Solidity Storage Layout Checker

Given some Solidity smart contract(s), extract all structs and check if their members could be laid out more efficient (=occupy less storage slots).

Timeout

If the number of struct members is sufficiently high, the algorithm to find the most efficient layout will run "indefinitely". To guard against this, there is a default 10 second timeout to calculate the most efficient layout of any given struct. If the timeout is exceeded the calculation will exit and give the "current best slot count" as well as info that the timeout was reached. This timeout can be customized using the -t <secs> argument.

Dependencies

Makes use of solidity-parser-antlr to parse Solidity files.

Usage

usage: sslc [-h] [-v] -f path [path ...] [-oj path] [-ot path]

Solidity storage layout checker

Optional arguments:
  -h, --help          Show this help message and exit.
  -v, --version       Show program's version number and exit.
  -f path [path ...]  input solidity file(s), supports glob
  -oj path            write output to JSON file
  -ot path            write output to text file
  -t secs             brute force timeout, default 10s

without install

npx sslc -f ~/my-solidity-project/contracts/*.sol

with install

npm i -g sslc
sslc -f ~/my-solidity-project/contracts/*.sol

Output

The script will print text output using Solidity syntax to stdout. It is also possible to save the text output to a file and/or save JSON output to a file.

Text output

struct MyFirstStruct { // file: SomeContract.sol | contract: SomeContract

  uint8 myFirstVar; // bytes: 1
  //---------- end of slot | bytes taken: 1 | bytes free: 31
  
  bytes32[] mySecondVar; // bytes: 32
  //---------- end of slot | bytes taken: 32 | bytes free: 0
  
  bool myThirdVar; // bytes: 1
  //---------- end of slot | bytes taken: 1 | bytes free: 31
  
  uint256 myFourthVar; // bytes: 32
  //---------- end of slot | bytes taken: 32 | bytes free: 0
  
  bool myFourthVar; // bytes: 1
  //---------- end of slot | bytes taken: 1 | bytes free: 31
 
} // slots that can be saved = 2

struct MyParentStruct { // file: SomeOtherContract.sol | contract: ParentContract

  uint8 myFirstVar; // bytes: 1
  //---------- end of slot | bytes taken: 1 | bytes free: 31
  
  uint256 mySecondVar; // bytes: 32
  //---------- end of slot | bytes taken: 32 | bytes free: 0
  
  uint16 myThirdVar; // bytes: 2
  //---------- end of slot | bytes taken: 2 | bytes free: 30
  
} // slots that can be saved = 1

struct MyOtherStruct { // file: SomeOtherContract.sol | contract: SomeOtherContract

  uint256 myFirstVar; // bytes: 32
  //---------- end of slot | bytes taken: 32 | bytes free: 0
  
  address mySecondVar; // bytes: 20
  //---------- end of slot | bytes taken: 20 | bytes free: 12
 
} // slots that can be saved = 0

// STRUCTS THAT CAN BE OPTIMIZED
// =============================
// file: SomeContract.sol
// contract: SomeContract
// struct: MyFirstStruct
// slots saved: 2
// -----------------------------
// file: SomeOtherContract.sol
// contract: ParentContract
// struct: MyParentStruct
// slots saved: 1
// -----------------------------

JSON output

[
    {
        "file": "SomeContract.sol",
        "contract": "SomeContract",
        "struct": "MyFirstStruct",
        "slotsSaved": 2,
        "timedout": false
    },
    {
        "file": "SomeOtherContract.sol",
        "contract": "ParentContract",
        "struct": "MyParentStruct",
        "slotsSaved": 1,
        "timedout": false
    }
]

Test

npm test

TODO

• do the same for the layout of variables of a given contract

License

MIT