Unexpected Event::End(...) or missing field '...'

[jimy-byerley]

Hello dear maintainers

I'm trying to alter ethercat-esi to use quick_xml instead of serde-xml-rs. This is pretty straight forward as ethercat-esi crate is only using the serde macros and calling the xml parser at one place.

// ethercat-esi//src/lib.rs
let raw_info: parser::EtherCATInfo = quick_xml::de::from_str(xml)
            .map_err(|e| Error::new(ErrorKind::Other, e.to_string()))?;

Running this code (in lib or in a test file of that crate) gives me the following output on both xml files

$ target/debug/test/some ~/erob-custom.xml
Error: Custom { kind: Other, error: "Unexpected `Event::End(\"Groups\")`" }

// then I comment the Groups section in the xml
$ target/debug/test/some ~/erob-custom.xml
Error: Custom { kind: Other, error: "missing field `ProductCode`" }

// then I change quick-xml version from v0.27.1 to v0.26.0
$ target/debug/test/some ~/erob-custom.xml
Error: Custom { kind: Other, error: "missing field `Sm`" }

These fields and the Groups markups are good in the xml files. And it doesn't seems to come from the serde declarations of the xml data (in ethercat-esi/src/mod.rs), so I suggest there is an issue with the way the quick_xml functions are calling or checking results of the serde deserialization functions. (especially since the error is not the same depending on the version of quick_xml)
How do you think I could solve this problem ?

[jimy-byerley]

I forgot to add the xml files I was using for tests: xml.zip

[Mingun]

This is duplicate of #510 and the error is generated by this (and the others Option<Vec<T>>) piece of code:
https://github.com/ethercat-rs/ethercat-esi/blob/3d295ca4c1f8c86f1046a85ce93d14b5d85dcc04/src/parser/mod.rs#L43-L46

This is already fixed in master and I plan to release soon (I think in week or two). You can also change the definition to Vec<T> with the default value as suggested here.

[jimy-byerley]

Thank you very much for your quick answer
I tried both the solutions you proposed, but I still get the missing field issue

Here are the branches where I put the modifications you suggested

• quick-xml-fix modifies ethercat-esi to use quick-xml master branch (commit 40b1448)
• no-options modifies ethercat-esi to use quick-xml = 1.27.1 and remove mentions of Option<Vec>

Is there something I missed ? 🤔

[Mingun]

Yeah, forgot to mention that you should also tweak your mappings, because quick-xml expect that attributes are named starting from @. Check out the reference.

[jimy-byerley]

Indeed, I didn't paid pattention to the fact that quick-xml wasn't implicitely using attributes instead of fields when they were missing. Sorry for that.
I tweaked it as you said. It does find more fields, but now it it gets an even stranger error: missing field '@StartAddress'

[Mingun]

Probably that attribute is really missed? Check the all Sm elements in your XML to see if that true.

[jimy-byerley]

Unfortunately it is not missing 🤔
The same error happens with the unit tests of ethercat-esi, those fields are not missing either but what is strange is that only @StartAddress is not found whereas before a lot of fields where. I wonder if there is something special about it. I double checked for mistypes but it appears to be fine ...

[jimy-byerley]

Maybe it will be easier to reproduce the issue using the unit tests rather than using my xml files.
those are the failing unit tests in ethercat-esi:

• parser::tests::device
• parser::tests::ethercat_info_crated_by_igh
• parser::tests::ethercat_info_crated_by_weidmueller

[Mingun]

Ok, there is a bug when you have a list in the enum variant:

#[test]
fn issue567() {
    #[derive(Debug, Deserialize, PartialEq)]
    struct Device {
        #[serde(rename = "$value")]
        items: Vec<DeviceProperty>,
    }

    #[derive(Debug, Deserialize, PartialEq)]
    enum DeviceProperty {
        Sm(Vec<()>),
    }

    assert_eq!(// currently failed with Unexpected::End
        Device {
            items: vec![
                DeviceProperty::Sm(vec![]),
            ]
        },
        // Currently failed at unwrap() with UnexpectedEnd(b"Device")
        from_str("<Device><Sm/></Device>").unwrap()
    );
}

[jimy-byerley]

Hum, like for Option<Vec> I guess 🤔

[Mingun]

The error probably in the line 2723:

quick-xml/src/de/mod.rs

Lines 2715 to 2725 in 642de0a

	fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
	where
	T: DeserializeSeed<'de>,
	{
	match self.peek()? {
	DeEvent::Eof => Ok(None),
	// Start(tag), End(tag), Text
	_ => seed.deserialize(&mut **self).map(Some),
	}
	}

We should pass the deserializer with another implementation of deserialize_seq method here. The implementation should be similar to

quick-xml/src/de/map.rs

Lines 708 to 715 in 642de0a

	struct SeqItemDeserializer<'de, 'a, 'm, R>
	where
	R: XmlRead<'de>,
	{
	/// Access to the map that created this deserializer. Gives access to the
	/// context, such as list of fields, that current map known about.
	map: &'m mut MapAccess<'de, 'a, R>,
	}

but with de: &Deserializer instead of map: &MapAccess.