Sending a csv file via HTTP

The send_location_to_server.py example works flawlessly on my Pico LTE using Webhook.site. Now I would like to send a file via HTTP. I can do this easily with the requests library on a PC to Webhook.site. How can I do it on my Pico LTE?

I tried the post_from_file() function in post.py but I think I misunderstood the purpose of that function - I think it assumes I have json or something of the post header, body, etc in that file - is that right? So is there a way to send a csv file via HTTP?

And follow-up question: I understand I could just read the file and post it as text. I was hoping to reduce memory use. Is that possible or will whatever solution is available with the PicoLTE libraries just upload the whole file to memory anyway?