---
title: "2026-08-26 Histo vxData S3 TIFF compatibility investigation"
description: "Investigated the current-main presign, browser range-request, CORS, and overlay flow for S3-backed histology TIFFs."
image: "https://docs.virdx.dev/img/virdx-social-card.png"
---

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# 2026-08-26 Histo vxData S3 TIFF compatibility investigation

## Work Done

- Read the mono workspace and vxdata-api/dashboard frontend guidance plus the histo knowledge indexes.
- Traced `s3://` HistoScan and HistoMap URLs through vxdata-api GET presigning into the dashboard `geotiff` browser reader.
- Checked the viewer dependency's request behavior: it sends GET requests with single byte ranges, requires 206 responses, and does not issue HEAD requests.
- Found that object-store CORS is not configured in mono and the frontend itself records that the S3 endpoint sends no `Access-Control-Allow-Origin`; the dev-only proxy exists but the histology viewer does not use its URL rewrite helper.
- Identified additional failure modes: hour-long presigned URLs are cached indefinitely; tile errors and overlay resolution errors are swallowed; and overlays ignore their resolved source type, so mixed local/S3 or TIFF/Zarr sources fail.
- No product code was changed. No deployed Ceph credentials or safe deployed endpoint were available for a live probe.

## Lessons Learned: Pitfalls

- API CORS and object-store CORS are separate. vxdata-api CORS cannot help TIFF bytes because the browser fetches the presigned object URL directly.
- `Accept-Ranges` is useful evidence but the viewer's real contract is a readable cross-origin 206 response with `Content-Range`; a full-file 200 is explicitly rejected.
- A presigned GET URL should not be assumed to support HEAD. The current viewer does not need HEAD.

## Lessons Learned: Improvements

- Add a durable histo serving SOP with the exact Ceph bucket CORS contract and a browser-level range probe.
- Add an integration test that loads a real pyramidal TIFF from an S3-compatible service, pans/zooms, enables a map overlay, and checks request status and headers.
- Document whether production presigns use a browser-reachable public gateway rather than an internal service hostname.

Source: https://docs.virdx.dev/knowledge/inbox/2026-08-26-histo-vxdata-s3-tiff-compatibility/index.mdx