结合使用 MCP 与 Web3：如何保护执行区块链交易的智能体

from google.adk.agents import Agent

from web3 import Web3

ETH_RPC_URL = "RPC URL"

# (This is the tool function defined in the next section)

def craft_eth_transaction(to_address: str, amount: float, from_address: str, chain_id: int):

   # Step 1: Fetch the sender's next transaction count (nonce)

   # Step 2: Determine transaction type (ETH transfer or smart contract call)

   # Step 3: Construct the 'data' field using ABI

   # Step 4: Assemble and return the final, unsigned transaction

# The Agent is defined with a simple, non-custodial instruction

root_agent = Agent(

   name="transaction_crafter_agent",

   model="gemini-2.0-flash",

   description="An agent that crafts Ethereum transactions for a front-end to send via MetaMask.",

   instruction=(

       "You are an agent that crafts ETH transactions. "

       "Your only job is to collect the information from the user to craft Ethereum transactions.. "

       "The sender's address will be provided to you as context, along with the chain ID."

       "Use the `craft_eth_transaction` tool to generate the transaction object. "

       "The tool will return a JSON object that is ready to be sent to MetaMask. "

       "Leave gas and gasPrice fields empty; MetaMask will set them."

       "**IMPORTANT:** After using the tool, you must present the final transaction JSON in the response, formatted exactly like this:\\n"

       "   ```json\\n"

       "   {\\n"

       "     \\"to\\": \\"0x...\\",\\n"

       "     \\"from\\": \\"0x...\\",\\n"

       "     \\"value\\": \\"0x...\\",\\n"

       "     \\"nonce\\": \\"0x...\\",\\n"

       "     \\"chainId\\": \\"0xaa36a7\\"\\n"

       "   }\\n"

       "   ```\\n"

   ),

   tools=[craft_eth_transaction],

)

/**

* Step 1: Process the agent's response to extract the crafted transaction data.

* The agent's only output is a standard, unsigned transaction object.

*/

function extractTransactionFromAgentResponse(agentEvents) {

   const functionResponse = agentEvents.find(

       e => e.content?.parts?.[0]?.functionResponse?.name === 'craft_eth_transaction'

   )?.content.parts[0].functionResponse;

   if (functionResponse?.response?.success) {

       // The raw transaction object, ready for the user's wallet

       return functionResponse.response.transaction;

   }

   return null;

}

/**

* Step 2: Pass the crafted transaction to the user's wallet for execution.

* This function triggers a MetaMask pop-up, putting the user in full control.

*/

async function executeMetaMaskTransaction(txData) {

   if (!txData || typeof window.ethereum === 'undefined') {

       console.error("Invalid transaction data or MetaMask not found.");

       return;

   }

   try {

       // The 'eth_sendTransaction' call asks the wallet to sign and send.

       // The private key is never exposed to our web application.

       const txHash = await window.ethereum.request({

           method: 'eth_sendTransaction',

           params: [txData], // txData is the JSON object from the agent

       });

       console.log(`Transaction sent successfully! Hash: ${txHash}`);

       return txHash;

   } catch (error) {

       // This error typically means the user rejected the transaction in MetaMask.

       console.error("Transaction failed or was rejected by user:", error);

   }

}