in_stdin: support stdin plugin on windows

[cosmo0920]

On Windows, it's a bit of works needed to support in_stdin capability.
In this PR, we're finally enabling a capability to handle stdin on Windows.

Closes #11120.

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Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change

cmd> echo {"message":"Hey"} | .\bin\fluent-bit -i stdin -ostdout -v

• Debug log output from testing the change

Fluent Bit v5.0.6
* Copyright (C) 2015-2026 The Fluent Bit Authors
* Fluent Bit is a CNCF graduated project under the Fluent organization
* https://fluentbit.io

______ _                  _    ______ _ _           _____  _____
|  ___| |                | |   | ___ (_) |         |  ___||  _  |
| |_  | |_   _  ___ _ __ | |_  | |_/ /_| |_  __   _|___ \ | |/' |
|  _| | | | | |/ _ \ '_ \| __| | ___ \ | __| \ \ / /   \ \|  /| |
| |   | | |_| |  __/ | | | |_  | |_/ / | |_   \ V //\__/ /\ |_/ /
\_|   |_|\__,_|\___|_| |_|\__| \____/|_|\__|   \_/ \____(_)\___/


[2026/05/19 16:54:58.246] [ info] Configuration:
[2026/05/19 16:54:58.246] [ info]  flush time     | 1.000000 seconds
[2026/05/19 16:54:58.246] [ info]  grace          | 5 seconds
[2026/05/19 16:54:58.246] [ info]  daemon         | 0
[2026/05/19 16:54:58.246] [ info] ___________
[2026/05/19 16:54:58.246] [ info]  inputs:
[2026/05/19 16:54:58.246] [ info]      stdin
[2026/05/19 16:54:58.246] [ info] ___________
[2026/05/19 16:54:58.246] [ info]  filters:
[2026/05/19 16:54:58.246] [ info] ___________
[2026/05/19 16:54:58.246] [ info]  outputs:
[2026/05/19 16:54:58.246] [ info]      stdout.0
[2026/05/19 16:54:58.246] [ info] ___________
[2026/05/19 16:54:58.246] [ info]  collectors:
[2026/05/19 16:54:58.248] [ info] [fluent bit] version=5.0.6, commit=6474297f3d, pid=40488
[2026/05/19 16:54:58.248] [debug] [engine] maxstdio set: 512
[2026/05/19 16:54:58.248] [debug] [engine] coroutine stack size: 98302 bytes (96.0K)
[2026/05/19 16:54:58.248] [ info] [storage] ver=1.5.4, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2026/05/19 16:54:58.248] [ info] [simd    ] disabled
[2026/05/19 16:54:58.248] [ info] [cmetrics] version=2.1.3
[2026/05/19 16:54:58.248] [ info] [ctraces ] version=0.7.1
[2026/05/19 16:54:58.248] [ info] [input:stdin:stdin.0] initializing
[2026/05/19 16:54:58.248] [ info] [input:stdin:stdin.0] storage_strategy='memory' (memory only)
[2026/05/19 16:54:58.248] [debug] [stdin:stdin.0] created event channels: read=816 write=820
[2026/05/19 16:54:58.248] [debug] [input:stdin:stdin.0] buf_size=16000
[2026/05/19 16:54:58.248] [debug] [stdout:stdout.0] created event channels: read=828 write=832
[2026/05/19 16:54:58.249] [ info] [sp] stream processor started
[2026/05/19 16:54:58.250] [ info] [output:stdout:stdout.0] worker #0 started
[2026/05/19 16:54:58.250] [ info] [engine] Shutdown Grace Period=5, Shutdown Input Grace Period=2
[2026/05/19 16:54:59.255] [debug] [task] created task=0000016C430621D0 id=0 OK
[2026/05/19 16:54:59.255] [debug] [output:stdout:stdout.0] task_id=0 assigned to thread #0
[0] stdin.0: [[1779177298.351077800, {}], {"message"=>"Hey"}]
[2026/05/19 16:54:59.256] [debug] [out flush] cb_destroy coro_id=0
[2026/05/19 16:54:59.256] [debug] [task] destroy task=0000016C430621D0 (task_id=0)
[2026/05/19 16:55:02] [engine] caught signal (SIGINT)
[2026/05/19 16:55:02.280] [ warn] [engine] service will shutdown in max 5 seconds
[2026/05/19 16:55:02.280] [ info] [engine] pausing all inputs..
[2026/05/19 16:55:03.292] [ info] [engine] service has stopped (0 pending tasks)
[2026/05/19 16:55:03.292] [ info] [output:stdout:stdout.0] thread worker #0 stopping...
[2026/05/19 16:55:03.292] [ info] [output:stdout:stdout.0] thread worker #0 stopped

• Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• Run local packaging test showing all targets (including any new ones) build.
• Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• Documentation required for this feature

Backporting

• Backport to latest stable release.

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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
  • Improved Windows compatibility for the stdin input plugin by enabling it as a default input option on Windows systems. Enhanced platform-specific handling to increase reliability and stability when reading from standard input sources, ensuring consistent and predictable behavior across different types of input streams on Windows.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: b256bbae-0555-4db2-ac00-32e5d3a6439f

📥 Commits

Reviewing files that changed from the base of the PR and between 6474297 and 183f5e4.

📒 Files selected for processing (3)

• cmake/windows-setup.cmake
• plugins/in_stdin/in_stdin.c
• plugins/in_stdin/in_stdin.h

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📝 Walkthrough

Walkthrough

The PR enables the stdin input plugin on Windows by adding Windows-specific I/O handling. It detects stdin type (pipe vs. console), implements platform-aware availability checking via Win32 APIs, switches to time-based collection polling on Windows, and conditionally manages file descriptors and cleanup paths.

Changes

Windows stdin input plugin support

Layer / File(s)	Summary
Data structures and Windows constants plugins/in_stdin/in_stdin.h	Header adds Windows includes, FLB_STDIN_WIN32_COLLECT_NSEC polling constant, and stdin_handle/stdin_type struct fields to track Windows stdin state.
Windows I/O implementation and collection integration plugins/in_stdin/in_stdin.c	Introduces stdin_win32_available() (using PeekNamedPipe() and _kbhit()) and stdin_read() wrapper; updates collection path to use the wrapper and handle zero-byte returns on Windows pipes without treating as EOF.
Initialization and Windows stdin handle acquisition plugins/in_stdin/in_stdin.c	Initialize ctx->fd = -1, then on Windows acquire stdin handle via GetStdHandle()/GetFileType() before duplicating with _dup(_fileno(stdin)) (non-Windows uses dup(STDIN_FILENO)).
Collector registration and polling strategy plugins/in_stdin/in_stdin.c	Windows registers time-based polling via FLB_STDIN_WIN32_COLLECT_NSEC; non-Windows retains event-based collector watching ctx->fd.
Error handling and resource cleanup plugins/in_stdin/in_stdin.c	Close ctx->fd using _close() on Windows or close() elsewhere in both init error paths and normal shutdown, guarded by ctx->fd >= 0.
Build configuration cmake/windows-setup.cmake	Enable FLB_IN_STDIN input plugin when FLB_WINDOWS_DEFAULTS CMake option is set.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related issues

• Windows support for stdin plugin #11120 — The PR directly implements Windows-specific stdin support (CMake enablement plus new Windows I/O helpers, handle management, and polling logic) to address the requested Windows stdin plugin feature.

Suggested labels

docs-required

Suggested reviewers

• edsiper

Poem

🐰 On Windows, stdin now speaks clear,
With PeekNamedPipe and polling near,
Console and pipes both find their way,
Time-based collection saves the day!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% 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 'in_stdin: support stdin plugin on windows' clearly and concisely describes the main change: enabling stdin input plugin support on the Windows platform.
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 docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch cosmo0920-support-stdin-on-windows

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[chatgpt-codex-connector]

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