Function safe_app::ffi::mutable_data::mdata_get_value

#[no_mangle]
pub unsafe extern "C" fn mdata_get_value(
    app: *const App, 
    info_h: MDataInfoHandle, 
    key_ptr: *const u8, 
    key_len: usize, 
    user_data: *mut c_void, 
    o_cb: extern "C" fn(_: *mut c_void, _: FfiResult, _: *const u8, _: usize, _: u64)
)

Get value at the given key from the mutable data. The arguments to the callback are: 1. user data 2. error code 3. pointer to content 4. content length 5. entry version

Please notice that if a value is fetched from a private MutableData, it's not automatically decrypted.