URL usage of nested messages causes nil pointer in proto3

[grpc-ecosystem]

URL usage of nested messages causes nil pointer in proto3

[mwitkow]

Yup, indeed, intalizing the field seems to have worked:

    if protoReq.Deployment == nil {
        protoReq.Deployment = &DeploymentId{}
    }
    protoReq.Deployment.Name, err = runtime.String(val)
    if err != nil {
        return nil, err
    }

The tricky bit is to initialize the field without knowing what the type is. Some reflection perhaps? Or template-generating a NewDeploymentField that will act like Deployment.Reset()

[mwitkow]

The following function is my (probably misguided) stab at reflecting out of the problem. It instantiates all missing structs along the way.

func instantiateMissingStructs(structPtr interface{}, fieldPath string) (error) {
    fieldNames := strings.Split(fieldPath, ".")
    ptrToStruct := reflect.ValueOf(structPtr)
    if ptrToStruct.Kind() != reflect.Ptr {
        return fmt.Errorf("structPtr must be a pointer struct, is %v", ptrToStruct.Kind())
    }
    currentStruct := reflect.Indirect(ptrToStruct)
    if currentStruct.Kind() != reflect.Struct {
        return fmt.Errorf("structPtr must be a pointer to a struct, is %v.", ptrToStruct.Kind())
    }
    for _, name := range fieldNames {
        fieldV := currentStruct.FieldByName(name)
        if fieldV.Kind() != reflect.Ptr {
            return fmt.Errorf("field %v must be a pointer", name)
        }
        concreteType := fieldV.Type().Elem()
        if concreteType.Kind() != reflect.Struct {
            return fmt.Errorf("field %v must be a pointer to a struct", name)
        }
        if fieldV.IsNil() {
            fieldV.Set(reflect.New(concreteType))
        }
        currentStruct = reflect.Indirect(fieldV)
    }
    return nil
}

For example in the above example, this would instantiate the missing DeploymentId struct under the Deployment field.

instantiateMissingStructs(&protoReq, "Deployment")

Or if the URL reference was to deployment.app.id, and the assignment was protoReq.Deployment.App.Id, the following one would instantiate both DeploymentId and AppId:

instantiateMissingStructs(&protoReq, "Deployment.App")

Any idea where to hook this up? I guess gengo/grpc-gateway/protoc-gen-grpc-gateway/gengateway/generator.go, but I don't know how to do the tests for it :(

[mwitkow]

So yea, if golang/protobuf#54 makes it instantiate a new type, this is trivial.
Otherwise, I think I'll make a PR that reuse the query filter magic.

[mwitkow]

So I didn't realise that the grpc-gateway already had a reflection instantiator for the query filtering. The above pull request contains the fix that reuses this.

[mwitkow]

@yugui, do you need anything from me in relation to #34 to get this fixed? :)

[yugui]

Sorry for my late reply. I have just merged #34.

On Tue, Aug 11, 2015 at 4:36 PM Michal Witkowski [email protected]
wrote:

@yugui https://github.com/yugui, do you need anything from me in
relation to #34 #34 to get
this fixed? :)

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