WalletConnect

The BCH WalletConnect specification was created in July of 2023 and has become popular since. The standard integrates nicely with CashScript contract development as it was designed with CashScript contract usage in mind.

You can find a full list of Bitcoin Cash dapps supporting WalletConnect on Tokenaut.cash.

tip

The specification is called 'wc2-bch-bcr' and has extra discussion and info on the BCH research forum.

signTransaction Interface

Most relevant for smart contract usage is the BCH-WalletConnect signTransaction interface.

This is a most generic interface to propose a bitcoincash transaction to a wallet which reconstructs it and signs it on behalf of the wallet user.

signTransaction: (
  options: {
    transaction: string | TransactionBCH,
    sourceOutputs: (Input | Output | ContractInfo)[],
    broadcast?: boolean,
    userPrompt?: string
  }
) => Promise<{ signedTransaction: string, signedTransactionHash: string } | undefined>;

Important to note is how the wallet knows which inputs to sign:

To signal that the wallet needs to sign an input, the app sets the corresponding input's unlockingBytecode to empty Uint8Array.

signTransaction Example

Create wcTransactionObj

Example code from the 'Cash-Ninjas' minting dapp repository, link to source code.

import { Contract } from "cashscript";
import { hexToBin, decodeTransaction } from "@bitauth/libauth";

async function transactionWalletConnect(){
  // use the CashScript SDK to build a transaction
  const rawTransactionHex = await transaction.build();
  const decodedTransaction = decodeTransaction(hexToBin(rawTransactionHex));

  // set input unlockingBytecode to empty Uint8Array for wallet signing
  decodedTransaction.inputs[1].unlockingBytecode = Uint8Array.from([]);

  // construct list SourceOutputs, see source code
  const listSourceOutputs = constructSourceOutputs(decodedTransaction, utxoInfo, contract)

  // wcTransactionObj to pass to signTransaction endpoint
  const wcTransactionObj = {
    transaction: decodedTransaction,
    sourceOutputs: listSourceOutputs,
    broadcast: true,
    userPrompt: "Mint Cash-Ninja NFT"
  };

  // pass wcTransactionObj to WalletConnect client
  const signResult = await signTransaction(wcTransactionObj);

  // Handle signResult success / failure
}

signTransaction Client interaction

Below is an implementation of signTransaction used earlier, this is where the communication with the client for 'signTransaction' takes place. See the source code for signClient, connectedChain and session details.

import SignClient from '@walletconnect/sign-client';
import { stringify } from "@bitauth/libauth";

async function signTransaction(options){
  try {
    const result = await signClient.request({
      chainId: connectedChain,
      topic: session.topic,
      request: {
        method: "bch_signTransaction",
        params: JSON.parse(stringify(options)),
      },
    });
    return result;
  } catch (error) {
    return undefined;
  }
}