research XML libraries

[briandorsey]

Needs:

• no_std support
• read and write XML
• 100% Rust (not wrapping a C library, for example)
• able to parse iXML (#36) and _PMX chunks

Consider:

• https://github.com/faassen/xot (also a nice list of other libraries there.

[briandorsey]

Looked at:

• https://github.com/faassen/xot
• https://github.com/kornelski/xml-rs (maybe with https://docs.rs/serde-xml-rs/latest/serde_xml_rs/index.html
• https://github.com/tafia/quick-xml

The last two look like the most popular libraries, and xot looks like a hobby project from someone who really gets XML, so worth consideration.

It doesn't look like any of them have no_std support. :/ I guess we just have to go with that for now and figure that out a work-around in the future.

xml-rs is slower, but seems to have better standards compliance (supports UTF-16, for example)... since the metadata chunks are relatively small... probably OK to go with a library that's slower, but more likely to support variations found in the field. Leaning towards xml-rs currently. It also specifically claims no use of unsafe rust.

[briandorsey]

Some XML parsing writeups:

• Nice write up of larger scale stream parsing of XML, highlighting quick-xml and encoding_rs to handle the UTF-16 conversion: https://usethe.computer/posts/14-xmhell.html More perf focused than our use case, but the UTF-16 handling is relevant.
• https://capnfabs.net/posts/parsing-huge-xml-quickxml-rust-serde/ - hybrid approach using quick-xml to find records, and serde to parse just them.