roxmltree

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.

Fo more details see docs/parsing.md.

Alternatives

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 string_cache crate.
4. Binary size overhead according to cargo-bloat.
5. Depends on build flags.

Performance

test large_roxmltree     ... bench:   3,976,162 ns/iter (+/- 16,229)
test large_sdx_document  ... bench:   7,501,511 ns/iter (+/- 33,603)
test large_xmltree       ... bench:  20,821,266 ns/iter (+/- 80,124)
test large_elementtree   ... bench:  21,388,702 ns/iter (+/- 115,590)
test large_treexml       ... bench:  21,469,671 ns/iter (+/- 192,099)

test medium_roxmltree    ... bench:     732,136 ns/iter (+/- 6,410)
test medium_sdx_document ... bench:   2,548,236 ns/iter (+/- 14,502)
test medium_elementtree  ... bench:   8,505,173 ns/iter (+/- 26,123)
test medium_treexml      ... bench:   8,146,522 ns/iter (+/- 19,378)
test medium_xmltree      ... bench:   8,217,647 ns/iter (+/- 22,061)

test tiny_roxmltree      ... bench:       5,039 ns/iter (+/- 46)
test tiny_sdx_document   ... bench:      18,204 ns/iter (+/- 145)
test tiny_elementtree    ... bench:      30,865 ns/iter (+/- 280)
test tiny_treexml        ... bench:      30,698 ns/iter (+/- 468)
test tiny_xmltree        ... bench:      30,338 ns/iter (+/- 231)

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

test large_quick_xml     ... bench:   1,220,067 ns/iter (+/- 20,723)
test large_xmlparser     ... bench:   2,079,871 ns/iter (+/- 12,220)
test large_xmlrs         ... bench:  19,628,313 ns/iter (+/- 241,729)

test medium_quick_xml    ... bench:     246,421 ns/iter (+/- 17,438)
test medium_xmlparser    ... bench:     408,831 ns/iter (+/- 4,351)
test medium_xmlrs        ... bench:   7,430,009 ns/iter (+/- 40,350)

test tiny_quick_xml      ... bench:       2,329 ns/iter (+/- 67)
test tiny_xmlparser      ... bench:       3,313 ns/iter (+/- 22)
test tiny_xmlrs          ... bench:      28,511 ns/iter (+/- 232)

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

• Apache License v2.0
• MIT license

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.