Contract SDK

The Smart Contract SDK, designed to facilitate the development of community-driven projects. The SDK serves as an upper layer wrapper for the Greenfield-Contracts library, which implements the cross-chain communication functionality. By providing a user-friendly interface to the underlying interface, the SDK simplifies the development process and enables developers to create and manage a variety of greenfield resources, like bucket, group, and object on BSC through smart contract directly.

The SDK is organized into four primary parts: BaseApp, BucketApp, ObjectApp, and GroupApp. These components serve as the building blocks for developers. The BaseApp serves as the foundation for the other three components, providing common functions required by the BucketApp, ObjectApp, and GroupApp.

The BucketApp is responsible for managing bucket-related operations, while the ObjectApp handles object-related actions. The GroupApp, being the most complex of the four, is designed to handle group-related operations.

Each of these components is equipped with unique functions and virtual functions that can be implemented to suit specific project needs.

Components

1. BaseApp: Contains common functions used by the other components, as well as three virtual functions that need to be implemented for specific project requirements.
2. BucketApp: A specialized module designed to handle bucket-related operations, such as creating and deleting buckets, and processing bucket resource calls.
3. ObjectApp: A specialized module focused on object-related operations, specifically object deletion since creating objects from BSC is not supported.
4. GroupApp: A more complex module that handles group-related operations, such as creating, deleting, and updating groups, and managing group resource calls.

BaseApp

The BaseApp contains common functions that are shared by BucketApp, ObjectApp, and GroupApp. These functions are essential for setting up and managing the environment for cross-chain operations. The BaseApp provides the following core functions:

1. _getTotalFee(): This function returns the total value required to send a cross-chain package.
2. Setters: There are several setters available for configuring various aspects of the smart contract, such as:
3. callbackGasLimit: Sets the gas limit for the callback function.
4. failureHandleStrategy: Sets the strategy for handling failures during the execution of the smart contract.

In addition to these functions, BaseApp provides three virtual functions:

1. greenfieldCall(uint32 status, uint8 resourceType, uint8 operationType, uint256 resourceId, bytes calldata callbackData): This function is a callback hook designed to handle cross-chain response. It is a virtual function that needs to be implemented by developers to define custom behaviors for different types of resources and operation types. This function is triggered when a cross-chain operation is completed on greenfield side and return a package to bsc, allowing developers to execute specific actions or update states in response to the completion of an operation. If the developers don’t need callback, this function(as well as other callback related functions) can be undefined.
2. retryPackage(uint8 resourceType): This function handles the retry mechanism for a package, based on its resource type. Developers should implement this function to define the behavior when a package needs to be retried.
3. skipPackage(uint8 resourceType): This function allows for skipping a package, based on its resource type. Developers should implement this function to define the behavior when a package needs to be skipped.

By implementing these virtual functions, developers can customize the behavior of their smart contracts to meet their specific requirements. With the BaseApp component, developers have a solid foundation on which to build their smart contract applications using BucketApp, ObjectApp, and GroupApp.

BucketApp

The BucketApp component is a specialized module designed to handle bucket-related operations in the smart contract SDK. This component offers a range of functions to create, delete, and manage buckets, as well as to route and handle various bucket resource operations. Below, we provide a detailed overview of the functions included in the BucketApp:

1. _bucketGreenfieldCall(uint32 status, uint8 operationType, uint256 resourceId, bytes calldata callbackData): This function serves as a router for bucket resource callback. It processes and directs the call based on the provided parameters.
2. _retryBucketPackage(): This function retries a failed bucket resource package.
3. _skipBucketPackage(): This function skips a failed bucket resource package.
4. _createBucket(address _creator, string memory _name, BucketStorage.BucketVisibilityType _visibility, address _paymentAddress, address _spAddress, uint256 _expireHeight, uint32 _globalVirtualGroupFamilyId, bytes calldata _sig, uint64 _chargedReadQuota): This function sends a create bucket cross-chain request to greenfield without a callback. It takes various parameters, such as creator, name, visibility type, charged read quota, service provider address, expire height, global virtual family id and signature.
5. _createBucket(address _creator, string memory _name, BucketStorage.BucketVisibilityType _visibility, address _paymentAddress, address _spAddress, uint256 _expireHeight, uint32 _globalVirtualGroupFamilyId, bytes calldata _sig, uint64 _chargedReadQuota, address _refundAddress, PackageQueue.FailureHandleStrategy _failureHandleStrategy, bytes memory _callbackData, uint256 _callbackGasLimit): This function sends a create bucket cross-chain request to greenfield with a callback. It takes the same parameters as the previous function, along with some additional parameters for the callback.
6. _deleteBucket(uint256 _tokenId): This function sends a delete bucket cross-chain request to greenfield without a callback, using the provided token ID.
7. _deleteBucket(uint256 _tokenId, address _refundAddress, PackageQueue.FailureHandleStrategy _failureHandleStrategy, bytes memory _callbackData, uint256 _callbackGasLimit): This function sends a delete bucket cross-chain request to greenfield with a callback, using the provided token ID and callback data.

In addition to these functions, the BucketApp provides two virtual functions:

1. _createBucketCallback(uint32 _status, uint256 _tokenId, bytes memory _callbackData): Developers can implement this function to define the behavior for the create bucket callback. The function receives the status, token ID, and callback data as parameters.
2. _deleteBucketCallback(uint32 _status, uint256 _tokenId, bytes memory _callbackData): Developers can implement this function to define the behavior for the delete bucket callback. The function receives the status, token ID, and callback data as parameters.

By implementing these virtual functions, developers can tailor the BucketApp component to suit their specific bucket-related operations and handle the corresponding callbacks as needed.

ObjectApp

The ObjectApp component is a specialized module designed to handle object-related operations in the smart contract SDK. This component offers a range of functions to manage objects and process object resource operations. However, please note that creating objects from BSC is currently not supported. Below, we provide a detailed overview of the functions included in the ObjectApp:

1. _objectGreenfieldCall(uint32 status, uint8 operationType, uint256 resourceId, bytes calldata callbackData): This function serves as a router for object resource callback. It processes and directs the call based on the provided parameters.
2. _retryObjectPackage(): This function retries a failed object resource package.
3. _skipObjectPackage(): This function skips a failed object resource package.
4. _deleteObject(uint256 _tokenId): This function deletes an object using the provided token ID. As creating objects from BSC is not supported, the ObjectApp focuses on deletion operations.
5. _deleteObject(uint256 _tokenId, address _refundAddress, PackageQueue.FailureHandleStrategy _failureHandleStrategy, bytes memory _callbackData, uint256 _callbackGasLimit): This function deletes an object with a callback, using the provided token ID and callback data.

In addition to these functions, the ObjectApp provides one virtual function:

1. _deleteObjectCallback(uint32 _status, uint256 _tokenId, bytes memory _callbackData): Developers need to implement this function to define the behavior for the delete object callback. The function receives the status, token ID, and callback data as parameters.

By implementing this virtual function, developers can customize the ObjectApp component to handle object deletion operations and manage the corresponding callbacks as needed.

GroupApp

The GroupApp component is a specialized module designed to handle group-related operations in the smart contract SDK. This component is more complex compared to the BucketApp and ObjectApp, as it offers a range of functions to create, delete, update, and manage groups. Below, we provide a detailed overview of the functions included in the GroupApp:

1. _groupGreenfieldCall(uint32 status, uint8 operationType, uint256 resourceId, bytes calldata callbackData): This function serves as a router for group resource callback. It processes and directs the call based on the provided parameters.
2. _retryGroupPackage(): This function retries a failed group resource package.
3. _skipGroupPackage(): This function skips a failed group resource package.
4. _createGroup(address _owner, string memory _groupName): This function creates a new group with the provided owner address and group name.
5. _createGroup(address _refundAddress, PackageQueue.FailureHandleStrategy _failureHandleStrategy, bytes memory _callbackData,, address _owner, string memory _groupName, uint256 _callbackGasLimit): This function creates a new group with a callback, using the provided owner address, group name, and callback data.
6. _deleteGroup(uint256 _tokenId): This function deletes a group using the provided token ID.
7. _deleteGroup(uint256 _tokenId, address _refundAddress, PackageQueue.FailureHandleStrategy _failureHandleStrategy, bytes memory _callbackData, uint256 _callbackGasLimit): This function deletes a group with a callback, using the provided token ID and callback data.
8. _updateGroup(address _owner, uint256 _tokenId, uint8 _opType, address[] memory _members, uint64[] memory _expiration): This function updates a group based on the provided owner address, token ID, operation type, and an array of member addresses.
9. _updateGroup(address _owner, uint256 _tokenId, uint8 _opType, address[] memory _members, uint64[] memory _expiration, address _refundAddress, PackageQueue.FailureHandleStrategy _failureHandleStrategy, bytes memory _callbackData, uint256 _callbackGasLimit): This function updates a group with a callback, using the provided owner address, token ID, operation type, an array of member addresses, and callback data.

In addition to these functions, the GroupApp provides three virtual functions:

1. _createGroupCallback(uint32 _status, uint256 _tokenId, bytes memory _callbackData): Developers need to implement this function to define the behavior for the create group callback. The function receives the status, token ID, and callback data as parameters.
2. _deleteGroupCallback(uint32 _status, uint256 _tokenId, bytes memory _callbackData): Developers need to implement this function to define the behavior for the delete group callback. The function receives the status, token ID, and callback data as parameters.
3. _updateGroupCallback(uint32 _status, uint256 _tokenId, bytes memory _callbackData): Developers need to implement this function to define the behavior for the update group callback. The function receives the status, token ID, and callback data as parameters.

By implementing these virtual functions, developers can customize the GroupApp component to suit their specific group-related operations and handle the corresponding callbacks as needed.

Integration Example

We will walk you through the process of creating a decentralized Ebook shop using the Contract SDK as an example.

Prerequisites

Before starting, make sure you have the following tools installed:

• Node.js
• Foundry

Installation

$ npm install @bnb-chain/greenfield-contracts-sdk

Alternatively, you can obtain the contracts directly from the GitHub repository (bnb-chain/greenfield-contracts-sdk). When doing so, ensure that you specify the appropriate release.

Steps

1. Import the desired contracts, for example in examples/ebook-shop.sol:

pragma solidity ^0.8.0;

import "@bnb-chain/greenfield-contracts-sdk/BucketApp.sol";
import "@bnb-chain/greenfield-contracts-sdk/ObjectApp.sol";
import "@bnb-chain/greenfield-contracts-sdk/GroupApp.sol";
import "@bnb-chain/greenfield-contracts-sdk/interface/IERC1155.sol";
import "@bnb-chain/greenfield-contracts-sdk/interface/IERC721NonTransferable.sol";
import "@bnb-chain/greenfield-contracts-sdk/interface/IERC1155NonTransferable.sol";
...

contract EbookShop is BucketApp, ObjectApp, GroupApp {
 ...
}

1. Define the initialize function. Initialize the global variables in the init function. You can use the internal init functions:

   function initialize(
       address _crossChain,
       address _bucketHub,
       address _objectHub,
       address _groupHub,
       address _ebookToken,
       address _paymentAddress,
       uint256 _callbackGasLimit,
       address _refundAddress,
       uint8 _failureHandleStrategy,
       ...
   ) public initializer {
       __base_app_init_unchained(_crossChain, _callbackGasLimit, _refundAddress, _failureHandleStrategy);
       __bucket_app_init_unchained(_bucketHub);
       __group_app_init_unchained(_groupHub);
       __object_app_init_unchained(_objectHub);
   
       ...
   }
   

2. Define and override the greenfieldCall, retryPackage and skipPackage functions if your dApp needs callback. You can route calls with the help of the internal method:

   function greenfieldCall(
       uint32 status,
       uint8 resoureceType,
       uint8 operationType,
       uint256 resourceId,
       bytes calldata callbackData
   ) external override(BucketApp, ObjectApp, GroupApp) {
       require(msg.sender == crossChain, string.concat("EbookShop: ", ERROR_INVALID_CALLER));
   
       if (resoureceType == RESOURCE_BUCKET) {
           _bucketGreenfieldCall(status, operationType, resourceId, callbackData);
       } else if (resoureceType == RESOURCE_OBJECT) {
           _objectGreenfieldCall(status, operationType, resourceId, callbackData);
       } else if (resoureceType == RESOURCE_GROUP) {
           _groupGreenfieldCall(status, operationType, resourceId, callbackData);
       } else {
           revert(string.concat("EbookShop: ", ERROR_INVALID_RESOURCE));
       }
   }
   
   function retryPackage(uint8 resoureceType) external override onlyOperator {
       if (resoureceType == RESOURCE_BUCKET) {
           _retryBucketPackage();
       } else if (resoureceType == RESOURCE_OBJECT) {
           _retryObjectPackage();
       } else if (resoureceType == RESOURCE_GROUP) {
           _retryGroupPackage();
       } else {
           revert(string.concat("EbookShop: ", ERROR_INVALID_RESOURCE));
       }
   }
   
   function skipPackage(uint8 resoureceType) external override onlyOperator {
       if (resoureceType == RESOURCE_BUCKET) {
           _skipBucketPackage();
       } else if (resoureceType == RESOURCE_OBJECT) {
           _skipObjectPackage();
       } else if (resoureceType == RESOURCE_GROUP) {
           _skipGroupPackage();
       } else {
           revert(string.concat("EbookShop: ", ERROR_INVALID_RESOURCE));
       }
   }
   

3. Next you need to define the main functional parts of the app. You can send cross-chain request to system contracts with the help of internal functions like below:

   /**
    * @dev Create a new series.
    * 
    * Assuming the sp provider's info will be provided by the front-end.
    */
   function createSeries(
       string calldata name,
       BucketStorage.BucketVisibilityType visibility,
       uint64 chargedReadQuota,
       address spAddress,
       uint256 expireHeight,
       bytes calldata sig
   ) external payable {
       require(bytes(name).length > 0, string.concat("EbookShop: ", ERROR_INVALID_NAME));
       require(seriesId[name] == 0, string.concat("EbookShop: ", ERROR_RESOURCE_EXISTED));
   
       bytes memory _callbackData = bytes(name); // use name as callback data
       _createBucket(msg.sender, name, visibility, chargedReadQuota, spAddress, expireHeight, sig, _callbackData); // send cross-chain request
   }
   
   /**
    * @dev Provide an ebook's ID to publish it.
    *
    * An ERC1155 token will be minted to the owner.
    * Other users can buy the ebook by calling `buyEbook` function with given price.
    */
   function publishEbook(uint256 _ebookId, uint256 price) external {
       require(
           IERC721NonTransferable(objectToken).ownerOf(_ebookId) == msg.sender,
           string.concat("EbookShop: ", ERROR_INVALID_CALLER)
       );
       require(ebookGroup[_ebookId] != 0, string.concat("EbookShop: ", ERROR_GROUP_NOT_EXISTED));
       require(price > 0, string.concat("EbookShop: ", ERROR_INVALID_PRICE));
   
       ebookPrice[_ebookId] = price;
       IERC1155(ebookToken).mint(msg.sender, _ebookId, 1, "");
   }
   
   /**
    * @dev Provide an ebook's ID to buy it.
    *
    * Buyer will be added to the group of the ebook.
    * An ERC1155 token will be minted to the buyer.
    */
   function buyEbook(uint256 _ebookId) external payable {
       require(ebookPrice[_ebookId] > 0, string.concat("EbookShop: ", ERROR_EBOOK_NOT_ONSHELF));
   
       uint256 price = ebookPrice[_ebookId];
       require(msg.value >= price, string.concat("EbookShop: ", ERROR_NOT_ENOUGH_VALUE));
   
       IERC1155(ebookToken).mint(msg.sender, _ebookId, 1, "");
   
       uint256 _groupId = ebookGroup[_ebookId];
       address _owner = IERC721NonTransferable(groupToken).ownerOf(_groupId);
       address[] memory _member = new address[](1);
       _member[0] = msg.sender;
       _updateGroup(_owner, _groupId, UPDATE_ADD, _member);
   }
   
   /**
    * @dev Provide an ebook's ID to downshelf it.
    *
    * The ebook will be removed from the shelf and cannot be bought.
    * Those who have already purchased are not affected.
    */
   function downshelfEbook(uint256 _ebookId) external {
       require(
           IERC721NonTransferable(objectToken).ownerOf(_ebookId) == msg.sender,
           string.concat("EbookShop: ", ERROR_INVALID_CALLER)
       );
       require(ebookPrice[_ebookId] > 0, string.concat("EbookShop: ", ERROR_EBOOK_NOT_ONSHELF));
   
       ebookPrice[_ebookId] = 0;
   }
   ...
   

4. Besides, you may need to provide a function for user to register their own resource that were created at greenfield side and then mirrored to BSC manually:

   /**
    * @dev Register bucket resource that mirrored from GreenField to BSC.
    */
   function registerSeries(string calldata name, uint256 tokenId) external {
       require(
           IERC721NonTransferable(bucketToken).ownerOf(tokenId) == msg.sender,
           string.concat("EbookShop: ", ERROR_INVALID_CALLER)
       );
       require(bytes(name).length > 0, string.concat("EbookShop: ", ERROR_INVALID_NAME));
       require(seriesId[name] == 0, string.concat("EbookShop: ", ERROR_RESOURCE_EXISTED));
   
       seriesName[tokenId] = name;
       seriesId[name] = tokenId;
   }
   ...
   

5. Define other view functions, internal functions and access control system according to your own needs.