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EncodeFunctionData

The EncodeFunctionData action is a core utility that converts smart contract function calls into calldata (hexadecimal data) that can be used in blockchain transactions. This is a crucial step when preparing to interact with any smart contract on EVM-compatible blockchains.

Purpose​

When interacting with smart contracts, you need to encode your function calls into a specific format that the Ethereum Virtual Machine (EVM) can interpret. The EncodeFunctionData action handles this encoding process, converting a function name and its arguments into the hexadecimal calldata required for blockchain transactions.

When to Use It​

Use this action when you need to:

  • Prepare data for smart contract interactions
  • Create the data payload for a transaction
  • Manually build complex transaction sequences
  • Generate calldata to estimate gas costs before executing a transaction

Input Parameters​

ParameterTypeDescriptionRequired
abiStringstringThe contract ABI as a JSON stringYes
functionNamestringThe name of the function to encodeYes
argsStringstringThe function arguments as a JSON string arrayNo

Code Example​

Here's a practical example showing how to encode an ERC-20 token transfer:

// Example: Encoding an ERC-20 token transfer
const result = await agent.runAction("encode_function_data", {
  // ERC-20 Transfer function ABI
  abiString: '[{"inputs":[{"name":"to","type":"address"},{"name":"value","type":"uint256"}],"name":"transfer","outputs":[{"name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"}]',
  
  // Function name to call
  functionName: "transfer",
  
  // Arguments: recipient address and amount (1 token with 18 decimals)
  argsString: '["0x742d35Cc6634C0532925a3b844Bc454e4438f44e", "1000000000000000000"]'
});

console.log(result);
// Output: "Encoded Data: 0xa9059cbb000000000000000000000000742d35cc6634c0532925a3b844bc454e4438f44e0000000000000000000000000000000000000000000000000de0b6b3a7640000"

Real-world Application​

Using with SendTransaction​

The encoded data is typically used as input for the send_transaction action:

// Step 1: Encode the function data
const encodedData = await agent.runAction("encode_function_data", {
  abiString: '[{"inputs":[{"name":"to","type":"address"},{"name":"value","type":"uint256"}],"name":"transfer","outputs":[{"name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"}]',
  functionName: "transfer",
  argsString: '["0x742d35Cc6634C0532925a3b844Bc454e4438f44e", "1000000000000000000"]'
});

// Extract just the hex data part (removing the "Encoded Data: " prefix)
const hexData = encodedData.replace("Encoded Data: ", "");

// Step 2: Use the encoded data in a transaction
const txResult = await agent.runAction("send_transaction", {
  to: "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48", // USDC contract address
  data: hexData,
  value: "0" // No ETH being sent
});

Interacting with Complex DeFi Protocols​

For more complex DeFi interactions (like Uniswap swaps), you would encode the appropriate function with its parameters:

const swapData = await agent.runAction("encode_function_data", {
  abiString: '[{"inputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"},{"internalType":"uint256","name":"amountOutMin","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"swapExactTokensForTokens","outputs":[{"internalType":"uint256[]","name":"amounts","type":"uint256[]"}],"stateMutability":"nonpayable","type":"function"}]',
  functionName: "swapExactTokensForTokens",
  argsString: '[
    "1000000000000000000", 
    "950000000000000000",
    ["0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2", "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48"],
    "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
    "1714559999"
  ]'
});

Error Handling​

The action provides helpful error messages for common issues:

  • Function not found:

    Error: Failed to encode function data: Function 'transferr' not found on ABI. Check spelling and ABI correctness.

  • Invalid argument types:

    Error: Failed to encode function data: Expected a value of type 'address' but received '123' (type: string).

  • Invalid JSON format:

    Error: Failed to encode function data: Unexpected token in JSON at position 5.

Under the Hood​

The EncodeFunctionData action uses the viem library's encodeFunctionData function to perform the encoding. It validates inputs using Zod for type safety and comprehensive error handling.

Tips for Success​

  1. Ensure Correct ABI: The ABI must exactly match the contract you're interacting with
  2. Check Parameter Types: Arguments must match the expected types in the function signature
  3. Format JSON Correctly: Both abiString and argsString must be valid JSON strings
  4. Handle Big Numbers Properly: For uint256 values (like token amounts), use string representation to avoid precision issues