ERC-7504: Dynamic Contracts standard.

Architectural pattern for writing client-friendly one-to-many proxy contracts (aka 'dynamic contracts') in Solidity.

This repository implements ERC-7504: Dynamic Contracts [DRAFT]. This repository provides core interfaces and preset implementations that:

• Provide guardrails for writing dynamic contracts that can have functionality added, updated or removed over time.
• Enables scaling up contracts by eliminating the restriction of contract size limit altogether.

⚠️ ERC-7504 [DRAFT] is now published and open for feedback! You can read the EIP and provide your feedback at its ethereum-magicians discussion link.

Installation

Forge projects:

forge install https://github.com/thirdweb-dev/dynamic-contracts

Hardhat / JS based projects:

npm install @thirdweb-dev/dynamic-contracts

Project structure

src
|
|-- core
|   |- Router: "Minmal abstract contract implementation of EIP-7504 Router."
|   |- RouterPayable: "A Router with `receive` as a fixed function."
|
|-- presets
|   |-- ExtensionManager: "Defined storage layout and API for managing a router's extensions."
|   |-- DefaultExtensionSet: "A static store of a set of extensions, initialized on deployment."
|   |-- BaseRouter: "A Router with an ExtensionManager."
|   |-- BaseRouterWithDefaults: "A BaseRouter initialized with extensions on deployment."
|
|-- interface: "Interfaces for core and preset contracts."
|-- example: "Example dynamic contracts built with presets."
|-- lib: "Storage layouts and helper libraries."

Running locally

This repository is a forge project. (forge handbook)

Clone the repository:

git clone https://github.com/thirdweb-dev/dynamic-contracts.git

Install dependencies:

forge install

Compile contracts:

forge build

Run tests:

forge test

Generate documentation

forge doc --serve --port 4000

Core concepts

An “upgradeable smart contract” is actually two kinds of smart contracts considered together as one system:

1. Proxy smart contract: The smart contract whose state/storage we’re concerned with.
2. Implementation smart contract: A stateless smart contract that defines the logic for how the proxy smart contract’s state can be mutated.

The job of a proxy contract is to forward any calls it receives to the implementation contract via delegateCall. As a shorthand — a proxy contract stores state, and always asks an implementation contract how to mutate its state (upon receiving a call).

ERC-7504 introduces a Router smart contract.

Instead of always delegateCall-ing the same implementation contract, a Router delegateCalls a particular implementation contract (i.e. “Extension”) for the particular function call it receives.

A router stores a map from function selectors → to the implementation contract where the given function is implemented. “Upgrading a contract” now simply means updating what implementation contract a given function, or functions are mapped to.

Getting started

The simplest way to write a Router contract is to extend the preset BaseRouter available in this repository.

import "lib/dynamic-contracts/src/presets/BaseRouter.sol";

The BaseRouter contract comes with an API to add/replace/remove extensions from the contract. It is an abstract contract, and expects its consumer to implement the _isAuthorizedCallToUpgrade function, which specifies the conditions under which Extensions can be added, replaced or removed. The rest of the implementation is generic and usable for all purposes.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@thirdweb-dev/dynamic-contracts/src/presets/BaseRouter.sol";

/// Example usage of `BaseRouter`, for demonstration only

contract SimpleRouter is BaseRouter {

    address public deployer;

    constructor() {
        deployer = msg.sender;
    }

    /// @dev Returns whether all relevant permission checks are met before any upgrade.
    function _isAuthorizedCallToUpgrade() internal view virtual override returns (bool) {
        return msg.sender == deployer;
    }
}

Choosing a permission model

The main decision as a Router contract author is to decide the permission model to add/replace/remove extensions. This repository offers some examples of a few possible permission models:

• RouterImmutable

  This is a preset you can use to create static contracts that cannot be updated or get new functionality. This still allows you to create modular contracts that go beyond the contract size limit, but guarantees that the original functionality cannot be altered. With this model, you would pass all the Extensions for this contract at construction time, and guarantee that the functionality is immutable.

• RouterUpgradeable

  This a is a preset that allows the contract owner to add / replace / remove extensions. The contract owner can be changed. This is a very basic permission model, but enough for some use cases. You can expand on this and use a permission based model instead for example.

• RouterRegistryContrained

  This is a preset that allows the owner to change extensions if they are defined on a given registry contract. This is meant to demonstrate how a protocol ecosystem could constrain extensions to known, audited contracts, for instance. The registry and router upgrade models are of course too basic for production as written.

Writing extension smart contracts

An Extension contract is written like any other smart contract, except that its state must be defined using a struct within a library and at a well defined storage location. This storage technique is known as storage structs.

Example: ExtensionManagerStorage defines the storage layout for the ExtensionManager contract.

// SPDX-License-Identifier: MIT
// @author: thirdweb (https://github.com/thirdweb-dev/dynamic-contracts)

pragma solidity ^0.8.0;

import "./StringSet.sol";
import "../interface/IExtension.sol";

library ExtensionManagerStorage {

    /// @custom:storage-location erc7201:extension.manager.storage
    bytes32 public constant EXTENSION_MANAGER_STORAGE_POSITION = keccak256(abi.encode(uint256(keccak256("extension.manager.storage")) - 1));

    struct Data {
        /// @dev Set of names of all extensions stored.
        StringSet.Set extensionNames;
        /// @dev Mapping from extension name => `Extension` i.e. extension metadata and functions.
        mapping(string => IExtension.Extension) extensions;
        /// @dev Mapping from function selector => metadata of the extension the function belongs to.
        mapping(bytes4 => IExtension.ExtensionMetadata) extensionMetadata;
    }

    function data() internal pure returns (Data storage data_) {
        bytes32 position = EXTENSION_MANAGER_STORAGE_POSITION;
        assembly {
            data_.slot := position
        }
    }
}

Each Extension of a router must occupy a unique, unused storage location. This is important to ensure that state updates defined in one Extension doesn't conflict with the state updates defined in another Extension, leading to corrupted state.

Extensions: logical grouping of functionality

By itself, the core Router contract does not specify how to store or fetch appropriate implementation addresses for incoming function calls.

While the Router pattern allows to point to a different contract for each function, in practice functions are usually groupped by functionality related to a shared state (a read and a set function for example).

To make the pattern more practical, we created a generic BaseRouter contract that makes it easy to have logical group of functions plugged in and out of it, each group of functions being implemented in a separate implementation contract. We refer to each such implementation contract as an extension.

BaseRouter maintains a function_signature → implementation mapping, and provides an API for updating that mapping. By updating the values stored in this map, functionality can be added to, removed from or updated in the smart contract.

Deploying a Router

Deploying a contract in the router pattern looks a little different from deploying a regular contract.

1. Deploy all your Extension contracts first. You only need to do this once per Extension. Deployed Extensions can be re-used by many different Router contracts.

2. Deploy your Router contract that implements BaseRouter.

3. Add extensions to your router via the API available in BaseRouter. (Alternatively, you can use BaseRouterDefaults which can be initialized with a set of extensions on deployment.)

Extensions - Grouping logical functionality together

By itself, the core Router contract does not specify how to store or fetch appropriate implementation addresses for incoming function calls.

While the Router pattern allows to point to a different contract for each function, in practice functions are usually groupped by functionality related to a shared state (a read and a set function for example).

To make the pattern more practical, we created a generic BaseRouter contract that makes it easy to have logical group of functions plugged in and out of it, each group of functions being implemented in a separate implementation contract. We refer to each such implementation contract as an extension.

BaseRouter maintains a function_signature → implementation mapping, and provides an API for updating that mapping. By updating the values stored in this map, functionality can be added to, removed from or updated in the smart contract.

Extension to Extension communication

When splitting logic between multiple extensions in a Router, one might want to access data from one Extension to another.

A simple way to do this is by casting the current contract address as the Extension (ideally its interface) we're trying to call. This works from both a Router or any of its extensions.

Here's an example of accessing a IPermission extension from another one:

modifier onlyAdmin(address _asset) {
  /// we access our IPermission extension by casting our own address
  IPermissions(address(this)).hasAdminRole(msg.sender);
}

Note that if we don't have an IPermission extension added to our Router, this method will revert.

Upgrading Extensions

Just like any upgradeable contract, there are limitations on how the data structure of the updated contract is modified. While the logic of a function can be updated safely, changing the data structure of a contract requires careful consideration.

A good rule of thumb to follow is:

• It is safe to append new fields to an existing data structure
• It is not safe to update the type or order of existing structs; deprecate and add new ones instead.

Refer to this article for more information.

API reference

You can generate and view the full API reference for all contracts, interfaces and libraries in the repository by running the repository locally and running:

forge doc --serve --port 4000

Router

import "@thirdweb-dev/dynamic-contracts/src/core/Router.sol";

The Router smart contract implements the ERC-7504 Router interface.

For any given function call made to the Router contract that reaches the fallback function, the contract performs a delegateCall on the address returned by getImplementationForFunction(msg.sig).

This is an abstract contract that expects you to override and implement the following functions:

• getImplementationForFunction

  function getImplementationForFunction(bytes4 _functionSelector) public view virtual returns (address implementation);

fallback

delegateCalls the appropriate implementation address for the given incoming function call.

The implementation address to delegateCall MUST be retrieved from calling getImplementationForFunction with the incoming call's function selector.

fallback() external payable virtual;

Revert conditions:

• getImplementationForFunction(msg.sig) == address(0)

_delegate

delegateCalls an implementation smart contract.

function _delegate(address implementation) internal virtual;

getImplementationForFunction

Returns the implementation address to delegateCall for the given function selector.

function getImplementationForFunction(bytes4 _functionSelector) public view virtual returns (address implementation);

Parameters

Name	Type	Description
_functionSelector	bytes4	The function selector to get the implementation address for.

Returns

Name	Type	Description
implementation	address	The implementation address to delegateCall for the given function selector.

ExtensionManager

import "@thirdweb-dev/dynamic-contracts/src/presets/ExtensionManager.sol";

The ExtensionManager contract provides a defined storage layout and API for managing and fetching a router's extensions. This contract implements the ERC-7504 RouterState interface.

The contract's storage layout is defined in src/lib/ExtensionManagerStorage:

struct Data {
    StringSet.Set extensionNames;
    mapping(string => IExtension.Extension) extensions;
    mapping(bytes4 => IExtension.ExtensionMetadata) extensionMetadata;
}

The following are some helpful invariant properties of ExtensionManager:

• Each extension has a non-empty, unique name which is stored in extensionNames.

• Each extension's metadata specifies a non-zero-address implementation.

• A function fn has a non-empty metadata i.e. extensionMetadata[fn] value if and only if it is a part of some extension Ext such that:

  • extensionNames contains Ext.metadata.name
  • extensions[Ext.metadata.name].functions includes fn.

This contract is meant to be used along with a Router contract, where an upgrade to the Router means updating the storage of ExtensionManager. For example, the preset contract BaseRouter inherits Router and ExtensionManager and overrides the getImplementationForFunction function as follows:

function getImplementationForFunction(bytes4 _functionSelector) public view virtual override returns (address) {
        return getMetadataForFunction(_functionSelector).implementation;
    }

This contract is an abstract contract that expects you to override and implement the following functions:

• isAuthorizedCallToUpgrade

  function _isAuthorizedCallToUpgrade() internal view virtual returns (bool);

onlyAuthorizedCall

Checks that a call to any external function is authorized.

modifier onlyAuthorizedCall();

Revert conditions:

• !_isAuthorizedCallToUpgrade()

getAllExtensions

Returns all extensions of the Router.

function getAllExtensions() external view virtual override returns (Extension[] memory allExtensions);

Returns

Name	Type	Description
allExtensions	Extension[]	An array of all extensions.

getMetadataForFunction

Returns the extension metadata for a given function.

function getMetadataForFunction(bytes4 functionSelector) public view virtual returns (ExtensionMetadata memory);

Parameters

Name	Type	Description
functionSelector	bytes4	The function selector to get the extension metadata for.

Returns

Name	Type	Description
<none>	ExtensionMetadata	metadata The extension metadata for a given function.

getExtension

Returns the extension metadata and functions for a given extension.

function getExtension(string memory extensionName) public view virtual returns (Extension memory);

Parameters

Name	Type	Description
extensionName	string	The name of the extension to get the metadata and functions for.

Returns

Name	Type	Description
<none>	Extension	The extension metadata and functions for a given extension.

addExtension

Add a new extension to the router.

function addExtension(Extension memory _extension) external onlyAuthorizedCall;

Parameters

Name	Type	Description
_extension	Extension	The extension to add.

Revert conditions:

• Extension name is empty.
• Extension name is already used.
• Extension implementation is zero address.
• Selector and signature mismatch for some function in the extension.
• Some function in the extension is already a part of another extension.

replaceExtension

Fully replace an existing extension of the router.

The extension with name extension.name is the extension being replaced.

function replaceExtension(Extension memory _extension) external onlyAuthorizedCall;

Parameters

Name	Type	Description
_extension	Extension	The extension to replace or overwrite.

Revert conditions:

• Extension being replaced does not exist.
• Provided extension's implementation is zero address.
• Selector and signature mismatch for some function in the provided extension.
• Some function in the provided extension is already a part of another extension.

removeExtension

Remove an existing extension from the router.

function removeExtension(string memory _extensionName) external onlyAuthorizedCall;

Parameters

Name	Type	Description
_extensionName	string	The name of the extension to remove.

Revert conditions:

• Extension being removed does not exist.

enableFunctionInExtension

Enables a single function in an existing extension.

Makes the given function callable on the router.

function enableFunctionInExtension(string memory _extensionName, ExtensionFunction memory _function)
    external
    onlyAuthorizedCall;

Parameters

Name	Type	Description
_extensionName	string	The name of the extension to which extFunction belongs.
_function	ExtensionFunction	The function to enable.

Revert conditions:

• Provided extension does not exist.
• Selector and signature mismatch for some function in the provided extension.
• Provided function is already a part of another extension.

disableFunctionInExtension

Disables a single function in an Extension.

function disableFunctionInExtension(string memory _extensionName, bytes4 _functionSelector)
    external
    onlyAuthorizedCall;

Parameters

Name	Type	Description
_extensionName	string	The name of the extension to which the function of functionSelector belongs.
_functionSelector	bytes4	The function to disable.

Revert conditions:

• Provided extension does not exist.
• Provided function is not part of provided extension.

_getExtension

Returns the Extension for a given name.

function _getExtension(string memory _extensionName) internal view returns (Extension memory);

_setMetadataForExtension

Sets the ExtensionMetadata for a given extension.

function _setMetadataForExtension(string memory _extensionName, ExtensionMetadata memory _metadata) internal;

_deleteMetadataForExtension

Deletes the ExtensionMetadata for a given extension.

function _deleteMetadataForExtension(string memory _extensionName) internal;

_setMetadataForFunction

Sets the ExtensionMetadata for a given function.

function _setMetadataForFunction(bytes4 _functionSelector, ExtensionMetadata memory _metadata) internal;

_deleteMetadataForFunction

Deletes the ExtensionMetadata for a given function.

function _deleteMetadataForFunction(bytes4 _functionSelector) internal;

_enableFunctionInExtension

Enables a function in an Extension.

function _enableFunctionInExtension(string memory _extensionName, ExtensionFunction memory _extFunction)
    internal
    virtual;

_disableFunctionInExtension

Note: bytes4(0) is the function selector for the receive function. So, we maintain a special fn selector-signature mismatch check for the receive function.

Disables a given function in an Extension.

function _disableFunctionInExtension(string memory _extensionName, bytes4 _functionSelector) internal;

_removeAllFunctionsFromExtension

Removes all functions from an Extension.

function _removeAllFunctionsFromExtension(string memory _extensionName) internal;

_canAddExtension

Returns whether a new extension can be added in the given execution context.

function _canAddExtension(Extension memory _extension) internal virtual returns (bool);

_canReplaceExtension

Returns whether an extension can be replaced in the given execution context.

function _canReplaceExtension(Extension memory _extension) internal virtual returns (bool);

_canRemoveExtension

Returns whether an extension can be removed in the given execution context.

function _canRemoveExtension(string memory _extensionName) internal virtual returns (bool);

_canEnableFunctionInExtension

Returns whether a function can be enabled in an extension in the given execution context.

function _canEnableFunctionInExtension(string memory _extensionName, ExtensionFunction memory)
    internal
    view
    virtual
    returns (bool);

_canDisableFunctionInExtension

Returns whether a function can be disabled in an extension in the given execution context.

function _canDisableFunctionInExtension(string memory _extensionName, bytes4 _functionSelector)
    internal
    view
    virtual
    returns (bool);

_extensionManagerStorage

Returns the ExtensionManager storage.

function _extensionManagerStorage() internal pure returns (ExtensionManagerStorage.Data storage data);

isAuthorizedCallToUpgrade

To override; returns whether all relevant permission and other checks are met before any upgrade.

function _isAuthorizedCallToUpgrade() internal view virtual returns (bool);

BaseRouter

import "@thirdweb-dev/dynamic-contracts/src/presets/BaseRouter"

BaseRouter inherits Router and ExtensionManager. It overrides the Router.getImplementationForFunction function to use the extensions stored in the ExtensionManager contract's storage system.

This contract is an abstract contract that expects you to override and implement the following functions:

• isAuthorizedCallToUpgrade

  function _isAuthorizedCallToUpgrade() internal view virtual returns (bool);

getImplementationForFunction

Returns the implementation address to delegateCall for the given function selector.

function getImplementationForFunction(bytes4 _functionSelector) public view virtual override returns (address);

Parameters

Name	Type	Description
_functionSelector	bytes4	The function selector to get the implementation address for.

Returns

Name	Type	Description
<none>	address	implementation The implementation address to delegateCall for the given function selector.

Feedback

The best, most open way to give feedback/suggestions for the router pattern is to open a github issue, or comment in the ERC-7504 ethereum-magicians discussion.

Additionally, since thirdweb will be maintaining this repository, you can reach out to us at [email protected] or join our discord.

Authors

• thirdweb