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.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.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.
Here is an example deserializing crates.io source:
// Cargo.toml
// [dependencies]
// serde = { version = "1.0", features = [ "derive" ] }
// quick-xml = { version = "0.22", features = [ "serialize" ] }
use serde::Deserialize;
use quick_xml::de::{from_str, DeError};
#[derive(Debug, Deserialize, PartialEq)]
struct Link {
rel: String,
href: String,
sizes: Option<String>,
}
#[derive(Debug, Deserialize, PartialEq)]
#[serde(rename_all = "lowercase")]
enum Lang {
En,
Fr,
De,
}
#[derive(Debug, Deserialize, PartialEq)]
struct Head {
title: String,
#[serde(rename = "link", default)]
links: Vec<Link>,
}
#[derive(Debug, Deserialize, PartialEq)]
struct Script {
src: String,
integrity: String,
}
#[derive(Debug, Deserialize, PartialEq)]
struct Body {
#[serde(rename = "script", default)]
scripts: Vec<Script>,
}
#[derive(Debug, Deserialize, PartialEq)]
struct Html {
lang: Option<String>,
head: Head,
body: Body,
}
fn crates_io() -> Result<Html, DeError> {
let xml = "<!DOCTYPE html>
<html lang=\"en\">
<head>
<meta charset=\"utf-8\">
<meta http-equiv=\"X-UA-Compatible\" content=\"IE=edge\">
<meta name=\"viewport\" content=\"width=device-width, initial-scale=1\">
<title>crates.io: Rust Package Registry</title>
<!-- EMBER_CLI_FASTBOOT_TITLE --><!-- EMBER_CLI_FASTBOOT_HEAD -->
<link rel=\"manifest\" href=\"/manifest.webmanifest\">
<link rel=\"apple-touch-icon\" href=\"/cargo-835dd6a18132048a52ac569f2615b59d.png\" sizes=\"227x227\">
<link rel=\"stylesheet\" href=\"/assets/vendor-8d023d47762d5431764f589a6012123e.css\" integrity=\"sha256-EoB7fsYkdS7BZba47+C/9D7yxwPZojsE4pO7RIuUXdE= sha512-/SzGQGR0yj5AG6YPehZB3b6MjpnuNCTOGREQTStETobVRrpYPZKneJwcL/14B8ufcvobJGFDvnTKdcDDxbh6/A==\" >
<link rel=\"stylesheet\" href=\"/assets/cargo-cedb8082b232ce89dd449d869fb54b98.css\" integrity=\"sha256-S9K9jZr6nSyYicYad3JdiTKrvsstXZrvYqmLUX9i3tc= sha512-CDGjy3xeyiqBgUMa+GelihW394pqAARXwsU+HIiOotlnp1sLBVgO6v2ZszL0arwKU8CpvL9wHyLYBIdfX92YbQ==\" >
<link rel=\"shortcut icon\" href=\"/favicon.ico\" type=\"image/x-icon\">
<link rel=\"icon\" href=\"/cargo-835dd6a18132048a52ac569f2615b59d.png\" type=\"image/png\">
<link rel=\"search\" href=\"/opensearch.xml\" type=\"application/opensearchdescription+xml\" title=\"Cargo\">
</head>
<body>
<!-- EMBER_CLI_FASTBOOT_BODY -->
<noscript>
<div id=\"main\">
<div class='noscript'>
This site requires JavaScript to be enabled.
</div>
</div>
</noscript>
<script src=\"/assets/vendor-bfe89101b20262535de5a5ccdc276965.js\" integrity=\"sha256-U12Xuwhz1bhJXWyFW/hRr+Wa8B6FFDheTowik5VLkbw= sha512-J/cUUuUN55TrdG8P6Zk3/slI0nTgzYb8pOQlrXfaLgzr9aEumr9D1EzmFyLy1nrhaDGpRN1T8EQrU21Jl81pJQ==\" ></script>
<script src=\"/assets/cargo-4023b68501b7b3e17b2bb31f50f5eeea.js\" integrity=\"sha256-9atimKc1KC6HMJF/B07lP3Cjtgr2tmET8Vau0Re5mVI= sha512-XJyBDQU4wtA1aPyPXaFzTE5Wh/mYJwkKHqZ/Fn4p/ezgdKzSCFu6FYn81raBCnCBNsihfhrkb88uF6H5VraHMA==\" ></script>
</body>
</html>
}";
let html: Html = from_str(xml)?;
assert_eq!(&html.head.title, "crates.io: Rust Package Registry");
Ok(html)
}This has largely been inspired by serde-xml-rs.
quick-xml follows its convention for deserialization, including the
$value special name.
Original quick-xml was developed by @tafia and abandoned around end of 2021.
If you have an input of the form <foo abc="xyz">bar</foo>, and you want to get at the bar, you can use the special name $value:
struct Foo {
pub abc: String,
#[serde(rename = "$value")]
pub body: String,
}If your XML files look like <root><first>value</first><second>value</second></root>, you can
(de)serialize them with the special name prefix $unflatten=:
struct Root {
#[serde(rename = "$unflatten=first")]
first: String,
#[serde(rename = "$unflatten=second")]
other_field: String,
}The $primitive prefix lets you serialize enum variants without associated values (internally referred to as unit variants) as primitive strings rather than self-closing tags. Consider the following definitions:
enum Foo {
#[serde(rename = "$primitive=Bar")]
Bar
}
struct Root {
foo: Foo
}Serializing Root { foo: Foo::Bar } will then yield <Root foo="Bar"/> instead of <Root><Bar/></Root>.
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!
MIT