Why do we need to add 4 bytes of random characters when interacting with contracts?

[lucky1024]

When I looked at the source code, I found the following snippet:

async function createTx(
  arweave: Arweave,
  wallet: JWKInterface | 'use_wallet',
  contractId: string,
  input: any,
  tags: { name: string; value: string }[],
  target: string = '',
  winstonQty: string = '0',
  reward?: string,
): Promise<Transaction> {
  const options: Partial<CreateTransactionInterface> = {
    data: Math.random().toString().slice(-4),                                // Why need this?
    reward,
  };

Does anyone know why we need the random string?

SmartWeave/src/contract-interact.ts

Line 302 in 23ed88b

data: Math.random().toString().slice(-4),

[ppedziwiatr]

I'm by no means an expert here, but I believe it is needed to generate the tx.id properly
Check out how the arweave.js generates the id:
https://github.com/ArweaveTeam/arweave-js/blob/8494b561958949b6dc4256c8f2f5d77e93ae11e5/src/common/transactions.ts#L203

https://github.com/ArweaveTeam/arweave-js/blob/8494b561958949b6dc4256c8f2f5d77e93ae11e5/src/common/lib/transaction.ts#L237-L254

[lucky1024]

@ppedziwiatr I don't think the data field is required for generating tx.id. For example, tx https://viewblock.io/arweave/tx/iCLuc7Aj3xFOOWX5qFZCz5UVRTVn8k6quM2ouiockHA don't have data field (Size 0B).

[ppedziwiatr]

To be more precise - I believe it is required to ensure the uniqueness of the tx ids (in case two transactions with exact same parameters would be posted) - which in case of SmartWeave is crucial...

The flow goes like that (from the links that I've pasted in previous response):

let dataToSign = await transaction.getSignatureData();
let rawSignature = await this.crypto.sign(jwk, dataToSign, options);
let id = await this.crypto.hash(rawSignature);

The dataToSign is generated like that:

if (!this.data_root) {
          await this.prepareChunks(this.data);
        }

        const tagList: [Uint8Array, Uint8Array][] = this.tags.map((tag) => [
          tag.get("name", { decode: true, string: false }),
          tag.get("value", { decode: true, string: false }),
        ]);

        return await deepHash([
          ArweaveUtils.stringToBuffer(this.format.toString()),
          this.get("owner", { decode: true, string: false }),
          this.get("target", { decode: true, string: false }),
          ArweaveUtils.stringToBuffer(this.quantity),
          ArweaveUtils.stringToBuffer(this.reward),
          this.get("last_tx", { decode: true, string: false }),
          tagList,
          ArweaveUtils.stringToBuffer(this.data_size),
          this.get("data_root", { decode: true, string: false }),
        ]);

So - just in (probably very rare - but still possible) case, that all of the parameters of two transactions are the same - the randomly generated data increases the chance of generating unique txId.

That's my understanding, but probably someone from core Arweave team will be able to explain this better.

[lucky1024]

@ppedziwiatr Thank you for your further detailed explanation.
May be the last_tx field in tx can be used to generate uniqueness txid. https://docs.arweave.org/developers/server/http-api#field-definitions