# getStorageAt

### REQUEST

```
POST https://mainnet-slice-rpc.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](https://github.com/ethereum/wiki/wiki/JSON-RPC#the-default-block-parameter)

#### EXAMPLE

```
## JSON-RPC over HTTPS POST
curl https://mainnet-slice-rpc.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://mainnet-slice-rpc.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

```
{
    "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`,

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

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

Retrieving the value of pos0 is straight forward:

```bash
curl https://mainnet-slice-rpc.com \
    -X POST \
    -H "Content-Type: application/json" \
    -d '{"jsonrpc":"2.0", "method": "eth_getStorageAt", "params": ["0x295a70b2de5e3953354a6a8344e616ed314d7251
```

```
{
    "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:

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

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

```js
keccak(
    decodeHex(
        '000000000000000000000000391694e7e0b0cce554cb130d723a9d27458f9298' +
            '0000000000000000000000000000000000000000000000000000000000000001'
    )
);
```

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

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

Now to fetch the storage:

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

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