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Command: sockatmark | Section: 3 | Source: FreeBSD | File: sockatmark.3.gz
SOCKATMARK(3) FreeBSD Library Functions Manual SOCKATMARK(3)
NAME
sockatmark - determine whether the read pointer is at the OOB mark
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/socket.h>
int
sockatmark(int s);
DESCRIPTION
To find out if the read pointer is currently pointing at the mark in the
data stream, the sockatmark() function is provided. If 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.
#include <sys/socket.h>
...
oob()
{
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;
(void) read(rem, waste, sizeof (waste));
}
if (recv(rem, &mark, 1, MSG_OOB) < 0) {
perror("recv");
...
}
...
}
RETURN VALUES
Upon successful completion, the 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 errno is set
to indicate the error.
ERRORS
The sockatmark() call fails if:
[EBADF] The s argument is not a valid descriptor.
[ENOTTY] The s argument is a descriptor for a file, not a
socket.
SEE ALSO
recv(2), send(2)
Stuart Sechrest, An Introductory 4.4BSD Interprocess Communication
Tutorial. https://docs.freebsd.org/44doc/psd/20.ipctut/paper.pdf
Samuel J. Leffler, Robert S. Fabry, William N. Joy, Phil Lapsley, Steve
Miller, and Chris Torek, An Advanced 4.4BSD Interprocess Communication
Tutorial, https://docs.freebsd.org/44doc/psd/21.ipc/paper.pdf.
HISTORY
The sockatmark() function was introduced by IEEE Std 1003.1-2001
("POSIX.1"), to standardize the historical SIOCATMARK ioctl(2). The
ENOTTY error instead of the usual ENOTSOCK is to match the historical
behavior of SIOCATMARK.
FreeBSD 14.1-RELEASE-p8 July 3, 2022 FreeBSD 14.1-RELEASE-p8