Sejin Park

It's because of protoc in gripmock image is 3.12.2 which cannot support optional field. I tried to fix it, but all of my effort was unnecessary.

It might seem your application failed to establish connection to kafka. It's just my guess.

Oh, I understood. You mean that kafka cli should initialize connection between kafka server and then return err if it couldn't, right? I agree with  that.

I think bumping up of protoc image version in gripmock is proper answer for this.

Is there any news about this feature?

Ok I will try to support this feature by contribution. Thank you for your answer and a happy new year!