sockatmark(3) [mojave man page]

SOCKATMARK(3)						   BSD 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)

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.

BSD
								 October 13, 2002							       BSD

SOCKATMARK(3)						     Linux Programmer's Manual						     SOCKATMARK(3)

NAME

       sockatmark - determine whether socket is at out-of-band mark

SYNOPSIS

       #include <sys/socket.h>

       int sockatmark(int sockfd);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sockatmark(): _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600

DESCRIPTION

       sockatmark() returns a value indicating whether or not the socket referred to by the file descriptor sockfd 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.

RETURN VALUE

       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.

ERRORS

       EBADF  sockfd is not a valid file descriptor.

       EINVAL sockfd is not a file descriptor to which sockatmark() can be applied.

VERSIONS

       sockatmark() was added to glibc in version 2.2.4.

CONFORMING TO

       POSIX.1-2001.

NOTES

       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.

BUGS

       Prior to glibc 2.4, sockatmark() did not work.

EXAMPLE

       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(sockfd);
	       if (atmark == -1) {
		   perror("sockatmark");
		   break;
	       }

	       if (atmark)
		   break;

	       s = read(sockfd, buf, BUF_LEN) <= 0);
	       if (s == -1)
		   perror("read");
	       if (s <= 0)
		   break;
	   }

	   if (atmark == 1) {
	       if (recv(sockfd, &oobdata, 1, MSG_OOB) == -1) {
		   perror("recv");
		   ...
	       }
	   }

SEE ALSO

       fcntl(2), recv(2), send(2), tcp(7)

COLOPHON

       This  page is part of release 3.44 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2008-12-03							     SOCKATMARK(3)