fix: show indeterminate progress instead of NaN% when downloading a prefix/folder

[liuhaodongliu990-cmyk]

fix: show indeterminate progress instead of NaN% when downloading a prefix/folder

Target repository: minio/object-browser
Type: Bug fix
Component: Console / Object Browser — Downloads / Uploads widget

Summary

The Console Downloads / Uploads widget shows NaN% (and a full progress bar) when a user downloads a folder / common prefix.
This is a frontend progress-math bug. The objects on disk are intact: HEAD / GET on individual keys return a valid Content-Length, and prefix download still streams a zip with HTTP 200.
Downloading a prefix calls:

GET /api/v1/buckets/{bucket}/objects/download?prefix={url-encoded-prefix}/

The handler streams Content-Type: application/zip with Content-Disposition: attachment; filename="<folder>.zip" and no Content-Length (the archive is generated on the fly).
The browser download helper then computes:

xhr.addEventListener("progress", function (event) {
  const percent = Math.round((event.loaded / objectSize) * 100);
  onProgress(percent);
});

For a prefix, objectSize comes from the object listing and is 0 (S3 common prefixes have no size). That yields loaded / 0 === Infinity / NaN, which the widget renders as NaN%.
The zip request can still return 200 and transfer bytes. Users think the download is broken and retry the same prefix.
Single-object downloads are unaffected: the same endpoint sets Content-Length and progress is a real percentage.

How to reproduce

1. Run MinIO with the embedded Console (reproduced on RELEASE.2026-08-04T00-00-00Z and RELEASE.2026-06-18T00-00-00Z).
2. Create a prefix that contains several objects (a mix of small files and multipart objects larger than 5 MiB is enough).
3. In the object browser, stay on the parent listing and click Download on the folder (do not enter the folder and download a single object).
4. Open Downloads / Uploads.

Actual

Progress text is NaN%. The bar looks full / complete.

Expected

A real percentage when the total size is known, or an indeterminate state such as Downloading… / — when the total size is unknown.

Evidence

Prefix (folder) download — zip, no length:

HTTP/2 200
content-disposition: attachment; filename="<prefix-leaf>.zip"
content-type: application/zip
# no Content-Length

Single object via the same Console API:

HTTP/2 200
content-disposition: attachment; filename="example.jsonl"
content-type: application/octet-stream
content-length: 154

S3 HEAD on a large object under that prefix:

HTTP 200
Content-Length: 83838105
Accept-Ranges: bytes
ETag: "…-16"

The bundled Console JS uses event.loaded / objectSize * 100 and never checks objectSize > 0 or event.lengthComputable. Folder completion is special-cased with prefix.endsWith("/"), so the transfer can still be treated as success while the percent stays NaN.

Proposed change

Keep the streaming zip API as-is. Buffering the whole archive just to set Content-Length is expensive and still goes through the in-memory xhr.responseType = "blob" path.
Fix the client:

xhr.addEventListener("progress", (event) => {
  let percent: number | null = null;
  if (typeof objectSize === "number" && objectSize > 0) {
    percent = Math.min(100, Math.round((event.loaded / objectSize) * 100));
  } else if (event.lengthComputable && event.total > 0) {
    percent = Math.min(100, Math.round((event.loaded / event.total) * 100));
  }
  onProgress(percent); // null => indeterminate UI, never "NaN%"
});

In the Downloads / Uploads row:

• if percent === null, show Downloading… (or hide the %) and use an indeterminate bar;
• if percent is a number, show {percent}% as today.
  Zero-byte files (objectSize === 0 and the key does not end with /) should show 0% or 100% after completion, not NaN%.

Test plan

• Download a folder / prefix that contains multiple objects: widget must not show NaN%; show indeterminate progress until the zip finishes.
• Download a single object with a known size: widget still shows 0% → 100%.
• Download a zero-byte file (not a prefix): widget must not show NaN%.
• Cancel a prefix download from the widget: row clears and no leftover NaN% entry.
• Confirm S3 HEAD / GET of existing objects is unchanged (no on-disk layout change).

Environment

Item	Value
MinIO	RELEASE.2026-08-04T00-00-00Z (linux/amd64); also seen on RELEASE.2026-06-18T00-00-00Z
Console	Embedded object browser on :9001
API	TLS-only (--certs-dir)
Mode	Single-node xl-single
Browser	Chromium-based (Downloads / Uploads widget)

Notes

This PR does not change on-disk object layout or S3 API behavior.
Optional follow-up (out of scope): prefix zip is fully buffered as an XHR blob before the browser save dialog. Large prefixes (100+ MiB of video) can still look stuck even after NaN% is fixed. A later change could use a streaming download (<a download> / File System Access) for prefixes.