SOCKATMARK(3) | Library Functions Manual | SOCKATMARK(3) |
sockatmark
—
determine whether the read pointer is at the out-of-band
data mark
#include
<sys/socket.h>
int
sockatmark
(int
s);
The sockatmark
() function returns 1 if the
read pointer for the socket s is currently at the
out-of-band data mark. Otherwise, it returns 0 if the socket doesn't have an
out-of-band data mark or if there is normal data to be received before the
mark.
Upon successful completion, the
sockatmark
() function returns the value 1 if the
read pointer is pointing at the out-of-band data mark, 0 if it is not.
Otherwise the value -1 is returned and the global variable
errno is set to indicate the error.
The routine used in the historical 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 mark; char waste[BUFSIZ]; for (;;) { if ((mark = sockatmark(rem)) == -1) { perror("sockatmark"); break; } if (mark) break; (void) read(rem, waste, sizeof (waste)); } if (recv(rem, &mark, 1, MSG_OOB) == -1) { perror("recv"); ... } ... }
The sockatmark
() call fails if:
The sockatmark
() function conforms to
IEEE Std 1003.1-2008 (“POSIX.1”).
The sockatmark
() function was introduced
by IEEE Std 1003.1-2001 (“POSIX.1”) to
standardize the historical SIOCATMARK
ioctl(2). The
sockatmark
() function appeared in
OpenBSD 5.7.
The ENOTTY
error is returned instead of
the usual ENOTSOCK
error to match the historical
behavior of SIOCATMARK
.
June 20, 2019 | OpenBSD-current |