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hts/initiateSwap

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

  const requester = {
    assetType: 'HBAR', // 'HBAR' | 'TOKEN' | 'NFT'
    to: '0.0.1',
    amount: 1
  }
  const responder = {
    assetType: 'TOKEN', // 'HBAR' | 'TOKEN' | 'NFT'
    amount: 10,
    assetId: '0.0.4279119' // For NFT, the format is tokenId/serialNumber
  }

  await window.ethereum.request({
    method: 'wallet_invokeSnap',
    params: {
      snapId,
      request: {
        method: 'hts/initiateSwap',
        params: {
          network: 'testnet',
          atomicSwaps: [{
            requester,
            responder
          }],
          memo?: // Optional param - type string
          maxFee?: // Optional param - type number(in hbars)
          /* 
            Uncomment the below line if you want to connect 
            to a non-metamask account
          */
          // ...externalAccountParams
        }
      }
    }
  })
}

Both the requester and responder must be passed
You can have multiple atomic swaps as part of the same transaction with multiple requester and responder but all the parties must call the hts/completeSwap API to complete the transaction or the transaction will fail
The responder must must sign the transaction by calling hts/completeSwap API within 30 minutes or the transaction will fail
Swap cannot be initiated with the same token. So, for example, requester cannot try to swap 1 Hbar with the responder for 10 Hbar

What the API does

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.
Parses the arguments that were passed
Uses scheduled transaction to implement the atomic swap feature whereby the requester initiates the swap with the responder by calling this API upon which the snap sends this transaction as a scheduled transaction to the ledger. Within 30 minutes, if the responder calls the hts/completeSwap API with the scheduleId of the transaction, the swap is complete.
Returns the transaction receipt as response

Example of how the Atomic Swap is performed

Let's assume Alice wants to swap her 1 Hbar with 10 Tuum token that Bob has(basically a peer to peer swap)

Alice calls the snap API for hts/initiateSwap and as part of the parameters, she says she wants to give her 1 Hbar to Bob if Bob can give Alice 10 Tuum tokens
Snap creates this atomic swap transaction and sends it to the network as a scheduled transaction with a max expiry of 30 minutes
Snap returns the schedule Id for this transaction
Alice lets Bob know about this atomic swap transaction and gives him the schedule Id
Bob queries the schedule Id and verifies everything looks good
Bob calls the snap API for hts/completeSwap with the schedule Id
The scheduled transaction is executed and the atomic swap transaction is complete

An example response:

{
    "currentAccount": {
        "metamaskEvmAddress": "0x0b3628d1b838993b5fceec8b2a26502e7a8e5241",
        "externalEvmAddress": "",
        "hederaAccountId": "0.0.3581604",
        "hederaEvmAddress": "0xca53f9c93d30e0b7212d67901e5a24fb090d542b",
        "publicKey": "0x0206022cea4c6dd6d2e7263b8802253971de922f5380661d97cba82dee66f57ad6",
        "balance": {
            "hbars": 88.13421155,
            "timestamp": "Fri, 26 Apr 2024 17:50:12 GMT",
            "tokens": {
                "0.0.4279119": {
                    "balance": 50,
                    "decimals": 1,
                    "tokenId": "0.0.4279119",
                    "name": "NewTuum",
                    "symbol": "NEWTUUM",
                    "tokenType": "FUNGIBLE_COMMON",
                    "supplyType": "INFINITE",
                    "totalSupply": "50",
                    "maxSupply": "0"
                }
            }
        },
        "network": "testnet",
        "mirrorNodeUrl": "https://testnet.mirrornode.hedera.com"
    },
    "receipt": {
        "status": "SUCCESS",
        "accountId": "",
        "fileId": "",
        "contractId": "",
        "topicId": "",
        "tokenId": "",
        "scheduleId": "0.0.4285081",
        "exchangeRate": {
            "hbars": 30000,
            "cents": 333977,
            "expirationTime": "Fri, 26 Apr 2024 20:00:00 GMT",
            "exchangeRateInCents": 11.132566666666667
        },
        "topicSequenceNumber": "0",
        "topicRunningHash": "",
        "totalSupply": "0",
        "scheduledTransactionId": "0.0.3581604@1714159254.939190271?scheduled",
        "serials": [],
        "duplicates": [],
        "children": []
    }
}

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.