Add error information to responses

[IljaN]

Currently an rpc-get call results in a 500 internal server error if a key does not exist. It is impossible from a caller perspective to distinguish between not found and real failures.

Proposal:

• Refactor the protobuf definition like described here i.e wrap results in to XXXResponse envelopes which contain an additional error struct.

• Instead directly exposing the generated client write a wrapper which transparently unpacks the above envelope and does transparent error-handling? Tough not sure if this would be compatible with micro? Maybe this can be achieved differently?

[refs]

I rather go with the "return nothing" approach here. WDYT?

[IljaN]

I rather go with the "return nothing" approach here. WDYT?
Yes this would work.

Yes would be possible. But wouldn't this break the if err !=nil pattern at the consumer thus requiring to check for empty Record?

[refs]

We had a deeper look @butonic and I this morning and found a few things we need to tackle. The first and most crucial one is this.

Then there's the issue of whether we should enforce using go-micro clients to handle requests between services vs using the grpc go client, which, this needs TBC, go-micro allows to via setting an environment variable.

If we have to set it on stone I would settle for go-micro client.

[butonic]

This came up again. And we should use the go-micro errors package, which allows adding error detauls to the error in a similar way that google developed it, which is the official recommendation aka gRPC Richer Error Model

cc @C0rby