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Implemented Approve, Allowance, and TransferFrom of ERC-20
FAB-18275 Signed-off-by: Julian Castrence <juliancastrence@ibm.com>
This commit is contained in:
Julian Castrence
denyeart
parent
c6956e5057
commit
79485c5bab
1 changed files with 168 additions and 47 deletions
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@ -11,6 +11,9 @@ import (
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// Define key names for options
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const totalSupplyKey = "totalSupply"
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// Define objectType names for prefix
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const allowancePrefix = "allowance"
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// SmartContract provides functions for transferring tokens between accounts
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type SmartContract struct {
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contractapi.Contract
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@ -87,60 +90,17 @@ func (s *SmartContract) Mint(ctx contractapi.TransactionContextInterface, amount
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// recipient account must be a valid clientID as returned by the ClientID() function.
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func (s *SmartContract) Transfer(ctx contractapi.TransactionContextInterface, recipient string, amount int) error {
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if amount < 0 { // transfer of 0 is allowed in ERC20, so just validate against negative amounts
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return fmt.Errorf("transfer amount cannot be negative")
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}
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// Get ID of submitting client identity
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clientID, err := ctx.GetClientIdentity().GetID()
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if err != nil {
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return fmt.Errorf("failed to get client id: %v", err)
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}
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clientCurrentBalanceBytes, err := ctx.GetStub().GetState(clientID)
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err = transferHelper(ctx, clientID, recipient, amount)
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if err != nil {
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return fmt.Errorf("failed to read client account %s from world state: %v", clientID, err)
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return fmt.Errorf("failed to transfer: %v", err)
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}
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if clientCurrentBalanceBytes == nil {
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return fmt.Errorf("client account %s has no balance", clientID)
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}
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clientCurrentBalance, _ := strconv.Atoi(string(clientCurrentBalanceBytes)) // Error handling not needed since Itoa() was used when setting the account balance, guaranteeing it was an integer.
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if clientCurrentBalance < amount {
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return fmt.Errorf("client account %s has insufficient funds", clientID)
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}
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recipientCurrentBalanceBytes, err := ctx.GetStub().GetState(recipient)
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if err != nil {
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return fmt.Errorf("failed to read recipient account %s from world state: %v", recipient, err)
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}
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var recipientCurrentBalance int
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// If recipient current balance doesn't yet exist, we'll create it with a current balance of 0
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if recipientCurrentBalanceBytes == nil {
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recipientCurrentBalance = 0
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} else {
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recipientCurrentBalance, _ = strconv.Atoi(string(recipientCurrentBalanceBytes)) // Error handling not needed since Itoa() was used when setting the account balance, guaranteeing it was an integer.
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}
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clientUpdatedBalance := clientCurrentBalance - amount
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recipientUpdatedBalance := recipientCurrentBalance + amount
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err = ctx.GetStub().PutState(clientID, []byte(strconv.Itoa(clientUpdatedBalance)))
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if err != nil {
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return err
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}
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err = ctx.GetStub().PutState(recipient, []byte(strconv.Itoa(recipientUpdatedBalance)))
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if err != nil {
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return err
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}
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log.Printf("client %s balance updated from %d to %d", clientID, clientCurrentBalance, clientUpdatedBalance)
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log.Printf("recipient %s balance updated from %d to %d", recipient, recipientCurrentBalance, recipientUpdatedBalance)
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return nil
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}
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@ -213,7 +173,168 @@ func (s *SmartContract) TotalSupply(ctx contractapi.TransactionContextInterface)
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totalSupply, _ = strconv.Atoi(string(totalSupplyBytes)) // Error handling not needed since Itoa() was used when setting the totalSupply, guaranteeing it was an integer.
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}
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log.Printf("The totalSupply was queried: %d total tokens", totalSupply)
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return totalSupply, nil
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log.Printf("TotalSupply: %d tokens", totalSupply)
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return totalSupply, nil
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}
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// Approve allows the spender to withdraw from the calling client's token account.
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// The spender can withdraw multiple times if necessary, up to the value amount.
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func (s *SmartContract) Approve(ctx contractapi.TransactionContextInterface, spender string, value int) error {
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// Get ID of submitting client identity
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owner, err := ctx.GetClientIdentity().GetID()
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if err != nil {
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return fmt.Errorf("failed to get client id: %v", err)
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}
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// Create allowanceKey
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allowanceKey, err := ctx.GetStub().CreateCompositeKey(allowancePrefix, []string{owner, spender})
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if err != nil {
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return fmt.Errorf("failed to create the composite key for prefix %s: %v", allowancePrefix, err)
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}
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// Update the state of the smart contract by adding the allowanceKey and value
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err = ctx.GetStub().PutState(allowanceKey, []byte(strconv.Itoa(value)))
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if err != nil {
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return fmt.Errorf("failed to update state of smart contract for key %s: %v", allowanceKey, err)
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}
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log.Printf("client %s approved a withdrawal allowance of %d for spender %s", owner, value, spender)
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return nil
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}
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// Allowance returns the amount still available for the spender to withdraw from the owner.
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func (s *SmartContract) Allowance(ctx contractapi.TransactionContextInterface, owner string, spender string) (int, error) {
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// Create allowanceKey
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allowanceKey, err := ctx.GetStub().CreateCompositeKey(allowancePrefix, []string{owner, spender})
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if err != nil {
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return 0, fmt.Errorf("failed to create the composite key for prefix %s: %v", allowancePrefix, err)
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}
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// Read the allowance amount from the world state
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allowanceBytes, err := ctx.GetStub().GetState(allowanceKey)
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if err != nil {
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return 0, fmt.Errorf("failed to read allowance for %s from world state: %v", allowanceKey, err)
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}
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var allowance int
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// If no current allowance, set allowance to 0
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if allowanceBytes == nil {
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allowance = 0
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} else {
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allowance, err = strconv.Atoi(string(allowanceBytes)) // Error handling not needed since Itoa() was used when setting the totalSupply, guaranteeing it was an integer.
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}
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log.Printf("The allowance left for spender %s to withdraw from owner %s: %d", spender, owner, allowance)
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return allowance, nil
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}
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// TransferFrom transfers the value amount from the "from" address to the "to" address.
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// This function triggers a Transfer event.
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func (s *SmartContract) TransferFrom(ctx contractapi.TransactionContextInterface, from string, to string, value int) error {
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// Get ID of submitting client identity
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spender, err := ctx.GetClientIdentity().GetID()
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if err != nil {
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return fmt.Errorf("failed to get client id: %v", err)
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}
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// Create allowanceKey
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allowanceKey, err := ctx.GetStub().CreateCompositeKey(allowancePrefix, []string{from, spender})
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if err != nil {
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return fmt.Errorf("failed to create the composite key for prefix %s: %v", allowancePrefix, err)
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}
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// Retrieve the allowance of the spender
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currentAllowanceBytes, err := ctx.GetStub().GetState(allowanceKey)
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if err != nil {
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return fmt.Errorf("failed to retrieve the allowance for %s from world state: %v", allowanceKey, err)
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}
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var currentAllowance int
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currentAllowance, _ = strconv.Atoi(string(currentAllowanceBytes)) // Error handling not needed since Itoa() was used when setting the totalSupply, guaranteeing it was an integer.
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// Check if transferred value is less than allowance
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if currentAllowance < value {
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return fmt.Errorf("spender does not have enough allowance for transfer")
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}
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// Initiate the transfer
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err = transferHelper(ctx, from, to, value)
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if err != nil {
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return fmt.Errorf("failed to transfer: %v", err)
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}
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// Decrease the allowance
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updatedAllowance := currentAllowance - value
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err = ctx.GetStub().PutState(allowanceKey, []byte(strconv.Itoa(updatedAllowance)))
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if err != nil {
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return err
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}
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log.Printf("spender %s allowance updated from %d to %d", spender, currentAllowance, updatedAllowance)
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return nil
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}
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// Helper Functions
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// transferHelper is a helper function that transfers tokens from the "from" address to the "to" address.
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// Dependant functions include Transfer and TransferFrom.
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func transferHelper(ctx contractapi.TransactionContextInterface, from string, to string, value int) error {
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if value < 0 { // transfer of 0 is allowed in ERC20, so just validate against negative amounts
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return fmt.Errorf("transfer amount cannot be negative")
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}
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fromCurrentBalanceBytes, err := ctx.GetStub().GetState(from)
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if err != nil {
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return fmt.Errorf("failed to read client account %s from world state: %v", from, err)
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}
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if fromCurrentBalanceBytes == nil {
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return fmt.Errorf("client account %s has no balance", from)
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}
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fromCurrentBalance, _ := strconv.Atoi(string(fromCurrentBalanceBytes)) // Error handling not needed since Itoa() was used when setting the account balance, guaranteeing it was an integer.
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if fromCurrentBalance < value {
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return fmt.Errorf("client account %s has insufficient funds", from)
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}
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toCurrentBalanceBytes, err := ctx.GetStub().GetState(to)
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if err != nil {
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return fmt.Errorf("failed to read recipient account %s from world state: %v", to, err)
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}
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var toCurrentBalance int
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// If recipient current balance doesn't yet exist, we'll create it with a current balance of 0
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if toCurrentBalanceBytes == nil {
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toCurrentBalance = 0
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} else {
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toCurrentBalance, _ = strconv.Atoi(string(toCurrentBalanceBytes)) // Error handling not needed since Itoa() was used when setting the account balance, guaranteeing it was an integer.
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}
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fromUpdatedBalance := fromCurrentBalance - value
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toUpdatedBalance := toCurrentBalance + value
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err = ctx.GetStub().PutState(from, []byte(strconv.Itoa(fromUpdatedBalance)))
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if err != nil {
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return err
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}
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err = ctx.GetStub().PutState(to, []byte(strconv.Itoa(toUpdatedBalance)))
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if err != nil {
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return err
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}
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log.Printf("client %s balance updated from %d to %d", from, fromCurrentBalance, fromUpdatedBalance)
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log.Printf("recipient %s balance updated from %d to %d", to, toCurrentBalance, toUpdatedBalance)
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return nil
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}
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