Hello ! I'm new to arduino and I would like to know if it is possible to get the current url from a browser. For example if the arduino is connected via usb, and a user is connected to http://monsite.com, can the arduino notice it ? Thanks
That's what the Host: header is for
maximedavid: a user is connected to http://monsite.com, can the arduino notice it ?
If you mean a user on the PC (running a browser on the PC) then the Arduino can't detect that directly. If you're willing and able to run software on the PC, there are ways to detect what page(s) are displayed but they're going to be browser-specific. If you have full control over the PC you could also set up a web proxy which keeps track of what URLs were requested. It's heading towards quite a complicated solution though, and would be trivial to bypass, so if you were thinking of this as some sort of DIY net nanny, I suggest you'd be better off just using a 3rd party implementation.
If your arduino is using an Ethernet shield with server code and you want the ip address of the connecting browser, the below might have info.