Sample Chaincode

A transaction chaincode implements the service logic. The example transaction chaincode provided in this section is used to transfer money between users. The validity of the transaction data in the form of a ciphertext is verified using the homomorphic encryption library to detect unauthorized operations, if any. This chaincode implements the functions of balance initialization, balance query, and money transfer.

Initializing the Balance

After a user is registered successfully, the balance of the user must be initialized. The default value is 0.

Input

Parameter	Type	Description	Mandatory
PubKey	string	Public key	Yes
Balance	string	Initial balance	Yes

Processing

Invoking the ValidateInitBalance API to verify the validity of the balance range for endorsement

PubKey := string(args[0])
BalanceInfo := string(args[1]) 
//PubKey := string(args[2])

hashPubkey, err := t.calcAddr(PubKey)
logger.Debug("encrypt initial balance")
//validate balance
cipherBalance,err := pswapi_cc.ValidateInitBalance(BalanceInfo,PubKey)
 if err != nil {
    logger.Error("fail to Validate InitBalance ")
    return shim.Error("fail toValidate InitBalance")
 }

Output

Parameter	Type	Description
newCipherBalance	string	Balance ciphertext

Querying the Balance

The balance can be queried using the account address. For details, see the queryBalance API of the transaction_demo.

The following table lists the parameters of the queryBalance API.

-	Parameter	Type	Description
Input	addr	string	Account address
Output	cipherbalance	string	Ciphertext of the account balance
Output	err	error	Error message

Money Transfer

Input

Parameter	Type	Description	Mandatory
AddrA	string	Address of user A (payer)	Yes
AddrB	string	Address of user B (payee)	Yes
txinfo	String	Transaction information PrepareTxInfo	Yes

Processing
1. Obtain the current balances of users A and B (cipherBalanceAKeyABlock and cipherBalanceBKeyBBlock) from the ledger based on the account addresses.
2. Verify the validity of the certificates.
```
newCipherBalanceA,newCipherBalanceB,newCipherTxA,newCipherTxB, err := pswapi_cc.ValidateTxInfo(txInfo, cipherBalanceAKeyABlock, cipherBalanceBKeyBBlock)
 if err != nil {
    logger.Error("fail to validate trans information")
    return shim.Error("fail to validate trans information")
 }
```
3. Provide the updated balances (ciphertext).
  The ledger content of a service needs to be customized. The encrypted balance amount is added to the users' ledgers. A storage structure is defined in the demo. After the storage structure is saved, a transaction record object is saved in JSON format.
```
type TransRecord struct {
    FromAddr string
    ToAddr   string
    TXType   string
    Balance  string
    TX       string
    remark   string
 }
```