# roxmltree
[](https://travis-ci.org/RazrFalcon/roxmltree)
[](https://crates.io/crates/roxmltree)
[](https://docs.rs/roxmltree)
[](https://www.rust-lang.org)
Represents an [XML 1.0](https://www.w3.org/TR/xml/) document as a read-only tree.
```rust
// Find element by id.
let doc = roxmltree::Document::parse("<rect id='rect1'/>").unwrap();
```
## 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](#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](https://lxml.de/).
But unlike *lxml*, *roxmltree* does support comments outside the root element.
Fo more details see [docs/parsing.md](https://github.com/RazrFalcon/roxmltree/blob/master/docs/parsing.md).
## Alternatives
| Element namespace resolving | ✔ | ✔ | ✔ | ✔ | ~<sup>1</sup> | |
| Attribute namespace resolving | ✔ | ✔ | | | ✔ | |
| [Entity references] | ✔ | ✔ | ⚠ | ⚠ | ⚠ | ⚠ |
| [Character references] | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ |
| [Attribute-Value normalization] | ✔ | ✔ | | | | |
| Comments | ✔ | ✔ | | | ✔ | |
| Processing instructions | ✔ | ✔ | ⚠ | | ✔ | |
| UTF-8 BOM | ✔ | ✔ | ⚠ | ⚠ | ⚠ | ⚠ |
| Non UTF-8 input | | ✔ | | | | |
| Complete DTD support | | ✔ | | | | |
| Position preserving<sup>2</sup> | ✔ | ✔ | | | | |
| HTML support | | ✔ | | | | |
| Tree modification | | ✔ | ✔ | ✔ | ✔ | ✔ |
| Writing | | ✔ | ✔ | ✔ | ✔ | ✔ |
| No **unsafe** | ✔ | | ✔ | ~<sup>3</sup> | | ✔ |
| Language | Rust | C | Rust | Rust | Rust | Rust |
| Size overhead<sup>4</sup> | **~73KiB** | ~1.4MiB<sup>5</sup> | ~80KiB | ~96KiB | ~135KiB | ~110KiB |
| Dependencies | **1** | ?<sup>5</sup> | 2 | 18 | 2 | 14 |
| Tested version | 0.7.0 | 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](examples/print_pos.rs) for details.
3. In the `string_cache` crate.
4. Binary size overhead according to [cargo-bloat](https://github.com/RazrFalcon/cargo-bloat).
5. Depends on build flags.
[Entity references]: https://www.w3.org/TR/REC-xml/#dt-entref
[Character references]: https://www.w3.org/TR/REC-xml/#NT-CharRef
[Attribute-Value Normalization]: https://www.w3.org/TR/REC-xml/#AVNormalize
[libxml2]: http://xmlsoft.org/
[xmltree]: https://crates.io/crates/xmltree
[elementtree]: https://crates.io/crates/elementtree
[treexml]: https://crates.io/crates/treexml
[sxd-document]: https://crates.io/crates/sxd-document
## Performance
```text
test large_roxmltree ... bench: 5,147,695 ns/iter (+/- 75,762)
test large_sdx_document ... bench: 9,452,579 ns/iter (+/- 37,298)
test large_xmltree ... bench: 28,383,408 ns/iter (+/- 46,793)
test large_treexml ... bench: 28,992,626 ns/iter (+/- 122,244)
test large_elementtree ... bench: 29,991,730 ns/iter (+/- 58,134)
test medium_roxmltree ... bench: 935,837 ns/iter (+/- 1,001)
test medium_sdx_document ... bench: 3,619,042 ns/iter (+/- 8,863)
test medium_xmltree ... bench: 10,181,629 ns/iter (+/- 13,994)
test medium_treexml ... bench: 10,338,760 ns/iter (+/- 11,040)
test medium_elementtree ... bench: 10,840,762 ns/iter (+/- 16,162)
test tiny_roxmltree ... bench: 6,346 ns/iter (+/- 129)
test tiny_sdx_document ... bench: 27,464 ns/iter (+/- 91)
test tiny_xmltree ... bench: 43,838 ns/iter (+/- 107)
test tiny_treexml ... bench: 44,794 ns/iter (+/- 263)
test tiny_elementtree ... bench: 45,431 ns/iter (+/- 175)
```
*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 large_xmlparser ... bench: 1,961,131 ns/iter (+/- 66,145)
test large_xmlrs ... bench: 25,582,284 ns/iter (+/- 76,500)
test medium_xmlparser ... bench: 451,180 ns/iter (+/- 1,523)
test medium_xmlrs ... bench: 9,368,598 ns/iter (+/- 10,995)
test tiny_xmlparser ... bench: 3,756 ns/iter (+/- 32)
test tiny_xmlrs ... bench: 39,293 ns/iter (+/- 63)
```
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.
[xml-rs]: https://crates.io/crates/xml-rs
[xmlparser]: https://crates.io/crates/xmlparser
## 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](tests/dom-api.rs) to see how it can be converted into a Rust one.
## License
Licensed under either of
- [Apache License v2.0](LICENSE-APACHE)
- [MIT license](LICENSE-MIT)
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.