MultiSigLib

MultiSigLib is a lightweight Solidity library that adds majority-vote membership management to your contracts. It encapsulates all multisig state in a single State struct and exposes simple methods to vote to add or remove members with a strict-majority threshold (floor(n/2) + 1). It emits events for off-chain indexing and supports versioning of the member set to guarantee unique vote keys.

Features

• Strict majority threshold: threshold = floor(membersCount / 2) + 1
• Add/Remove members via voting
• Double-vote protection with per-proposal versioned keys
• Minimum members guard (≥ 3)
• Event emission for every important action
• Stateless library (all storage lives in your contract via State)
• Composable: host multiple independent multisigs in a single contract (e.g., teamState, treasuryState)

Installation

Using Foundry:

forge install jeremy-then/MultiSigLib@main

Or specifying a version:

forge install jeremy-then/[email protected]

Import paths

• If your repo name is multisig-lib:

  import "multisig-lib/src/MultiSigLib.sol";

• Optional short alias: this library ships a remappings.txt with multisig/=src/, so you can:

  import "multisig/MultiSigLib.sol";

Quick Start

Minimal consumer contract:

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

import "multisig-lib/src/MultiSigLib.sol";

contract MyMultisig {

    using MultiSigLib for MultiSigLib.State;

    MultiSigLib.State private state;

    constructor(address[] memory initialMembers) {
        state.init(initialMembers);
    }

    function voteAdd(address candidate) external {
        state.voteToAddNewMember(candidate);
    }

    function voteRemove(address member) external {
        state.voteToRemoveMember(member);
    }

    function isMember(address who) external view returns (bool) {
        return MultiSigLib.isMember(state, who);
    }

    function membersCount() external view returns (uint256) { return state.getMembersCount(); }
    function threshold()    external view returns (uint256) { return state.getThreshold(); }
    function version()      external view returns (uint256) { return state.getMultisigVersion(); }

}

Constructor input

• Pass ≥ 3 unique, non-zero addresses to init.
• The multisig version starts at 1. Every add/remove increments the version.

Events

• NewMemberCandidateVoted(address candidate, address voter)
• NewMemberAdded(address member, uint256 multisigVersion)
• MemberRemovalVoted(address member, address voter)
• MemberRemoved(address member)

These are emitted from the consumer contract’s address (since libraries run in the context of the caller).

API

All functions are internal, called as state.fn(...) (except where noted for ambiguity):

• init(State storage state, address[] memory initialMembers)
• voteToAddNewMember(State storage state, address candidate)
• voteToRemoveMember(State storage state, address member)
• Views:
  • isMember(State storage state, address who) -> bool (call as MultiSigLib.isMember(state, who) to avoid name clash with the internal mapping)
  • getMembersCount(State storage state) -> uint256
  • getThreshold(State storage state) -> uint256
  • getMultisigVersion(State storage state) -> uint256
  • getNewMemberVotesForCandidate(State storage state, address candidate) -> uint256
  • getRemoveMemberVotesForMember(State storage state, address member) -> uint256
  • getAddNewMemberProposedAtVersion(State storage state, address candidate) -> uint256
  • getRemoveMemberProposedAtVersion(State storage state, address member) -> uint256

Design Notes

• State struct: Libraries cannot store persistent state. The State struct lives in your contract and contains the mappings/counters.
• Versioning: Each proposal stores proposedAtMultisigVersion and uses (voter, subject, version) to create a unique vote key, so members can vote multiple times for the same member/candidate they voted before but after a successful version upgrade.
• Threshold: recalculated after every composition change (floor(n/2)+1).
• Min members: removal cannot finalize if it would drop below 3 members.

Testing

Run tests

forge test -vv

License

MIT — see LICENSE.

Contributing

• Open an issue for bugs or feature requests.
• PRs welcome (please include tests).