Merkle proof for Smart Contract mapping field data

Question

I'm trying to get merkle proof for Ethereum Smart Contract mapping field data. I created test smart contract and deployed to test network. Smart Contract Code like following code:

contract TestSmartContract {

mapping(string => string) mappingField;
address sender;

function TestSmartContract() public {
    sender = msg.sender;
}

function addData(string key,  string value) public {
    mappingField[key] = value;
}}

I invoked smart contract addData method with test data.

"a","1"
"b","2"
"c","3"

After invoking smart contract, I tried to get value with web3 library, it works and i can get value for "a" key as "1".

var slot = "0".repeat(64);
            var key = web3.fromAscii('a');
            contractAddress = "0xac3f3d7286d8092be72d0011865a393ea722f609";
            var keccak256 = web3.sha3(key + slot, { encoding: 'hex' });
            web3.eth.getStorageAt(
                contractAddress,  
                keccak256,
                function (err, result) {
                    console.log(web3.toUtf8(result))
                    console.log(result);
                }
            );

As a final stage, I tried to create Merkle Proof for Key "a". I tried to use https://github.com/zmitton/eth-proof library for retrieving Merkle Proofs. But it gives "storageNode not found" error. You can find my test code below:

const Web3 = require('web3');
const EP = require('eth-proof')

var chainDataPath = '/Users/ramazan.girgin/chain-tmp/privchain/geth/chaindata/';
try {
    var latestBlockHash = 'f02052990b2ea9daa445c0a4655cb3a395a84c8300cba8258b8faf4357b109c7'
    Web3.providers.HttpProvider.prototype.sendAsync = Web3.providers.HttpProvider.prototype.send;
    var eP = new EP(
        new Web3.providers.HttpProvider("http://127.0.0.1:8545"),
        latestBlockHash,
        chainDataPath
    )
    contractAddress = 'ac3f3d7286d8092be72d0011865a393ea722f609';
    eP.getStorageProof(contractAddress, '0','0x61').then((result) => {
        console.log(result)
    }).catch((e) => {
        console.log(e)
    })
} catch (e) {
    console.log(e)
}

Actually, ZMitton uses https://github.com/ethereumjs/merkle-patricia-tree in this library. But i think there was a problem while sending path for storageTrie.findPath function in library getStorageProof method or i can incorrect values for getStorageProof() method. In the other hand, if i call getStorageProof for sender field , it gives complete proof.

eP.getStorageProof(contractAddress, '1').then((result) => {
            console.log(result)
        }).catch((e) => {
            console.log(e)
        })

How can i retrieve merkle proof for mapping field in Smart Contract? Or how can i calculate correct path for storageTrie.findPath function parameter ?

Thanks in advance

Ramazan

Answer 1

The https://github.com/zmitton/eth-proof is deprecated, you should use this new RPC calls https://github.com/ethereum/EIPs/issues/1186