Accessing Private Data

همه داده های قرارداد هوشمند قابل خواندن هستند. بیایید ببینیم چگونه می‌توانیم داده‌های خصوصی را بخوانیم. در این فرآیند خواهید آموخت که Solidity چگونه متغیرهای حالت را ذخیره می‌کند.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

/*
Note: cannot use web3 on JVM, so use the contract deployed on Goerli
Note: browser Web3 is old so use Web3 from truffle console

Contract deployed on Goerli
0x534E4Ce0ffF779513793cfd70308AF195827BD31
*/

/*
# Storage
- 2 ** 256 slots
- 32 bytes for each slot
- data is stored sequentially in the order of declaration
- storage is optimized to save space. If neighboring variables fit in a single
  32 bytes, then they are packed into the same slot, starting from the right
*/

contract Vault {
    // slot 0
    uint256 public count = 123;
    // slot 1
    address public owner = msg.sender;
    bool public isTrue = true;
    uint16 public u16 = 31;
    // slot 2
    bytes32 private password;

    // constants do not use storage
    uint256 public constant someConst = 123;

    // slot 3, 4, 5 (one for each array element)
    bytes32[3] public data;

    struct User {
        uint256 id;
        bytes32 password;
    }

    // slot 6 - length of array
    // starting from slot hash(6) - array elements
    // slot جایی که array element is stored = keccak256(slot)) + (index * elementSize)
    // جایی که slot = 6 and elementSize = 2 (1 (uint) +  1 (bytes32))
    User[] private users;

    // slot 7 - empty
    // entries are stored at hash(key, slot)
    // جایی که slot = 7, key = map key
    mapping(uint256 => User) private idToUser;

    constructor(bytes32 _password) {
        password = _password;
    }

    function addUser(bytes32 _password) public {
        User memory user = User({id: users.length, password: _password});

        users.push(user);
        idToUser[user.id] = user;
    }

    function getArrayLocation(uint256 slot, uint256 index, uint256 elementSize)
        public
        pure
        returns (uint256)
    {
        return
            uint256(keccak256(abi.encodePacked(slot))) + (index * elementSize);
    }

    function getMapLocation(uint256 slot, uint256 key)
        public
        pure
        returns (uint256)
    {
        return uint256(keccak256(abi.encodePacked(key, slot)));
    }
}

/*
slot 0 - count
web3.eth.getStorageAt("0x534E4Ce0ffF779513793cfd70308AF195827BD31", 0, console.log)
slot 1 - u16, isTrue, owner
web3.eth.getStorageAt("0x534E4Ce0ffF779513793cfd70308AF195827BD31", 1, console.log)
slot 2 - password
web3.eth.getStorageAt("0x534E4Ce0ffF779513793cfd70308AF195827BD31", 2, console.log)

slot 6 - array length
getArrayLocation(6, 0, 2)
web3.utils.numberToHex("111414077815863400510004064629973595961579173665589224203503662149373724986687")
Note: We can also use web3 to get data location
web3.utils.soliditySha3({ type: "uint", value: 6 })
1st user
web3.eth.getStorageAt("0x534E4Ce0ffF779513793cfd70308AF195827BD31", "0xf652222313e28459528d920b65115c16c04f3efc82aaedc97be59f3f377c0d3f", console.log)
web3.eth.getStorageAt("0x534E4Ce0ffF779513793cfd70308AF195827BD31", "0xf652222313e28459528d920b65115c16c04f3efc82aaedc97be59f3f377c0d40", console.log)
Note: use web3.toAscii to convert bytes32 to alphabet
2nd user
web3.eth.getStorageAt("0x534E4Ce0ffF779513793cfd70308AF195827BD31", "0xf652222313e28459528d920b65115c16c04f3efc82aaedc97be59f3f377c0d41", console.log)
web3.eth.getStorageAt("0x534E4Ce0ffF779513793cfd70308AF195827BD31", "0xf652222313e28459528d920b65115c16c04f3efc82aaedc97be59f3f377c0d42", console.log)

slot 7 - empty
getMapLocation(7, 1)
web3.utils.numberToHex("81222191986226809103279119994707868322855741819905904417953092666699096963112")
Note: We can also use web3 to get data location
web3.utils.soliditySha3({ type: "uint", value: 1 }, {type: "uint", value: 7})
user 1
web3.eth.getStorageAt("0x534E4Ce0ffF779513793cfd70308AF195827BD31", "0xb39221ace053465ec3453ce2b36430bd138b997ecea25c1043da0c366812b828", console.log)
web3.eth.getStorageAt("0x534E4Ce0ffF779513793cfd70308AF195827BD31", "0xb39221ace053465ec3453ce2b36430bd138b997ecea25c1043da0c366812b829", console.log)
*/