build fixes: out_stackdriver int64_t line var, gzip endian-safe magic check

[edsiper]

Two build/CI fixes found while investigating the failed v5.0.9 staging build (https://github.com/fluent/fluent-bit/actions/runs/28693445706/job/85098879153):

1. out_stackdriver: use int64_t for source_location_line

On 32-bit targets (arm/v7) long is 32-bit while int64_t is long long, so stackdriver_format() failed to compile when passing &source_location_line to extract_source_location(), which expects int64_t *:

/src/fluent-bit/plugins/out_stackdriver/stackdriver.c:2450:61: error: passing argument 2 of 'extract_source_location' from incompatible pointer type [-Wincompatible-pointer-types]
note: expected 'int64_t *' {aka 'long long int *'} but argument is of type 'long int *'

Declare the variable as int64_t to match the function signature on all architectures.

2. gzip: read magic number endian-safely in streaming decompressor

Found via the s390x unit-test job on this PR: the gzip header magic was memcpy'd into a uint16_t and compared against 0x8B1F, which only holds on little-endian hosts. On big-endian targets a valid stream was rejected with invalid magic bytes : 1f8b. Read the field with read_le16() so the comparison works regardless of host byte order.

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🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved source line number handling for Stackdriver output to better preserve accuracy with larger values.
  • Fixed gzip header validation to correctly interpret stored magic bytes as little-endian, with clearer error reporting when validation fails.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR changes the Stackdriver output plugin’s source line variable type and updates gzip header magic-byte validation to decode the stored value as little-endian before comparison.

Changes

Stackdriver Source Location Type Fix

Layer / File(s)	Summary
Variable type correction plugins/out_stackdriver/stackdriver.c	source_location_line type changed from long to int64_t in stackdriver_format.

Gzip Header Magic-Byte Decode

Layer / File(s)	Summary
Little-endian magic-byte check src/flb_gzip.c	The gzip magic-number check now uses read_le16(...) before comparison, and the failure log prints the decoded value.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title is concise and accurately summarizes the two main fixes: the out_stackdriver line type change and the gzip magic check endian fix.

✨ 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 out_stackdriver-fix-int64-build

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