How to assert gRPC error codes client side in Go

Question

Given the following gRPC server side code:

import (
    "google.golang.org/grpc/codes"
    "google.golang.org/grpc/status"
    ....
)

....

func (s *Router) Assign(ctx context.Context, req *api.Request(*api.Response, error) {

    return nil, status.Errorf(codes.PermissionDenied,
}

....

What is the recommended technique for asserting client side that the error is of code = codes.PermissionDenied ?

Answer 1

Let's say your server returns codes.PermissionDenined like this

...
return nil, status.Error(codes.PermissionDenied, "PERMISSION_DENIED_TEXT")

If your client is Golang as well can also use the status library function FromError to parse the error. I use a switch to determine the error code returned like so

// client
    assignvar, err := s.MyFunctionCall(ctx, ...)
    if err != nil {
        if e, ok := status.FromError(err); ok {
            switch e.Code() {
            case codes.PermissionDenied:
                fmt.Println(e.Message()) // this will print PERMISSION_DENIED_TEST
            case codes.Internal:
                fmt.Println("Has Internal Error")
            case codes.Aborted:
                fmt.Println("gRPC Aborted the call")
            default:
                fmt.Println(e.Code(), e.Message())
            }
        }
        else {
            fmt.Printf("not able to parse error returned %v", err)
        }
    }