Allow overriding the default gRPC status to HTTP status rules for an unframed gRPC response

[ikhoon]

An unframed gRPC service statically maps gRPC status to HTTP status based on https://github.com/googleapis/googleapis/blob/master/google/rpc/code.proto.
I got a question from Armera slack channel. https://line-armeria.slack.com/archives/C1NGPBUH2/p1625735446194500

How can I map StatusRuntimeException to http status codes?

Unfortunately, the answer is no. We don't provide a way to customize the default mapping rules at the moment.
It would be nice to take a custom mapping function using GrpcServiceBuilder.

[ikhoon]

We can introduce an interface to let users override the mapping from gRPC status to HTTP status for unframed gRPC requests.

interface UnframedGrpcStatusFunction {
    // The default mapping.
	static of() {
        return (ctx, status, cause) -> GrpcStatus.grpcStatusToHttpStatus(status);
    }

    // If null is returned, fallback to the default mapping.
    // 'cause' could be captured from `RequestLog.responseCause()`
    @Nullable
	HttpStatus apply(ServiceRequestContext ctx, Status status, @Nullable Throwable cause);

    default UnframedGrpcStatusFunction orElse(UnframedGrpcStatusFunction other) {
        return (ctx, status, cause) -> {
            // apply 'other' if the current status function returns null.
        };
    }
}


GrpcService.builder()
           .unframedGrpcStatusMapping(unframedGrpcStatusFunction);

The UnframedGrpcStatusFunction set via GrpcServiceBuilder could be used in UnframedGrpcErrorHandler with a breaking change.
As UnframedGrpcErrorHandler is an unstable API, we can add UnframedGrpcStatusFunction as the 4th parameter.

armeria/grpc/src/main/java/com/linecorp/armeria/server/grpc/UnframedGrpcErrorHandler.java

Line 111 in ef93d4c

HttpResponse handle(ServiceRequestContext ctx, Status status, AggregatedHttpResponse response);

[jupiny]

Thanks for the detailed guide. Let me take this issue 😄

[jupiny]

As UnframedGrpcErrorHandler is an unstable API,

One question, could you explain about this part? 😭
Currently, unframedGrpcErrorHandler can be set in GrpcServiceBuilder, can't it?

[ikhoon]

As UnframedGrpcErrorHandler is an unstable API,

One question, could you explain about this part? 😭 Currently, unframedGrpcErrorHandler can be set in GrpcServiceBuilder, can't it?

Yes, it is. Currently, the status mapping is hard-coded.

armeria/grpc/src/main/java/com/linecorp/armeria/server/grpc/UnframedGrpcErrorHandler.java

Line 92 in ef93d4c

final HttpStatus httpStatus = GrpcStatus.grpcStatusToHttpStatus(status);

We need to pass UnframedGrpcStatusFunction to UnframedGrpcErrorHandler so that UnframedGrpcErrorHandler uses UnframedGrpcStatusFunction when building HttpResponse.

 public interface UnframedGrpcErrorHandler {
-    HttpResponse handle(ServiceRequestContext ctx, Status status, AggregatedHttpResponse response);
+    HttpResponse handle(ServiceRequestContext ctx, Status status, AggregatedHttpResponse response, UnframedGrpcStatusFunction statusFunction);

[jupiny]

Ah, sorry for the misunderstanding the meaning of UnstableApi;
I checked a description about UnstableApi.

/**
 * Indicates the API of the target is not mature enough to guarantee the compatibility between releases.
 * Its behavior, signature or even existence might change without a prior notice at any point.
 */

So you said I could add the breaking change simply. Thank you for answer 🙇