Function us_socket_context_on_close 

pub unsafe extern "C" fn us_socket_context_on_close(
    ssl: c_int,
    context: *mut us_socket_context_t,
    on_close: Option<unsafe extern "C" fn(s: *mut us_socket_t, code: c_int, reason: *mut c_void) -> *mut us_socket_t>,
)