Nestjs TS2339: Property buffer does not exist on type File

Question

In my NestJs application I have a file that is coming from a controller endpoint and it looks like this:

const file = {
  fieldname: "file",
  originalname: "filename.png",
  encoding: "7bit",
  mimetype: "image/jpeg",
  buffer: BufferObject,
  size: 2751
}

To parse the file and get data from it I use the following function:

public async fileOperation(file: File): Promise<OperationResult> {
  const uploadedData = file.buffer.toString();
  ...

However, this code doesn't compile: TS2339: Property buffer does not exist on type File.

What did you try and what were you expecting?
I'm trying to make an operation in an uploaded file without the use of any.
The current code looks like this, it complies and its functional:

public async fileOperation(file: any): Promise<OperationResult> {
  // eslint-disable-next-line @typescript-eslint/no-unsafe-call,@typescript-eslint/no-unsafe-member-access,@typescript-eslint/no-unsafe-assignment
  const uploadedData = file.buffer.toString();
  ...

I expect to have a native type that can define the uploaded file.

Answer 1

Thanks to Jay McDoniel's comment I was able to solve this the following way: First npm install -D @types/multer which was not installed in my application.
Then:

public async fileOperation(file: Express.Multer.File): Promise<OperationResult> {
  const uploadedData = file.buffer.toString();