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perf(browse): stream files into the offline zip instead of buffering all bytes

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downloadFsSubtree pre-read every file's arrayBuffer() and handed the raw
ArrayBuffer to JSZip, so the entire subtree's bytes sat in the JS heap at
once before zipping — the likely OOM on a large local folder despite the
size warning. Hand JSZip the File (a Blob backed by disk) instead; it reads
each lazily during generateAsync, dropping peak memory to roughly the zip
output plus JSZip's working set.

Also document, on downloadUrl, why server-side download errors aren't
surfaced as toasts: the <a download> click is fire-and-forget, and the
folder path targets zddc-server's streamed virtual "<dir>.zip" endpoint —
routing it through fetch() to make errors catchable would defeat the
streaming for arbitrarily large archives. Left as a known, documented
limitation rather than a buffering regression.

All 6 browse Playwright specs pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
ZDDC 2026-06-03 15:33:50 -05:00
parent b2c16063c4
commit d524966f00
1 changed files with 11 additions and 2 deletions
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13
browse/js/download.js
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@ -44,6 +44,12 @@
}
// Trigger a download from a same-origin server URL via Content-Disposition.
// NOTE: an <a download> click is fire-and-forget — a server error
// (401/403/404/5xx) can't be observed here, so failures surface only as
// the browser's own download error, not a toast. This is deliberate: the
// folder path points at zddc-server's streamed virtual "<dir>.zip"
// endpoint, and buffering it through fetch() to make errors catchable
// would defeat the streaming (the archive can be arbitrarily large).
function downloadUrl(filename, url) {
var a = document.createElement('a');
a.href = url;
@ -97,9 +103,12 @@
var zip = new window.JSZip();
for (var i = 0; i < files.length; i++) {
ev.statusInfo('Zipping ' + rootHandle.name + '… (' + (i + 1) + '/' + files.length + ')');
// Hand JSZip the File (a Blob, backed by disk) rather than
// pre-reading every file's arrayBuffer — otherwise the whole
// tree's raw bytes sit in the JS heap at once before zipping.
// JSZip reads each Blob lazily during generateAsync.
var f = await files[i].handle.getFile();
var buf = await f.arrayBuffer();
zip.file(rootHandle.name + '/' + files[i].relPath, buf);
zip.file(rootHandle.name + '/' + files[i].relPath, f);
}
ev.statusInfo('Generating ' + rootHandle.name + '.zip…');
var blob = await zip.generateAsync({ type: 'blob' });