Writing chaincode using Go

Every chaincode needs to implement a Chaincode interface. There are two methods defined in the interface:

type Chaincode interface {
 Init (stub ChaincodeStubInterface) pb.Response
 Invoke (stub ChaincodeStubInterface) pb.Response
}

Here, the Init method is called to allow the chaincode to create an initial state and the data initialization after the chaincode container has been established for the first time. The Invoke method is called to interact with the ledger (to query or update the asset) in the proposed transaction.

ChaincodeStubInterface provides the API for apps to access and modify their ledgers. Here are some important APIs:

type ChaincodeStubInterface interface {
    InvokeChaincode(chaincodeName string, args [][]byte, channel string) pb.Response
    GetState(key string) ([]byte, error)
    PutState(key string, value []byte) error
    DelState(key string) error
    GetQueryResult(query string) (StateQueryIteratorInterface, error)
    GetTxTimestamp() (*timestamp.Timestamp, error)
    GetTxID() string
    GetChannelID() string
}

Examples of important APIs include the following:

• InvokeChaincode: Calls the chaincode function
• GetState: Returns the value of the specified key from the ledger
• PutState: Adds the key and the value to the ledger

Now that we understand some basic chaincode APIs, let's start to write our chaincode for IT asset management.