/* nonBlock.c
 *
 * From Richard Stevens book, p.140,
 * 	[Advanced Prog in Unix Envir.]
 *
 * Illlustrating nonblocking I/O
 * We can issue open/read/write and not block.
 * Two ways to get nonblocking I/O for a descriptor:
 * 	-- when we call open to get the descriptor, we
 * 		specify the O_NONBLOCK flag (Sect.3.3)
 * 	-- For an already open descriptor, we call fcntl()
 * 		to turn on the O_NONBLOCK file status flag.
** 
** In file /usr/include/sys/fcntl.h, there is
** the posix style _FNONBLOCK and O_NONBLOCK
 *
 * Chee: 2/15/2005
 * ***************************************************/

// Steven's own header file, in his Appendix B
// #include "ourhdr.h"

#include <sys/types.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>

char buf[1000000];

//////////////////////////////////////////////////
// set_fl is defined in p.66, Program 3.5
void
set_fl(int fd, int flags) // flag=file status flags to turn on
{
	int val;
	if ((val = fcntl(fd, F_GETFL, 0)) < 0)
		perror("fcntl F_GETFL error");
	val |= flags;	// turn on flags
	if (fcntl(fd, F_SETFL, val)<0)
		perror("fcntl F_SETFL error");
}

//////////////////////////////////////////////////
// clr_fl is defined in p.66, Program 3.5
// 	It is just set_fl with one line changed!
void
clr_fl(int fd, int flags) // flag=file status flags to turn on
{
	int val;
	if ((val = fcntl(fd, F_GETFL, 0)) < 0)
		perror("fcntl F_GETFL error");
	val &= ~flags;	// turn off flags
	if (fcntl(fd, F_SETFL, val)<0)
		perror("fcntl F_SETFL error");
}

//////////////////////////////////////////////////
int
main (void)
{
	int ntowrite, nwrite;
	char *ptr;

	ntowrite = read(STDIN_FILENO, buf, sizeof(buf));
	fprintf(stderr, "read %d bytes\n", ntowrite);

	set_fl(STDOUT_FILENO, O_NONBLOCK);	// set nonblocking
	//	

	for (ptr = buf; ntowrite > 0; ){
		errno = 0;
		nwrite = write(STDOUT_FILENO, ptr, ntowrite);
		fprintf(stderr, "nwrite = %d, errno = %d\n", nwrite, errno);
		if (nwrite >0){
			ptr += nwrite;
			ntowrite -= nwrite;
		}
	}
	clr_fl(STDOUT_FILENO, O_NONBLOCK); 	// clear nonblocking

	exit(0);
}