setPath

    pub fn setPath(w: *Header, prefix: []const u8, sub_path: []const u8) !void {
        const max_prefix = w.prefix.len;
        const max_name = w.name.len;
        const sep = std.fs.path.sep_posix;

        if (prefix.len + sub_path.len > max_name + max_prefix or prefix.len > max_prefix)
            return error.NameTooLong;

        // both fit into name
        if (prefix.len > 0 and prefix.len + sub_path.len < max_name) {
            @memcpy(w.name[0..prefix.len], prefix);
            w.name[prefix.len] = sep;
            @memcpy(w.name[prefix.len + 1 ..][0..sub_path.len], sub_path);
            return;
        }

        // sub_path fits into name
        // there is no prefix or prefix fits into prefix
        if (sub_path.len <= max_name) {
            @memcpy(w.name[0..sub_path.len], sub_path);
            @memcpy(w.prefix[0..prefix.len], prefix);
            return;
        }

        if (prefix.len > 0) {
            @memcpy(w.prefix[0..prefix.len], prefix);
            w.prefix[prefix.len] = sep;
        }
        const prefix_pos = if (prefix.len > 0) prefix.len + 1 else 0;

        // add as much to prefix as you can, must split at /
        const prefix_remaining = max_prefix - prefix_pos;
        if (std.mem.findLast(u8, sub_path[0..@min(prefix_remaining, sub_path.len)], &.{'/'})) |sep_pos| {
            @memcpy(w.prefix[prefix_pos..][0..sep_pos], sub_path[0..sep_pos]);
            if ((sub_path.len - sep_pos - 1) > max_name) return error.NameTooLong;
            @memcpy(w.name[0..][0 .. sub_path.len - sep_pos - 1], sub_path[sep_pos + 1 ..]);
            return;
        }

        return error.NameTooLong;
    }