time: time_tz: Handle conversion rules of windows and IANA tzinfo

[cosmo0920]

In the current Fluent Bit code base, there is no conversion rules between windows timezone and IANA provided timezone information.
So, we need to implement this conversion rule map as built-in capability in Fluent Bit.

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Testing
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Documentation

• Documentation required for this feature

Backporting

• Backport to latest stable release.

---

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

• New Features

  • Time zone conversion utilities for mapping between Windows and IANA identifiers.
  • UTC offset lookup for both Windows and IANA time zone strings.

• Improvements

  • Thread-safe initialization for reliable, efficient conversions.

• Tests

  • Added unit tests covering mappings, UTC offset lookups, and failure cases.

[coderabbitai]

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📝 Walkthrough

Walkthrough

Adds public APIs and implementations for Windows↔IANA timezone name conversions and fixed standard UTC offset lookups, backed by a static mapping table with thread-safe indexed initialization and binary-search lookups, plus unit tests and build integration.

Changes

Time Zone Conversion

Layer / File(s)	Summary
Public API contract include/fluent-bit/flb_time.h	Four new public declarations for Windows↔IANA zone conversion and UTC offset resolution via long *offset.
Timezone mapping table src/flb_time_tz.c	Adds the static Windows↔IANA mapping table and the fixed-standard UTC offset values used by lookups.
Index initialization and sorting src/flb_time_tz.c	Thread-safe pthread_once initialization that constructs pointer indexes, deduplicates Windows keys, and sorts arrays for binary search.
Windows → IANA lookup src/flb_time_tz.c	flb_time_windows_zone_to_iana using bsearch with case-insensitive Windows-key matching; returns mapped IANA string or NULL.
IANA → Windows lookup src/flb_time_tz.c	flb_time_iana_zone_to_windows using bsearch with case-sensitive IANA-key matching; returns mapped Windows string or NULL.
Windows → UTC offset src/flb_time_tz.c	flb_time_windows_zone_to_utc_offset validates args, bsearches, writes *offset and returns 0 on match or -1 on error/no match.
IANA → UTC offset src/flb_time_tz.c	flb_time_iana_zone_to_utc_offset validates args, bsearches, writes *offset and returns 0 on match or -1 on error/no match.
Build integration src/flb_time.c	Includes flb_time_tz.c to compile/link the timezone helpers.
Unit tests tests/internal/flb_time.c	Adds <string.h>, four tests for the conversions and offset lookups, and updates TEST_LIST to register them.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Suggested labels

backport to v4.2.x

Suggested reviewers

• edsiper
• fujimotos
• koleini

Poem

🐰 Across the world, the time zones hum,
Windows meets IANA, now they come,
Offsets found and names aligned,
A rabbit's table, neatly signed,
Hopping time, one mapping drum.

🚥 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 pull request title clearly and directly summarizes the main change: adding conversion rules to handle Windows and IANA timezone conversions in Fluent Bit's time handling component.
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
• Commit unit tests in branch cosmo0920-handle-conversion-rules-of-windows-and-iana-tzinfo

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Reviewed commit: ef28805e1c

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[coderabbitai]

🧹 Nitpick comments (2)

src/flb_time_tz.c (2)

510-578: ⚖️ Poor tradeoff

Optional: linear scans over ~460 entries per call.

Each conversion does an O(n) walk of the table (~460 rows). If these helpers end up on a per-record path, consider a sorted table + binary search or a small hash to reduce lookup cost. Fine to defer if calls are infrequent (e.g., config-time resolution).

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/flb_time_tz.c` around lines 510 - 578, The current lookup functions
(flb_time_windows_zone_to_iana, flb_time_iana_zone_to_windows,
flb_time_windows_zone_to_utc_offset, flb_time_iana_zone_to_utc_offset) perform
linear scans over the windows_iana_timezones table (~460 entries) which is O(n)
per call; replace these linear scans with a faster lookup by either (a) building
two lookup tables at module init (e.g., a hash map for Windows->entry and one
for IANA->entry) or (b) sorting the arrays and using binary_search; implement
case-insensitive key handling for Windows names (strcasecmp semantics) when
populating/looking up, keep the current function signatures and return
semantics, and ensure the initialization is thread-safe or performed at startup
before any lookups.

---

20-28: ⚡ Quick win

Include the public header instead of re-declaring the prototypes.

flb_time.h already declares these four functions, but this file forward-declares them locally (Lines 25-28) and never includes the header. If a public signature changes, the compiler won't catch a mismatch between the declaration and the definition here. Include <fluent-bit/flb_time.h> and drop the local prototypes.

♻️ Proposed change

 `#include` <fluent-bit/flb_compat.h>
+#include <fluent-bit/flb_time.h>
 
 `#include` <stddef.h>
 `#include` <string.h>
-
-const char *flb_time_windows_zone_to_iana(const char *windows_zone);
-const char *flb_time_iana_zone_to_windows(const char *iana_zone);
-int flb_time_windows_zone_to_utc_offset(const char *windows_zone, long *offset);
-int flb_time_iana_zone_to_utc_offset(const char *iana_zone, long *offset);

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/flb_time_tz.c` around lines 20 - 28, Remove the four redundant local
forward declarations for flb_time_windows_zone_to_iana,
flb_time_iana_zone_to_windows, flb_time_windows_zone_to_utc_offset, and
flb_time_iana_zone_to_utc_offset and instead include the public header
flb_time.h (e.g. add `#include` <fluent-bit/flb_time.h>) so the compilation uses
the canonical prototypes; this ensures any signature changes are caught by the
compiler and avoids duplicate declarations.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@src/flb_time_tz.c`:
- Around line 510-578: The current lookup functions
(flb_time_windows_zone_to_iana, flb_time_iana_zone_to_windows,
flb_time_windows_zone_to_utc_offset, flb_time_iana_zone_to_utc_offset) perform
linear scans over the windows_iana_timezones table (~460 entries) which is O(n)
per call; replace these linear scans with a faster lookup by either (a) building
two lookup tables at module init (e.g., a hash map for Windows->entry and one
for IANA->entry) or (b) sorting the arrays and using binary_search; implement
case-insensitive key handling for Windows names (strcasecmp semantics) when
populating/looking up, keep the current function signatures and return
semantics, and ensure the initialization is thread-safe or performed at startup
before any lookups.
- Around line 20-28: Remove the four redundant local forward declarations for
flb_time_windows_zone_to_iana, flb_time_iana_zone_to_windows,
flb_time_windows_zone_to_utc_offset, and flb_time_iana_zone_to_utc_offset and
instead include the public header flb_time.h (e.g. add `#include`
<fluent-bit/flb_time.h>) so the compilation uses the canonical prototypes; this
ensures any signature changes are caught by the compiler and avoids duplicate
declarations.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 93345a33-5ed7-48d2-bfc0-238106f3ab5a

📥 Commits

Reviewing files that changed from the base of the PR and between 992a4e5 and ef28805.

📒 Files selected for processing (4)

• include/fluent-bit/flb_time.h
• src/CMakeLists.txt
• src/flb_time_tz.c
• tests/internal/flb_time.c

[coderabbitai]

🧹 Nitpick comments (1)

src/flb_time.c (1)

446-446: ⚖️ Poor tradeoff

Prefer compiling flb_time_tz.c as its own translation unit over #include-ing a .c file.

Including a .c file that contains externally-visible definitions is a code smell: it couples the two units, can confuse tooling/coverage, and risks ODR/duplicate-symbol issues if the file is ever picked up by the build glob. Since these are public APIs declared in flb_time.h, the cleaner approach is to add flb_time_tz.c to the build sources and drop this include.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/flb_time.c` at line 446, Remove the line that `#include`"s" flb_time_tz.c
from flb_time.c and instead compile flb_time_tz.c as a separate translation unit
by adding flb_time_tz.c to the project's build sources (e.g., the
Makefile/CMakeLists/meson build list). Ensure the public APIs declared in
flb_time.h and implemented in flb_time_tz.c remain unique (no duplicate
definitions) and update the build so linking picks up flb_time_tz.o; do not
leave any remaining `#include` of the .c file.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@src/flb_time.c`:
- Line 446: Remove the line that `#include`"s" flb_time_tz.c from flb_time.c and
instead compile flb_time_tz.c as a separate translation unit by adding
flb_time_tz.c to the project's build sources (e.g., the
Makefile/CMakeLists/meson build list). Ensure the public APIs declared in
flb_time.h and implemented in flb_time_tz.c remain unique (no duplicate
definitions) and update the build so linking picks up flb_time_tz.o; do not
leave any remaining `#include` of the .c file.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: d15c7956-9dde-40b7-a083-93c1ffaabea3

📥 Commits

Reviewing files that changed from the base of the PR and between b03eb52 and 9657cb8.

📒 Files selected for processing (4)

• include/fluent-bit/flb_time.h
• src/flb_time.c
• src/flb_time_tz.c
• tests/internal/flb_time.c

🚧 Files skipped from review as they are similar to previous changes (3)

• tests/internal/flb_time.c
• include/fluent-bit/flb_time.h
• src/flb_time_tz.c