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eth_getStorageAt
Returns the value from a storage position at a given address, or in other words, returns the state of the contract's storage, which may not be exposed via the contract's methods.
The
eth_getStorageAt command is used to obtain a value related to a storage position at the specified address, returning the exact state of the contract’s storage, which can’t be exposed by regular contract methods.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.
DATA- the value at this storage position.
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.blastapi.io/<project-id> \
-X POST \
-H "Content-Type: application/json" \
-d '{"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.blastapi.io/<id> \
-X POST \
-H "Content-Type: application/json" \
-d '{"jsonrpc":"2.0", "method": "eth_getStorageAt", "params": ["0x295a70b2de5e3953354a6a8344e616ed314d7251", "0x6661e9d6d8b923d5bbaab1b96e1dd51ff6ea2a93520fdc9eb75d059238b8c5e9", "latest"], "id": 1}'
Result
{
"jsonrpc":"2.0",
"id":1,
"result":"0x000000000000000000000000000000000000000000000000000000000000162e"
}
Last modified 10mo ago