What is the output of a piped file stream?

Perhaps the question is not worded in the greatest way but here's some more context. Using GridFSBucket, I'm able to store a file in mongo and obtain a download stream for that file. Here's my question. Let's say I wanted to send that file back as a response to my http request.

I do:

downloadStream.pipe(res);

On the client side now when I print the responseText, I get some long string with some funky characters that look to be encrypted. What is the format/type of this string/stream? How do I setup my response so that I can get the streamed data as an ArrayBuffer on my client side?

Thanks

via ribarcheto94