Function pio_to_json 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_to_json(
    net: *const PioNetwork,
    errbuf: *mut c_char,
    errlen: usize,
) -> *mut c_char

Serialize net to its model JSON: the same object a .pio.json package carries under model.balanced_network, without the surrounding document, and the same text the powerio-json format token writes. This is the bindings’ data transport; the token remains as a compatibility alias for file based workflows. Returns an owned C string (free with pio_string_free), NULL on error.