#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>


/**
 * @brief
 * @details
 *       Usage: mycpy <src> <dst> <bufsize>
 *
 * @param    argc
 * @param    argv
 *
 * @return  int
 */
int main(int argc, char** argv)
{
    if (argc < 4)
    {
        fprintf(stderr, "Usage: %s <src> <dst> <bufsize>\n", argv[0]);
        exit(1);
    }

    int bufsize = atoi(argv[3]);

    int  sfd, dfd;
    char buf[bufsize];
    int  len, ret, pos;

    sfd = open(argv[1], O_RDONLY);
    if (sfd < 0)
    {
        perror("open");
        exit(1);
    }

    dfd = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0600);
    if (dfd < 0)
    {
        // !!!
        close(sfd);
        perror("open");
        exit(1);
    }

    while (1)
    {
        len = read(sfd, buf, bufsize);
        if (len < 0)
        {
            perror("read");
            break;
        }
        if (len == 0)
            break;

        pos = 0;
        while (len > 0)
        {
            /* 可能没写完被别的中断打断 */
            ret = write(dfd, buf + pos, len);
            if (ret < 0)
            {
                perror("write");
                exit(1);
            }
            pos += ret;
            len -= ret;
        }
    }

    close(dfd);
    close(sfd);

    exit(0);
}