/*
 * copy-file-syscalls.c
 *
 * usage: ./copy-file source-file destination-file
 */

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

#define BYTES_PER_ITERATION 10240

int
main(int argc, char *argv[])
{
    int src_fd, dst_fd;
    char *src_filename, *dst_filename;
    int n;
    char buf[BYTES_PER_ITERATION];

    /* check command-line args */
    if(argc != 3) {
        printf("usage: %s src_filename dst_filename\n", argv[0]);
        exit(1);
    }
    src_filename = argv[1];
    dst_filename = argv[2];

    /* open files */
    if((src_fd = open(src_filename, O_RDONLY)) < 0) {
        perror("open");
        exit(2);
    }

    if((dst_fd = open(dst_filename, O_CREAT | O_WRONLY, 0666)) < 0) {
        perror("open");
        exit(3);
    }

    /* do the copy */
    while((n = read(src_fd, buf, BYTES_PER_ITERATION)) > 0) {
        n = write(dst_fd, buf, n);
        if(n < 0) {
            perror("write");
            exit(4);
        }
    }

    /* according to the read(2) manpage, it returns 0 on EOF and negative on 
     * error */
    if(n < 0) {
        perror("read");
        exit(5);
    }

    /* clean up */
    close(src_fd);
    close(dst_fd);
}