Setup Check: Discover Hidden HTTP/WebDAV Limits and Performance Regressions

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Is your feature request related to a problem? Please describe.

Administrators often lack clear, actionable visibility into the effective (real-world) constraints of their Nextcloud deployment:

• Practical maximum upload size (non‑chunked vs chunked).
• Hidden timeout ceilings (web server, reverse proxy, PHP/FPM, network).
• Effective throughput (upload / download bit rates per connection).
• Behavior and correctness of chunked uploads and HTTP range requests.
• Maximum feasible assembled upload size given timeouts + chunk sizing.
• Whether current performance diverges from historical baselines.

Without systematic measurement:

• Issues surface reactively (user complaints, failed large transfers).
• It’s unclear which layer (client, proxy, PHP/FPM, storage backend) is constraining performance.
• Administrators lack a repeatable diagnostic tool to communicate health or guide configuration tuning.

Describe the solution you'd like

Introduce one or more Setup Checks that can:

1. Run an automated sequence of controlled WebDAV operations (upload/download tests, range requests, chunked vs non‑chunked uploads).
2. Determine or estimate:
   • Max non‑chunked upload size before rejection (status codes / early termination).
   • Largest reliable chunk size for chunked uploads.
   • Time to assemble a multi‑chunk file before any timeout occurs.
   • Effective upload throughput (sustained bit rate) over a representative interval.
   • Effective download throughput (sustained bit rate).
   • Functional status of HTTP Range (partial download) support.
   • Derived maximum feasible upload size (given chunk size × assembly / timeout constraints).
   • Derived practical maximum download size within typical timeout envelopes.
3. Optionally store historical snapshots (baseline vs current) for trend comparison.
4. Provide actionable, human‑readable guidance (e.g., “PHP max_execution_time likely limiting multi‑GB assembly” or “Reverse proxy body size limit reached at X MB” or whatever).
5. Expose results:
   • Admin UI (setup checks / serverinfo).
   • OCC command (scriptable / monitoring integration).
   • Optional user‑level simplified check (e.g., “Test my connection”) for self‑diagnostics and support triage.

Describe alternatives you've considered

• Manual ad hoc testing (slow, non-repeatable).
• Custom external scripting (reinvents logic; no UI integration).
• Rely only on logs + guessing (reactive and incomplete).
• Third‑party synthetic monitoring (generic; lacks Nextcloud-specific semantics).
• Indirect tests such as simple third-party hosted speed testers (not instance specific; too generic)

Additional context

Initial implementation:

• Tests: non‑chunked max size probe (binary search), chunk size probe, short-duration upload/download throughput sampling, Range request verification, assembly timeout detection (bounded attempt).
• Packaging: either integrate as a general setup check or provide as an on-demand task within the Server Info app (Optionally the latter could expose the former for easier monitoring)
• Result formatting: JSON (for API) plus a summarized UI view.
• Basic recommendations mapped from findings (e.g., if failure at N MB + HTTP 413 → suggest checking client_max_body_size / LimitRequestBody / post_max_size or whatever).

Future extensions:

• Scheduled periodic runs with retention (e.g. last 30 data points).
• User-facing micro test (a more limited subset of tests and guardrails)

Risks / Considerations

• Test traffic overhead (cap test duration and data volumes).
• Privacy / data locality (use generated dummy data; never touch user files).
• Potential false positives if run during resource contention (recommend a “quiet window” or multiple samples).
• Multi‑tenant / large installations may need adjustable limits (configurable ceilings).
• Flag to disable, limit data volume, or require explicit confirmation for low-resource installations.

Related:

• #53526

Documentation integration:

• Server Tuning
• Large File Uploading
• HTTP Server Configuration
• Reverse Proxy Configuration
• PHP Configuration
• Client configuration

No implementation files or tests are named. Start by reviewing the existing setup checks or Server Info app and related issue #53526, then narrow the broad proposal to a bounded initial implementation. Done should include the listed WebDAV measurements, JSON results, summarized UI output, and basic recommendations.