How to send chaincode error to the calling application

Question

I want to develop an app in which the app makes call to the chaincode and the chaincode returns the transaction status. Now i want this status to be shown on the frontend, on the calling application. How can i do it?

Answer 1

To pass message all the way to the front end, the chaincode should conform to the following APIs:

// Chaincode interface must be implemented by all chaincodes. The fabric runs
// the transactions by calling these functions as specified.
type Chaincode interface {
    // Init is called during Instantiate transaction after the chaincode container
    // has been established for the first time, allowing the chaincode to
    // initialize its internal data
    Init(stub ChaincodeStubInterface) pb.Response

    // Invoke is called to update or query the ledger in a proposal transaction.
    // Updated state variables are not committed to the ledger until the
    // transaction is committed.
    Invoke(stub ChaincodeStubInterface) pb.Response
}

and the pb.Response is:

// A response with a representation similar to an HTTP response that can
// be used within another message.
type Response struct {
    // A status code that should follow the HTTP status codes.
    Status int32 `protobuf:"varint,1,opt,name=status" json:"status,omitempty"`
    // A message associated with the response code.
    Message string `protobuf:"bytes,2,opt,name=message" json:"message,omitempty"`
    // A payload that can be used to include metadata with this response.
    Payload []byte `protobuf:"bytes,3,opt,name=payload,proto3" json:"payload,omitempty"`
}

You can use shim facade functions to return error and success statuses which is defined in response.go.
Ex: func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
    fmt.Println("ex02 Invoke")
    function, args := stub.GetFunctionAndParameters()
    if function == "invoke" {
        // Make payment of X units from A to B
        return t.invoke(stub, args)
    } else if function == "delete" {
        // Deletes an entity from its state
        return t.delete(stub, args)
    } else if function == "query" {
        // the old "Query" is now implemtned in invoke
        return t.query(stub, args)
    }

    return shim.Error("Invalid invoke function name. Expecting \"invoke\" \"delete\" \"query\"")
}

This example will return error if you pass wrong parameters to call the chaincode.. Go through, understand things and then implement one of your own..