Problem with getting response metadata from the Unary Interceptors API

[ghost]

I try to implement the Promise-based client with my gRPC-web and I have a problem with getting metadata from Unary Interceptors API. In the gRPC blog: https://grpc.io/blog/grpc-web-interceptor/ they recommend using the response.getMetadata() in the Unary Interceptors invoker callback. So after the implementation, my response metadata is returned only a x-envoy-upstream-service-time

However, if I use the gRPC-web callback-based API. It must return my custom value in status metadata. Thank you for the advice!

[stanley-cheung]

There are 2 concepts here: initial metadata vs trailing metadata. In your callback-based example above, you are accessing the trailing metadata via the .on('status', ... callback. status.metadata in that callback is the trailing metadata.

In your promise-based interceptor, response.getMetadata() gets you the initial metadata. In order to access the trailing metadata in your promise-based interceptor, you need response.getStatus().metadata.

Similarly, in your callback-based client, .on('metadata', ...) will get you the initial metadata.

See this unit test on how to access both the initial and trailing metadata in your promise-based UnaryInterceptor.

[ghost]

@stanley-cheung, I use the JavaScript implementation compare with the UnaryInterceptor TypeScript example.

After that, I try to develop the UnaryInterceptor. However, the browser console alert the TypeError: response.getStatus is not a function at eval and TypeError: response.getResponseMessage is not a function at eval. So please advise me, did I do something wrong with my code or not? Thank you for your help.

[stanley-cheung]

Ah. I see. You probably run into this particular issue: #877 (comment), where some of the symbols/functions for the UnaryResponse class (in your code, the response object) has been optimized away by the closure compiler. This should be fixed in #886 in master. I will probably cut a new release 1.2.1. which will contain this fix soon.