feat(providers): opt-in ZERO_RESPONSE_HEADER_TIMEOUT override for slow first-byte deployments

[FabioLeitao]

Summary

Adds an opt-in ZERO_RESPONSE_HEADER_TIMEOUT environment variable for the shared HTTP transport's response header timeout, as approved on the issue: it mirrors ZERO_STREAM_IDLE_TIMEOUT and leaves the default at 120s.

• accepts a Go duration (5m, 300s) or bare seconds (300);
• 0, off, none and disabled (case-insensitive) remove the limit;
• an unparseable, non-positive or overflowing value falls back to the 120s default instead of silently removing the limit;
• the shared transport resolves the timeout when the client is first taken (sharedStallClient()), not at package init, so the transport and the resolver cannot drift;
• the constant and the resolver are documented next to the idle-timeout equivalents in providerio.

Why: a local model server that must load a large model can take longer than 120s to send the first byte (measured 1-5 minutes on a throttled local Ollama), so an otherwise-alive request is aborted. Anyone who does not set the variable sees no change.

Verified against a throttled local Ollama: ZERO_RESPONSE_HEADER_TIMEOUT=5s fails at ~6.4s, =300s succeeds at ~223s (a request that would have hit the old 120s ceiling).

Also changes ZERO_STREAM_IDLE_TIMEOUT (overflow only)

Following review, both resolvers share one bare-seconds parser with an overflow guard. For ZERO_STREAM_IDLE_TIMEOUT this changes one edge case: a bare-seconds value too large for time.Duration used to wrap and could disable the idle timeout; it now keeps the default. Every other input behaves as before.

Linked issue

Fixes #1038

Checklist

• The linked issue already has the issue-approved label.
• go build ./... and go vet ./... pass locally.
• go test ./... passes locally, with umask 022 TMPDIR=/tmp TZ=UTC. Without those settings my workstation (umask 0027, non-default TMPDIR, UTC-3) fails file-mode, sandbox-golden, socket-path and one TUI date test; the same packages fail the same way on a checkout without this change.
• gofmt clean.
• Tests added/updated for the change (resolver table tests, an end-to-end transport test, overflow cases; run under -race).
• UI changes: none.

Verification

On head afba2ddd, based on main at 99721c76:

• make fmt-check, go vet ./..., go test -count=1 ./..., go test -race ./internal/providers/providerio, go run ./cmd/zero-release build, go run ./cmd/zero-release smoke, make vulncheck, git diff HEAD --check: pass.
• make lint-static: only the 4 findings already on main (installtest, proxydial x2, web_fetch.go); none in changed files.
• Cross-compile (go vet + go test -c) for windows/amd64, darwin/amd64, darwin/arm64: pass. Tests were not run on macOS or Windows.
• Each new test fails when its part of the fix is reverted (for example, putting DefaultResponseHeaderTimeout back on the transport fails TestHTTPClientTransportUsesResolvedHeaderTimeout).
• gosec and semgrep (p/golang): no new findings compared with main. gitleaks on the branch commits: clean.
• No dependency changes (go.mod/go.sum untouched).

Notes

Prepared with AI assistance (Claude Code) and reviewed and measured by the human author (HITL), per the contribution guidelines.

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Reviewing files that changed from the base of the PR and between 2e820b3 and afba2dd.

📒 Files selected for processing (3)

• internal/providers/providerio/providerio.go
• internal/providers/providerio/providerio_test.go
• internal/providers/providerio/stream_idle_resolve_test.go

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Walkthrough

The provider I/O package now checks bare-second timeout conversions and resolves ZERO_RESPONSE_HEADER_TIMEOUT. Shared HTTP clients are cached by resolved response-header timeout, and their transports use that timeout. Tests cover resolution, timeout enforcement, and client reuse.

Changes

Provider timeout configuration

Layer / File(s)	Summary
Resolve and validate timeout values internal/providers/providerio/providerio.go, internal/providers/providerio/stream_idle_resolve_test.go, internal/providers/providerio/response_header_timeout_resolve_test.go	Bare-second timeout values are checked before conversion. Stream idle timeout resolution uses the default for invalid or overflowing values. The response-header timeout resolver supports Go duration strings, bare seconds, and disable values; invalid values use the 120-second default.
Configure and cache shared clients internal/providers/providerio/providerio.go, internal/providers/providerio/providerio_test.go	The shared HTTP client cache uses the resolved response-header timeout as its key. Each client transport uses that timeout. Tests verify timeout enforcement, client replacement when the timeout changes, and reuse when it remains unchanged.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Feature · Severity of issue fixed: Medium

Suggested reviewers: vasanthdev2004, euxaristia

Merge Risk: ⚪ Minimal · up to afba2

This adds an opt-in response-header timeout setting and keeps the 120-second default when the variable is unset. No merge-blocking risk is evident.

Security Architecture Review

Security architecture risk: 🔵 Low · up to afba2

The default remains protected. Explicitly disabling the limit can let a slow or hostile endpoint hold a request open until cancellation, but the setting is locally controlled and existing cancellation and authentication controls remain in place.

Retained concerns

• Low · security · inferred: Explicitly disabling the response-header timeout removes the existing pre-header stall bound across default-client provider consumers. A slow or hostile configured endpoint can then hold an established request indefinitely if its caller supplies neither a deadline nor cancellation. Stream watchdogs and idle-pool cleanup do not cover this phase. This is a configuration-dependent availability exposure, not a demonstrated cancellation bypass.

Security review details

Security Blast Radius

• inferred — The setting affects default-client provider instances within a process, not just the slow local endpoint motivating the change. Exposure is outbound request availability; caller-supplied clients remain outside this policy. Tenant isolation and deployment-wide propagation cannot be determined from the supplied topology evidence.

Security Findings and Attack Paths

• inferred — The conditional attack path requires a disabled header limit, an endpoint able to withhold headers, and a caller that does not terminate the request. Caller cancellation still breaks this path. The canonical security input contains no retained findings and reports unknown coverage; this assessment does not treat that as proof of safety.

Trust Boundaries and Controls

• observed — Malformed configuration preserves the bounded default, explicit custom-client ownership is retained, and request contexts continue through HTTP dispatch. Authentication resolution and credential headers remain separate from timeout configuration. Permissions governing process environment changes are not established by repository source.

Resilience and Maintainability Implications

• observed — Source tests exercise timeout enforcement against delayed headers, acquisition of a separate client after configuration changes, and reuse for unchanged settings. These assertions support deadline enforcement and cache identity, but do not establish bounded resources under repeated distinct settings or deployment-level rollback behavior.

Hardening Proposals

• proposed — Prefer a finite extended timeout for slow deployments. Where disablement is necessary, document the need for caller deadlines or cancellation. If repeated runtime reconfiguration is supported, define bounded cache ownership and cleanup rather than retaining every historical transport.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue [#1038] requires an opt-in response-header timeout for slow local Ollama requests, Go-duration or bare-second values, and an unchanged 120-second default. The reviewed code applies the resolved …
Out of Scope Changes check	✅ Passed	The changes are limited to shared HTTP timeout handling and related tests. Overflow checks for ZERO_STREAM_IDLE_TIMEOUT protect the same timeout parsing pattern from wrapping into a disabled watchdo…
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the opt-in response-header timeout override for deployments with slow first-byte responses.

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Inline comments:
Review comments at @internal/providers/providerio/providerio.go:
- Line 149: In the bare-seconds parsing path, validate the value against the
maximum representable time.Duration in seconds before multiplying by
time.Second; values that exceed the limit must use the existing fallback. Add
regression coverage for overflowing bare-second values.

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📒 Files selected for processing (2)

• internal/providers/providerio/providerio.go
• internal/providers/providerio/response_header_timeout_resolve_test.go

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[Vasanthdev2004]

Thanks for picking this up. The env parsing matches ResolveStreamIdleTimeout line for line, the default stays at 120s, and the wiring works end to end: with ZERO_RESPONSE_HEADER_TIMEOUT=300s in the environment, the shared transport's ResponseHeaderTimeout comes out at 5m. Two test gaps before it goes in:

• Nothing pins the transport to the resolver. TestResolveResponseHeaderTimeout calls the resolver directly, so putting DefaultResponseHeaderTimeout back on the transport still passes the whole package.
• TestHTTPClientReturnsStallHardenedSharedClient now depends on the developer's shell. sharedHTTPClient is built at package init, so with ZERO_RESPONSE_HEADER_TIMEOUT=300s set it fails with "ResponseHeaderTimeout = 5m0s, want 120s". On main it passes with the same variable set. The people most likely to have it set are the ones this PR is for.

One change covers both: build the client in a function the package var calls, and test that function under t.Setenv, once unset (120s) and once with an override. Having it return the idle closer's stop function lets the test clean up after itself. The existing test can then stop asserting on the init-time value.

CodeRabbit's overflow note is real, but the idle resolver on main has the same bare-seconds multiply. If you take it, one parse helper that both resolvers call would keep them identical.

CI hadn't run: both runs were waiting behind the fork gate, and I approved them after reading the diff. Requesting changes for the two tests.

[FabioLeitao]

@Vasanthdev2004 — addressed in afba2ddd: sharedStallClient() now resolves ResolveResponseHeaderTimeout() and takes sharedHTTPClients.mu before reading/writing the cache (keyed by the resolved timeout), so the shared transport actually honors ZERO_RESPONSE_HEADER_TIMEOUT instead of reusing a fixed client built once on first call. Added TestHTTPClientTransportUsesResolvedHeaderTimeout to prove it: a 200ms timeout fails fast against a 1s-delayed handler, and a 2s timeout lets a 50ms handler succeed.

[FabioLeitao]

@Vasanthdev2004 thanks for the review. Both test gaps are closed on the current head (afba2ddd), and I checked each one by reverting the fix rather than only running the suite:

• Transport pinned to the resolver. sharedStallClient() now resolves ResolveResponseHeaderTimeout() when the shared client is taken, not at package init. TestHTTPClientTransportUsesResolvedHeaderTimeout drives a real request: a 200ms timeout fails fast against a 1s-delayed handler, and a 2s timeout lets a 50ms handler succeed. Putting DefaultResponseHeaderTimeout back on the transport fails it:

  --- FAIL: TestHTTPClientTransportUsesResolvedHeaderTimeout
  FAIL	github.com/Gitlawb/zero/internal/providers/providerio
  

• No dependency on the developer's shell. With ZERO_RESPONSE_HEADER_TIMEOUT=300s exported, go test ./internal/providers/providerio passes (also with -race), because nothing asserts on an init-time value any more.
• Overflow. I took CodeRabbit's note: bare seconds above the representable time.Duration keep the default (2e820b38, e3a3f237), and both resolvers share that check so they stay identical, as you suggested.

On the checklist line about go test ./... not being fully green locally: I traced it. All the failures came from my workstation's environment, not from this branch. A restrictive umask (0027) breaks the file-mode assertions, a non-default TMPDIR changes the sandbox golden and the peer-messaging socket path, and a non-UTC timezone breaks one TUI date test. With umask 022 TMPDIR=/tmp TZ=UTC the whole suite passes, and without those settings the same packages fail the same way on a checkout that does not contain this change. I updated the PR description to say that, and added a Verification section listing what was run on this head.

The CI runs for this head are waiting behind the fork gate (action_required). Could you approve them and take another look when you have time?