Encode u32 as i64

[marcelbuesing]

What do you think about encoding u32 as i64?
I currently have the issue that I basically generate my Rust code from protobuf definitions, which I then want to decode and encode using bson. Now changing all protobuf defintions to i32 just because bson does not support unsigned ints does not seem really reasonable to me. I know this does not cover the u64, downside I guess is here the inconsistency.

fn serialize_u32(self, value: u32) -> EncoderResult<Bson> {
        Ok(Bson::I64(value as i64))
}

[kyeah]

Thanks for the issue! We want to avoid making implicit casting decisions like this, but I do agree that in some cases, it's valuable to have these conversions as optional features. We have a u2f compat module (see documentation here), and these could be expanded to u2i.

[marcelbuesing]

Probably not a bad idea. I kind of need something though that requires no modification of the structs. Since the code is generated I can not add #[serde(with = "bson::compat::u2i")] to every field.
Taking the already implemented u2f as an example is there already a way to encode unsigned as float without adding the attibute? It not, would it be feasible to add a function similar to to_bson_compat(&x, CompatOpt::U2F)which defines a "global" unsigned encoding policy?

[kyeah]

Currently the u2f attribute is the only way to do this. A to_bson_compat function may be possible, but if not, perhaps a global feature flag is useful to enable this behavior by default.

[zonyitoo]

Hmm, enabling it with a feature flag is better.

[reitermarkus]

I'm facing a similar problem, but in the other direction, i.e. deserializing unsigned types to signed types. Could this be added as part of the u2i feature?

There is also different behaviour between from_value and from_str, here's a minimal example:

use bson::Bson;
use serde_json::Value;

fn main() {
  assert_eq!(Bson::from(serde_json::from_str::<Value>("6").unwrap()), Bson::I64(6));
  assert_eq!(serde_json::from_str::<Bson>("6").unwrap(), Bson::I64(6));
}

which results in a invalid type: integer 6, expected a signed integer error with the from_str call.