/roxmltree

Represent an XML 1.0 document as a read-only tree.

Primary LanguageRustApache License 2.0Apache-2.0

roxmltree

Build Status Crates.io Documentation Rust 1.31+

Represents an XML 1.0 document as a read-only tree.

// Find element by id.
let doc = roxmltree::Document::parse("<rect id='rect1'/>").unwrap();
let elem = doc.descendants().find(|n| n.attribute("id") == Some("rect1")).unwrap();
assert!(elem.has_tag_name("rect"));

Why read-only?

Because in some cases all you need is to retrieve some data from an XML document. And for such cases, we can make a lot of optimizations.

As for roxmltree, it's fast not only because it's read-only, but also because it uses xmlparser, which is many times faster than xml-rs. See the Performance section for details.

Parsing behavior

Sadly, XML can be parsed in many different ways. roxmltree tries to mimic the behavior of Python's lxml. But unlike lxml, roxmltree does support comments outside the root element.

For more details see docs/parsing.md.

Alternatives

Feature/Crate roxmltree libxml2 xmltree sxd-document minidom
Element namespace resolving ✓ ✓ ✓ ~1 ✓
Attribute namespace resolving ✓ ✓ ✓ ✓
Entity references ✓ ✓ × × ×
Character references ✓ ✓ ✓ ✓ ✓
Attribute-Value normalization ✓ ✓
Comments ✓ ✓ ✓ ✓
Processing instructions ✓ ✓ ✓ ✓
UTF-8 BOM ✓ ✓ × × ✓
Non UTF-8 input ✓
Complete DTD support ✓
Position preserving2 ✓ ✓
HTML support ✓
Tree modification ✓ ✓ ✓ ✓
Writing ✓ ✓ ✓ ✓
No unsafe ✓ ✓ ~3
Language Rust C Rust Rust Rust
Size overhead4 ~67KiB ~1.4MiB5 ~118KiB ~138KiB ~63KiB
Dependencies 1 ?5 2 2 2
Tested version 0.10.0 2.9.8 0.10.0 0.3.2 0.11.1
License MIT / Apache-2.0 MIT MIT MIT MIT

Legend:

  • ✓ - supported
  • × - parsing error
  • ~ - partial
  • nothing - not supported

Notes:

  1. No default namespace propagation.
  2. roxmltree keeps all node and attribute positions in the original document, so you can easily retrieve it if you need it. See examples/print_pos.rs for details.
  3. In the memchr crate.
  4. Binary size overhead according to cargo-bloat.
  5. Depends on build flags.

There is also elementtree and treexml crates, but they are abandoned for a long time.

Performance

test large_roxmltree     ... bench:   3,344,633 ns/iter (+/- 9,063)
test large_minidom       ... bench:   5,101,156 ns/iter (+/- 98,146)
test large_sdx_document  ... bench:   7,583,625 ns/iter (+/- 20,025)
test large_xmltree       ... bench:  20,792,783 ns/iter (+/- 523,851)

test medium_roxmltree    ... bench:     659,865 ns/iter (+/- 7,519)
test medium_minidom      ... bench:   1,176,302 ns/iter (+/- 7,317)
test medium_sdx_document ... bench:   2,510,734 ns/iter (+/- 18,054)
test medium_xmltree      ... bench:   7,678,284 ns/iter (+/- 174,265)

test tiny_roxmltree      ... bench:       4,178 ns/iter (+/- 23)
test tiny_minidom        ... bench:       7,468 ns/iter (+/- 88)
test tiny_sdx_document   ... bench:      18,202 ns/iter (+/- 91)
test tiny_xmltree        ... bench:      29,425 ns/iter (+/- 877)

roxmltree uses xmlparser internally, while sdx-document uses its own implementation, xmltree uses the xml-rs and minidom uses quick-xml. Here is a comparison between xmlparser, xml-rs and quick-xml:

test large_quick_xml     ... bench:   1,245,293 ns/iter (+/- 532,460)
test large_xmlparser     ... bench:   1,615,152 ns/iter (+/- 11,505)
test large_xmlrs         ... bench:  19,024,349 ns/iter (+/- 1,102,255)

test medium_quick_xml    ... bench:     246,507 ns/iter (+/- 3,300)
test medium_xmlparser    ... bench:     337,958 ns/iter (+/- 2,465)
test medium_xmlrs        ... bench:   6,944,242 ns/iter (+/- 29,862)

test tiny_quick_xml      ... bench:       2,328 ns/iter (+/- 67)
test tiny_xmlparser      ... bench:       2,578 ns/iter (+/- 931)
test tiny_xmlrs          ... bench:      27,343 ns/iter (+/- 3,299)

You can try it yourself by running cargo bench in the benches dir.

Notes:

  • Since all libraries have a different XML support, benchmarking is a bit pointless.
  • Tree crates may use different xml-rs crate versions.
  • We do not bench the libxml2, because xmlReadFile() will parse only an XML structure, without attributes normalization and stuff. So it's hard to compare. And we have to use a separate benchmark utility.
  • quick-xml is faster than xmlparser because it's more forgiving for the input, while xmlparser is very strict and does a lot of checks, which are expensive. So performance difference is mainly due to validation.

Safety

  • This library must not panic. Any panic should be considered a critical bug and reported.
  • This library forbids unsafe code.

Non-goals

  • Complete XML support.
  • Tree modification and writing.
  • XPath/XQuery.

API

This library uses Rust's idiomatic API based on iterators. In case you are more familiar with browser/JS DOM APIs - you can check out tests/dom-api.rs to see how it can be converted into a Rust one.

License

Licensed under either of

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.