Spanner: Provide a way to get the gRPC status code from a SpannerException

[sebright]

Is your feature request related to a problem? Please describe.

I wanted to convert exceptions thrown by google-cloud-spanner to instances of io.grpc.Status. For example, I wanted to set the status on OpenCensus tracing spans, and OpenCensus provides a utility that takes a gRPC Status.

I wasn't able to find an easy way to get the io.grpc.Status.Code from a SpannerException. However, I noticed that SpannerException has a getErrorCode() method that returns a com.google.cloud.spanner.ErrorCode, and ErrorCode has a field of type io.grpc.Status.Code:
https://github.com/googleapis/google-cloud-java/blob/b6a364a101560f0eb7499176649b53f3cab08854/google-cloud-clients/google-cloud-spanner/src/main/java/com/google/cloud/spanner/ErrorCode.java#L58

Describe the solution you'd like

I'm not sure what is the best solution. I assume that SpannerException.getErrorCode() doesn't return a io.grpc.Status.Code because io.grpc.Status.Code includes OK and an exception is always an error. One solution is to make the existing ErrorCode.getGrpcStatus()
method public.

Describe alternatives you've considered
I am currently working around this issue by parsing the enum name, though it is fragile:

Status.Code.valueOf(((SpannerException) e).getErrorCode().toString())

Additional context
Add any other context or screenshots about the feature request here.

[sebright]

/cc @olavloite @skuruppu

[olavloite]

The error code used by SpannerException always corresponds to the status code, so what you can do is the following:

SpannerException se = ...;
Status status = Status.fromCodeValue(se.getCode());

@sebright Does that work for you?

[olavloite]

@sebright Friendly ping.
Is this still needed, or is the above work-around good enough?

[sebright]

Sorry for the delay. I would rather not rely on getCode(), because it is defined in BaseServiceException (https://github.com/googleapis/java-core/blob/21d98a098a6d008085a770516d8a6f9010f3ecdd/google-cloud-core/src/main/java/com/google/cloud/BaseServiceException.java#L290-L291), so it's not specific to gRPC errors. I also couldn't find any documentation for the meaning of the integer code. It would help if BaseGrpcServiceException (superclass of SpannerException) overrode getCode() and documented that it returned the gRPC status code.

I would still prefer a method that returns a io.grpc.Status.Code, because it would be more type safe and harder to misinterpret the error space.