How to construct the data structure with correct values for their attributes within a Pallet for data submitted by a polkadotJS app

Question

Client App creates an Input as follows using polkadotJS to submit to Substrate Module as follows

import { ApiPromise, WsProvider } from '@polkadot/api';
const { Keyring } = require('@polkadot/keyring');
import { u8aToHex } from '@polkadot/util';


async function objectToByteArray() {
    let attributes = {
        "current_fraction": 1,
    };
    const jsonString = JSON.stringify(attributes);
    const uint8Array = Uint8Array.from(Buffer.from(jsonString));
    console.log('Uint8Array', uint8Array);
    /*
      [
        123,  34,  99, 117, 114, 114,
        101, 110, 116,  95, 102, 114,
        97,  99, 116, 105, 111, 110,
        34,  58,  49, 125
        ]
    */
    const byteArray = u8aToHex(uint8Array);
    console.log('Byte array', byteArray);
    /*
    Byte array 0x7b2263757272656e745f6672616374696f6e223a317d
    */
}

objectToByteArray();

In Substrate Module Inside a function it greeted by the following function the bytearray will accepts by the value parameter in following function

#[pallet::weight(T::WeightInfo::set_attribute())]
pub fn set_attribute(
    origin: OriginFor<T>,
    collection: T::CollectionId,
    maybe_item: Option<T::ItemId>,
    key: BoundedVec<u8, T::KeyLimit>,
    value: BoundedVec<u8, T::ValueLimit>,
) -> DispatchResult {
    let maybe_check_owner = T::ForceOrigin::try_origin(origin)
    // Code here
    Ok(())
}

I need to reconstruct the original object within pallet and I tried the following Approach

// Mapping Object declared on Substrate side

#[derive(Clone, Encode, Decode, Eq, PartialEq, RuntimeDebug, Default, TypeInfo, MaxEncodedLen)]
pub struct SomeName {
    pub current_fraction: u32,
}

let val = SomeName::decode(&mut &value[..]).map_err(|_| Error::<T, I>::Error)?;

Unfortunately the reconstructioned objects value for curent_fraction shows as 1969431163 instead of 1

How to fix this issue?

Answer 1

JS encode:

const registry = new TypeRegistry();
const someNameInstance = registry.createType('{"current_fraction":"u32"}', { current_fraction: 123 });
const encoded = someNameInstance.toU8a();

console.log('Encoded:', encoded);
// Encoded: Uint8Array(4) [ 123, 0, 0, 0 ]

Rust decode:

#[derive(Debug, Decode)]
pub struct SomeName {
    pub current_fraction: u32,
}

println!("{:?}", SomeName::decode(&mut [123, 0, 0, 0].as_slice()));
// Ok(SomeName { current_fraction: 123 })