approve_token_spending
Authorize token spending for cross-chain trading on Paloma DEX by approving a spender contract to access your tokens on supported EVM chains.
Instructions
Approve token spending for trading (two-step approval process).
Args:
chain_id: Chain ID (1, 10, 56, 100, 137, 8453, 42161)
token_address: Address of token to approve
spender_address: Address that will spend the tokens (typically Trader contract)
amount: Amount to approve in wei (defaults to unlimited)
Returns:
JSON string with approval transaction details.Input Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| chain_id | Yes | ||
| token_address | Yes | ||
| spender_address | Yes | ||
| amount | No |
Implementation Reference
- padex.py:1483-1594 (handler)The main handler function for the 'approve_token_spending' tool. It performs a safe two-step ERC-20 approval: first resets any existing allowance to 0, then approves the new amount (unlimited by default). Executes actual blockchain transactions on the specified chain using the configured Web3 client and account private key.
async def approve_token_spending(ctx: Context, chain_id: str, token_address: str, spender_address: str, amount: Optional[str] = None) -> str: """Approve token spending for trading (two-step approval process). Args: chain_id: Chain ID (1, 10, 56, 100, 137, 8453, 42161) token_address: Address of token to approve spender_address: Address that will spend the tokens (typically Trader contract) amount: Amount to approve in wei (defaults to unlimited) Returns: JSON string with approval transaction details. """ 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(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) # Use unlimited approval if no amount specified approval_amount = int(amount) if amount else MAX_AMOUNT # Check current allowance current_allowance = token_contract.functions.allowance( paloma_ctx.address, spender_address ).call() transactions = [] # Step 1: Reset allowance to 0 if it exists if current_allowance > 0: reset_tx_data = token_contract.functions.approve(spender_address, 0).build_transaction({ 'from': paloma_ctx.address, 'gas': 100000, 'gasPrice': web3.to_wei(config.gas_price_gwei, 'gwei'), 'nonce': web3.eth.get_transaction_count(paloma_ctx.address) }) # Sign and send reset transaction signed_reset = paloma_ctx.account.sign_transaction(reset_tx_data) reset_tx_hash = web3.eth.send_raw_transaction(signed_reset.rawTransaction) # Wait for confirmation reset_receipt = web3.eth.wait_for_transaction_receipt(reset_tx_hash) transactions.append({ "step": "reset_allowance", "tx_hash": reset_tx_hash.hex(), "status": "success" if reset_receipt.status == 1 else "failed" }) # Step 2: Set new allowance approve_tx_data = token_contract.functions.approve(spender_address, approval_amount).build_transaction({ 'from': paloma_ctx.address, 'gas': 100000, 'gasPrice': web3.to_wei(config.gas_price_gwei, 'gwei'), 'nonce': web3.eth.get_transaction_count(paloma_ctx.address) }) # Sign and send approval transaction signed_approve = paloma_ctx.account.sign_transaction(approve_tx_data) approve_tx_hash = web3.eth.send_raw_transaction(signed_approve.rawTransaction) # Wait for confirmation approve_receipt = web3.eth.wait_for_transaction_receipt(approve_tx_hash) transactions.append({ "step": "set_allowance", "tx_hash": approve_tx_hash.hex(), "status": "success" if approve_receipt.status == 1 else "failed", "approved_amount": str(approval_amount) }) # Get token symbol for display try: token_symbol = token_contract.functions.symbol().call() except: token_symbol = "Unknown" result = { "chain": config.name, "chain_id": config.chain_id, "token_address": token_address, "token_symbol": token_symbol, "spender_address": spender_address, "owner_address": paloma_ctx.address, "approved_amount": str(approval_amount), "is_unlimited": approval_amount == MAX_AMOUNT, "transactions": transactions, "all_successful": all(tx["status"] == "success" for tx in transactions) } return json.dumps(result, indent=2) except Exception as e: logger.error(f"Error approving token spending: {e}") return f"Error approving token spending: {str(e)}" - padex.py:198-239 (helper)Minimal ERC-20 ABI used by the approve_token_spending handler, including essential functions: balanceOf, decimals, symbol, approve, and allowance.
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" } - padex.py:299-302 (helper)Trading constants used in approval logic, including MAX_AMOUNT for unlimited approvals.
MAX_AMOUNT = 2**256 - 1 # Maximum approval amount GAS_MULTIPLIER = 3 # Divide by this for 33% gas buffer MAX_SPREAD = 0.4 # 40% maximum spread limit - padex.py:1483-1483 (registration)FastMCP decorator that registers the approve_token_spending function as an MCP tool, automatically generating input schema from signature and docstring.
async def approve_token_spending(ctx: Context, chain_id: str, token_address: str, spender_address: str, amount: Optional[str] = None) -> str: