[cosmo0920]

Implemented the fix and regression coverage.

• TCP DNS now uses the same cancellation deadline as UDP, allowing the waiting task to resume.
• Timeout logs show the configured host and port.
• Added TCP/UDP timeout tests and integration tests for error/debug timeout logging.

The TCP regression fails against the original code and passes with the fix. DNS and HTTP runtime tests passed:

ctest --test-dir build -R '^(flb-it-network_dns|flb-rt-out_http)$' --output-on-failure --timeout 90

Integration verification used the rebuilt binary:

$env:FLUENT_BIT_BINARY = (Resolve-Path build/bin/fluent-bit.exe).Path
tests/integration/.venv/Scripts/python.exe -m pytest tests/integration/scenarios/networking tests/integration/scenarios/out_es -q --basetemp=build/pytest-dns-final
tests/integration/.venv/Scripts/python.exe -m pytest tests/integration/scenarios/out_es -q -k unrecoverable --basetemp=build/pytest-dns-recheck

The first run had 12 passes and one metrics-endpoint HTTP 404; both affected cases passed on rerun.

Closes #12594.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

Summary by CodeRabbit

• Bug Fixes
  • DNS lookup timeouts now apply consistently to both TCP and UDP lookups, helping prevent lookups from remaining pending indefinitely. Configuring a non-positive timeout continues to leave the lookup deadline disabled.
  • Timeout logs now show the configured upstream host and port, including when a TLS handshake stalls. The configured error or debug log level is preserved, and logs no longer show an unavailable address in place of the upstream details.
  • DNS timeout handling now completes lookups cleanly when timer setup fails or a deadline expires.

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📝 Code Review	🔄 Running since 2026-10-23T08:58:38.398374Z	6e42a54	PR opened

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• include/fluent-bit/flb_network.h

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📝 Walkthrough

DNS lookups now use a deadline for both UDP and TCP modes when the adjusted timeout is positive. Upstream timeout messages report the configured host and port. Unit and integration tests cover timeout behavior, cleanup, and log output.

Changes: DNS timeouts and upstream logging

Layer / File(s)	Summary
DNS lookup deadline and cleanup include/fluent-bit/flb_network.h, src/flb_network.c, tests/internal/network_dns.c, tests/internal/CMakeLists.txt	DNS lookups with a c-ares socket now receive a deadline for positive timeouts, for both UDP and TCP. Unit tests cover timeout handling, disabled deadlines, deferred cleanup, and an upstream connection timeout before DNS completes.
Upstream timeout message and integration coverage src/flb_upstream.c, tests/integration/scenarios/networking/tests/test_upstream_timeout.py	Upstream timeout messages now report the configured host and port. The integration test checks the message, log level, and absence of unavailable:0.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant Upstream
  participant flb_net_getaddrinfo
  participant dns_timer
  participant c-ares
  Upstream->>flb_net_getaddrinfo: Start DNS lookup
  flb_net_getaddrinfo->>dns_timer: Schedule deadline for positive timeout
  dns_timer->>c-ares: Cancel lookup on timeout
  dns_timer->>flb_net_getaddrinfo: Mark lookup finished

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Possibly related PRs

• fluent/fluent-bit#12635: Changes the timer branch in flb_net_getaddrinfo for non-positive timeouts and overlaps with this PR's DNS deadline behavior.

Merge Risk: ⚪ Minimal · up to 01e24

The reviewed change has no verified merge-blocking issue.

Pre-merge checks: 3 · 2

Failed checks: 2 warnings

Check name	Status	Explanation	Resolution
Linked Issues check		Issue #12594 has two coding requirements. (1) A TCP DNS lookup must stop after the connect timeout and let the task follow the normal retry or drop path. Met. In src/flb_network.c, flb_net_getaddrinfo…	In src/flb_upstream.c, add a DNS-stage indication to the timeout log for a connection that has no socket yet and is still waiting for name resolution. The message must name the configured host and port and state that the timeout occurred wh…
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 15 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 3 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title "upstream: network: mitigate tcp dns timeouts" matches the main change. The PR applies the UDP cancellation deadline to TCP DNS lookups in src/flb_network.c so that a waiting task can resume…
Out of Scope Changes check		The changed files map to the objectives in #12594. src/flb_network.c applies the DNS deadline to TCP and UDP lookups. src/flb_upstream.c changes the timeout log target. include/fluent-bit/flb_network.…

Full details: Title check

Explanation

The title "upstream: network: mitigate tcp dns timeouts" matches the main change. The PR applies the UDP cancellation deadline to TCP DNS lookups in src/flb_network.c so that a waiting task can resume, and it adds upstream timeout logging with the configured host and port. The title is short, specific, and uses the subsystem prefix style. It does not mention the logging change, but the PR objectives treat that as secondary, so the title is not overly broad.

Full details: Out of Scope Changes check

Explanation

The changed files map to the objectives in #12594. src/flb_network.c applies the DNS deadline to TCP and UDP lookups. src/flb_upstream.c changes the timeout log target. include/fluent-bit/flb_network.h adds a public declaration for flb_net_getaddrinfo(). That function already existed in src/flb_network.c, and the declaration supports the internal DNS unit test in tests/internal/network_dns.c, so it is a supporting change. tests/internal/CMakeLists.txt registers that test. The integration test covers the timeout log. No unrelated behavior or files were identified. The header change was checked from the diff only; the test call site was not opened.

Full details: Linked Issues check

Explanation

Issue #12594 has two coding requirements. (1) A TCP DNS lookup must stop after the connect timeout and let the task follow the normal retry or drop path. Met. In src/flb_network.c, flb_net_getaddrinfo() now arms dns_timer for any created c-ares socket when timeout > 0, for both TCP and UDP. flb_net_getaddrinfo_timeout_handler() cancels the query and clears the timer. (2) The timeout message must name the configured upstream host and port and indicate that the timeout occurred while resolving the hostname. Partly met. In src/flb_upstream.c, flb_upstream_conn_timeouts() now prints u->tcp_host and u->tcp_port instead of flb_connection_get_remote_address(), so the message no longer shows 'tcp://unavailable:0'. The message text and reason string are otherwise unchanged ('connection #%i to %s:%i timed out after %i seconds (%s)'), so it does not state that the connection was waiting for DNS resolution. The issue's expected-behavior example uses 'while resolving the host name', and the supplied PR objectives list this DNS-stage indication as a requested change. The PR description does not claim it. The internal tests and the integration test check host, port, log level, and the absence of 'unavailable:0'; none checks a DNS-stage phrase.

Resolution

In src/flb_upstream.c, add a DNS-stage indication to the timeout log for a connection that has no socket yet and is still waiting for name resolution. The message must name the configured host and port and state that the timeout occurred while resolving the host name. Keep the existing error and debug level selection. Extend tests/integration/scenarios/networking/tests/test_upstream_timeout.py (or an equivalent test) to assert this phrase at both log levels.

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @src/flb_network.c:
- Around line 1209-1242: Update the lookup flow around ares_socket_created so it
creates the DNS timer only when timeout is greater than zero. When a socket was
created but timeout is zero, yield the coroutine without scheduling a timer;
preserve the existing timer and cancellation behavior for positive timeouts.

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• src/flb_network.c
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• tests/internal/network_dns.c

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