check_token_allowance

Instructions

Args:
    chain_id: Chain ID (1, 10, 56, 100, 137, 8453, 42161)
    token_address: Address of the token
    owner_address: Address of the token owner
    spender_address: Address of the spender (typically Trader contract)

Returns:
    JSON string with allowance information.

Implementation Reference

• padex.py:1816-1894 (handler)

  The handler function decorated with @mcp.tool() that implements the core logic for checking ERC20 token allowances on specified EVM chains using Web3.py contract calls.

  async def check_token_allowance(ctx: Context, chain_id: str, token_address: str, owner_address: str, spender_address: str) -> str:
      """Check token allowance for a specific owner and spender.
      
      Args:
          chain_id: Chain ID (1, 10, 56, 100, 137, 8453, 42161)
          token_address: Address of the token
          owner_address: Address of the token owner
          spender_address: Address of the spender (typically Trader contract)
      
      Returns:
          JSON string with allowance information.
      """
      try:
          paloma_ctx = ctx.request_context.lifespan_context
          
          if chain_id not in CHAIN_CONFIGS:
              return f"Error: Unsupported chain ID {chain_id}"
          
          config = CHAIN_CONFIGS[chain_id]
          
          if chain_id not in paloma_ctx.web3_clients:
              return f"Error: Web3 client not available for {config.name}"
          
          # Validate addresses
          if not Web3.is_address(token_address):
              return f"Error: Invalid token address: {token_address}"
          
          if not Web3.is_address(owner_address):
              return f"Error: Invalid owner address: {owner_address}"
          
          if not Web3.is_address(spender_address):
              return f"Error: Invalid spender address: {spender_address}"
          
          web3 = paloma_ctx.web3_clients[chain_id]
          token_contract = web3.eth.contract(address=token_address, abi=ERC20_ABI)
          
          # Get allowance and token info
          allowance = token_contract.functions.allowance(owner_address, spender_address).call()
          
          try:
              token_symbol = token_contract.functions.symbol().call()
              token_decimals = token_contract.functions.decimals().call()
              balance = token_contract.functions.balanceOf(owner_address).call()
          except:
              token_symbol = "Unknown"
              token_decimals = 18
              balance = 0
          
          allowance_display = float(allowance) / (10 ** token_decimals)
          balance_display = float(balance) / (10 ** token_decimals)
          
          result = {
              "chain": config.name,
              "chain_id": config.chain_id,
              "token": {
                  "address": token_address,
                  "symbol": token_symbol,
                  "decimals": token_decimals
              },
              "owner_address": owner_address,
              "spender_address": spender_address,
              "allowance": {
                  "wei": str(allowance),
                  "display": str(allowance_display),
                  "is_unlimited": allowance == MAX_AMOUNT
              },
              "owner_balance": {
                  "wei": str(balance),
                  "display": str(balance_display)
              },
              "needs_approval": allowance == 0,
              "sufficient_allowance": allowance >= balance if balance > 0 else True
          }
          
          return json.dumps(result, indent=2)
          
      except Exception as e:
          logger.error(f"Error checking token allowance: {e}")
          return f"Error checking token allowance: {str(e)}"

• padex.py:198-239 (helper)

  Minimal ERC20 ABI including the allowance(), balanceOf(), decimals(), and symbol() functions used by the check_token_allowance handler to query contract state.

  ERC20_ABI = [
      {
          "constant": True,
          "inputs": [{"name": "_owner", "type": "address"}],
          "name": "balanceOf",
          "outputs": [{"name": "balance", "type": "uint256"}],
          "type": "function"
      },
      {
          "constant": True,
          "inputs": [],
          "name": "decimals",
          "outputs": [{"name": "", "type": "uint8"}],
          "type": "function"
      },
      {
          "constant": True,
          "inputs": [],
          "name": "symbol",
          "outputs": [{"name": "", "type": "string"}],
          "type": "function"
      },
      {
          "constant": False,
          "inputs": [
              {"name": "spender", "type": "address"},
              {"name": "amount", "type": "uint256"}
          ],
          "name": "approve",
          "outputs": [{"name": "", "type": "bool"}],
          "type": "function"
      },
      {
          "constant": True,
          "inputs": [
              {"name": "owner", "type": "address"},
              {"name": "spender", "type": "address"}
          ],
          "name": "allowance",
          "outputs": [{"name": "", "type": "uint256"}],
          "type": "function"
      }