fabric-samples/token-account-based/chaincode-go/chaincode/token_contract.go

package chaincode

import (
	"fmt"
	"log"
	"strconv"

	"github.com/hyperledger/fabric-contract-api-go/contractapi"
)

// SmartContract provides functions for transferring tokens between accounts
type SmartContract struct {
	contractapi.Contract
}

// Mint creates new tokens and adds them to minter's account balance
func (s *SmartContract) Mint(ctx contractapi.TransactionContextInterface, amount int) error {

	// Check minter authorization - this sample assumes Org1 is the central banker with privilege to mint new tokens
	clientMSPID, err := ctx.GetClientIdentity().GetMSPID()
	if err != nil {
		return fmt.Errorf("failed to get MSPID: %v", err)
	}
	if clientMSPID != "Org1MSP" {
		return fmt.Errorf("client is not authorized to mint new tokens")
	}

	// Get ID of submitting client identity
	minter, err := ctx.GetClientIdentity().GetID()
	if err != nil {
		return fmt.Errorf("failed to get client id: %v", err)
	}

	if amount <= 0 {
		return fmt.Errorf("mint amount must be a positive integer")
	}

	currentBalanceBytes, err := ctx.GetStub().GetState(minter)
	if err != nil {
		return fmt.Errorf("failed to read minter account %s from world state: %v", minter, err)
	}

	var currentBalance int

	// If minter current balance doesn't yet exist, we'll create it with a current balance of 0
	if currentBalanceBytes == nil {
		currentBalance = 0
	} else {
		currentBalance, _ = strconv.Atoi(string(currentBalanceBytes)) // Error handling not needed since Itoa() was used when setting the account balance, guaranteeing it was an integer.
	}

	updatedBalance := currentBalance + amount

	err = ctx.GetStub().PutState(minter, []byte(strconv.Itoa(updatedBalance)))
	if err != nil {
		return err
	}

	log.Printf("minter account %s balance updated from %d to %d", minter, currentBalance, updatedBalance)

	return nil
}

// Transfer transfers tokens from client account to recipient account.
// recipient account must be a valid clientID as returned by the ClientID() function.
func (s *SmartContract) Transfer(ctx contractapi.TransactionContextInterface, recipient string, amount int) error {

	if amount < 0 { // transfer of 0 is allowed in ERC20, so just validate against negative amounts
		return fmt.Errorf("transfer amount cannot be negative")
	}

	// Get ID of submitting client identity
	clientID, err := ctx.GetClientIdentity().GetID()
	if err != nil {
		return fmt.Errorf("failed to get client id: %v", err)
	}

	clientCurrentBalanceBytes, err := ctx.GetStub().GetState(clientID)
	if err != nil {
		return fmt.Errorf("failed to read client account %s from world state: %v", clientID, err)
	}

	if clientCurrentBalanceBytes == nil {
		return fmt.Errorf("client account %s has no balance", clientID)
	}

	clientCurrentBalance, _ := strconv.Atoi(string(clientCurrentBalanceBytes)) // Error handling not needed since Itoa() was used when setting the account balance, guaranteeing it was an integer.

	if clientCurrentBalance < amount {
		return fmt.Errorf("client account %s has insufficient funds", clientID)
	}

	recipientCurrentBalanceBytes, err := ctx.GetStub().GetState(recipient)
	if err != nil {
		fmt.Errorf("failed to read recipient account %s from world state: %v", recipient, err)
	}

	var recipientCurrentBalance int
	// If recipient current balance doesn't yet exist, we'll create it with a current balance of 0
	if recipientCurrentBalanceBytes == nil {
		recipientCurrentBalance = 0
	} else {
		recipientCurrentBalance, _ = strconv.Atoi(string(recipientCurrentBalanceBytes)) // Error handling not needed since Itoa() was used when setting the account balance, guaranteeing it was an integer.
	}

	clientUpdatedBalance := clientCurrentBalance - amount
	recipientUpdatedBalance := recipientCurrentBalance + amount

	err = ctx.GetStub().PutState(clientID, []byte(strconv.Itoa(clientUpdatedBalance)))
	if err != nil {
		return err
	}

	err = ctx.GetStub().PutState(recipient, []byte(strconv.Itoa(recipientUpdatedBalance)))
	if err != nil {
		return err
	}

	log.Printf("client %s balance updated from %d to %d", clientID, clientCurrentBalance, clientUpdatedBalance)
	log.Printf("recipient %s balance updated from %d to %d", recipient, recipientCurrentBalance, recipientUpdatedBalance)

	return nil
}

// BalanceOf returns the balance of the given account
func (s *SmartContract) BalanceOf(ctx contractapi.TransactionContextInterface, account string) (int, error) {
	balanceBytes, err := ctx.GetStub().GetState(account)
	if err != nil {
		return 0, fmt.Errorf("failed to read from world state: %v", err)
	}
	if balanceBytes == nil {
		return 0, fmt.Errorf("the account %s does not exist", account)
	}

	balance, _ := strconv.Atoi(string(balanceBytes)) // Error handling not needed since Itoa() was used when setting the account balance, guaranteeing it was an integer.

	return balance, nil
}

// ClientAccountBalance returns the balance of the requesting client's account
func (s *SmartContract) ClientAccountBalance(ctx contractapi.TransactionContextInterface) (int, error) {

	// Get ID of submitting client identity
	clientID, err := ctx.GetClientIdentity().GetID()
	if err != nil {
		return 0, fmt.Errorf("failed to get client id: %v", err)
	}

	balanceBytes, err := ctx.GetStub().GetState(clientID)
	if err != nil {
		return 0, fmt.Errorf("failed to read from world state: %v", err)
	}
	if balanceBytes == nil {
		return 0, fmt.Errorf("the account %s does not exist", clientID)
	}

	balance, _ := strconv.Atoi(string(balanceBytes)) // Error handling not needed since Itoa() was used when setting the account balance, guaranteeing it was an integer.

	return balance, nil
}

// ClientAccountID returns the id of the requesting client's account.
// In this implementation, the client account ID is the clientId itself.
// Users can use this function to get their own account id, which they can then give to others as the payment address
func (s *SmartContract) ClientAccountID(ctx contractapi.TransactionContextInterface) (string, error) {

	// Get ID of submitting client identity
	clientAccountID, err := ctx.GetClientIdentity().GetID()
	if err != nil {
		return "", fmt.Errorf("failed to get client id: %v", err)
	}

	return clientAccountID, nil
}