Calculating Memory Positions in Solidity Diamond EIP-2535 AppStorage

Question

I'm trying to calculate the memory positions of a smart contract which uses the Diamond pattern so I can use w3.getStorageAt, but I'm having some issues with finding the correct positions.

This is my contract I'm trying to read storage from, and I wrote my own contract which mirrors the LibAppStorage.sol struct so I could use foundry to get the storage positions.

This gives me e.g.

{
      "astId": 91,
      "contract": "LibAppStorage.sol:MyContract",
      "label": "petName",
      "offset": 0,
      "slot": "24",
      "type": "t_mapping(t_uint256,t_string_storage)"
    },

I know that all diamond storage is offset by a specific hash location, which I think should be DIAMOND_APP_STORAGE_POSITION = keccak256("diamond.app.storage"). However when I try using getStorageAt, I keep getting null values.

DIAMOND_APP_STORAGE_POSITION = Web3.keccak(text="diamond.app.storage")

offsets = {
    "petName": 24,
}

myKey = 8350
print("Diamond app storage position: ")
print(DIAMOND_APP_STORAGE_POSITION)
print(w3.eth.get_storage_at("0x0e22B5f3E11944578b37ED04F5312Dfc246f443C", DIAMOND_APP_STORAGE_POSITION))
print("Petname offset: ")
petNameOffset = Web3.to_hex(Web3.to_bytes(offsets["petName"]))
print(petNameOffset)
print("Petname position: ")
print(w3.eth.get_storage_at("0x0e22B5f3E11944578b37ED04F5312Dfc246f443C", Web3.keccak(text=petNameOffset + "diamond.app.storage")))
print(w3.eth.get_storage_at("0x0e22B5f3E11944578b37ED04F5312Dfc246f443C", Web3.keccak(text=petNameOffset + "diamond.app.storage")))
print("My Petname position: ")
print(w3.eth.get_storage_at("0x0e22B5f3E11944578b37ED04F5312Dfc246f443C", Web3.keccak(text=str(myKey) + str(offsets["petName"]) + "diamond.app.storage")))

Diamond app storage position: b'1\xc1\xf8@#\x97\xe5\xb1\xe3\xd7_=\xa7 |\xe6\xf5EV\xb2z\xfer7Bv\x8cNK\xe5\x0c\xe0' b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00' Petname offset: 0x18 Petname position: b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00' b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00' My Petname position: b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'

Does anyone know the proper way to access Diamond contract storage using a client?