sendfile.c

ssize_t
nxs_sendfile(const int out_fd, const int in_fd,
    off_t *offset, const size_t size) {

#if defined(__linux__)

    const ssize_t nw = sendfile(out_fd, in_fd, offset, size);
    return nw;

#elif defined(__FreeBSD__)

    off_t sbytes = 0;
    const ssize_t nw = sendfile(in_fd, out_fd, *offset, size,
            NULL, &sbytes,
            /* FreeBSD: need to wait for file fd read event ? */
            /* SF_MNOWAIT | SF_NODISKIO */
            0);
    *offset += sbytes;

    T("out=%d in=%d *offset=%ld size=%lu nw=%ld sbytes=%ld", out_fd, in_fd,
        *offset, size, nw, sbytes
    );
    return sbytes;

#elif defined(__APPLE__)

    off_t len = size;
    const int r =sendfile(in_fd, out_fd, *offset, &len, NULL, 0);
    *offset += len;
    return 0 == r ? len : -1;

#endif
}