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)
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.
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.