Chain Interoperability Tool: Building Cross-Chain Applications

1.1 Chain Interoperability Tool Overview

Chain Interoperability Tool in the CapsureLabs Developer Toolkit enables developers to create applications that interact across multiple blockchains. Using this tool, developers can facilitate data and asset transfers, achieve interoperability between blockchain networks, and build robust multi-chain applications. This documentation provides an introduction to multi-blockchain interactions, common interoperability patterns, and sample code using Polkadot.js to enable cross-chain functionality.

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1.2 Interoperability Patterns

The main patterns in cross-chain interactions include:

• Asset Wrapping: Wrapping tokens from one chain to use them on another.

• Cross-Chain Messaging: Sending messages between chains for transaction or data requests.

• Interoperable Smart Contracts: Writing smart contracts capable of interacting across chains.

• Cross-Chain Bridges: Using a bridge to link chains directly, facilitating data and asset transfer.

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1.3 Using Polkadot.js for Multi-Blockchain Interactions

Polkadot, built with Substrate, is designed for cross-chain compatibility, supporting various blockchains via parachains that connect to its Relay Chain. Using Polkadot.js, we can build JavaScript-based applications that interact with the Polkadot network, parachains, and compatible blockchains.

Setting Up Polkadot.js

To integrate with Polkadot:

1. Install the @polkadot/api package:

npm install @polkadot/api

1. Connect to a Polkadot-Compatible Chain:

const { ApiPromise, WsProvider } = require('@polkadot/api');

async function connectToChain() {
    const wsProvider = new WsProvider('wss://rpc.polkadot.io');
    const api = await ApiPromise.create({ provider: wsProvider });
    console.log('Connected to the chain:', api.genesisHash.toHex());
}

connectToChain();

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1.4 Code for Cross-Chain Interaction

Cross-Chain Token Transfer

Step 1: Initialize Connection to Source and Target Chains

const { ApiPromise, WsProvider, Keyring } = require('@polkadot/api');

async function initConnections() {
    const sourceWsProvider = new WsProvider('wss://rpc.polkadot.io');
    const targetWsProvider = new WsProvider('wss://rpc.kusama.network');

    const sourceApi = await ApiPromise.create({ provider: sourceWsProvider });
    const targetApi = await ApiPromise.create({ provider: targetWsProvider });

    return { sourceApi, targetApi };
}

Step 2: Create Account and Execute Cross-Chain Transfer

async function transferTokens(sourceApi, targetApi) {
    const keyring = new Keyring({ type: 'sr25519' });
    const sender = keyring.addFromUri('//Alice'); // Sample account

    // Specify transfer details
    const receiverAddress = '<receiver_address_on_target_chain>';
    const amount = 1000000000; // Specify token amount

    // Execute transfer on source chain
    const unsub = await sourceApi.tx.balances
        .transfer(receiverAddress, amount)
        .signAndSend(sender, ({ events = [], status }) => {
            if (status.isInBlock) {
                console.log(`Transfer in block: ${status.asInBlock}`);
            } else if (status.isFinalized) {
                console.log(`Transfer finalized in block: ${status.asFinalized}`);
                unsub();
            }
        });
}

(async () => {
    const { sourceApi, targetApi } = await initConnections();
    await transferTokens(sourceApi, targetApi);
})();

Step 3: Handling Cross-Chain Data

Use the Polkadot Cross-Consensus Message Format (XCM) to transmit data or messages between chains. This functionality allows you to pass arbitrary messages or smart contract calls between compatible chains.

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