wasm: openUrl reads remote files by HTTP range requests (range-read M4)

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]>

examples/wasm-viewer/test/run.sh

@@ -1,11 +1,17 @@
 #!/usr/bin/env bash
 # Build the wasm package (../build.sh), test it under Node against files
-# written by h5py and netCDF4 (make_fixture.py), then load the viewer page
-# in headless Chromium if one is found (browser.sh).
+# written by h5py and netCDF4 (make_fixture.py) — opened from bytes, and
+# opened by URL from a local range-capable HTTP server (serve.py) — then
+# load the viewer page in headless Chromium if one is found (browser.sh).
 #
 # Needs node, the wasm-bindgen CLI (see ../build.sh) and a Python with h5py,
 # netCDF4 and numpy: CLAWHDF5_PYTHON names it (default python3). Without that
 # Python the test is skipped, unless CLAWHDF5_REQUIRE_INTEROP=1.
+#
+# WASM_BIG_MB (default 200) sizes the large file of the range-request
+# budget test (0 leaves it out); it is written under TMPDIR.
+# CLAWHDF5_WASM_CORPUS=DIR also compares every HDF5 file under DIR (up to
+# 16 MiB) read over HTTP with the same file read from bytes.
 set -euo pipefail
 
 HERE="$(cd "$(dirname "$0")" && pwd)"
@@ -23,9 +29,24 @@ fi
 
 bash "$HERE/../build.sh"
 fix="$(mktemp -d)"
-trap 'rm -rf "$fix"' EXIT
-"$PY" "$HERE/make_fixture.py" "$fix"
-node "$HERE/test.mjs" "$HERE/../pkg" "$fix"
+server=""
+cleanup() {
+    [ -n "$server" ] && kill "$server" 2>/dev/null || true
+    rm -rf "$fix"
+}
+trap cleanup EXIT
+WASM_BIG_MB="${WASM_BIG_MB:-200}" "$PY" "$HERE/make_fixture.py" "$fix"
+
+# The fixtures (and the corpus) over HTTP with range support.
+roots=(--root "fix=$fix")
+[ -n "${CLAWHDF5_WASM_CORPUS:-}" ] && roots+=(--root "corpus=$CLAWHDF5_WASM_CORPUS")
+"$PY" "$HERE/serve.py" "${roots[@]}" > "$fix/port" &
+server=$!
+for _ in $(seq 50); do
+    [ -s "$fix/port" ] && break
+    sleep 0.1
+done
+node "$HERE/test.mjs" "$HERE/../pkg" "$fix" "http://127.0.0.1:$(head -1 "$fix/port")"
 
 # The page itself, in headless Chromium when one is available.
 status=0