roxmltree

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

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

| Feature/Crate | roxmltree | [libxml2] | [xmltree] | [elementtree] | [sxd-document] | [treexml] | | ------------------------------- | :--------------: | :-----------------: | :--------------: | :--------------: | :--------------: | :--------------: | | 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 | Rust | | Size overhead⁴ | ~73KiB | ~1.4MiB⁵ | ~80KiB | ~96KiB | ~135KiB | ~110KiB | | Dependencies | 1 | ?⁵ | 2 | 18 | 2 | 14 | | Tested version | 0.6.0 | 2.9.8 | 0.8.0 | 0.5.0 | 0.3.0 | 0.7.0 | | License | MIT / Apache-2.0 | MIT | MIT | BSD-3-Clause | 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 string_cache crate.
4. Binary size overhead according to cargo-bloat.
5. Depends on build flags.

Performance

```text test largeroxmltree ... bench: 5,660,398 ns/iter (+/- 104,723) test largesdxdocument ... bench: 9,562,290 ns/iter (+/- 45,585) test largexmltree ... bench: 32,797,800 ns/iter (+/- 134,016) test largetreexml ... bench: 31,380,063 ns/iter (+/- 71,732) test largeelementtree ... bench: 32,121,979 ns/iter (+/- 264,842)

test mediumroxmltree ... bench: 1,094,562 ns/iter (+/- 6,030) test mediumsdxdocument ... bench: 3,791,252 ns/iter (+/- 41,929) test mediumtreexml ... bench: 10,975,247 ns/iter (+/- 22,692) test mediumxmltree ... bench: 11,601,320 ns/iter (+/- 46,216) test mediumelementtree ... bench: 11,550,227 ns/iter (+/- 17,991)

test tinyroxmltree ... bench: 7,697 ns/iter (+/- 41) test tinysdxdocument ... bench: 28,031 ns/iter (+/- 101) test tinyxmltree ... bench: 47,199 ns/iter (+/- 110) test tinytreexml ... bench: 50,399 ns/iter (+/- 55) test tinyelementtree ... bench: 51,569 ns/iter (+/- 165) ```

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 and xml-rs:

```text test largexmlparser ... bench: 2,485,710 ns/iter (+/- 1,246) test largexmlrs ... bench: 28,252,304 ns/iter (+/- 27,852)

test mediumxmlparser ... bench: 624,192 ns/iter (+/- 1,040) test mediumxmlrs ... bench: 10,237,568 ns/iter (+/- 13,497)

test tinyxmlparser ... bench: 4,986 ns/iter (+/- 84) test tinyxmlrs ... bench: 45,832 ns/iter (+/- 50) ```

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.

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.

Dependency

Rust >= 1.18

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.