getStorageAt

REQUEST

POST https://mainet.rpc.aarmascan.com

HEADER

Content-Type: application/json

REQUEST PARAMS

• ADDRESS [required] - a string representing the address (20 bytes) of the storage

• STORAGE POSITION [required] - a hex code of the position in the storage

• BLOCK PARAMETER [required] - an integer block number, or the string "latest", "earliest" or "pending", see the default block parameter

EXAMPLE

Explain## JSON-RPC over HTTPS POST
curl https://mainet.rpc.aarmascan.com
    -X POST \
    -H "Content-Type: application/json" \
    -d '{"jsonrpc":"2.0","method":"eth_getStorageAt","params": ["0x295a70b2de5e3953354a6a8344e616ed314d7251", "0x6661e9d6d8b923d5bbaab1b96e1dd51ff6ea2a93520fdc9eb75d059238b8c5e9", "0x65a8db"],"id":1}'

## JSON-RPC over WSS
wscat -c ws://mainet.rpc.ctexscan.com
>{"jsonrpc":"2.0","method":"eth_getStorageAt","params": ["0x295a70b2de5e3953354a6a8344e616ed314d7251", "0x6661e9d6d8b923d5bbaab1b96e1dd51ff6ea2a93520fdc9eb75d059238b8c5e9", "0x65a8db"],"id":1}

RESPONSE

RESULT FIELDS

• STORAGE VALUE - a hex code of the integer indicating the value of the storage position at the provided address

BODY

Explain{
    "jsonrpc": "2.0",
    "id": 1,
    "result": "0x0000000000000000000000000000000000000000000000000000000000000000"
}

Calculating the correct position depends on the storage to retrieve. Consider the following contract deployed at 0x295a70b2de5e3953354a6a8344e616ed314d7251 by address 0x391694e7e0b0cce554cb130d723a9d27458f9298,

Explaincontract Storage {
    uint pos0;
    mapping(address => uint) pos1;

    function Storage() {
        pos0 = 1234;
        pos1[msg.sender] = 5678;
    }
}

Retrieving the value of pos0 is straight forward:

Explaincurl https://aarmarpc.com \
    -X POST \
    -H "Content-Type: application/json" \
    -d '{"jsonrpc":"2.0", "method": "eth_getStorageAt", "params": ["0x295a70b2de5e3953354a6a8344e616ed314d7251

Explain{
    "jsonrpc": "2.0",
    "id": 1,
    "result": "0x00000000000000000000000000000000000000000000000000000000000004d2"
}

Retrieving an element of the map is harder. The position of an element in the map is calculated with:

keccak(LeftPad32(key, 0), LeftPad32(map position, 0))

This means to retrieve the storage on pos1["0x391694e7e0b0cce554cb130d723a9d27458f9298"] we need to calculate the position with:

Explainkeccak(
    decodeHex(
        '000000000000000000000000391694e7e0b0cce554cb130d723a9d27458f9298' +
            '0000000000000000000000000000000000000000000000000000000000000001'
    )
);

The geth console which comes with the web3 library can be used to make the calculation:

Explain> var key = "000000000000000000000000391694e7e0b0cce554cb130d723a9d27458f9298" + "0000000000000000000000000000000000000000000000000000000000000001"
undefined
> web3.sha3(key, {"encoding": "hex"})
"0x6661e9d6d8b923d5bbaab1b96e1dd51ff6ea2a93520fdc9eb75d059238b8c5e9"

Now to fetch the storage:

Explaincurl https://aarmarpc.com \
    -X POST \
    -H "Content-Type: application/json" \
    -d '{"jsonrpc":"2.0", "method": "eth_getStorageAt", "params": ["0x295a70b2de5e3953354a6a8344e616ed314d7251", "0x6661e9d6d8b923d5bbaab1b96e1dd51ff6ea2a93520fdc9eb75d059238b8c5e9", "0x65a8db"], "id": 1}'

Explain{
    "jsonrpc": "2.0",
    "id": 1,
    "result": "0x000000000000000000000000000000000000000000000000000000000000162e"
}