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

/* Read n bytes from the file descriptor fd and place them into the memory region 
 * referred to by vptr.  This function handles errors and some buffer management.
 */

ssize_t		
readn(int fd, void *vptr, size_t n)
{
    size_t	nleft;
    ssize_t	nread;
    char	*ptr;
    
    ptr = vptr;
    nleft = n;
    while (nleft > 0) {
	if ( (nread = read(fd, ptr, nleft)) < 0) {
	    if (errno == EINTR)
		nread = 0;		/* and call read() again */
	    else
		return(-1);
	} else if (nread == 0)
	    break;				/* EOF */
	
	nleft -= nread;
	ptr   += nread;
    }
    return(n - nleft);		/* return >= 0 */
}

/* A public wrapper for readn that prints an error message if readn fails.
 */
ssize_t
Readn(int fd, void *ptr, size_t nbytes)
{
    ssize_t n;
    
    if ( (n = readn(fd, ptr, nbytes)) < 0)
	perror("readn error");
    return(n);
}