EVM Transactions
This doc covers how to interact with the EvmTx type returned by the Skip Go API
Intro
- When a user needs to transfer or swap from an EVM chain (e.g. Ethereum mainnet, Arbitrum, Optimism, etc…), the Skip Go API will return an
EvmTx
type for the developer to pass to the user for signing - Unlike CosmosSDK transactions, EVM transactions do not have a notion of messages, so this object doesn’t correspond 1-to-1 to a “message”, which might be a more familiar notion to Cosmos developers
- This doc is intended for CosmosSDK developers who aren’t already familiar with the concepts of transaction construction in the EVM and need to use
EvmTx
to help their users move from/to EVM chains.
EvmTx
Data Structure
The EvmTx has 4 fields that the developer needs to understand:
to
: The address of the smart contract or externally owned account (EOA) with which this transaction interacts, as a hex-string prefixed with 0x (e.g. 0xfc05aD74C6FE2e7046E091D6Ad4F660D2A159762)value
: The amount ofwei
this transaction sends to the contract its interacting with (1 ETH = 1^18 WEI)data
: The calldata this transaction uses to call the smart contract it interacts with, as a hex string. The data bytes will be interpreted according to the application-binary-interface (ABI) of the contract that’s being interacted with. If this field is empty, it means the transaction is sending funds to an address, rather than calling a contract.required_erc20_approvals
: The permissions that must be granted to a specific smart contract to spend or transfer a certain amount of their ERC-20 tokens on behalf of the end user. This allows smart contracts to execute expressive flows that may involve moving some amount of the user’s ERC-20 tokens- If this field is non-empty, the approval must be granted, signed, and submitted before the
EvmTx
populated by the other fields in the response can be submitted to the network. Otherwise, it will fail to execute with a permission error. - Skip’s
ERC20Approval
object has 3 fields that define approval: _token_contract
: The address of the ERC-20 token on which the approval is granted _spender
: The address of the contract to which the approval will grant spend authority *amount
: The amount oftoken_contract
tokens the approval will grant thespender
to spend - Check out EIP-2612 for more information on ERC-20 approvals.
- If this field is non-empty, the approval must be granted, signed, and submitted before the
chain_id
: This is the same as in the Cosmos context (simply an identifier for the chain), but it’s an int instead of a string
For more information on transactions, check out the Ethereum foundation’s docs
Example constructing & signing an EVM Transaction
1. Install Signing Library and Skip Library
To enable EVM transactions in your application, first install an EVM developer library. The most popular options are:
The code snippets below use viem.
npm i viem
npm i @skip-go/client
1. Initialize the SkipClient
client with the EVM WalletClient
object
All 3 libraries mentioned above allow you to create WalletClient “signer” objects that:
- Use an RPC provider under the hood to query the chain for necessary data to create transactions (e.g. nonce, gas price, etc…)
- Expose an API that allows constructing, signing, and broadcasting transactions
You need to set up the getEVMSigner
function in the SkipClient
constructor to initialize this signer object for the a given EVM chain.
For example, with Viem, we do the following:
import { createWalletClient, custom} from 'viem';
import * as chains from 'viem/chains';
import { SkipClient } from '@skip-go/client';
const
const skipClient = new SkipClient({
getEVMSigner: async (chainID) => {
const chain = extractChain({
chains: Object.values(chains),
id: parseInt(chainID)
});
const evmWalletClient = createWalletClient({
chain: chain,
transport: custom(window.ethereum!)
});
return evmWalletClient;
}
});
2. Request Route using SkipClient
and get required chain
Next, request your route as normal:
const route = await skipClient.route({
amountIn: "1000",
sourceAssetDenom: "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
sourceAssetChainID: "1",
destAssetDenom: "0xaf88d065e77c8cC2239327C5EDb3A432268e5831",
destAssetChainID: "42161",
smartRelay: true,
smartSwapOptions: {
splitRoutes: true
}
};
3. Get User Addresses for all Required Chains
Use the route to determine the chains for which you need to supply a user address (the source, destination, and all intermediate chains that require a recovery address for receiving tokens in case of a failure)
let userAddresses = []
const requiredAddresses = route.requiredChainAddresses;
// iterate over chain IDs for chains that require addresses
for (const chainID of requiredAddresses) {
// Check that the chain is an EVM chain
if (parseInt(chainID)) {
// use signer library to get address from wallet
const chain = extractChain({
chains: Object.values(chains),
id: parseInt(chainID)
});
const evmWalletClient = createWalletClient({
chain: chain,
transport: custom(window.ethereum!)
});
const [address] = await client.requestAddresses();
// add to map
userAddresses.append({address: address, chainID: chainID})
} else {
// handle cosmos and SVM wallets -- not shown
}
});
return evmWalletClient;
}
4. Execute the Route using SkipClient
Finally, you can use SkipClient.executeRoute
to prompt the user to sign the approval(s) and transaction, and submit the transaction on chain.
await skipClient.executeRoute({
route:route,
userAddresses: userAddresses
});
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