So you're running the stock lwIP that comes with ESP32? If so, I don't
know how "vanilla" this is and how they keep their copy of lwIP up to
I checked the source. Anyway it is not vanilla, and moreover it is a quite old version, so recv ignores the nonblocking flag.
> - Is it possible to check if any byte is already in the buffer ready to
> be received?
Yes, you can use nonblocking receive. Again, see sockets.c if you need
As I said before there is no nonblocking receive. Are you aware of any other way to check if data is ready to be received or not?