How to handle incoming requests in a Flutter app?

Question

Mobile development

Good afternoon.
Let's say there is a flutter application built for web.
Let's say I launched it at localhost:9000.

For example, I'll send a request to it from the terminal:

curl --request POST -d 'test_raw_data' http://localhost:9000

How can I process an incoming POST request in an application?

Thank you all in advance for your replies =)