建立用go编写的链码时出错

Question

When I try to modify the example described in this hyperledger example I get some error when adding this external library in order to get the History of the chaincode state.
Why does that happen?

I add the library with govendor, but when I run this command:

docker exec -e "CORE_PEER_LOCALMSPID=Org1MSP" -e "CORE_PEER_MSPCONFIGPATH=/opt/gopath/src/github.com/hyperledger/fabric/peer/crypto/peerOrganizations/org1.example.com/users/[e-mail]/msp" cli peer chaincode instantiate -o orderer.example.com:7050 -C mychannel -n $CC_NAME -l "$LANGUAGE" -v 1.0 -c $INIT_STR -P "OR ('Org1MSP.member','Org2MSP.member')"

I get this error:

Error: Error endorsing chaincode:
rpc error: code = Unknown desc = error starting container: Failed to generate platform-specific docker build: Error returned from build: 2 "# firstExample chaincode/input/src/firstExample/firstStep.go:104:11: cannot assign *"github.com/hyperledger/fabric/protos/ledger/queryresult".KeyModification to kM (type *"firstExample/vendor/github.com/hyperledger/fabric/protos/ledger/queryresult".KeyModification) in multiple assignment chaincode/input/src/firstExample/firstStep.go:146:11: cannot assign *"github.com/hyperledger/fabric/protos/ledger/queryresult".KeyModification to kM (type *"firstExample/vendor/github.com/hyperledger/fabric/protos/ledger/queryresult".KeyModification) in multiple assignment chaincode/input/src/firstExample/firstStep.go:156:11: cannot assign *"github.com/hyperledger/fabric/protos/ledger/queryresult".KeyModification to kM (type *"firstExample/vendor/github.com/hyperledger/fabric/protos/ledger/queryresult".KeyModification) in multiple assignment

I have some troubles with this. I'm sure that the library is imported because if I build the chaincode written in go with the command:

go build 

I get no errors.
Please help me!

Answer 1

It's very hard to guess without seeing actual code which cause the compilation error, while it seems that you are not taking care of the second parameter which returned by HistoryQueryIteratorInterface#Next() API or even ChaincodeStubInterface#GetHistoryForKey(). Please see example of how to use those APIs correctly:

// GetPreviousValue reads previous value of given key
func (pm *personManagement) GetPreviousValue(params []string, stub shim.ChaincodeStubInterface) peer.Response {
    historyIer, err := stub.GetHistoryForKey(params[0])

    if err != nil {
        errMsg := fmt.Sprintf("[ERROR] cannot retrieve history of key <%s>, due to %s", params[0], err)
        fmt.Println(errMsg)
        return shim.Error(errMsg)
    }

    if historyIer.HasNext() {
        modification, err := historyIer.Next()
        if err != nil {
            errMsg := fmt.Sprintf("[ERROR] cannot read key record modification, key <%s>, due to %s", params[0], err)
            fmt.Println(errMsg)
            return shim.Error(errMsg)
        }
        fmt.Println("Returning information about", string(modification.Value))
        return shim.Success(modification.Value)
    }


    fmt.Printf("No history found for key %s
", params[0])
    return shim.Success([]byte(fmt.Sprintf("No history for key %s", params[0])))
}

NOTE: Please pay attention that historyIer.Next() returns history value and the error.