Is it possible to return custom errors in python gRPC server?

Question

I have a .proto file:

// Protocol Buffers Language version
syntax = "proto3";

package my_package;

// -----------------Cart service-----------------

service CartService {
    rpc AddItem(AddItemRequest) returns (AddItemResponse) {}
}

message CartItem {
    string product_id = 1;
    int32  quantity = 2;
}

message AddItemRequest {
    string user_id = 1;
    CartItem item = 2;
}

message AddItemResponse {
    string user_id = 1;
}

In my AddItem method I want to return a custom error like cart_not_found:

class CartService(my_package_pb2_grpc.CartServiceServicer):
    def AddItem(self, request, context):
         context.set_code(StatusCode.CART_NOT_FOUND)
         context.set_details('Cart Not Found!')
         return context

The above code does not work as gRPC status codes are limited to some basic list. How can I return custom errors in gRPC?

EDIT-1:

I've seen examples that set machine readable code in details like below:

context.set_code(grpc.StatusCode.INTERNAL)
context.set_details('cart_not_found')
return context

But this has its own limitation and I cannot set description for the error or any other custom key.

The other method is to return error in every message you have like below:

message AddItemResponse {
    string user_id = 1;
    Error error = 2;
}

message Error {
    string code = 1;
    string message = 2;
}

This implementation has one drawback that services need to check for error existence and then handle the error otherwise process the response.

user3126412 · Accepted Answer · 2019-05-22 18:10:41Z

0

You can return custom KV pairs in trailing metadata.

Example from unit test: https://github.com/grpc/grpc/blob/master/src/python/grpcio_tests/tests/unit/_metadata_code_details_test.py#L430

answered May 22, 2019 at 18:10

user3126412

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Comments

Lidi Zheng · Accepted Answer · 2019-05-28 18:26:23Z

0

There is an example for returning custom error at https://github.com/grpc/grpc/tree/master/examples/python/errors.

answered May 28, 2019 at 18:26

Lidi Zheng

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