hcs/getTopicMessages

How to call the API from an app

Hedera Wallet Snap connects to your currently connected Metamask account by default. To learn how apps can connect to Hedera Wallet Snap using a non-metamask(external) account, refer to this documentation.

Then, depending on whether you're trying to connect to a metamask account or a non-metamask account, you can call the snap API in the following way:

const snapId = `npm:@hashgraph/hedera-wallet-snap`

const snapAPI = async () => {
  const externalAccountParams = {
    externalAccount: {
      accountIdOrEvmAddress: '0.0.12345',
      curve: 'ED25519'
    }
  }

  await window.ethereum.request({
    method: 'wallet_invokeSnap',
    params: {
      snapId,
      request: {
        method: 'hcs/getTopicMessages',
        params: {
          network: 'testnet',
          topicId: '0.0.4617270',
          sequenceNumber?, // Optional param - type: number
          /* 
            Uncomment the below line if you want to connect 
            to a non-metamask account
          */
          // ...externalAccountParams
        }
      }
    }
  })
}

• If you pass in sequenceNumber, it will only retrieve content for that specific message.

What the API does

1. Retrieves the currently connected account the user has selected on Metamask. If it's the first time, a new snap account is created and the account info is saved in snap state.
2. Parses the arguments that were passed.

3. Calls the Hedera Mirror Node Get Topic Messages API to retrieve messages written to the topic from a mirror node.
4. Returns the transaction receipt as response

An example response:

{
    "currentAccount": {
        "metamaskEvmAddress": "0x0b3628d1b838993b5fceec8b2a26502e7a8e5241",
        "externalEvmAddress": "",
        "hederaAccountId": "0.0.3581604",
        "hederaEvmAddress": "0xca53f9c93d30e0b7212d67901e5a24fb090d542b",
        "publicKey": "0x0206022cea4c6dd6d2e7263b8802253971de922f5380661d97cba82dee66f57ad6",
        "balance": {
            "hbars": 86.77513646,
            "timestamp": "Tue, 23 Jul 2024 18:34:03 GMT",
            "tokens": {
                "0.0.4284934": {
                    "balance": 0,
                    "decimals": 1,
                    "tokenId": "0.0.4284934",
                    "name": "Pulse",
                    "symbol": "PULSE",
                    "tokenType": "FUNGIBLE_COMMON",
                    "supplyType": "INFINITE",
                    "totalSupply": "0",
                    "maxSupply": "0"
                }
            }
        },
        "network": "testnet",
        "mirrorNodeUrl": "https://testnet.mirrornode.hedera.com"
    },
    "topicMessages": [
        {
            "chunk_info": {
                "initial_transaction_id": {
                    "account_id": "0.0.3581604",
                    "nonce": 0,
                    "scheduled": false,
                    "transaction_valid_start": "Tue, 23 Jul 2024 18:33:50 GMT"
                },
                "number": 1,
                "total": 1
            },
            "consensus_timestamp": "Tue, 23 Jul 2024 18:34:03 GMT",
            "message": "Zmlyc3QgbWVzc2FnZQ==",
            "payer_account_id": "0.0.3581604",
            "running_hash": "u6lxAMZ0d19vh2GCc5gNGClxzqQeK2Zd7TZorA2WiaaKGlENN7nYtDAktM+0Ly7T",
            "running_hash_version": 3,
            "sequence_number": 1,
            "topic_id": "0.0.4617270"
        }
    ]
}

Live Demo on CodePen

• Note: Visit https://pulse.tuum.tech/ to activate your hedera account before you interact with the demo
• If you're getting any errors with the live demo, make sure you go through the FAQs section to learn about what you may be missing. You need to install Metamask in your browser for the live demo to work.
• To ease the integration of Hedera Wallet Snap on an application, we have created a template web application that you can run locally and check out the code in its entirety to learn how you can integrate and interact with various APIs exposed by Hedera Wallet Snap. Check out the full source code at template application github repository.
• You can also check out the API reference to learn how each API works.