openUrl(url, opts) returns a RemoteFile with the methods of H5File
(kind, list, info, attrs, attrErrors, read, readHyperslab), each a
promise, and stats(). It runs every call through the restartable
LazyStorage: a pass that misses reports the byte ranges, js/remote.js
fetches them with fetch() and Range headers (six at a time), and the
pass is re-run. This keeps the main thread free without a Worker or
synchronous XHR (h5wasm's lazy files need both), as the design doc
recommends; the cost is re-running a pass per wave of misses.
Every answer is checked: a 206 with exactly the bytes asked for, and
the same ETag/Last-Modified and length as at open, else an error (never
data). A server that ignores Range (200) is downloaded whole, up to
maxDownload (512 MiB), unless fallback: "error". Options: blockSize,
cacheSize, headers, credentials, parallel, fetch.
test/serve.py is a range-capable static server with request counting
(and /norange/ for a server without range support). test.mjs repeats
every fixture check on files opened by URL (1 MiB and 512 B blocks),
checks the request budget on a 200 MB h5py file (list, three small
reads and a window of the big dataset: 5 requests, 6 MiB), the
download fallback, and HTTP errors, changed files and wrong answers;
with CLAWHDF5_WASM_CORPUS every corpus file is compared with open(bytes).
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
