Parameters

DATA, 20 Bytes - Address of the storage.
QUANTITY - Integer of the position in the storage.
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.

Example

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:

Request

curl https://eth-mainnet.unifra.io/v1/your-api-key \
-X POST \
-H "Content-Type: application/json" \
-d '{"jsonrpc":"2.0", "method": "eth_getStorageAt", "params": ["0x295a70b2de5e3953354a6a8344e616ed314d7251", "0x0", "latest"], "id": 1}'

URL: https://eth-mainnet.unifra.io/v1/your-api-key
RequestType: POST
Body:
{
    "jsonrpc":"2.0",
    "method":"eth_getStorageAt",
    "params":["0x295a70b2de5e3953354a6a8344e616ed314d7251", "0x0", "latest"],
    "id":1
}

Result

{
	"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:

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:

Request

curl https://eth-mainnet.unifra.io/v1/your-api-key \
-X POST \
-H "Content-Type: application/json" \
-d '{"jsonrpc":"2.0", "method": "eth_getStorageAt", "params": ["0x295a70b2de5e3953354a6a8344e616ed314d7251", "0x6661e9d6d8b923d5bbaab1b96e1dd51ff6ea2a93520fdc9eb75d059238b8c5e9", "latest"], "id": 1}'

URL: https://eth-mainnet.unifra.io/v1/your-api-key
RequestType: POST
Body:
{
    "jsonrpc":"2.0",
    "method":"eth_getStorageAt",
    "params":["0x295a70b2de5e3953354a6a8344e616ed314d7251", "0x6661e9d6d8b923d5bbaab1b96e1dd51ff6ea2a93520fdc9eb75d059238b8c5e9", "latest"],
    "id":1
}

Result

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

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