IO error EOF getting through

[vorner]

Let's say I have this code:

extern crate serde_cbor;

use std::collections::HashMap;

use serde_cbor::{from_slice, to_vec};

fn main() {
    let mut data = HashMap::new();
    data.insert(42, "Hello");
    let encoded = to_vec(&data).expect("Failed to encode");
    let decoded: HashMap<usize, String> = from_slice(&encoded[..encoded.len() - 1]).expect("Failed to decode");
}

The last line correctly fails, as the last byte is missing. However, this is the error I get:

Failed to decode: Io(Error { repr: Custom(Custom { kind: UnexpectedEof, error: StringError("failed to fill whole buffer") }) })

Looking at the documentation, I'd expect the error to be Eof, not Io(Custom(… io-based-eof…)). To be fair, the documentation doesn't explicitly say that all EOF-based errors are going to be reported as Eof, but it was still a bit surprise.

[pyfisch]

The Eof variant was never used in the current code and should have been removed long ago. The Error enum should be improved somehow probably it should be more like serde_json::Error. Thanks for reporting this!

[vorner]

Hmm. Then I'd like to know if EOF in data can cause only the Io(Custom(EOF)) or something else too. Because I wrote a crate to deserialize CBOR from a network stream (tokio-serde-cbor) and some way to detect if I have enough data to decode a „frame“ is needed.

(The serde_json::Error has is_eof for that purpose)

[pyfisch]

All io errors are preserved in Error::Io. The std::io::Error has a method kind to get the kind and then test for a UnexpectedEoferror.

[vorner]

Yes, I already handle that one.

I was asking if an EOF in input can cause another error I'd need to handle. Currently I do this:
https://github.com/vorner/tokio-serde-cbor/blob/master/src/lib.rs#L95

I thought the IO error handling is a temporary workaround, but now it seems like it is going to stay there. So I would like to be sure there's no other branch I need to add.

[pyfisch]

Yes IO error handling is (probably) here to stay. Would you prefer if I adapted the error type from serde_json for serde_cbor?

[vorner]

The serd_json way is nice, clean and convenient.

However, I didn't really ask for any particular code or API changes. I just wanted to know if what I do is correct/enough or if I should handle some other case as well O:-).