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

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.

[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 🙇

[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. https://github.com/line/armeria/blob/ef93d4cbe1657c339875b1dbc970b2f8ef848087/grpc/src/main/java/com/linecorp/armeria/server/grpc/UnframedGrpcErrorHandler.java#L111