Decoding ERC20 Approval Transactions Example

decodingexample.py

from eth_abi import decode
from eth_utils import to_checksum_address

def decode_erc20_approve(calldata: str, token_decimals: int = 18) -> dict:
    """
    Decode ERC-20 approve calldata with human-readable output
   
    Parameters:
    - calldata: The hex calldata string
    - token_decimals: Number of decimals for the token (default: 18)
   
    Returns: Dictionary with decoded information
    """
    # Remove '0x' prefix if present
    hex_data = calldata[2:] if calldata.startswith("0x") else calldata
   
    # Extract function selector and parameters
    selector = hex_data[:8]
    params_hex = hex_data[8:]
   
    # Decode parameters using eth_abi.decode (equivalent to decode_abi in earlier versions)
    # Note: We're explicitly using decode as the ABI decoder function
    spender, amount = decode(["address", "uint256"], bytes.fromhex(params_hex))
   
    # Convert to human-readable format
    spender_address = to_checksum_address(spender)
    amount_raw = amount
    amount_normalized = amount / (10 ** token_decimals)
   
    return {
        "function": "approve(address,uint256)",
        "selector": f"0x{selector}",
        "spender": spender_address,
        "amount_raw": amount_raw,
        "amount_normalized": amount_normalized,
        "token_decimals": token_decimals
    }

# Example usage
calldata = "0x095ea7b30000000000000000000000006a000f20005980200259b80c510200304000106800000000000000000000000000000000000000000000000000000000017d7840"
result = decode_erc20_approve(calldata, token_decimals=6)  # USDC has 6 decimals

print("Calldata Breakdown:")
print(f"Function: {result['function']}")
print(f"Function Selector: {result['selector']}")
print(f"Spender Address: {result['spender']}")
print(f"Raw Amount: {result['amount_raw']}")
print(f"Normalized Amount: {result['amount_normalized']} USDC")
print(f"\nSummary: Approving {result['amount_normalized']} USDC to {result['spender']}")