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)
|