How to use code written in `std` in `no_std` during runtime?

Question

I have a piece of code written in std, and it is bypassing/not-included in runtime as it should work but I want to use it in runtime environment, is there a way to use it. As the code written in std will not compile with native substrate no_std build.

Basically code is parsing a json and storing its key value in a StorageMap which we will get during runtime and it is a dynamic value which will change after every era.

Piece of code is as follows:

#[pallet::call]
impl<T: Config> Pallet<T> {
    #[pallet::weight(10_000 + T::DbWeight::get().writes(1))]
    pub fn esg_score(origin: OriginFor<T>, json_data: Vec<u8>) -> DispatchResult {
        let signer = ensure_signed(origin)?;
        #[cfg(feature = "std")]
        let parseAndStoreData = |jsonStr: &str| {
            let parsed: ListOfScores = serde_json::from_str(jsonStr).unwrap()
            for item in parsed.0 {
                <GetScore::<T>>::insert(item.account.clone(), item.score);
            }
                                
            #[cfg(feature = "std")]
            parseAndStoreEsgData(&String::from_utf8_lossy(&json_data[..])[..]);         
            Self::deposit_event(Event::Stored(json_data, signer.clone()));
            Ok(())
    }

Answer 1

Check my previous answer: Compiled code withe #[cfg(feature = "std")] and facing issues while setting up staging environment

---

You should transform that code/lib to no_std.

For your example, String is a Vec actually. You should use the Vec<u8> directly.

If you want to play with JSON object, I think there are some crates that provide a json::from_bytes(&json_data) method.

• serde_json no-std support