How can chaincode get the block height in Hyperledger Fabric 2.x?

Question

I'm coding in Hyperledger Fabric 2.4. I need to query the current block height in the chaincode but I didn't find such a function. How can I achieve this?

Answer 1

Chaincode can obtain information about the channel, using the system chaincode. The system chaincode is "built-in" when a blockchain network is up

channel information(with block height) can be obtained through the QSCC system chaincode.

Query system chaincode (QSCC) runs in all peers to provide ledger APIs which include block query, transaction query etc

import (
    "fmt"
    "github.com/hyperledger/fabric-chaincode-go/shim"
    pb "github.com/hyperledger/fabric-protos-go/peer"
    "github.com/golang/protobuf/proto"
    commonProto "github.com/hyperledger/fabric-protos-go/common"
)

func (t *MyChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
    // ... your chaincode logic ...

    // Define the system chaincode you want to call and the arguments.
    // In this example, we'll query the block height using the "qscc" system chaincode.
    sysCC := "qscc"
    fcn := "GetChainInfo"
    channelID := "mychannel"

    // Call the system chaincode
    response := stub.InvokeChaincode(sysCC, [][]byte{[]byte(fcn), []byte(channelID)}, channelID)

    // Check the response for errors
    if response.Status != shim.OK {
        errMsg := fmt.Sprintf("Error invoking '%s' chaincode: %s", sysCC, response.Message)
        return shim.Error(errMsg)
    }

    // Process the response payload
    result := response.Payload

    // Unmarshal the response payload
    chainInfo := &commonProto.BlockchainInfo{}
    err := proto.Unmarshal(result, chainInfo)
    if err != nil {
        errMsg := fmt.Sprintf("Error unmarshaling BlockchainInfo: %s", err)
        return shim.Error(errMsg)
    }

    // Get the block height
    blockHeight := chainInfo.GetHeight()

    // ... do something with the block height

    // ... continue with your chaincode logic and return the appropriate response
}

Answer 2

Thanks for the answer! I always got 0.

Is the line correct, the channelID appeared twice.

response := stub.InvokeChaincode(sysCC, [][]byte{[]byte(fcn), []byte(channelID)}, channelID)

should it be

response := stub.InvokeChaincode(sysCC, [][]byte{[]byte(fcn)}, channelID)