fix: stop uploads hanging forever when the connection drops mid-transfer

[pkeuter]

The libcurl multi-pump loop called select() with a nullptr timeout (block forever). A connection that drops mid-upload without a clean RST/FIN never makes the socket ready, so select() blocked indefinitely and the synchronous Execute() wedged the calling thread permanently -- no further uploads could run. Normal uploads also had no timeout configured (only the RDMA control plane set one), so libcurl had nothing to enforce even when woken.

• Bound the select() wait to 1s so the loop keeps pumping libcurl.
• Handle maxfd < 0 with a short poll-sleep instead of an invalid select() call (which also errors out / terminates on Windows).
• Set a default low-speed timeout (1 byte/s for 60s) so a stalled transfer aborts with CURLE_OPERATION_TIMEDOUT. Gated on timeout_secs <= 0 to leave the RDMA control plane's explicit timeouts unchanged.

Summary by CodeRabbit

• Bug Fixes
  • Fixed HTTP requests that could hang indefinitely when network transfer stalls. Now detects low-speed transfers and terminates them gracefully instead of waiting forever.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 3df3e92b-f90a-43e9-8711-d6612a22079c

📥 Commits

Reviewing files that changed from the base of the PR and between e68f450 and f07563a.

📒 Files selected for processing (1)

• src/http.cc

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📝 Walkthrough

Walkthrough

src/http.cc gains <chrono> and <thread> includes plus a kStallTimeoutSecs = 60 constant. When timeout_secs <= 0, Request::execute() now sets libcurl low-speed detection options to abort stalled transfers. The synchronous polling loop replaces an unbounded select() with a 1-second bounded timeout and a 100ms sleep when libcurl reports no fds.

Changes

Stall timeout and bounded select loop

Layer / File(s)	Summary
Includes and stall timeout constant src/http.cc	Adds <chrono> and <thread> headers and defines kStallTimeoutSecs = 60 as the internal low-speed stall threshold constant.
Low-speed abort config and bounded select loop src/http.cc	When timeout_secs <= 0, sets CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME to abort stalled transfers after 60 seconds. Rewrites the synchronous poll loop to initialize maxfd = -1, call requests.fdset(...), use a 1-second select() timeout, sleep 100ms if no fds are available, and break with a log on select() failure.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐇 Hoppity-hop through the network tube,
No more hanging forever — how rude!
Sixty seconds of stillness? We bail,
A bounded select keeps progress on trail.
The rabbit says: timeouts are cool! 🕐

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main fix: preventing uploads from hanging indefinitely when network connections drop mid-transfer. It directly relates to the core problem addressed in the PR.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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