在Express（node.js）中动态限制上传文件大小

我正在开发一个简单的应用程序，允许用户上传他们的内容。我想限制Express将接受的文件大小。我知道我可以使用

I'm developing a simple app that will allow users to upload their content. I want to limit the file size which Express will accept. I know I can use

app.use(express.limit('2mb'));

但我想要动态更改限制。某些用户将有更高的限制。

but I want to change the limit dynamically. Certain users will have higher limits.

最好的解决方案是FIRST检查 content-length 标题和THEN如果文件大小低于限制，则开始解析上传，但Express会自动将文件上传到磁盘（/ tmp目录）。所以如果有人发送1GB的文件，这个文件将被解析并保存到磁盘，即使我不想允许。

The best solution would be to FIRST check the content-length header and THEN start to parse the upload if file size is below the limit but Express automatically saves file uploads to disk (/tmp directory). So if someone sends 1GB file, this file will be parsed and saved to disk even when I don't want to allow that.

提前感谢！