Option<T> does not round-trip

[apoelstra]

extern crate serde_cbor;

fn main() {
    let obj1 = Some(10u32);

    let mut v = vec![];
    assert!(serde_cbor::ser::to_writer(&mut v, &obj1).is_ok());
    println!("{:?}", v);
    let obj2: Result<Option<u32>, _> = serde_cbor::de::from_reader(&v[..]);

    assert_eq!(obj1, obj2.unwrap());
}

This code fails with
thread '<main>' panicked at 'called Result::unwrap()on anErr value: SyntaxError(invalid syntax: "incorrect type", 0)', ../src/libcore/result.rs:738

I have code in production that fails with "trailing bytes" when I have a structure whose last element is an Option; I haven't produced a small test case because it's such a PITA to write Serialize/Deserialize impls for structures.

[pyfisch]

This is a serde problem. The deserialization to Option is not implemented for integer values. There is already an issue for this serde-rs/serde#217.

[pyfisch]

The mentioned is was a bit different. So this is not fixed.

@erickt Is it possible to make options round trip in languages like JSON and CBOR?

[erickt]

@pyfisch: Yes, you should be able to. Here's how serde_json does it by overriding Deserializer::deserialize_option.

[pyfisch]

Sorry that it took so long. It was a bit more complicated than expected since I had to add one byte lookahead to the parser to correctly parse options.