Serializing and deserializing to JSON

[imobachgs]

Hi all!

First of all, thanks a lot for such a fantastic project!

I have been playing around with serializing/deserializing zvariant values and, somehow, I expected the following test to pass:

use serde::{Deserialize, Serialize};

#[derive(Deserialize, Serialize, Debug, PartialEq, Clone)]
struct Data {
    pub inner: zvariant::OwnedValue,
}

#[cfg(test)]
mod tests {
    use super::Data;
    use zbus::zvariant;

    #[test]
    fn ser_and_der() {
        let value = zvariant::Value::new("variant-value");
        let inner = zvariant::StructureBuilder::new()
            .add_field("value1".to_string())
            .add_field("value2")
            .append_field(zvariant::Value::new(value)) // let's try to get a variant
            .build();

        let data = Data {
            inner: inner.into(),
        };
        let as_json = serde_json::to_string_pretty(&data).unwrap();
        println!("{}", &as_json);
        let data_again: Data = serde_json::from_str(&as_json).unwrap();
        assert_eq!(data, data_again);
    }
}

I am converting a data structure (Data) into a JSON string and back. However, it fails when I try to get the original object again (the signature "(ssv)" looks good to me).

failures:

---- tests::ser_and_der stdout ----
{
  "inner": {
    "zvariant::Value::Signature": "(ssv)",
    "zvariant::Value::Value": [
      "value1",
      "value2",
      {
        "zvariant::Value::Signature": "s",
        "zvariant::Value::Value": "variant-value"
      }
    ]
  }
}
thread 'tests::ser_and_der' panicked at src/lib.rs:27:63:
called `Result::unwrap()` on an `Err` value: Error("invalid length 1, expected >= 5 characters in dict entry signature", line: 8, column: 8)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Perhaps it is a stupid thing to do and it is not supported. But I had to ask. Please, any hint?

Regards,
Imo

[zeenix]

First of all, thanks a lot for such a fantastic project!

Thanks. :)

   let inner = zvariant::StructureBuilder::new()
            .add_field("value1".to_string())
            .add_field("value2")
            .append_field(zvariant::Value::new(value)) // let's try to get a variant
            .build();

Firstly, you don't need to use append_field method to be able to add variant type. Just use add_field. A Structure keeps all fields as a Value as the type has to be dynamic so when a field is a Value itself, it becomes Value::Value(Value..) internally.

I am converting a data structure (Data) into a JSON string and back. However, it fails when I try to get the original object again (the signature "(ssv)" looks good to me).

Because of how D-Bus format works, our (de)serializer and Value ser/de impls have to do some special tricks, which makes zvariant a bit incompatible with other format ser/de (especially self-explanatory text formats like JSON). There was an issue filed for this (#176, it was move from gitlab so don't get confused by my name on every comment :)) a while back but we couldn't find a good solution for this.

My advise is to not mix zvariant ser/de with other formats if your data contains variants. Best translate between them.

[imobachgs]

I see, I had that impression. Oh, and using add_field is much better :-)

I will change the approach then.

Thank you!

[zeenix]

I see, I had that impression.

Actually, this particular case of being able to read back a Value that your serialize, sounds like something that should be possible to fix. Most likely the serialized format will look a bit strange but I think that's not as big an issue. :) I created an issue for this.

However, keep in mind that I may not get around to look into this any time soon unless I manage to finish the pending 4.0 releases sooner than expected. :)