Show HN: Xmloxide – an agent made rust replacement for libxml2

Hacker News · Feb 28, 2026 · Collected from RSS

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xmloxide A pure Rust reimplementation of libxml2 — the de facto standard XML/HTML parsing library in the open-source world. libxml2 became officially unmaintained in December 2025 with known security issues. xmloxide aims to be a memory-safe, high-performance replacement that passes the same conformance test suites. Features Memory-safe — arena-based tree with zero unsafe in the public API Conformant — 100% pass rate on the W3C XML Conformance Test Suite (1727/1727 applicable tests) Error recovery — parse malformed XML and still produce a usable tree, just like libxml2 Multiple parsing APIs — DOM tree, SAX2 streaming, XmlReader pull, push/incremental HTML parser — error-tolerant HTML 4.01 parsing with auto-closing and void elements XPath 1.0 — full expression parser and evaluator with all core functions Validation — DTD, RelaxNG, and XML Schema (XSD) validation Canonical XML — C14N 1.0 and Exclusive C14N serialization XInclude — document inclusion processing XML Catalogs — OASIS XML Catalogs for URI resolution xmllint CLI — command-line tool for parsing, validating, and querying XML Zero-copy where possible — string interning for fast comparisons No global state — each Document is self-contained and Send + Sync C/C++ FFI — full C API with header file (include/xmloxide.h) for embedding in C/C++ projects Minimal dependencies — only encoding_rs (library has zero other deps; clap is CLI-only) Quick Start use xmloxide::Document; let doc = Document::parse_str("<root><child>Hello</child></root>").unwrap(); let root = doc.root_element().unwrap(); assert_eq!(doc.node_name(root), Some("root")); assert_eq!(doc.text_content(root), "Hello"); Serialization use xmloxide::Document; use xmloxide::serial::serialize; let doc = Document::parse_str("<root><child>Hello</child></root>").unwrap(); let xml = serialize(&doc); assert_eq!(xml, "<root><child>Hello</child></root>"); XPath Queries use xmloxide::Document; use xmloxide::xpath::{evaluate, XPathValue}; let doc = Document::parse_str("<library><book><title>Rust</title></book></library>").unwrap(); let root = doc.root_element().unwrap(); let result = evaluate(&doc, root, "count(book)").unwrap(); assert_eq!(result.to_number(), 1.0); SAX2 Streaming use xmloxide::sax::{parse_sax, SaxHandler, DefaultHandler}; use xmloxide::parser::ParseOptions; struct MyHandler; impl SaxHandler for MyHandler { fn start_element(&mut self, name: &str, _: Option<&str>, _: Option<&str>, _: &[(String, String, Option<String>, Option<String>)]) { println!("Element: {name}"); } } parse_sax("<root><child/></root>", &ParseOptions::default(), &mut MyHandler).unwrap(); HTML Parsing use xmloxide::html::parse_html; let doc = parse_html("<p>Hello <br> World").unwrap(); let root = doc.root_element().unwrap(); assert_eq!(doc.node_name(root), Some("html")); Error Recovery use xmloxide::parser::{parse_str_with_options, ParseOptions}; let opts = ParseOptions::default().recover(true); let doc = parse_str_with_options("<root><unclosed>", &opts).unwrap(); for diag in &doc.diagnostics { eprintln!("{}", diag); } CLI Tool # Parse and pretty-print xmllint --format document.xml # Validate against a schema xmllint --schema schema.xsd document.xml xmllint --relaxng schema.rng document.xml xmllint --dtdvalid schema.dtd document.xml # XPath query xmllint --xpath "//title" document.xml # Canonical XML xmllint --c14n document.xml # Parse HTML xmllint --html page.html Module Overview Module Description tree Arena-based DOM tree (Document, NodeId, NodeKind) parser XML 1.0 recursive descent parser with error recovery parser::push Push/incremental parser for chunked input html Error-tolerant HTML 4.01 parser sax SAX2 streaming event-driven parser reader XmlReader pull-based parsing API serial XML serializer and Canonical XML (C14N) xpath XPath 1.0 expression parser and evaluator validation::dtd DTD parsing and validation validation::relaxng RelaxNG schema validation validation::xsd XML Schema (XSD) validation xinclude XInclude 1.0 document inclusion catalog OASIS XML Catalogs for URI resolution encoding Character encoding detection and transcoding ffi C/C++ FFI bindings (include/xmloxide.h) Performance Parsing throughput is competitive with libxml2 — within 3-4% on most documents, and 12% faster on SVG. Serialization is 1.5-2.4x faster thanks to the arena-based tree design. XPath is 1.1-2.7x faster across all benchmarks. Parsing: Document Size xmloxide libxml2 Result Atom feed 4.9 KB 26.7 µs (176 MiB/s) 25.5 µs (184 MiB/s) ~4% slower SVG drawing 6.3 KB 58.5 µs (103 MiB/s) 65.6 µs (92 MiB/s) 12% faster Maven POM 11.5 KB 76.9 µs (142 MiB/s) 74.2 µs (148 MiB/s) ~4% slower XHTML page 10.2 KB 69.5 µs (139 MiB/s) 61.5 µs (157 MiB/s) ~13% slower Large (374 KB) 374 KB 2.15 ms (169 MiB/s) 2.08 ms (175 MiB/s) ~3% slower Serialization: Document Size xmloxide libxml2 Result Atom feed 4.9 KB 11.3 µs 17.5 µs 1.5x faster Maven POM 11.5 KB 20.1 µs 47.5 µs 2.4x faster Large (374 KB) 374 KB 614 µs 1397 µs 2.3x faster XPath: Expression xmloxide libxml2 Result Simple path (//entry/title) 1.51 µs 1.63 µs 8% faster Attribute predicate (//book[@id]) 5.91 µs 15.99 µs 2.7x faster count() function 1.09 µs 1.67 µs 1.5x faster string() function 1.32 µs 1.77 µs 1.3x faster Key optimizations: arena-based tree for fast serialization, byte-level pre-checks for character validation, bulk text scanning, ASCII fast paths for name parsing, zero-copy element name splitting, inline entity resolution, XPath // step fusion with fused axis expansion, inlined tree accessors, and name-test fast paths for child/descendant axes. # Run benchmarks (requires libxml2 system library) cargo bench --features bench-libxml2 --bench comparison_bench Testing 785 unit tests across all modules 112 FFI tests covering the full C API surface (including SAX streaming) libxml2 compatibility suite — 119/119 tests passing (100%) covering XML parsing, namespaces, error detection, and HTML parsing W3C XML Conformance Test Suite — 1727/1727 applicable tests passing (100%) Integration tests covering real-world XML documents, edge cases, and error recovery cargo test --all-features C/C++ FFI xmloxide provides a C-compatible API for embedding in C/C++ projects (like Chromium, game engines, or any codebase that currently uses libxml2). # Build shared + static libraries (uses the included Makefile) make # Or build individually: make shared # .so / .dylib / .dll make static # .a / .lib # Build and run the C example make example #include "xmloxide.h" xmloxide_document *doc = xmloxide_parse_str("<root>Hello</root>"); uint32_t root = xmloxide_doc_root_element(doc); char *name = xmloxide_node_name(doc, root); // "root" char *text = xmloxide_node_text_content(doc, root); // "Hello" xmloxide_free_string(name); xmloxide_free_string(text); xmloxide_free_doc(doc); The full API — including tree navigation and mutation, XPath evaluation, serialization (plain and pretty-printed), HTML parsing, DTD/RelaxNG/XSD validation, C14N, and XML Catalogs — is declared in include/xmloxide.h. Migrating from libxml2 libxml2 xmloxide (Rust) xmloxide (C FFI) xmlReadMemory Document::parse_str xmloxide_parse_str xmlReadFile Document::parse_file xmloxide_parse_file xmlParseDoc Document::parse_bytes xmloxide_parse_bytes htmlReadMemory html::parse_html xmloxide_parse_html xmlFreeDoc (drop Document) xmloxide_free_doc xmlDocGetRootElement doc.root_element() xmloxide_doc_root_element xmlNodeGetContent doc.text_content(id) xmloxide_node_text_content xmlNodeSetContent doc.set_text_content(id, s) xmloxide_set_text_content xmlGetProp doc.attribute(id, name) xmloxide_node_attribute xmlSetProp doc.set_attribute(...) xmloxide_set_attribute xmlNewNode doc.create_node(...) xmloxide_create_element xmlNewText doc.create_node(Text{..}) xmloxide_create_text xmlAddChild doc.append_child(p, c) xmloxide_append_child xmlAddPrevSibling doc.insert_before(ref, c) xmloxide_insert_before xmlUnlinkNode doc.remove_node(id) xmloxide_remove_node xmlCopyNode doc.clone_node(id, deep) xmloxide_clone_node xmlGetID doc.element_by_id(s) xmloxide_element_by_id xmlDocDumpMemory serial::serialize(&doc) xmloxide_serialize xmlDocDumpFormatMemory serial::serialize_with_options xmloxide_serialize_pretty htmlDocDumpMemory serial::html::serialize_html xmloxide_serialize_html xmlC14NDocDumpMemory serial::c14n::canonicalize xmloxide_canonicalize xmlXPathEvalExpression xpath::evaluate xmloxide_xpath_eval xmlValidateDtd validation::dtd::validate xmloxide_validate_dtd xmlRelaxNGValidateDoc validation::relaxng::validate xmloxide_validate_relaxng xmlSchemaValidateDoc validation::xsd::validate_xsd xmloxide_validate_xsd xmlXIncludeProcess xinclude::process_xincludes xmloxide_process_xincludes xmlLoadCatalog Catalog::parse xmloxide_parse_catalog xmlSAX2... callbacks sax::SaxHandler trait xmloxide_sax_parse xmlTextReaderRead reader::XmlReader xmloxide_reader_read xmlCreatePushParserCtxt parser::PushParser xmloxide_push_parser_new xmlParseChunk PushParser::push xmloxide_push_parser_push Thread safety: Unlike libxml2, xmloxide has no global state. Each Document is self-contained and Send + Sync. The FFI layer uses thread-local storage for the last error message — each thread has its own error state. No initialization or cleanup functions are needed. Fuzzing xmloxide includes fuzz targets for security testing: # Install cargo-fuzz (requires nightly) cargo install cargo-fuzz # Run a fuzz target cargo +nightly fuzz run fuzz_xml_parse cargo +nightly fuzz run fuzz_html_parse cargo +nightly fuzz run fuzz_xpath cargo +nightly fuzz run fuzz_roundtrip Building cargo build cargo test cargo clippy --all-targets --all-features -- -D warnings cargo bench Minimum supported Rust version: 1.81 Limitations No XML 1.1 — xmloxide implements XML 1.0 (Fifth Edition) only. XML 1.1 is rarely used and not planned. No XSLT — XSLT is a separate specification (libxslt) and is out of scope. No Schematron — Schematron validation is not implemented. DTD, RelaxNG, and XSD are supported. HTML 4.01 only — the HTML parser targets H