v4.0.0

Read the full announcement in the blog or check out the changelog.

Changelog

• Now targeting the 0.8.x line of Solidity compilers. For 0.6.x (resp 0.7.x) support, use version 3.4.0 (resp 3.4.0-solc-0.7) of OpenZeppelin.
• Context: making _msgData return bytes calldata instead of bytes memory (#2492)
• ERC20: removed the _setDecimals function and the storage slot associated to decimals. (#2502)
• Strings: addition of a toHexString function. (#2504)
• EnumerableMap: change implementation to optimize for key → value lookups instead of enumeration. (#2518)
• GSN: deprecate GSNv1 support in favor of upcoming support for GSNv2. (#2521)
• ERC165: remove uses of storage in the base ERC165 implementation. ERC165 based contracts now use storage-less virtual functions. Old behavior remains available in the ERC165Storage extension. (#2505)
• Initializable: make initializer check stricter during construction. (#2531)
• ERC721: remove enumerability of tokens from the base implementation. This feature is now provided separately through the ERC721Enumerable extension. (#2511)
• AccessControl: removed enumerability by default for a more lightweight contract. It is now opt-in through AccessControlEnumerable. (#2512)
• Meta Transactions: add ERC2771Context and a MinimalForwarder for meta-transactions. (#2508)
• Overall reorganization of the contract folder to improve clarity and discoverability. (#2503)
• ERC20Capped: optimize gas usage by enforcing the check directly in _mint. (#2524)
• Rename UpgradeableProxy to ERC1967Proxy. (#2547)
• ERC777: optimize the gas costs of the constructor. (#2551)
• ERC721URIStorage: add a new extension that implements the _setTokenURI behavior as it was available in 3.4.0. (#2555)
• AccessControl: added ERC165 interface detection. (#2562)
• ERC1155: make uri public so overloading function can call it using super. (#2576)

How to upgrade from 3.x

Since this version has moved a few contracts to different directories, users upgrading from a previous version will need to adjust their import statements. To make this easier, the package includes a script that will migrate import statements automatically. After upgrading to the latest version of the package, run:

npx openzeppelin-contracts-migrate-imports

Make sure you're using git or another version control system to be able to recover from any potential error in our script.

v4.0.0-beta.0

A beta release for Solidity 0.8. Read the announcement in the forum.

v3.4.0

Read the full announcement in the blog or check out the changelog.

Security Fixes

• ERC777: fix potential reentrancy issues for custom extensions to ERC777. (#2483)

If you're using our implementation of ERC777 from version 3.3.0 or earlier, and you define a custom _beforeTokenTransfer function that writes to a storage variable, you may be vulnerable to a reentrancy attack. If you're affected and would like assistance please write to [email protected]. Read more in the pull request.

v3.3.0

Read the full announcement in the forum or check out the changelog.

• Now supports both Solidity 0.6 and 0.7. Compiling with solc 0.7 will result in warnings. Install the solc-0.7 tag to compile without warnings.
• TimelockController: added a contract to augment access control schemes with a delay. (#2354)
• Address: added functionStaticCall, similar to the existing functionCall. (#2333)
• EnumerableSet: added Bytes32Set, for sets of bytes32. (#2395)

v3.2.1 for Solidity 0.7

This is a special release for Solidity 0.7 that gets rid of a warning in ERC777 using one of the new features of the language. (#2327)

Note: The variant for Solidity 0.7 can be installed using npm install @openzeppelin/[email protected].

v3.2.0

Welcome to a new release of OpenZeppelin Contracts! 👯

The big feature in this release is that we’ve migrated our proxy contracts from OpenZeppelin SDK into the Contracts project. We hope this will make more people aware of upgrades in Ethereum, and we also think the contracts will benefit greatly from the continued scrutiny by all of you in the community. This was also a migration of the proxies from Solidity 0.5 to 0.6, which we know some users have been waiting for.

For Solidity 0.7 users, a reminder that we have support for the newer compiler version published on npm under the tag solc-0.7, the latest release being 3.2.0-solc-0.7. We’re considering officially switching to 0.7 for the release after this one.

There is additionally a small breaking change in ERC20Snapshot that may affect some of its users. If you’re one of them please take a look at the changelog.

v3.1.0

This is the first release since v3.0, our last major release. It includes the long-awaited ERC1155 token and helpers for safe calls and downcasts, as well as a number of minor improvements.

To install this release, run:

npm install --save-dev @openzeppelin/contracts

ERC1155

This is a new token standard developed by the gaming industry, focusing on gas efficiency. It's key difference is that it is a multi-token contract: a single ERC1155 can be used to represent an arbitrary number of tokens, which is very useful in applications that require many tokens by removing the high gas costs associated with deploying them. Check out our new documentation page to learn more!.

More Replacements for call

The low-level call primitive can be hard to use correctly and is often considered unsafe. With the addition of sendValue in Contracts and try-catch in Solidity, there's only a few scenarios in which call is still needed, the most troublesome one being forwarding calls.

The new functionCall helpers can forward call data to a recipient contract while imitating Solidity's function call semantics, such as bubbling up revert reasons and rejecting calls to EOAs. We expect the addition of these functions to greatly reduce the need to rely on call.

Using SafeMath on Small Signed Integers

We've expanded the scope of the SafeCast library to also include signed integer downcasting, which allows for users that need small types (such as int8 or int32) to perform checked arithmetic on them by using SafeMath, and then downcast the result to the intended size.

OpenZeppelin Contracts 3.0.1

This is a small bugfix release, addressing an issue that allowed for some internal functions in ERC777 to be called with the zero address as one of their arguments.

This was reported in #2208, fixed in #2212 for the v2.5 branch, and ported to the v3.0 branch in #2213.

OpenZeppelin Contracts 2.5.1

This is a small bugfix release, addressing an issue that allowed for some internal functions in ERC777 to be called with the zero address as one of their arguments.

This was reported in #2208 and fixed in #2212.

OpenZeppelin Contracts 3.0

We're thrilled to finally announce the release of OpenZeppelin Contracts v3.0 ✨

Among other things, this release features the migration to Solidity v0.6, as well as a revamped access control system, streamlined token contracts, and new libraries for enumerable mappings.

To install this latest release, run:

npm install --save-dev @openzeppelin/contracts

What's New

• All contracts were migrated to Solidity v0.6.
• AccessControl was designed with help from the community and has replaced Roles contracts (such as MinterRole and PauserRole), which were removed.
• Crowdsales were removed: we'll continue to provide support for security issues on the v2.5 release, but will not bring them over to v3.0.
• We've added hooks, a new feature of the library that will make extending it easier than ever.
• ERC20 and ERC721 were simplified and streamlined, including all optional parts of the standard by default, and simplifying some of our own custom extensions.
• Support for better mapping types that let you efficiently iterate over all keys using EnumerableSet and EnumerableMap
• Many, many breaking changes with small improvements. We've also moved some contracts around (e.g. Ownable is now found under the access directory) and deleted some that were not being used. Head to our changelog to see the full list.

Compiling v0.6 Contracts

You can use the OpenZeppelin CLI to compile any Solidity v0.6 contract: just update the pragma statement on your source code and you'll be good to go!

pragma solidity ^0.6.0;

Note that you will need to use the v2.7 release of the CLI or newer to have Solidity v0.6 support. For detailed information about using the CLI compiler, head to its documenation.

Revamped Access Control

One of our most widely-used contracts is Ownable, providing a simple authorization scheme. However, this fell short in complex systems with multiple permissions.

The v3.0 release introduces AccessControl, a one-stop-shop for all authorization needs. It lets you easily define multiple roles with different permissions, as well as which accounts are allowed to grant and revoke each role. It also boosts transparency by enabling enumeration of all privileged accounts in a system.

AccessControl was designed with a security-first mindset, receiving input from a wide array of users and incorporating best practices in the field. Head to our Access Control guide for more information!

Preset Contracts

OpenZeppelin Contracts shine when you need the building blocks to get to the right feature set, but that's not all they can do! We've added a new family of Preset contracts starting with ERC20 and ERC721 tokens that you can quickly deploy as-is without having to write any Solidity code. Check out their documentation!

Migrating From OpenZeppelin Contracts v2.5

Other than the moved and deleted contracts mentioned above, the library API is pretty much the same as in the v2.5 release, so the migration should be straightforward. For instructions on how to update your Solidity v0.5 contracts to v0.6, refer to the official documentation.

If you're using the ERC20 or ERC721 tokens however, you'll have to remove all references to optional extensions (ERC20Detailed, ERC721Enumerable, etc.) - these have been included in the base contracts.

The other exception to this are contracts that use the Gas Station Network (GSN): if you're inheriting from GSNRecipient or one of the other GSN contracts, you'll need to add the following snippet to your contracts:

function _msgSender() internal view override(Context, GSNRecipient) returns (address payable) {
    return GSNRecipient._msgSender();
}

function _msgData() internal view override(Context, GSNRecipient) returns (bytes memory) {
    return GSNRecipient._msgData();
}

Using Hooks

To improve library flexibility, we're introducing hooks: functions that are called at specific moments during a contract's operation that you can use to hook into the internals and extend as you wish.

For example, the _beforeTokenTransfer hook in ERC20, ERC721 and ERC777 makes it very easy to add additional checks or actions to execute whenever tokens are transferred, minted or burned, regardless of what prompted it.

// Tokens can only be transferred, minted or burned if the contract is not paused
contract ERC20Pausable is ERC20, Pausable {
    function _beforeTokenTransfer(address from, address to, uint256 amount) 
        internal virtual override 
    {
        super._beforeTokenTransfer(from, to, amount);

        require(!paused(), "ERC20Pausable: token transfer while paused");
    }
}

As an additional benefit, using hooks will allow you to side-step some of the edge-cases product of the new override keyword.

Head over to our brand new guide on Extending the OpenZeppelin Contracts to learn more!

What's Next

We've started work in some exciting features for the upcoming releases, including fixed-point arithmetic and the ERC1155 token standard. To read more and find out how you can contribute, check out our Q2 2020 roadmap!