Pattern for rich error handling in gRPC
Include additional error details in the response Metadata. However, still make sure to provide a useful status code and message. In this case, you can add RegisterUserResponse
to the Metadata.
In gRPC Java, that would look like:
Metadata.Key<RegisterUserResponse> REGISTER_USER_RESPONSE_KEY =
ProtoUtils.keyForProto(RegisterUserResponse.getDefaultInstance());
...
Metadata metadata = new Metadata();
metadata.put(REGISTER_USER_RESPONSE_KEY, registerUserResponse);
responseObserver.onError(
Status.INVALID_ARGUMENT.withDescription("Email or password malformed")
.asRuntimeException(metadata));
Another option is to use the google.rpc.Status
proto which includes an additional Any
for details
. Support is coming to each language to handle the type. In Java, it'd look like:
// This is com.google.rpc.Status, not io.grpc.Status
Status status = Status.newBuilder()
.setCode(Code.INVALID_ARGUMENT.getNumber())
.setMessage("Email or password malformed")
.addDetails(Any.pack(registerUserResponse))
.build();
responseObserver.onError(StatusProto.toStatusRuntimeException(status));
google.rpc.Status
is cleaner in some languages as the error details can be passed around as one unit. It also makes it clear what parts of the response are error-related. On-the-wire, it still uses Metadata to pass the additional information.
You may also be interested in error_details.proto which contains some common types of errors.
I discussed this topic during CloudNativeCon. You can check out the slides and linked recording on YouTube.
We have 3 different ways we could handle the errors in gRPC. For example lets assume the gRPC server does not accept values above 20 or below 2.
Option 1: Using gRPC status codes.
if(number < 2 || number > 20){
Status status = Status.FAILED_PRECONDITION.withDescription("Not between 2 and 20");
responseObserver.onError(status.asRuntimeException());
}
Option 2: Metadata (we can pass objects via metadata)
if(number < 2 || number > 20){
Metadata metadata = new Metadata();
Metadata.Key<ErrorResponse> responseKey = ProtoUtils.keyForProto(ErrorResponse.getDefaultInstance());
ErrorCode errorCode = number > 20 ? ErrorCode.ABOVE_20 : ErrorCode.BELOW_2;
ErrorResponse errorResponse = ErrorResponse.newBuilder()
.setErrorCode(errorCode)
.setInput(number)
.build();
// pass the error object via metadata
metadata.put(responseKey, errorResponse);
responseObserver.onError(Status.FAILED_PRECONDITION.asRuntimeException(metadata));
}
Option 3: Using oneof - we can also use oneof to send error response
oneof response {
SuccessResponse success_response = 1;
ErrorResponse error_response = 2;
}
}
client side:
switch (response.getResponseCase()){
case SUCCESS_RESPONSE:
System.out.println("Success Response : " + response.getSuccessResponse().getResult());
break;
case ERROR_RESPONSE:
System.out.println("Error Response : " + response.getErrorResponse().getErrorCode());
break;
}
Check here for the detailed steps - https://www.vinsguru.com/grpc-error-handling/