
.Er ENOTSOCK
is to match the historical behavior of
.Dv SIOCATMARK .