Optimizing HTML Link Extraction With qipdb

html-link-extractor.wasm reads HTML and writes one link per line. Each line contains the decoded href and a simplified accessible name.

The old component did not recognize aria-labelledby. It also included comments, scripts, and styles in names. The corrected component fixes those cases and resolves repeated label references up to 9.9 times faster in V8.

Define Correct Output First #

The Compliance oracle has 20 exact input and output cases. It covers relative and absolute links, entities, nested text, image alt text, aria-label, aria-labelledby, duplicate IDs, forward references, comments, raw text, and malformed anchors.

The shipped artifact passed 11 cases. It failed all seven aria-labelledby cases because the attribute matcher used a length of 14. The name has 15 characters, so that branch could not run. It also stopped at the first same-name nested end tag and treated hidden source text as visible text.

The new JavaScript tests check the same behavior through the Content ABI. They also check maximum-size input, 1,100 IDs, and the label-heavy benchmark used below. The 1,100-ID case verifies the bounded index fallback.

This is still a small HTML scanner, not a browser parser. The oracle defines the supported subset. It does not claim full HTML parsing or complete Accessible Name Computation conformance.

Inspect The Corrected Baseline #

Correctness changes can change execution paths. The performance comparison therefore starts from a correctness-only build, not the shipped artifact.

On the 27,605-byte generated site-static/docs.html page, qipdb reported 904,750 executed instructions and 74,872 taken branches. The component searched from the start of the document for each label reference.

The same trace wrote ordinary URL and text bytes with scalar stores. Static analysis reported no memory.copy instruction.

The hypothesis had two parts:

Build a bounded ID index on the first aria-labelledby use. Resolve later references against that index.
Copy runs with no entity or whitespace boundary with memory.copy.

The index stores at most 1,024 IDs. If a document has more, the component uses the old scan for that render. This keeps memory bounded and preserves output. The index fits in the existing linear memory, so the module still declares 256 KiB.

Results #

The typical fixture is site-static/docs.html. Its SHA-256 is 5c8b68425aaa61b13806c7fa84ce36b27aaa0242d1aa040ab155a602923fb2d4. Both measured builds produce 3,121 bytes with SHA-256 30cc4a93d0192b412098f758a5894aefaa8b3a19d1bb1573861734e7936f17b4.

Five thousand alternating runs gave these measurements:

Measurement	Correctness-only	Indexed and bulk-copy	Change
wazero total	790.2 µs	796.2 µs	1% slower
V8 render	25.02 µs	22.40 µs	1.12× faster
qipdb instructions	904,750	827,633	-9%
qipdb branches taken	74,872	69,808	-7%

The second fixture has 128 IDs and 128 links. Each link names four labels. The 11,134-byte input has SHA-256 05630c5cdfda8dff17732aeea58d6053e08d9699a250b50d084095a6600b47d9. It produces 5,338 bytes with SHA-256 981ea3b40a980e3fae86bd5fe4a6fe21686b2d578292f6a8ba6a0b8b45ea779b.

Three hundred alternating runs gave these measurements:

Measurement	Correctness-only	Indexed and bulk-copy	Change
wazero total	25.99 ms	3.047 ms	8.53× faster
V8 render	868.3 µs	88.05 µs	9.86× faster
qipdb instructions	39,654,915	3,735,494	-91%
qipdb branches taken	2,609,090	203,642	-92%
qipdb calls	67,968	4,480	-93%

The indexed build adds code and two static memory.copy sites:

Artifact	Oracle cases	Raw Wasm	gzip Wasm	Brotli Wasm	Linear memory
Shipped	11/20	8,640 B	3,257 B	2,848 B	256 KiB
Correctness-only	20/20	9,674 B	3,633 B	3,174 B	256 KiB
Indexed and bulk-copy	20/20	11,143 B	4,073 B	3,556 B	256 KiB

The production build uses the indexed version. It adds 440 gzip bytes over the correctness-only build. The typical wazero difference is within 1%, the typical V8 result is faster, and repeated label resolution is much faster in both runtimes.

The benchmarks ran on a MacBook Air with an Apple M5 10-core CPU and 24 GB of memory, on macOS 26.6.2. The runtimes were wazero 1.11.0 and Node.js 26.3.0 with V8 14.6.202.34-node.20. Zig 0.15.2 built the modules.

Reproduce The Checks #

Build and test the component:

make -j \
  qip \
  text/html/html-link-extractor.wasm \
  compliance/html-link-extractor.comply.wasm \
  application/wasm/wasm-counts.wasm \
  components/interactive/qipdb.wasm

./qip comply \
  text/html/html-link-extractor.wasm \
  --with compliance/html-link-extractor.comply.wasm \
  --straight-line-oracles

node --test test/html-link-extractor.mjs

Generate the label-heavy input without storing it in the repository:

node tools/generate-html-link-extractor-benchmark.mjs \
  > /tmp/html-link-extractor-label-heavy.html

Keep a baseline artifact before rebuilding. Then compare both modules:

./qip bench \
  -i /tmp/html-link-extractor-label-heavy.html \
  -r 300 \
  --node \
  /tmp/html-link-extractor-correct-before-fast.wasm \
  text/html/html-link-extractor.wasm

Open the same input in qipdb. Press Space to finish execution, then press i to expand the counters:

npx @qip.dev/qipx tui \
  -F component=@text/html/html-link-extractor.wasm \
  -F input=@/tmp/html-link-extractor-label-heavy.html \
  components/interactive/qipdb.wasm

The shipped artifact has SHA-256 97cd6ae88b7e72bb13db8f42f162188878fc288b8d63fd4c84a9281ed22f723f. The correctness-only artifact has SHA-256 2fb3420c00cd497b2502ba8f0577cf8a82a1cf464a2834de85c6f905e569f71e. The final artifact has SHA-256 99e8ecffd248cb6eb10cb7ff5215c2a2067c71f2d01b800707c2c4a6fae95e80.

Both the shipped and final artifacts pass wasm-strict-profile.wasm. Neither passes the optional static loop or output proofs. Use a host time limit for untrusted input. The JavaScript capacity test verifies that the returned byte count stays within the advertised output buffer.

When Not To Use This Component #

Use a conforming HTML parser when browser error recovery, templates, foreign content, CSS visibility, or the complete accessible-name algorithm affects your result. Use this component for controlled HTML where its tested subset is sufficient.