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Lottery Game Contract

Description: This contract is moderately complex. It demonstrates the use of state variables, user interactions, and random number generation to create a basic lottery game.

Purpose: To introduce you to more advanced concepts such as state management, event handling, and randomization in smart contracts.

Difficulty Level: Moderate

Step 1 - Setting up your development environment​

  • Basic knowledge of terminal commands
  • IDE - Install VS Code

Install Required Packages

Terminal
dotnet new --install AElf.ContractTemplates

AELF.ContractTemplates contains various predefined templates for the ease of developing smart contracts on the aelf blockchain.

  • Install aelf deploy tool
Terminal
dotnet tool install --global aelf.deploy

aelf.deploy is a utility tool for deploying smart contracts on the aelf blockchain. Please remember to export PATH after installing aelf.deploy.

info

ℹ️ Note: If you have installed aelf.deploy and your terminal says that there is no such command available, please uninstall and install aelf.deploy.

Install Node.js and Yarn

Install aelf-command

Terminal
sudo npm i -g aelf-command

aelf-command is a CLI tool for interacting with the aelf blockchain, enabling tasks like creating wallets and managing transactions. Provide required permissions while installing aelf-command globally.

Step 2 - Develop Smart Contract​

Start Your Smart Contract Project​

  • Open your Terminal.

  • Enter the following command to generate a new project:

Terminal
mkdir lottery-game
cd lottery-game
dotnet new aelf -n LotteryGame

Adding Your Smart Contract Code​

Now that we have a template lottery game project, we can customise the template to incorporate our own contract logic. Lets start by implementing methods to provide basic functionality for updating and reading a message stored persistently in the contract state.

  • Enter this command in your Terminal.
Terminal
cd src

Defining Methods and Messages​

  • Rename the file name from Protobuf/contract/hello_world_contract.proto to lottery_game_contract.proto:
Terminal
mv Protobuf/contract/hello_world_contract.proto Protobuf/contract/lottery_game_contract.proto
  • open the project with your IDE.

The implementation of file src/Protobuf/contract/lottery_game_contract.proto is as follows:

lottery_game_contract.proto
syntax = "proto3";

import "aelf/core.proto";
import "aelf/options.proto";
import "google/protobuf/empty.proto";
import "google/protobuf/wrappers.proto";
import "Protobuf/reference/acs12.proto";
// The namespace of this class
option csharp_namespace = "AElf.Contracts.LotteryGame";

service LotteryGame {
  // The name of the state class the smart contract is going to use to access blockchain state
  option (aelf.csharp_state) = "AElf.Contracts.LotteryGame.LotteryGameState";
  option (aelf.base) = "Protobuf/reference/acs12.proto";

  rpc Initialize (google.protobuf.Empty) returns (google.protobuf.Empty) {
  }

  rpc Play (google.protobuf.Int64Value) returns (google.protobuf.Empty) {
  }

  rpc Withdraw (google.protobuf.Int64Value) returns (google.protobuf.Empty) {
  }

  rpc Deposit (google.protobuf.Int64Value) returns (google.protobuf.Empty) {
  }

  rpc TransferOwnership (aelf.Address) returns (google.protobuf.Empty) {
  }

  rpc GetPlayAmountLimit (google.protobuf.Empty) returns (PlayAmountLimitMessage) {
    option (aelf.is_view) = true;
  }

  rpc GetContractBalance (google.protobuf.Empty) returns (google.protobuf.Int64Value) {
    option (aelf.is_view) = true;
  }

  rpc GetOwner (google.protobuf.Empty) returns (google.protobuf.StringValue) {
    option (aelf.is_view) = true;
  }
}

// An event that will be emitted from contract method call when Play is called.
message PlayOutcomeEvent {
  option (aelf.is_event) = true;
  int64 amount = 1;
  int64 won = 2;
}

// An event that will be emitted from contract method call when Withdraw is called.
message WithdrawEvent {
  option (aelf.is_event) = true;
  int64 amount = 1;
  aelf.Address from = 2;
  aelf.Address to = 3;
}

// An event that will be emitted from contract method call when Deposit is called.
message DepositEvent {
  option (aelf.is_event) = true;
  int64 amount = 1;
  aelf.Address from = 2;
  aelf.Address to = 3;
}

// The message containing the play amount limits
message PlayAmountLimitMessage {
  int64 minimumAmount = 1;
  int64 maximumAmount = 2;
}

Define Contract States​

The implementation of file src/LotteryGameState.cs is as follows:

src/LotteryGameState.cs
using AElf.Sdk.CSharp.State;
using AElf.Types;

namespace AElf.Contracts.LotteryGame
{
    // The state class is access the blockchain state
    public partial class LotteryGameState : ContractState
    {
        // A state to check if contract is initialized
        public BoolState Initialized { get; set; }
        // A state to store the owner address
        public SingletonState<Address> Owner { get; set; }
    }
}

Contract Reference State​

  • Create a new file token_contract.proto under src/Protobuf/reference/.

  • Replace this code of implementation file of token_contract.proto:

token_contract.proto
/**
 * MultiToken contract.
 */
syntax = "proto3";

package token;

import "aelf/core.proto";
import "aelf/options.proto";
import "google/protobuf/empty.proto";
import "google/protobuf/wrappers.proto";

option csharp_namespace = "AElf.Contracts.MultiToken";

service TokenContract {
  // Create a new token.
  rpc Create (CreateInput) returns (google.protobuf.Empty) {
  }

  // Issuing some amount of tokens to an address is the action of increasing that addresses balance
  // for the given token. The total amount of issued tokens must not exceed the total supply of the token
  // and only the issuer (creator) of the token can issue tokens.
  // Issuing tokens effectively increases the circulating supply.
  rpc Issue (IssueInput) returns (google.protobuf.Empty) {
  }

  // Transferring tokens simply is the action of transferring a given amount of tokens from one address to another.
  // The origin or source address is the signer of the transaction.
  // The balance of the sender must be higher than the amount that is transferred.
  rpc Transfer (TransferInput) returns (google.protobuf.Empty) {
  }

  // The TransferFrom action will transfer a specified amount of tokens from one address to another.
  // For this operation to succeed the from address needs to have approved (see allowances) enough tokens
  // to Sender of this transaction. If successful the amount will be removed from the allowance.
  rpc TransferFrom (TransferFromInput) returns (google.protobuf.Empty) {
  }

  // The approve action increases the allowance from the Sender to the Spender address,
  // enabling the Spender to call TransferFrom.
  rpc Approve (ApproveInput) returns (google.protobuf.Empty) {
  }

  rpc BatchApprove (BatchApproveInput) returns (google.protobuf.Empty) {
  }

  // This is the reverse operation for Approve, it will decrease the allowance.
  rpc UnApprove (UnApproveInput) returns (google.protobuf.Empty) {
  }

  // This method can be used to lock tokens.
  rpc Lock (LockInput) returns (google.protobuf.Empty) {
  }

  // This is the reverse operation of locking, it un-locks some previously locked tokens.
  rpc Unlock (UnlockInput) returns (google.protobuf.Empty) {
  }

  // This action will burn the specified amount of tokens, removing them from the token’s Supply.
  rpc Burn (BurnInput) returns (google.protobuf.Empty) {
  }

  // Set the primary token of side chain.
  rpc SetPrimaryTokenSymbol (SetPrimaryTokenSymbolInput) returns (google.protobuf.Empty) {
  }

  // This interface is used for cross-chain transfer.
  rpc CrossChainTransfer (CrossChainTransferInput) returns (google.protobuf.Empty) {
  }

  // This method is used to receive cross-chain transfers.
  rpc CrossChainReceiveToken (CrossChainReceiveTokenInput) returns (google.protobuf.Empty) {
  }

  // The side chain creates tokens.
  rpc CrossChainCreateToken(CrossChainCreateTokenInput) returns (google.protobuf.Empty) {
  }

  // When the side chain is started, the side chain is initialized with the parent chain information.
  rpc InitializeFromParentChain (InitializeFromParentChainInput) returns (google.protobuf.Empty) {
  }

  // Handle the transaction fees charged by ChargeTransactionFees.
  rpc ClaimTransactionFees (TotalTransactionFeesMap) returns (google.protobuf.Empty) {
  }

  // Used to collect transaction fees.
  rpc ChargeTransactionFees (ChargeTransactionFeesInput) returns (ChargeTransactionFeesOutput) {
  }

  rpc ChargeUserContractTransactionFees(ChargeTransactionFeesInput) returns(ChargeTransactionFeesOutput){

  }

  // Check the token threshold.
  rpc CheckThreshold (CheckThresholdInput) returns (google.protobuf.Empty) {
  }

  // Initialize coefficients of every type of tokens supporting charging fee.
  rpc InitialCoefficients (google.protobuf.Empty) returns (google.protobuf.Empty){
  }

  // Processing resource token received.
  rpc DonateResourceToken (TotalResourceTokensMaps) returns (google.protobuf.Empty) {
  }

  // A transaction resource fee is charged to implement the ACS8 standards.
  rpc ChargeResourceToken (ChargeResourceTokenInput) returns (google.protobuf.Empty) {
  }

  // Verify that the resource token are sufficient.
  rpc CheckResourceToken (google.protobuf.Empty) returns (google.protobuf.Empty) {
  }

  // Set the list of tokens to pay transaction fees.
  rpc SetSymbolsToPayTxSizeFee (SymbolListToPayTxSizeFee) returns (google.protobuf.Empty){
  }

  // Update the coefficient of the transaction fee calculation formula.
  rpc UpdateCoefficientsForSender (UpdateCoefficientsInput) returns (google.protobuf.Empty) {
  }

  // Update the coefficient of the transaction fee calculation formula.
  rpc UpdateCoefficientsForContract (UpdateCoefficientsInput) returns (google.protobuf.Empty) {
  }

  // This method is used to initialize the governance organization for some functions,
  // including: the coefficient of the user transaction fee calculation formula,
  // the coefficient of the contract developer resource fee calculation formula, and the side chain rental fee.
  rpc InitializeAuthorizedController (google.protobuf.Empty) returns (google.protobuf.Empty){
  }

  rpc AddAddressToCreateTokenWhiteList (aelf.Address) returns (google.protobuf.Empty) {
  }
  rpc RemoveAddressFromCreateTokenWhiteList (aelf.Address) returns (google.protobuf.Empty) {
  }

  rpc SetTransactionFeeDelegations (SetTransactionFeeDelegationsInput) returns (SetTransactionFeeDelegationsOutput){
  }

  rpc RemoveTransactionFeeDelegator (RemoveTransactionFeeDelegatorInput) returns (google.protobuf.Empty){
  }

  rpc RemoveTransactionFeeDelegatee (RemoveTransactionFeeDelegateeInput) returns (google.protobuf.Empty){
  }

  rpc SetSymbolAlias (SetSymbolAliasInput) returns (google.protobuf.Empty){
  }

  // Get all delegatees' address of delegator from input
  rpc GetTransactionFeeDelegatees (GetTransactionFeeDelegateesInput) returns (GetTransactionFeeDelegateesOutput) {
    option (aelf.is_view) = true;
  }

  // Query token information.
  rpc GetTokenInfo (GetTokenInfoInput) returns (TokenInfo) {
    option (aelf.is_view) = true;
  }

  // Query native token information.
  rpc GetNativeTokenInfo (google.protobuf.Empty) returns (TokenInfo) {
    option (aelf.is_view) = true;
  }

  // Query resource token information.
  rpc GetResourceTokenInfo (google.protobuf.Empty) returns (TokenInfoList) {
    option (aelf.is_view) = true;
  }

  // Query the balance at the specified address.
  rpc GetBalance (GetBalanceInput) returns (GetBalanceOutput) {
    option (aelf.is_view) = true;
  }

  // Query the account's allowance for other addresses
  rpc GetAllowance (GetAllowanceInput) returns (GetAllowanceOutput) {
    option (aelf.is_view) = true;
  }

  // Query the account's available allowance for other addresses
  rpc GetAvailableAllowance (GetAllowanceInput) returns (GetAllowanceOutput) {
    option (aelf.is_view) = true;
  }

  // Check whether the token is in the whitelist of an address,
  // which can be called TransferFrom to transfer the token under the condition of not being credited.
  rpc IsInWhiteList (IsInWhiteListInput) returns (google.protobuf.BoolValue) {
    option (aelf.is_view) = true;
  }

  // Query the information for a lock.
  rpc GetLockedAmount (GetLockedAmountInput) returns (GetLockedAmountOutput) {
    option (aelf.is_view) = true;
  }

  // Query the address of receiving token in cross-chain transfer.
  rpc GetCrossChainTransferTokenContractAddress (GetCrossChainTransferTokenContractAddressInput) returns (aelf.Address) {
    option (aelf.is_view) = true;
  }

  // Query the name of the primary Token.
  rpc GetPrimaryTokenSymbol (google.protobuf.Empty) returns (google.protobuf.StringValue) {
    option (aelf.is_view) = true;
  }

  // Query the coefficient of the transaction fee calculation formula.
  rpc GetCalculateFeeCoefficientsForContract (google.protobuf.Int32Value) returns (CalculateFeeCoefficients) {
    option (aelf.is_view) = true;
  }

  // Query the coefficient of the transaction fee calculation formula.
  rpc GetCalculateFeeCoefficientsForSender (google.protobuf.Empty) returns (CalculateFeeCoefficients) {
    option (aelf.is_view) = true;
  }

  // Query tokens that can pay transaction fees.
  rpc GetSymbolsToPayTxSizeFee (google.protobuf.Empty) returns (SymbolListToPayTxSizeFee){
    option (aelf.is_view) = true;
  }

  // Query the hash of the last input of ClaimTransactionFees.
  rpc GetLatestTotalTransactionFeesMapHash (google.protobuf.Empty) returns (aelf.Hash){
    option (aelf.is_view) = true;
  }

  // Query the hash of the last input of DonateResourceToken.
  rpc GetLatestTotalResourceTokensMapsHash (google.protobuf.Empty) returns (aelf.Hash){
    option (aelf.is_view) = true;
  }
  rpc IsTokenAvailableForMethodFee (google.protobuf.StringValue) returns (google.protobuf.BoolValue) {
    option (aelf.is_view) = true;
  }
  rpc GetReservedExternalInfoKeyList (google.protobuf.Empty) returns (StringList) {
    option (aelf.is_view) = true;
  }

  rpc GetTransactionFeeDelegationsOfADelegatee(GetTransactionFeeDelegationsOfADelegateeInput) returns(TransactionFeeDelegations){
    option (aelf.is_view) = true;
  }

  rpc GetTokenAlias (google.protobuf.StringValue) returns (google.protobuf.StringValue) {
    option (aelf.is_view) = true;
  }

  rpc GetSymbolByAlias (google.protobuf.StringValue) returns (google.protobuf.StringValue) {
    option (aelf.is_view) = true;
  }
}

message TokenInfo {
  // The symbol of the token.f
  string symbol = 1;
  // The full name of the token.
  string token_name = 2;
  // The current supply of the token.
  int64 supply = 3;
  // The total supply of the token.
  int64 total_supply = 4;
  // The precision of the token.
  int32 decimals = 5;
  // The address that has permission to issue the token.
  aelf.Address issuer = 6;
  // A flag indicating if this token is burnable.
  bool is_burnable = 7;
  // The chain id of the token.
  int32 issue_chain_id = 8;
  // The amount of issued tokens.
  int64 issued = 9;
  // The external information of the token.
  ExternalInfo external_info = 10;
  // The address that owns the token.
  aelf.Address owner = 11;
}

message ExternalInfo {
  map<string, string> value = 1;
}

message CreateInput {
  // The symbol of the token.
  string symbol = 1;
  // The full name of the token.
  string token_name = 2;
  // The total supply of the token.
  int64 total_supply = 3;
  // The precision of the token
  int32 decimals = 4;
  // The address that has permission to issue the token.
  aelf.Address issuer = 5;
  // A flag indicating if this token is burnable.
  bool is_burnable = 6;
  // A whitelist address list used to lock tokens.
  repeated aelf.Address lock_white_list = 7;
  // The chain id of the token.
  int32 issue_chain_id = 8;
  // The external information of the token.
  ExternalInfo external_info = 9;
  // The address that owns the token.
  aelf.Address owner = 10;
}

message SetPrimaryTokenSymbolInput {
  // The symbol of the token.
  string symbol = 1;
}

message IssueInput {
  // The token symbol to issue.
  string symbol = 1;
  // The token amount to issue.
  int64 amount = 2;
  // The memo.
  string memo = 3;
  // The target address to issue.
  aelf.Address to = 4;
}

message TransferInput {
  // The receiver of the token.
  aelf.Address to = 1;
  // The token symbol to transfer.
  string symbol = 2;
  // The amount to to transfer.
  int64 amount = 3;
  // The memo.
  string memo = 4;
}

message LockInput {
  // The one want to lock his token.
  aelf.Address address = 1;
  // Id of the lock.
  aelf.Hash lock_id = 2;
  // The symbol of the token to lock.
  string symbol = 3;
  // a memo.
  string usage = 4;
  // The amount of tokens to lock.
  int64 amount = 5;
}

message UnlockInput {
  // The one want to un-lock his token.
  aelf.Address address = 1;
  // Id of the lock.
  aelf.Hash lock_id = 2;
  // The symbol of the token to un-lock.
  string symbol = 3;
  // a memo.
  string usage = 4;
  // The amount of tokens to un-lock.
  int64 amount = 5;
}

message TransferFromInput {
  // The source address of the token.
  aelf.Address from = 1;
  // The destination address of the token.
  aelf.Address to = 2;
  // The symbol of the token to transfer.
  string symbol = 3;
  // The amount to transfer.
  int64 amount = 4;
  // The memo.
  string memo = 5;
}

message ApproveInput {
  // The address that allowance will be increased.
  aelf.Address spender = 1;
  // The symbol of token to approve.
  string symbol = 2;
  // The amount of token to approve.
  int64 amount = 3;
}
message BatchApproveInput {
  repeated ApproveInput value = 1;
}

message UnApproveInput {
  // The address that allowance will be decreased.
  aelf.Address spender = 1;
  // The symbol of token to un-approve.
  string symbol = 2;
  // The amount of token to un-approve.
  int64 amount = 3;
}

message BurnInput {
  // The symbol of token to burn.
  string symbol = 1;
  // The amount of token to burn.
  int64 amount = 2;
}

message ChargeResourceTokenInput {
  // Collection of charge resource token, Symbol->Amount.
  map<string, int64> cost_dic = 1;
  // The sender of the transaction.
  aelf.Address caller = 2;
}

message TransactionFeeBill {
  // The transaction fee dictionary, Symbol->fee.
  map<string, int64> fees_map = 1;
}

message TransactionFreeFeeAllowanceBill {
  // The transaction free fee allowance dictionary, Symbol->fee.
  map<string, int64> free_fee_allowances_map = 1;
}

message CheckThresholdInput {
  // The sender of the transaction.
  aelf.Address sender = 1;
  // The threshold to set, Symbol->Threshold.
  map<string, int64> symbol_to_threshold = 2;
  // Whether to check the allowance.
  bool is_check_allowance = 3;
}

message GetTokenInfoInput {
  // The symbol of token.
  string symbol = 1;
}

message GetBalanceInput {
  // The symbol of token.
  string symbol = 1;
  // The target address of the query.
  aelf.Address owner = 2;
}

message GetBalanceOutput {
  // The symbol of token.
  string symbol = 1;
  // The target address of the query.
  aelf.Address owner = 2;
  // The balance of the owner.
  int64 balance = 3;
}

message GetAllowanceInput {
  // The symbol of token.
  string symbol = 1;
  // The address of the token owner.
  aelf.Address owner = 2;
  // The address of the spender.
  aelf.Address spender = 3;
}

message GetAllowanceOutput {
  // The symbol of token.
  string symbol = 1;
  // The address of the token owner.
  aelf.Address owner = 2;
  // The address of the spender.
  aelf.Address spender = 3;
  // The amount of allowance.
  int64 allowance = 4;
}

message CrossChainTransferInput {
  // The receiver of transfer.
  aelf.Address to = 1;
  // The symbol of token.
  string symbol = 2;
  // The amount of token to transfer.
  int64 amount = 3;
  // The memo.
  string memo = 4;
  // The destination chain id.
  int32 to_chain_id = 5;
  // The chain id of the token.
  int32 issue_chain_id = 6;
}

message CrossChainReceiveTokenInput {
  // The source chain id.
  int32 from_chain_id = 1;
  // The height of the transfer transaction.
  int64 parent_chain_height = 2;
  // The raw bytes of the transfer transaction.
  bytes transfer_transaction_bytes = 3;
  // The merkle path created from the transfer transaction.
  aelf.MerklePath merkle_path = 4;
}

message IsInWhiteListInput {
  // The symbol of token.
  string symbol = 1;
  // The address to check.
  aelf.Address address = 2;
}

message SymbolToPayTxSizeFee{
  // The symbol of token.
  string token_symbol = 1;
  // The charge weight of primary token.
  int32 base_token_weight = 2;
  // The new added token charge weight. For example, the charge weight of primary Token is set to 1.
  // The newly added token charge weight is set to 10. If the transaction requires 1 unit of primary token,
  // the user can also pay for 10 newly added tokens.
  int32 added_token_weight = 3;
}

message SymbolListToPayTxSizeFee{
  // Transaction fee token information.
  repeated SymbolToPayTxSizeFee symbols_to_pay_tx_size_fee = 1;
}

message ChargeTransactionFeesInput {
  // The method name of transaction.
  string method_name = 1;
  // The contract address of transaction.
  aelf.Address contract_address = 2;
  // The amount of transaction size fee.
  int64 transaction_size_fee = 3;
  // Transaction fee token information.
  repeated SymbolToPayTxSizeFee symbols_to_pay_tx_size_fee = 4;
}

message ChargeTransactionFeesOutput {
  // Whether the charge was successful.
  bool success = 1;
  // The charging information.
  string charging_information = 2;
}

message CallbackInfo {
  aelf.Address contract_address = 1;
  string method_name = 2;
}

message ExtraTokenListModified {
  option (aelf.is_event) = true;
  // Transaction fee token information.
  SymbolListToPayTxSizeFee symbol_list_to_pay_tx_size_fee = 1;
}

message GetLockedAmountInput {
  // The address of the lock.
  aelf.Address address = 1;
  // The token symbol.
  string symbol = 2;
  // The id of the lock.
  aelf.Hash lock_id = 3;
}

message GetLockedAmountOutput {
  // The address of the lock.
  aelf.Address address = 1;
  // The token symbol.
  string symbol = 2;
  // The id of the lock.
  aelf.Hash lock_id = 3;
  // The locked amount.
  int64 amount = 4;
}

message TokenInfoList {
  // List of token information.
  repeated TokenInfo value = 1;
}

message GetCrossChainTransferTokenContractAddressInput {
  // The chain id.
  int32 chainId = 1;
}

message CrossChainCreateTokenInput {
  // The chain id of the chain on which the token was created.
  int32 from_chain_id = 1;
  // The height of the transaction that created the token.
  int64 parent_chain_height = 2;
  // The transaction that created the token.
  bytes transaction_bytes = 3;
  // The merkle path created from the transaction that created the transaction.
  aelf.MerklePath merkle_path = 4;
}

message InitializeFromParentChainInput {
  // The amount of resource.
  map<string, int32> resource_amount = 1;
  // The token contract addresses.
  map<int32, aelf.Address> registered_other_token_contract_addresses = 2;
  // The creator the side chain.
  aelf.Address creator = 3;
}

message UpdateCoefficientsInput {
  // The specify pieces gonna update.
  repeated int32 piece_numbers = 1;
  // Coefficients of one single type.
  CalculateFeeCoefficients coefficients = 2;
}

enum FeeTypeEnum {
  READ = 0;
  STORAGE = 1;
  WRITE = 2;
  TRAFFIC = 3;
  TX = 4;
}

message CalculateFeePieceCoefficients {
  // Coefficients of one single piece.
  // The first char is its type: liner / power.
  // The second char is its piece upper bound.
  repeated int32 value = 1;
}

message CalculateFeeCoefficients {
  // The resource fee type, like READ, WRITE, etc.
  int32 fee_token_type = 1;
  // Coefficients of one single piece.
  repeated CalculateFeePieceCoefficients piece_coefficients_list = 2;
}

message AllCalculateFeeCoefficients {
  // The coefficients of fee Calculation.
  repeated CalculateFeeCoefficients value = 1;
}

message TotalTransactionFeesMap
{
  // Token dictionary that charge transaction fee, Symbol->Amount.
  map<string, int64> value = 1;
  // The hash of the block processing the transaction.
  aelf.Hash block_hash = 2;
  // The height of the block processing the transaction.
  int64 block_height = 3;
}

message TotalResourceTokensMaps {
  // Resource tokens to charge.
  repeated ContractTotalResourceTokens value = 1;
  // The hash of the block processing the transaction.
  aelf.Hash block_hash = 2;
  // The height of the block processing the transaction.
  int64 block_height = 3;
}

message ContractTotalResourceTokens {
  // The contract address.
  aelf.Address contract_address = 1;
  // Resource tokens to charge.
  TotalResourceTokensMap tokens_map = 2;
}

message TotalResourceTokensMap
{
  // Resource token dictionary, Symbol->Amount.
  map<string, int64> value = 1;
}

message StringList {
  repeated string value = 1;
}

message TransactionFeeDelegations{
  // delegation, symbols and its' amount
  map<string, int64> delegations = 1;
  // height when added
  int64 block_height = 2;
  //Whether to pay transaction fee continuously
  bool isUnlimitedDelegate = 3;
}

message TransactionFeeDelegatees{
  map<string,TransactionFeeDelegations> delegatees = 1;
}

message SetTransactionFeeDelegationsInput {
  // the delegator address
  aelf.Address delegator_address = 1;
  // delegation, symbols and its' amount
  map<string, int64> delegations = 2;
}

message SetTransactionFeeDelegationsOutput {
  bool success = 1;
}

message RemoveTransactionFeeDelegatorInput{
  // the delegator address
  aelf.Address delegator_address = 1;
}

message RemoveTransactionFeeDelegateeInput {
  // the delegatee address
  aelf.Address delegatee_address = 1;
}

message GetTransactionFeeDelegationsOfADelegateeInput {
  aelf.Address delegatee_address = 1;
  aelf.Address delegator_address = 2;
}

message GetTransactionFeeDelegateesInput {
  aelf.Address delegator_address = 1;
}

message GetTransactionFeeDelegateesOutput {
  repeated aelf.Address delegatee_addresses = 1;
}

message SetSymbolAliasInput {
  string symbol = 1;
  string alias = 2;
}

// Events

message Transferred {
  option (aelf.is_event) = true;
  // The source address of the transferred token.
  aelf.Address from = 1 [(aelf.is_indexed) = true];
  // The destination address of the transferred token.
  aelf.Address to = 2 [(aelf.is_indexed) = true];
  // The symbol of the transferred token.
  string symbol = 3 [(aelf.is_indexed) = true];
  // The amount of the transferred token.
  int64 amount = 4;
  // The memo.
  string memo = 5;
}

message Approved {
  option (aelf.is_event) = true;
  // The address of the token owner.
  aelf.Address owner = 1 [(aelf.is_indexed) = true];
  // The address that allowance be increased.
  aelf.Address spender = 2 [(aelf.is_indexed) = true];
  // The symbol of approved token.
  string symbol = 3 [(aelf.is_indexed) = true];
  // The amount of approved token.
  int64 amount = 4;
}

message UnApproved {
  option (aelf.is_event) = true;
  // The address of the token owner.
  aelf.Address owner = 1 [(aelf.is_indexed) = true];
  // The address that allowance be decreased.
  aelf.Address spender = 2 [(aelf.is_indexed) = true];
  // The symbol of un-approved token.
  string symbol = 3 [(aelf.is_indexed) = true];
  // The amount of un-approved token.
  int64 amount = 4;
}

message Burned
{
  option (aelf.is_event) = true;
  // The address who wants to burn token.
  aelf.Address burner = 1 [(aelf.is_indexed) = true];
  // The symbol of burned token.
  string symbol = 2 [(aelf.is_indexed) = true];
  // The amount of burned token.
  int64 amount = 3;
}

message ChainPrimaryTokenSymbolSet {
  option (aelf.is_event) = true;
  // The symbol of token.
  string token_symbol = 1;
}

message CalculateFeeAlgorithmUpdated {
  option (aelf.is_event) = true;
  // All calculate fee coefficients after modification.
  AllCalculateFeeCoefficients all_type_fee_coefficients = 1;
}

message RentalCharged {
  option (aelf.is_event) = true;
  // The symbol of rental fee charged.
  string symbol = 1;
  // The amount of rental fee charged.
  int64 amount = 2;
  // The payer of rental fee.
  aelf.Address payer = 3;
  // The receiver of rental fee.
  aelf.Address receiver = 4;
}

message RentalAccountBalanceInsufficient {
  option (aelf.is_event) = true;
  // The symbol of insufficient rental account balance.
  string symbol = 1;
  // The balance of the account.
  int64 amount = 2;
}

message TokenCreated {
  option (aelf.is_event) = true;
  // The symbol of the token.
  string symbol = 1;
  // The full name of the token.
  string token_name = 2;
  // The total supply of the token.
  int64 total_supply = 3;
  // The precision of the token.
  int32 decimals = 4;
  // The address that has permission to issue the token.
  aelf.Address issuer = 5;
  // A flag indicating if this token is burnable.
  bool is_burnable = 6;
  // The chain id of the token.
  int32 issue_chain_id = 7;
  // The external information of the token.
  ExternalInfo external_info = 8;
  // The address that owns the token.
  aelf.Address owner = 9;
}

message Issued {
  option (aelf.is_event) = true;
  // The symbol of issued token.
  string symbol = 1;
  // The amount of issued token.
  int64 amount = 2;
  // The memo.
  string memo = 3;
  // The issued target address.
  aelf.Address to = 4;
}

message CrossChainTransferred {
  option (aelf.is_event) = true;
  // The source address of the transferred token.
  aelf.Address from = 1;
  // The destination address of the transferred token.
  aelf.Address to = 2;
  // The symbol of the transferred token.
  string symbol = 3;
  // The amount of the transferred token.
  int64 amount = 4;
  // The memo.
  string memo = 5;
  // The destination chain id.
  int32 to_chain_id = 6;
  // The chain id of the token.
  int32 issue_chain_id = 7;
}

message CrossChainReceived {
  option (aelf.is_event) = true;
  // The source address of the transferred token.
  aelf.Address from = 1;
  // The destination address of the transferred token.
  aelf.Address to = 2;
  // The symbol of the received token.
  string symbol = 3;
  // The amount of the received token.
  int64 amount = 4;
  // The memo.
  string memo = 5;
  // The destination chain id.
  int32 from_chain_id = 6;
  // The chain id of the token.
  int32 issue_chain_id = 7;
  // The parent chain height of the transfer transaction.
  int64 parent_chain_height = 8;
  // The id of transfer transaction.
  aelf.Hash transfer_transaction_id =9;
}

message TransactionFeeDelegationAdded {
  option (aelf.is_event) = true;
  aelf.Address delegator = 1 [(aelf.is_indexed) = true];
  aelf.Address delegatee = 2 [(aelf.is_indexed) = true];
  aelf.Address caller = 3 [(aelf.is_indexed) = true];
}

message TransactionFeeDelegationCancelled {
  option (aelf.is_event) = true;
  aelf.Address delegator = 1 [(aelf.is_indexed) = true];
  aelf.Address delegatee = 2 [(aelf.is_indexed) = true];
  aelf.Address caller = 3 [(aelf.is_indexed) = true];
}

message SymbolAliasAdded {
  option (aelf.is_event) = true;
  string symbol = 1 [(aelf.is_indexed) = true];
  string alias = 2 [(aelf.is_indexed) = true];
}

message SymbolAliasDeleted {
  option (aelf.is_event) = true;
  string symbol = 1 [(aelf.is_indexed) = true];
  string alias = 2 [(aelf.is_indexed) = true];
}

Contract Reference State​

  • Navigate to src.

  • create a new file ContractReferences.cs.

The implementation of file src/ContractRefefrence.cs is as follows:

ContractReferences.cs
using AElf.Contracts.MultiToken;

namespace AElf.Contracts.LotteryGame
{
    public partial class LotteryGameState
    {
        internal TokenContractContainer.TokenContractReferenceState TokenContract { get; set; }
    }
}

Implement Lottery Game Smart Contract​

  • Navigate to src/LotteryGame.cs
LotteryGame.cs
using AElf.Contracts.MultiToken;
using AElf.Sdk.CSharp;
using AElf.Types;
using Google.Protobuf.WellKnownTypes;

namespace AElf.Contracts.LotteryGame
{
    // Contract class must inherit the base class generated from the proto file
    public class LotteryGame : LotteryGameContainer.LotteryGameBase
    {
        private const string TokenContractAddress = "ASh2Wt7nSEmYqnGxPPzp4pnVDU4uhj1XW9Se5VeZcX2UDdyjx"; // tDVW token contract address
        private const string TokenSymbol = "ELF";
        private const long MinimumPlayAmount = 1_000_000; // 0.01 ELF
        private const long MaximumPlayAmount = 1_000_000_000; // 10 ELF

        // Initializes the contract
        public override Empty Initialize(Empty input)
        {
            // Check if the contract is already initialized
            Assert(State.Initialized.Value == false, "Already initialized.");
            // Set the contract state
            State.Initialized.Value = true;
            // Set the owner address
            State.Owner.Value = Context.Sender;

            // Initialize the token contract
            State.TokenContract.Value = Address.FromBase58(TokenContractAddress);

            return new Empty();
        }

        // Plays the lottery game with a specified amount of tokens.
        // The method checks if the play amount is within the limit.
        // If the player wins, tokens are transferred from the contract to the sender and a PlayOutcomeEvent is fired with the won amount.
        // If the player loses, tokens are transferred from the sender to the contract and a PlayOutcomeEvent is fired with the lost amount.
        public override Empty Play(Int64Value input)
        {
            var playAmount = input.Value;

            // Check if input amount is within the limit
            Assert(playAmount is >= MinimumPlayAmount and <= MaximumPlayAmount, "Invalid play amount.");

            // Check if the sender has enough tokens
            var balance = State.TokenContract.GetBalance.Call(new GetBalanceInput
            {
                Owner = Context.Sender,
                Symbol = TokenSymbol
            }).Balance;
            Assert(balance >= playAmount, "Insufficient balance.");

            // Check if the contract has enough tokens
            var contractBalance = State.TokenContract.GetBalance.Call(new GetBalanceInput
            {
                Owner = Context.Self,
                Symbol = TokenSymbol
            }).Balance;
            Assert(contractBalance >= playAmount, "Insufficient contract balance.");

            if(IsWinner())
            {
                // Transfer the token from the contract to the sender
                State.TokenContract.Transfer.Send(new TransferInput
                {
                    To = Context.Sender,
                    Symbol = TokenSymbol,
                    Amount = playAmount
                });

                // Emit an event to notify listeners about the outcome
                Context.Fire(new PlayOutcomeEvent
                {
                    Amount = input.Value,
                    Won = playAmount
                });
            }
            else
            {
                // Transfer the token from the sender to the contract
                State.TokenContract.TransferFrom.Send(new TransferFromInput
                {
                    From = Context.Sender,
                    To = Context.Self,
                    Symbol = TokenSymbol,
                    Amount = playAmount
                });

                // Emit an event to notify listeners about the outcome
                Context.Fire(new PlayOutcomeEvent
                {
                    Amount = input.Value,
                    Won = -playAmount
                });
            }

            return new Empty();
        }

        // Withdraws a specified amount of tokens from the contract.
        // This method can only be called by the owner of the contract.
        // After the tokens are transferred, a WithdrawEvent is fired to notify any listeners about the withdrawal.
        public override Empty Withdraw(Int64Value input)
        {
            AssertIsOwner();

            // Transfer the token from the contract to the sender
            State.TokenContract.Transfer.Send(new TransferInput
            {
                To = Context.Sender,
                Symbol = TokenSymbol,
                Amount = input.Value
            });

            // Emit an event to notify listeners about the withdrawal
            Context.Fire(new WithdrawEvent
            {
                Amount = input.Value,
                From = Context.Self,
                To = State.Owner.Value
            });

            return new Empty();
        }

        // Deposits a specified amount of tokens into the contract.
        // This method can only be called by the owner of the contract.
        // After the tokens are transferred, a DepositEvent is fired to notify any listeners about the deposit.
       public override Empty Deposit(Int64Value input)
        {
            AssertIsOwner();

            // Transfer the token from the sender to the contract
            State.TokenContract.TransferFrom.Send(new TransferFromInput
            {
                From = Context.Sender,
                To = Context.Self,
                Symbol = TokenSymbol,
                Amount = input.Value
            });

            // Emit an event to notify listeners about the deposit
            Context.Fire(new DepositEvent
            {
                Amount = input.Value,
                From = Context.Sender,
                To = Context.Self
            });

            return new Empty();
        }

        // Transfers the ownership of the contract to a new owner.
        // This method can only be called by the current owner of the contract.
        public override Empty TransferOwnership(Address input)
        {
            AssertIsOwner();

            // Set the new owner address
            State.Owner.Value = input;

            return new Empty();
        }

        // A method that read the contract's play amount limit
        public override PlayAmountLimitMessage GetPlayAmountLimit(Empty input)
        {
            // Wrap the value in the return type
            return new PlayAmountLimitMessage
            {
                MinimumAmount = MinimumPlayAmount,
                MaximumAmount = MaximumPlayAmount
            };
        }

        // A method that read the contract's current balance
        public override Int64Value GetContractBalance(Empty input)
        {
            // Get the balance of the contract
            var balance = State.TokenContract.GetBalance.Call(new GetBalanceInput
            {
                Owner = Context.Self,
                Symbol = TokenSymbol
            }).Balance;

            // Wrap the value in the return type
            return new Int64Value
            {
                Value = balance
            };
        }

        // A method that read the contract's owner
        public override StringValue GetOwner(Empty input)
        {
            return State.Owner.Value == null ? new StringValue() : new StringValue {Value = State.Owner.Value.ToBase58()};
        }

        // Determines if the player is a winner.
        // This method generates a random number based on the current block height and checks if it's equal to 0.
        // If the random number is 0, the player is considered a winner.
        private bool IsWinner()
        {
            var randomNumber = Context.CurrentHeight % 2;
            return randomNumber == 0;
        }

        // This method is used to ensure that only the owner of the contract can perform certain actions.
        // If the context sender is not the owner, an exception is thrown with the message "Unauthorized to perform the action."
        private void AssertIsOwner()
        {
            Assert(Context.Sender == State.Owner.Value, "Unauthorized to perform the action.");
        }
    }

}

Building Smart Contract​

  • Build the new code with the following commands inside src folder:
Terminal
dotnet build

You should see LotteryGame.dll.patched in the directory lottery_game/src/bin/Debug/net.6.0

Step 3 - Deploy Smart Contract​

Create A Wallet​

To send transactions on the aelf blockchain, you must have a wallet.

  • Run this command to create aelf wallet.
Terminal
aelf-command create

result

  • You will be prompted to save your account, please do save your account as shown below:
Terminal
? Save account info into a file? (Y/n) Y

Make sure to choose Y to save your account information.

tip

ℹ️ Note: If you do not save your account information (by selecting n or N), do not export the wallet password. Only proceed to the next step if you have saved your account information.

  • Next, enter and confirm your password. Then export your wallet password as shown below:
Terminal
export WALLET_PASSWORD="YOUR_WALLET_PASSWORD"

Acquire Testnet Tokens (Faucet) for Development​

To deploy smart contracts or execute on-chain transactions on aelf, you'll require testnet ELF tokens.

Get ELF Tokens

Go to https://faucet-ui.aelf.dev Enter your address and click Get Tokens.

result

Deploy Smart Contract:

The smart contract needs to be deployed on the chain before users can interact with it.

Run the following command to deploy a contract. Remember to export the path of LotteryGame.dll.patched to CONTRACT_PATH.

Terminal
export CONTRACT_PATH=$(find ~+ . -path "*patched*" | head -n 1)
Terminal
aelf-deploy -a $WALLET_ADDRESS -p $WALLET_PASSWORD -c $CONTRACT_PATH -e https://tdvw-test-node.aelf.io/

  • Please wait for approximately 1 to 2 minutes. If the deployment is successful, it will provide you with the contract address. result

  • Copy the smart contract address from the address field result

  • Export your smart contract address:

Terminal
export CONTRACT_ADDRESS="YOUR_SMART_CONTRACT_ADDRESS e.g. 2LUmicHyH4RXrMjG4beDwuDsiWJESyLkgkwPdGTR8kahRzq5XS"
tip

ℹ️ Note: You are to copy the smart contract address as we will be referencing it in the next steps!

info

🎉 You have successfully deployed your dApp smart contract on the aelf testnet! In the next steps, we will be building the frontend components that allow us to interact with our deployed smart contract!

Step 4 - Interact with Your Deployed Smart Contract​

Approving Smart Contract Spending​

Terminal
aelf-command send ASh2Wt7nSEmYqnGxPPzp4pnVDU4uhj1XW9Se5VeZcX2UDdyjx -a $WALLET_ADDRESS -p $WALLET_PASSWORD -e https://tdvw-test-node.aelf.io Approve
tip

ℹ️ Note: ASh2Wt7nSEmYqnGxPPzp4pnVDU4uhj1XW9Se5VeZcX2UDdyjx is the contract address of Multitoken Contract on aelf Testnet dAppChain (tDVW).

When prompted, enter the following parameters to approve the spending of 90 ELF tokens:

Terminal
Enter the params one by one, type `Enter` to skip optional param:
? Enter the required param <spender>: "INSERT_YOUR_CONTRACT_ADDRESS_HERE"
? Enter the required param <symbol>: ELF
? Enter the required param <amount>: 9000000000

Initializing Lottery Game Contract​

Terminal
aelf-command send $CONTRACT_ADDRESS -a $WALLET_ADDRESS -p $WALLET_PASSWORD -e https://tdvw-test-node.aelf.io Initialize
  • Output:

result

Depositing funds into the Lottery Game Contract​

Terminal
aelf-command send $CONTRACT_ADDRESS -a $WALLET_ADDRESS -p $WALLET_PASSWORD -e https://tdvw-test-node.aelf.io Deposit
  • You will be prompted for the following:
Terminal
Enter the params one by one, type `Enter` to skip optional param:
? Enter the required param <value>: 20000
  • Output:

result

Playing the Lottery Game​

Terminal
aelf-command send $CONTRACT_ADDRESS -a $WALLET_ADDRESS -p $WALLET_PASSWORD -e https://tdvw-test-node.aelf.io Play
  • Let's check the balance
Terminal
aelf-command call ASh2Wt7nSEmYqnGxPPzp4pnVDU4uhj1XW9Se5VeZcX2UDdyjx -a $WALLET_ADDRESS -p $WALLET_PASSWORD -e https://tdvw-test-node.aelf.io GetBalance
  • You will be prompted for the following:
Terminal
Enter the required param <symbol>: ELF
Enter the required param <owner>: $WALLET_ADDRESS

Understanding Inter-Contract Calls in aelf​

In this section, we'll explore how inter-contract calls work in the aelf blockchain using the lottery game example from the tutorial. This will help you understand how different smart contracts can interact to perform complex operations.

1. Smart Contract Overview​

  • Lottery Contract: Manages the game, including buying tickets, drawing winners, and distributing prizes.
  • Token Contract: Handles the token transactions needed for buying lottery tickets.

2. Ticket Purchase Process​

  • Initiating Purchase: When a user wants to buy a lottery ticket, they interact with the Lottery Contract.
  • Token Transfer Requirement: The Lottery Contract must verify that the user has enough tokens and transfer those tokens to the lottery’s account to complete the purchase.

3. Initializing Contract Reference State​

  • Setting Contract Address: The Lottery Contract must first initialize its reference to the Token Contract by setting the correct contract address in its state.

4. Making an Inter-Contract Call​

  • Calling Token Contract: The Lottery Contract needs to interact with the Token Contract to transfer tokens.
    • Method Invocation: It calls a method in the Token Contract, such as Transfer.
    • Parameters: The call includes details like the sender’s address, the recipient’s address (the lottery account), and the amount of tokens.
  • Encoding and Sending: The parameters are encoded into a transaction format and sent to the Token Contract.

5. Processing in the Token Contract​

  • Token Transfer: The Token Contract processes the transfer request by deducting tokens from the user’s account and adding them to the lottery account.
  • Return Response: The Token Contract then returns a result indicating whether the transfer was successful or if it failed.

6. Handling the Response​

  • Lottery Contract’s Role: Once the Lottery Contract receives the response from the Token Contract, it checks if the transfer was successful.
  • Next Steps: If successful, the Lottery Contract updates the user's lottery ticket entries and continues with the game logic.

7. Authorization and Security​

  • Permission Checks: Ensures that the Lottery Contract is authorized to invoke methods in the Token Contract.
  • Secure Transactions: Ensures that token transfers are secure and correctly authorized.

8. Error Handling​

  • Failure Management: If the token transfer fails (e.g., due to insufficient funds), the Lottery Contract handles the error by potentially reverting the transaction or notifying the user.

By following these steps, you can see how inter-contract calls in aelf allow different contracts to work together smoothly. This modular approach helps in building complex applications like a lottery game by ensuring secure and authorized interactions between contracts.

🎯 Conclusion​

🎊 Congratulations!​

You've completed the Lottery Game Contract tutorial! Well done for mastering the steps and complexities involved. 🌟

📚 What You've Learned​

In this tutorial, you've explored:

  • 🛠️ Setting up your development environment for aelf blockchain.
  • 🎲 Developing a smart contract for a basic lottery game with state management and random number generation.
  • 🚀 Deploying and interacting with your Lottery Game Contract on the aelf network.

🔍 Final Output​

By now, you should have:

  • 📜 Successfully deployed your Lottery Game Contract on the aelf blockchain.
  • 🎉 Deposited funds and played the lottery game using smart contract interactions.

Ensure you've seen your ELF balance updated after playing the game to verify the contract's functionality.

➡️ What's Next?​

Now that you've tackled the Lottery Game Contract, consider exploring more advanced topics or other tutorials to expand your aelf blockchain development skills.

🚀 Keep innovating and building awesome decentralized applications!

Happy coding! 😊