Show HN: Xmloxide – an agent-made Rust replacement for libxml2

[jawiggins]

Recently several AI labs have published experiments where they tried to get AI coding agents to complete large software projects.

- Cursor attempted to make a browser from scratch: https://cursor.com/blog/scaling-agents

- Anthropic attempted to make a C Compiler: https://www.anthropic.com/engineering/building-c-compiler

I have been wondering if there are software packages that can be easily reproduced by taking the available test suites and tasking agents to work on projects until the existing test suites pass.

After playing with this concept by having Claude Code reproduce redis and sqlite, I began looking for software packages where an agent-made reproduction might actually be useful.

I found libxml2, a widely used, open-source C language library designed for parsing, creating, and manipulating XML and HTML documents. Three months ago it became unmaintained with the update, "This project is unmaintained and has [known security issues](https://gitlab.gnome.org/GNOME/libxml2/-/issues/346). It is foolish to use this software to process untrusted data.".

With a few days of work, I was able to create xmloxide, a memory safe rust replacement for libxml2 which passes the compatibility suite as well as the W3C XML Conformance Test Suite. Performance is similar on most parsing operations and better on serialization. It comes with a C API so that it can be a replacement for existing uses of libxml2.

- crates.io: https://crates.io/crates/xmloxide

- GitHub release: https://github.com/jonwiggins/xmloxide/releases/tag/v0.1.0

While I don't expect people to cut over to this new and unproven package, I do think there is something interesting to think about here in how coding agents like Claude Code can quickly iterate given a test suite. It's possible the legacy code problem that COBOL and other systems present will go away as rewrites become easier. The problem of ongoing maintenance to fix CVEs and update to later package versions becomes a larger percentage of software package management work.

[wooptoo]

A comment on libxml, not on your work: Funny how so many companies use this library in production and not one steps in to maintain this project and patch the issues. What a sad state of affairs we are in.

[nwellnhof]

About a day after I resigned as maintainer, SUSE stepped in and is now maintaining the project. As announced here [1], I'm currently trying a different funding model and started a GPL-licensed fork with many security and performance improvements [2].

It should also be noted that the remaining security issues in the core parser have to do with algorithmic complexity, not memory safety. Many other parts of libxml2 aren't security-critical at all.

[1] https://gitlab.gnome.org/GNOME/libxml2/-/issues/976

[2] https://codeberg.org/nwellnhof/libxml2-ee

[jawiggins]

Yeah I agree, maintaining OS projects has been a weird thing for a long time.

I know a few companies have programs where engineers can designate specific projects as important and give them funds. But it doesn't happen enough to support all the projects that currently need work, maybe AI coding tools will lower the cost of maintenance enough to improve this.

I do think there are two possible approaches that policy makers could consider.

1) There could probably be tax credits or deductions for SWEs who 'volunteer' their time to work on these projects.

2) Many governments have tried to create cyber reserve corps, I bet they could designate people as maintainers of key projects that they rely on to maintain both the projects as well as people skilled with the tools that they deem important.

[socalgal2]

funny how this myth won't die. Checking the commit history plenty of companies are contributing

redhat, apple, samsung, huawei, google, etc...

[ddlsmurf]

we need a tax on companies using or selling anything OSS, the funds of which go into OSS, the wealth it generated is insane, and it's nearly all just donations of experts

[da_chicken]

Feels like tragedy of the commons.

[kburman]

Amazing work! I'd love to hear more details about your workflow with Claude Code.

As a side note and this isn't a knock on your project specifically. I think the community needs to normalize disclaimers for "vibe-coded" packages. Consumers really need to understand the potential risks of relying on agent-generated code upfront.

[nine_k]

Even more interesting is how much did the effort cost.

Unlike the development work of old (pre-2025), work with high-end models incurs a very direct monetary cost, one burns tokens which cost money, and you can't have something as powerful to be running locally (even if you happened to have a Mac Pro Ultra with RAM maxed out).

Some of my friends burned through hundreds of dollars a day while doing large amounts of (allegedly efficient) work with Claude Code.

[jawiggins]

Yeah its a fair point. I wondered if it might be irresponsible to publish the package because it was made this way, but I suspect I'm not the first person to try and develop a package with Claude Code, so I think the best I can do is be honest about it.

As for the workflow, I think the best advice I can give is to setup as many guardrails and tools as possible, so Claude and do as many iterations before needing any intervention. So in this case I setup pre-commit hooks for linting and formatting, gave it access to the full testing suite, and let it rip. The majority of the work was done in a single thinking loop that lasted ~3 hours where Claude was able to run the tests, see what failed, and iterate until they all passed. From there, there was still lots of iterations to add features, clean up, test, and improve performance - but allowing Claude to iterate quickly on it's own without my involvement was crucial.

[socalgal2]

Do they? Tons of extremely popular human generated libraries are absolute trash. Just as an example, nearly all of the JS zip file libraries are dumpers fires. Same with QR code libraries and command line parsing libraries.

This feels like if you want to know if the code is good or bad, read the code and check the tests. Assuming human = good, LLM = bad does not make much sense given the amount of bad human code I've seen.

Sure, if the code is from a repuatable company or creator then I'd take that as a strong signal quality over an LLM but I wouldn't take a random human programmer as a strong signal over generated.

[hrtla]

Yes, you can rip off any sucker who published a test suite when the AI is trained on existing code as well. Congratulations, you will be showered with praise and AI mafia money.

[blegge]

> arena-based tree with zero unsafe in the public API

Why "in the public API"? Does this imply it's using unsafe behind the hood? If so, what for?

[gpm]

I agree the wording is a bit strange, but a quick grep of the repo shows that it doesn't imply that.

The only usages of unsafe are in src/ffi, which is only compiled when the ffi feature is enabled. ffi is fundamentally unsafe ("unsafe" meaning "the compiler can't automatically verify this code won't result in undefined behavior") so using it there is reasonable, and the rest of the crate is properly free of unsafe.

[fulafel]

It provides a libxml2-compatible C API and that accepted pointers, this would seem to necessitate unsafe at least.

[DetroitThrow]

Yeah I'm a bit confused because you can have an entirely unsafe code base with just the public interface marked as safe. No unsafe in the interface isn't a measure of safety at all.

[alexhans]

> I do think there is something interesting to think about here in how coding agents like Claude Code can quickly iterate given a test suite.

This is a point I've tried to advocate for a while. Specially to empower non coders and make them see that we CAN approach automation with control.

Some aspects will be the classic unit or integration tests for validation. Others, will be AI Evals [1] which to me could be the common language for product design for different families/disciplines who don't quite understand how to collaborate with each other.

The amount of progress in a short time is amazing to see.

- [1] https://ai-evals.io/

[koakuma-chan]

Please stop spreading this "AI evals" terminology. "evals" is what providers like OpenAI and Anthropic do with their models. If you wrote a test for a feature that uses an LLM, it's just a test, there's no need to say "evals." Having a separate term only further confuses people who already have no idea what that actually means.

[yobbo]

The code might be a little verbose which is tiresome for humans to read and follow. Structure and functions look idiomatic. It seems to be using xml parser idioms which makes it readable.

It could be doing double checks in both tokeniser and parser and things like that.

Actually looks like a good starting point and reference for someone working on xml parsers in rust.

[mkj]

Intriguing work! Does it panic on any bad inputs? That's better than memory unsafety of libxml2, but still a DoS concern for some servers.

[agentifysh]

lot of weird comments here getting upset AI was used but thanks for doing this

libxml2 is always one of those libraries that i used to have trouble with for different platforms

I think its great that more and more OSS projects get attention now with ai coding agents

[nicoburns]

How does it compare to the original in terms of source code size (number of lines of code?)

[jawiggins]

It's significantly smaller. Because Rust doesn't require header files or memory management, xmloxide is ~40k lines while libxml2 is ~150k lines.

[fourthark]

Does it fix the security flaws that caused the original project to be shut down?

[jawiggins]

Because it was written in C, libxml2's CVE history has been dominated by use-after-free, buffer overflows, double frees, and type confusion. xmloxide is written in pure Rust, so these entire vulnerability classes are eliminated at compile time.

[blegge]

https://gitlab.gnome.org/GNOME/libxml2/-/commit/0704f52ea4cd...

Doesn't seem to have shut down or even be unmaintained. Perhaps it was briefly, and has now been resurrected?

[notpushkin]

If by flaws you mean the security researchers spamming libxml2 with low effort stuff demanding a CVE for each one so they can brag about it – no, I don’t think anybody can fix that.

[Imustaskforhelp]

Can this work with XLSX (The Open XML format) & .odt format though these also use zip. It would be interesting to think if this can help solve this and create a rust GUI app with very basic XLSX doc editing as alternative to OpenOffice/LibreOffice.

[benatkin]

It would be interesting to try this approach out with mQuickJS, QuickJS or micropython. They could potentially run hoops around the ones that were first coded in Rust, such as Boa or RustPython.

[dmitrygr]

cool, now do it without the test suite that some human made for you

[mdavid626]

Can you add “made with AI” to the GitHub repo?

It’s time to make this mandatory.

Nothing against AI - just to inform people about quality, maintainability and future of this library. No human has mental model of the code, so don’t waste your time creating it - the original author didn’t either.

[agentifysh]

what would be the point ? why should this be mandatory ?

none of your arguments make sense here

[jawiggins]

Yes, in testing I did add four fuzzing targets to the repo:

1. fuzz_xml_parse: throws arbitrary bytes at the XML parser in both strict and recovery mode

2. fuzz_html_parse: throws arbitrary bytes at the HTML parser

3. fuzz_xpath: throws arbitrary XPath expressions at the evaluator

4. fuzz_roundtrip: parse → serialize → re-parse, checking that the pipeline never panics

Because this project uses memory safe rust, there isn't really the need to find the memory bugs that were the majority of libxml2's CVEs.

There is a valid point about logic bugs or infinite loops, which I suppose could be present in any software package, and I'm not sure of a way to totally rule out here.