sockatmark — determine whether socket is at out-of-band mark
#include <sys/socket.h>
int
sockatmark( |
int | fd); |
sockatmark() returns a value
indicating whether or not the socket referred to by the file
descriptor fd is at
the out-of-band mark. If the socket is at the mark, then 1 is
returned; if the socket is not at the mark, 0 is returned.
This function does not remove the out-of-band mark.
A successful call to sockatmark() returns 1 if the socket is at
the out-of-band mark, or 0 if it is not. On error, −1
is returned and errno is set to
indicate the error.
fd is not a
valid file descriptor.
fd is not a
file descriptor to which sockatmark() can be applied.
If sockatmark() returns 1,
then the out-of-band data can be read using the MSG_OOB flag of recv(2).
Out-of-band data is only supported on some stream socket protocols.
sockatmark() can safely be
called from a handler for the SIGURG signal.
sockatmark() is implemented
using the SIOCATMARK ioctl(2) operation.
The following code can be used after receipt of a SIGURG signal to read (and discard) all data up to the mark, and then read the byte of data at the mark:
char buf[BUF_LEN];
char oobdata;
int atmark, s;
for (;;) {
atmark = sockatmark(fd);
if (atmark == −1) {
perror("sockatmark");
break;
}
if (atmark)
break;
s = read(fd, buf, BUF_LEN) <= 0);
if (s == -1)
perror("read");
if (s <= 0)
break;
}
if (atmark == 1) {
if (recv(fd, &oobdata, 1, MSG_OOB) == −1) {
perror("recv");
...
}
}
fcntl(2), recv(2), send(2), tcp(7)
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