# 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.
For 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 |
| Size overhead<sup>4</sup> | ~61KiB | ~1.4MiB<sup>5</sup> | ~106KiB | ~121KiB | **~58KiB** |
| Dependencies | **1** | ?<sup>5</sup> | 2 | 2 | 2 |
| Tested version | 0.14.0 | 2.9.8 | 0.10.2 | 0.3.2 | 0.12.0 |
| 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](examples/print_pos.rs) for details.
3. In the `memchr` crate.
4. Binary size overhead according to [cargo-bloat](https://github.com/RazrFalcon/cargo-bloat).
5. Depends on build flags.
There is also `elementtree` and `treexml` crates, but they are abandoned for a long time.
[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
[sxd-document]: https://crates.io/crates/sxd-document
[minidom]: https://gitlab.com/xmpp-rs/xmpp-rs/-/tree/main/minidom
## Performance
### Parsing
```text
test large_roxmltree ... bench: 3,123,941 ns/iter (+/- 19,992)
test large_minidom ... bench: 4,969,218 ns/iter (+/- 163,727)
test large_sdx_document ... bench: 7,266,856 ns/iter (+/- 26,998)
test large_xmltree ... bench: 21,354,608 ns/iter (+/- 136,311)
test medium_roxmltree ... bench: 547,522 ns/iter (+/- 5,956)
test medium_minidom ... bench: 1,223,620 ns/iter (+/- 16,180)
test medium_sdx_document ... bench: 2,470,063 ns/iter (+/- 24,159)
test medium_xmltree ... bench: 8,083,860 ns/iter (+/- 25,363)
test tiny_roxmltree ... bench: 4,170 ns/iter (+/- 41)
test tiny_minidom ... bench: 7,495 ns/iter (+/- 81)
test tiny_sdx_document ... bench: 17,411 ns/iter (+/- 203)
test tiny_xmltree ... bench: 29,522 ns/iter (+/- 223)
```
*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*:
```text
test large_quick_xml ... bench: 1,286,273 ns/iter (+/- 27,174)
test large_xmlparser ... bench: 1,742,202 ns/iter (+/- 11,616)
test large_xmlrs ... bench: 19,615,797 ns/iter (+/- 105,848)
test medium_quick_xml ... bench: 248,169 ns/iter (+/- 3,885)
test medium_xmlparser ... bench: 386,658 ns/iter (+/- 1,721)
test medium_xmlrs ... bench: 7,387,753 ns/iter (+/- 18,668)
test tiny_quick_xml ... bench: 2,382 ns/iter (+/- 29)
test tiny_xmlparser ... bench: 2,788 ns/iter (+/- 20)
test tiny_xmlrs ... bench: 27,619 ns/iter (+/- 262)
```
### Iteration
```text
test xmltree_iter_descendants_expensive ... bench: 436,684 ns/iter (+/- 7,851)
test roxmltree_iter_descendants_expensive ... bench: 470,459 ns/iter (+/- 6,233)
test minidom_iter_descendants_expensive ... bench: 785,847 ns/iter (+/- 51,495)
test roxmltree_iter_descendants_inexpensive ... bench: 36,759 ns/iter (+/- 684)
test xmltree_iter_descendants_inexpensive ... bench: 168,541 ns/iter (+/- 1,885)
test minidom_iter_descendants_inexpensive ... bench: 215,615 ns/iter (+/- 38,101)
```
Where expensive refers to the matching done on each element. In these
benchmarks, *expensive* means searching for any node in the document which
contains a string. And *inexpensive* means searching for any element with a
particular name.
### Notes
You can try running the benchmarks yourself by running `cargo bench` in the `benches` dir.
- 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.
[xml-rs]: https://crates.io/crates/xml-rs
[quick-xml]: https://crates.io/crates/quick-xml
[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.