High performance xml pull reader/writer.
The reader:
- is almost zero-copy (use of
Cowwhenever possible) - is easy on memory allocation (the API provides a way to reuse buffers)
- support various encoding (with
encodingfeature), namespaces resolution, special characters.
Syntax is inspired by xml-rs.
use quick_xml::events::Event;
use quick_xml::reader::Reader;
let xml = r#"<tag1 att1 = "test">
<tag2><!--Test comment-->Test</tag2>
<tag2>Test 2</tag2>
</tag1>"#;
let mut reader = Reader::from_str(xml);
reader.config_mut().trim_text(true);
let mut count = 0;
let mut txt = Vec::new();
let mut buf = Vec::new();
// The `Reader` does not implement `Iterator` because it outputs borrowed data (`Cow`s)
loop {
// NOTE: this is the generic case when we don't know about the input BufRead.
// when the input is a &str or a &[u8], we don't actually need to use another
// buffer, we could directly call `reader.read_event()`
match reader.read_event_into(&mut buf) {
Err(e) => panic!("Error at position {}: {:?}", reader.buffer_position(), e),
// exits the loop when reaching end of file
Ok(Event::Eof) => break,
Ok(Event::Start(e)) => {
match e.name().as_ref() {
b"tag1" => println!("attributes values: {:?}",
e.attributes().map(|a| a.unwrap().value)
.collect::<Vec<_>>()),
b"tag2" => count += 1,
_ => (),
}
}
Ok(Event::Text(e)) => txt.push(e.unescape().unwrap().into_owned()),
// There are several other `Event`s we do not consider here
_ => (),
}
// if we don't keep a borrow elsewhere, we can clear the buffer to keep memory usage low
buf.clear();
}use quick_xml::events::{Event, BytesEnd, BytesStart};
use quick_xml::reader::Reader;
use quick_xml::writer::Writer;
use std::io::Cursor;
let xml = r#"<this_tag k1="v1" k2="v2"><child>text</child></this_tag>"#;
let mut reader = Reader::from_str(xml);
reader.config_mut().trim_text(true);
let mut writer = Writer::new(Cursor::new(Vec::new()));
loop {
match reader.read_event() {
Ok(Event::Start(e)) if e.name().as_ref() == b"this_tag" => {
// crates a new element ... alternatively we could reuse `e` by calling
// `e.into_owned()`
let mut elem = BytesStart::new("my_elem");
// collect existing attributes
elem.extend_attributes(e.attributes().map(|attr| attr.unwrap()));
// copy existing attributes, adds a new my-key="some value" attribute
elem.push_attribute(("my-key", "some value"));
// writes the event to the writer
assert!(writer.write_event(Event::Start(elem)).is_ok());
},
Ok(Event::End(e)) if e.name().as_ref() == b"this_tag" => {
assert!(writer.write_event(Event::End(BytesEnd::new("my_elem"))).is_ok());
},
Ok(Event::Eof) => break,
// we can either move or borrow the event to write, depending on your use-case
Ok(e) => assert!(writer.write_event(e).is_ok()),
Err(e) => panic!("Error at position {}: {:?}", reader.buffer_position(), e),
}
}
let result = writer.into_inner().into_inner();
let expected = r#"<my_elem k1="v1" k2="v2" my-key="some value"><child>text</child></my_elem>"#;
assert_eq!(result, expected.as_bytes());When using the serialize feature, quick-xml can be used with serde's Serialize/Deserialize traits.
The mapping between XML and Rust types, and in particular the syntax that allows you to specify the
distinction between elements and attributes, is described in detail in the documentation
for deserialization.
This has largely been inspired by serde-xml-rs.
quick-xml follows its convention for deserialization, including the
$value special name.
If you have an input of the form <foo abc="xyz">bar</foo>, and you want to get at the bar,
you can use either the special name $text, or the special name $value:
struct Foo {
#[serde(rename = "@abc")]
pub abc: String,
#[serde(rename = "$text")]
pub body: String,
}Read about the difference in the documentation.
Note that despite not focusing on performance (there are several unnecessary copies), it remains about 10x faster than serde-xml-rs.
encoding: support non utf8 xmlsserialize: support serdeSerialize/Deserialize
Benchmarking is hard and the results depend on your input file and your machine.
Here on my particular file, quick-xml is around 50 times faster than xml-rs crate.
// quick-xml benches
test bench_quick_xml ... bench: 198,866 ns/iter (+/- 9,663)
test bench_quick_xml_escaped ... bench: 282,740 ns/iter (+/- 61,625)
test bench_quick_xml_namespaced ... bench: 389,977 ns/iter (+/- 32,045)
// same bench with xml-rs
test bench_xml_rs ... bench: 14,468,930 ns/iter (+/- 321,171)
// serde-xml-rs vs serialize feature
test bench_serde_quick_xml ... bench: 1,181,198 ns/iter (+/- 138,290)
test bench_serde_xml_rs ... bench: 15,039,564 ns/iter (+/- 783,485)
For a feature and performance comparison, you can also have a look at RazrFalcon's parser comparison table.
Any PR is welcomed!
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