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Foundry Memory-Preserving Logging Library

The safeconsole library provides a foundry/hardhat-like console logging interface whereby the individual log functions do not modify the state of memory. This is important for debugging low-level assembly that may touch on and rely on the free memory pointer and the consistent state of memory beyond the free memory pointer. To ensure that the Solidity compiler does not allocate any memory unexpectedly the safeconsole.log functions accept bytes32 arguments instead of strings as they are kept on the stack. This means that the string part of log messages will have to be resricted to 32-character chunks.

logMemory

Besides the standard logging functions that can take various combinations of up to 4 bytes32, bool, address and uint256 arguments safeconsole also has a logMemory(uint256 offset, uint256 length) function that allows you to log a chunk of memory without modifying the state of memory:

assembly {
    mstore(0x00, 1)
    mstore(0x20, 2)
}
safeconsole.logMemory(0x00, 0x40);

// > 0x00000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000002

Installation

Foundry

  1. Install the library
forge install philogy/safeconsole --no-commit
  1. Just import the lib and use:

Example:

import {safeconsole} from "safeconsole/safeconsole.sol";

// Some example uses
safeconsole.log("My number: %d", 34);
safeconsole.log("Caller: %s", msg.sender);
safeconsole.log("Where in loop %d-%d", i, j);

Hardhat

  1. Install Foundry (I mean come on it's 2023)
  2. Check Foundry installation instructions

Truffle

Lmao ngmi. (Jk just install Hardhat and then check Hardhat installation instructions)

Caveats

  • certain safeconsole.log functions will increase msize, no function will modify msize if it's already larger than 0x1a0
  • safeconsole.log will treat all bytes32 arguments as strings and truncate them at their first 0x00-byte (.e.g hex"6162630064" will result in the string "abc" of length 3)
  • safeconsole.logMemory will increase msize if the offset argument is below 0x60