Decode of `assetId` hex string fails for signed payload because of `Option`

[Chralt98]

Error: Struct: failed on assetId: Option<MultiLocationV3>:: decodeU8aStruct: failed at 0x010300a10f043205e514… on interior (index 2/2): {"_enum":{"Here":"Null","X1":"JunctionV3","X2":"(JunctionV3,JunctionV3)","X3":"(JunctionV3,JunctionV3,JunctionV3)","X4":"(JunctionV3,JunctionV3,JunctionV3,JunctionV3)","X5":"(JunctionV3,JunctionV3,JunctionV3,JunctionV3,JunctionV3)","X6":"(JunctionV3,JunctionV3,JunctionV3,JunctionV3,JunctionV3,JunctionV3)","X7":"(JunctionV3,JunctionV3,JunctionV3,JunctionV3,JunctionV3,JunctionV3,JunctionV3)","X8":"(JunctionV3,JunctionV3,JunctionV3,JunctionV3,JunctionV3,JunctionV3,JunctionV3,JunctionV3)"}}:: decodeU8aStruct: failed at 0xa10f043205e514… on key (index 2/2): [u8;20]:: Expected input with 20 bytes (160 bits), found 7 bytes

In the above error it expects AccountKey20 (derived from [u8;20]). The index of this is 3 in JunctionV3. The assetId hex string always starts with 0x0103, in which 0x01 is used for parent: 1 and 0x03 should be used for X3 of JunctionsV3. However, the 0x03 occurs to be used not only for JunctionsV3 but also for the first entry into the tuple of X3, which is JunctionV3. So, it seems to be like a mistaken overlap for the decode functionality.

I want to use the following assetId (which is USDC on AssetHub for our Zeitgeist Parachain):

let parentsNumber = api.registry.createType('u8', 1);
let parachainCompactNumber = api.registry.createType('Compact<u32>', 1000);
// let parachain = api.registry.createType('JunctionV3', { Parachain: parachainCompactNumber });
let palletInstanceNumber = api.registry.createType('u8', 50);
// let palletInstance = api.registry.createType('JunctionV3', { PalletInstance: palletInstanceNumber });
let generalIndexNumber = api.registry.createType('Compact<u128>', 1337);
// let generalIndex = api.registry.createType('JunctionV3', { GeneralIndex: generalIndexNumber });
let assetId = api.registry.createType('TAssetConversion', {
  // eslint-disable-next-line sort-keys
  // 0x010300a10f043205e514 (parachain, palletInstance, generalIndex) [1,1,3,0,161,15,4,50,5,229,20]
  // 0x010305e51400a10f0432 (generalIndex, parachain, palletInstance) [1,1,3,5,229,20,0,161,15,4,50]
  // 0x010300a10f05e5140432 (parachain, generalindex, palletInstance) [1,1,3,0,161,15,5,229,20,4,50]
  // 0x0103043200a10f05e514 (palletInstance, parachain, generalIndex) [1,1,3,4,50,0,161,15,5,229,20]
  // 0x0103043205e51400a10f (palletInstance, generalIndex, parachain) [1,1,3,4,50,5,229,20,0,161,15]
  // 0x010305e514043200a10f (generalindex, palletInstance, parachain) [1,1,3,5,229,20,4,50,0,161,15]
  // parents: 0x01 or [1,1]
  // interior x3: 0x03 or [3]
  // generalIndex: 0x05e514 or [5,229,20]; the 5 is the index of JunctionV3 enum
  // palletInstance: 0x0432 or [4,50]; the 4 is the index of JunctionV3 enum; 50 is the palletInstance number
  // parachain: 0x0a10f or [0,161,15]; the 0 is the index of JunctionV3 enum
  parents: parentsNumber,
  interior: {
    x3: [
      { parachain: parachainCompactNumber },
      { palletInstance: palletInstanceNumber },
      { generalIndex: generalIndexNumber },
    ],
  },
});

Here is some useful debug output of @polkadot/types-codec:

Btw. I used a local fork of @polkadot/api and @polkadot/known-types to override the TAssetConversion for zeitgeist to be Option<MultiLocationV3>.

[Chralt98]

I'll move this to @polkadot/extension-dapp, because as soon as I sign with the extension, it wouldn't work. The asset id input for the polkadot api however is fine.

[Chralt98]

@TarikGul

Unfortunately, #5968 adds the Option to the hex asset id payload. This results in the asset id to include the option in the string through toPayload() for the signature here. So instead of asset id hex 0x010300a10f043205e514 it is then 0x01010300a10f043205e514, which then results in a decoding error somewhere down the line.

Also see #5967.

Maybe it's what you have been talking about here.

[TarikGul]

I want to use the following assetId (which is USDC on AssetHub for our Zeitgeist Parachain)

Little tip: When you are constructing a value like above, you shouldn't be using createType. But instead just have the value as an object, and let the API do all the encoding based on what the type is. (This could very well be your problem)>

Example:

const main = async () => {
    const api = await ApiPromise.create({
        provider: new WsProvider('wss://kusama-asset-hub-rpc.polkadot.io'),
        typesBundle: {
            spec: {
                'statemine': {
                    types: [
                        {
                            minmax: [0, undefined],
                            TAssetConversion: 'Option<MultiLocationV3>'
                        }
                    ]
                }
            }
        }
    });

    // Encoding here just to show it works.
    const asset = api.registry.createType('TAssetConversion', {
        parents: 1,
        interior: {
            X3: [
                { Parachain: 1000 },
                { PalletInstance: 50 },
                { GeneralIndex: 1337 }
            ]
        }
    })

    console.log(asset.unwrap().toJSON());
};

When you actually plug in the value lets say to the SignerPayload. You can just give it the Object of the Multilocation and let the API handle the encoding and decoding.

[Chralt98]

@TarikGul

It's interesting, I am using the Substrate front end template right now. As soon as I use the Polkadot extension, I get the following error:

Before the failure it correctly shows the assetId in the extension:

If I use the normal account selector for Alice, the transaction goes through and uses USDC as fee payment asset:

Btw. I don't use createType anymore:

[TarikGul]

Mmm, try and use master of the api. I just merged in #6083 which fixes how the assetId is decoded when a value is passed in from the signer. This was related to apps but it could also be related here.

I have it working on live Kusama, and Polkadot - but haven't checked the front end template yet.

[Chralt98]

Yes, perfect! This PR fixed it. Thanks!

[polkadot-js-bot]

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