Can serialize `serde_json::Value`, but can't deserialize it

[jeromegn]

I'm getting a WontImplement error.

I suppose I'm surprised I'm able to serialize a value I can't ever deserialize and I'm wondering if I'm doing something wrong!

I'm not entirely sure which of the WontImplement cases I'm hitting either.

I'm looking into storing as a String or Vec<u8> instead.

[iFreilicht]

Can you show the definition of your struct you're trying to deserialize to and the exact error you're getting? There's no way to help you if we don't know what you're doing.

[jeromegn]

Oh yes, my bad.

    #[test]
    fn postcard_test() -> Result<(), Box<dyn std::error::Error>> {
        #[derive(Debug, Serialize, Deserialize, Eq, PartialEq)]
        struct Json(serde_json::Value);

        let json = Json(serde_json::json!({"foo": "bar"}));

        let bytes = postcard::to_allocvec(&json)?;
        let json2 = postcard::from_bytes(&bytes)?;

        assert_eq!(json, json2);

        Ok(())
    }

[jamesmunns]

So, serde_json::Value uses some of the "the details of deserialization are in the format" features of Serde.

This is fine for JSON, but non-self-describing binary formats like postcard can't generally do this for deserialization. This is mentioned in the docs.

You COULD have a wrapper type for each of the variants of serde_json::Value, but they are currently defined to encode "directly" on the wire, so no enum variant is present on the wire.

Unfortunately, I think getting "WontImplement" is correct in this case.