XML parse broken after upgrading to 0.27

[Xuanwo]

In apache/opendal#1101, some XML related test failed after upgrading to 0.27.

Cases

quick-xml = { version = "0.27", features = ["serialize", "overlapped-lists"] }

use quick_xml::de;
use serde::Deserialize;

#[derive(Default, Debug, Deserialize)]
#[serde(default, rename_all = "PascalCase")]
struct Output {
    name: String,
    prefix: String,
    contents: Vec<Content>,
    common_prefixes: Option<Vec<CommonPrefix>>,
    marker: String,
    next_marker: Option<String>,
}

#[derive(Default, Debug, Deserialize)]
#[serde(default, rename_all = "PascalCase")]
struct CommonPrefix {
    prefix: String,
}

#[derive(Default, Debug, Deserialize)]
#[serde(default, rename_all = "PascalCase")]
struct Content {
    key: String,
    size: u64,
}

#[cfg(test)]
mod tests {
    use bytes::Buf;

    use super::*;

    #[test]
    fn test_parse_xml() {
        let bs = bytes::Bytes::from(
            r#"<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ListBucketResult xmlns="http://obs.cn-north-4.myhuaweicloud.com/doc/2015-06-30/">
    <Name>examplebucket</Name>
    <Prefix>obj</Prefix>
    <Marker>obj002</Marker>
    <NextMarker>obj004</NextMarker>
    <MaxKeys>1000</MaxKeys>
    <IsTruncated>false</IsTruncated>
    <Contents>
        <Key>obj002</Key>
        <LastModified>2015-07-01T02:11:19.775Z</LastModified>
        <ETag>"a72e382246ac83e86bd203389849e71d"</ETag>
        <Size>9</Size>
        <Owner>
            <ID>b4bf1b36d9ca43d984fbcb9491b6fce9</ID>
        </Owner>
        <StorageClass>STANDARD</StorageClass>
    </Contents>
    <Contents>
        <Key>obj003</Key>
        <LastModified>2015-07-01T02:11:19.775Z</LastModified>
        <ETag>"a72e382246ac83e86bd203389849e71d"</ETag>
        <Size>10</Size>
        <Owner>
            <ID>b4bf1b36d9ca43d984fbcb9491b6fce9</ID>
        </Owner>
        <StorageClass>STANDARD</StorageClass>
    </Contents>
    <CommonPrefixes>
        <Prefix>hello</Prefix>
    </CommonPrefixes>
    <CommonPrefixes>
        <Prefix>world</Prefix>
    </CommonPrefixes>
</ListBucketResult>"#,
        );
        let out: Output = de::from_reader(bs.reader()).expect("must success");

        assert_eq!(out.name, "examplebucket".to_string());
        assert_eq!(out.prefix, "obj".to_string());
        assert_eq!(out.marker, "obj002".to_string());
        assert_eq!(out.next_marker, Some("obj004".to_string()),);
        assert_eq!(
            out.contents
                .iter()
                .map(|v| v.key.clone())
                .collect::<Vec<String>>(),
            ["obj002", "obj003"],
        );
        assert_eq!(
            out.contents.iter().map(|v| v.size).collect::<Vec<u64>>(),
            [9, 10],
        );
        assert_eq!(
            out.common_prefixes
                .unwrap()
                .iter()
                .map(|v| v.prefix.clone())
                .collect::<Vec<String>>(),
            ["hello", "world"],
        )
    }
}

Errors:

running 1 test
thread 'services::obs::dir_stream::tests::test_parse_xml' panicked at 'must success: UnexpectedEnd([76, 105, 115, 116, 66, 117, 99, 107, 101, 116, 82, 101, 115, 117, 108, 116])', src/services/obs/dir_stream.rs:179:56
stack backtrace:
   0: rust_begin_unwind
             at /rustc/897e37553bba8b42751c67658967889d11ecd120/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at /rustc/897e37553bba8b42751c67658967889d11ecd120/library/core/src/panicking.rs:142:14
   2: core::result::unwrap_failed
             at /rustc/897e37553bba8b42751c67658967889d11ecd120/library/core/src/result.rs:1785:5
   3: core::result::Result<T,E>::expect
             at /rustc/897e37553bba8b42751c67658967889d11ecd120/library/core/src/result.rs:1064:23
   4: opendal::services::obs::dir_stream::tests::test_parse_xml
             at ./src/services/obs/dir_stream.rs:179:27
   5: opendal::services::obs::dir_stream::tests::test_parse_xml::{{closure}}
             at ./src/services/obs/dir_stream.rs:141:5
   6: core::ops::function::FnOnce::call_once
             at /rustc/897e37553bba8b42751c67658967889d11ecd120/library/core/src/ops/function.rs:248:5
   7: core::ops::function::FnOnce::call_once
             at /rustc/897e37553bba8b42751c67658967889d11ecd120/library/core/src/ops/function.rs:248:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
test services::obs::dir_stream::tests::test_parse_xml ... FAILED

failures:

failures:
    services::obs::dir_stream::tests::test_parse_xml

Maybe this bug also related to #530?

[Mingun]

No, this is duplicate of #510. As a workaround you could replace

common_prefixes: Option<Vec<CommonPrefix>>,

by

#[serde(default)] // Actually not needed because all your struct is serde(default)
common_prefixes: Vec<CommonPrefix>,

Probably this also would be a more convenient API, but if not, you could use #[serde(deserialize_with = "optional_vec")] (not tested):

fn optional_vec<'de, D, T>(deserializer: D) -> Result<Option<Vec<T>>, D::Error>
where
    D: Deserializer<'de>,
    T: Deserialize<'de>,
{
    let list = Vec::<T>::deserialize(deserializer)?;
    Ok(if list.is_empty() { None } else { Some(list) })
}

So I close this as duplicate.

[Xuanwo]

Ok, please also include this issue in the breaking changes docs. Because this used to work in old versions.

I'm willing to send a PR for this, WDYT?

[Mingun]

I would be glad if you do that.