eth_getStorageAt

Returns the value from a storage position at a given address.

Parameters:

1. DATA, 20 Bytes - address of the storage.

2. QUANTITY - integer of the position in the storage.

3. QUANTITY|TAG - integer block number, or the string "latest", "earliest" or "pending", see the default block parameter

Returns:

DATA - the value at this storage position.

Code Examples:

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:

var myHeaders = new Headers();
myHeaders.append("Content-Type", "application/json");

var raw = JSON.stringify({
  "method": "eth_getStorageAt",
  "params": [
    "0x295a70b2de5e3953354a6a8344e616ed314d7251",
    "0x0",
    "latest"
  ],
  "id": 1,
  "jsonrpc": "2.0"
});

var requestOptions = {
  method: 'POST',
  headers: myHeaders,
  body: raw,
  redirect: 'follow'
};

fetch("https://api.ebs.ezat.io/core/api/v1.0/rpc/aurora/mainnet?x-api-key-id=API-KEY-ID&x-api-key=API-KEY", requestOptions)
  .then(response => response.text())
  .then(result => console.log(result))
  .catch(error => console.log('error', error));

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

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

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

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

keccak(
  decodeHex(
    "000000000000000000000000391694e7e0b0cce554cb130d723a9d27458f9298" +
      "0000000000000000000000000000000000000000000000000000000000000001"
  )
)

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

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

Now to fetch the storage:

var myHeaders = new Headers();
myHeaders.append("Content-Type", "application/json");

var raw = JSON.stringify({
  "method": "eth_getStorageAt",
  "params": [
    "0x295a70b2de5e3953354a6a8344e616ed314d7251",
    "0x6661e9d6d8b923d5bbaab1b96e1dd51ff6ea2a93520fdc9eb75d059238b8c5e9",
    "latest"
  ],
  "id": 1,
  "jsonrpc": "2.0"
});

var requestOptions = {
  method: 'POST',
  headers: myHeaders,
  body: raw,
  redirect: 'follow'
};

fetch("https://api.ebs.ezat.io/core/api/v1.0/rpc/aurora/mainnet?x-api-key-id=API-KEY-ID&x-api-key=API-KEY", requestOptions)
  .then(response => response.text())
  .then(result => console.log(result))
  .catch(error => console.log('error', error));

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