S3 MultipartUploads accepts case insensitive 'ETag' headers

[jcborras]

Prevents case sensitive ETag header names.
Fixes #11201

Testing
YAML config includes an S3 output stage to an S3 compatible service, and an HTTP input stage which we will use for testing:

  inputs:
  - name: http
    listen: "0.0.0.0"
    port: 9880
    tag_key: log_tag_key  # the value of this attribute defines the event tag
  outputs:
  - name: s3
    log_level: trace
    match: '*'
    bucket: logs
    endpoint: REDACTED
    region: US
    json_date_format: iso8601
    json_date_key: ts
    part_size: 1M
    preserve_data_ordering: true
    profile: jcb-tester
    s3_key_format: /fluent-bit-logs/$TAG/%Y/%m/%d/%H
    use_put_object: false

To generate a large file to upload use the following script:

 for i in $(seq 128) ; do
   JSON="{\"log_tag_key\":\"log_tag\",\"msg\":\"This is my message\", \"ts\": \"$(date --utc --iso-8601=seconds)\", \"data\": \"$(dd if=/dev/random bs=1024 count=16 2> /dev/null | base64 --wrap=0)\" }" ;
   curl  --request POST --header "content-type: application/json" --data "$JSON" http://localhost:9880 ;
  done

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• Debug log output from testing the change

[2025/11/25 17:26:14.114997595] [ info] [output:s3:s3.0] UploadPart http status=200
[2025/11/25 17:26:14.115815938] [ info] [output:s3:s3.0] Successfully uploaded part #2 for /fluent-bit-logs/log_tag/2025/11/25/15, UploadId=AQAAAZq7nyPECHRyrbgGQ4S40hGAHSFeUEDbras, ETag=541c2b1cff8aafd05c8bc47144e001b8
[2025/11/25 17:26:14.117334902] [debug] [output:s3:s3.0] Successfully persisted upload data, UploadId=AQAAAZq7nyPECHRyrbgGQ4S40hGAHSFeUEDbras

Valgrind report:

==551332== 
==551332== HEAP SUMMARY:
==551332==     in use at exit: 0 bytes in 0 blocks
==551332==   total heap usage: 457,215 allocs, 457,215 frees, 695,242,903 bytes allocated
==551332== 
==551332== All heap blocks were freed -- no leaks are possible
==551332== 
==551332== For lists of detected and suppressed errors, rerun with: -s
==551332== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Backporting

Not required.

Summary by CodeRabbit

• Bug Fixes
  • Made detection of the ETag header in S3 multipart responses case-insensitive, improving compatibility with varied header casing and increasing reliability of multipart upload handling.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

The get_etag function in the S3 multipart upload handler now searches for the ETag header case-insensitively by using strcasestr() instead of strstr(), preserving existing parsing logic and error handling.

Changes

Cohort / File(s)	Summary
ETag header search case-insensitivity plugins/out_s3/s3_multipart.c	Replaced strstr() with strcasestr() in get_etag() to perform case-insensitive lookup of the ETag: response header. No other parsing or error-handling changes.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

• Single-line/single-function change.
• Review attention: confirm strcasestr() availability on target platforms or build-time compatibility.

Poem

🐰 I sniffed the headers, short and small,
A lowercase whisper, I heard the call.
Now ETag sings, no case to fear,
Multipart hops on, the path is clear.
🎉

Pre-merge checks and finishing touches

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: making S3 multipart uploads accept case-insensitive ETag headers, which is the core fix in the changeset.
Linked Issues check	✅ Passed	The code change successfully implements the core requirement from issue #11201: using case-insensitive search (strcasestr) instead of case-sensitive search (strstr) to locate the ETag header.
Out of Scope Changes check	✅ Passed	The changeset contains only the focused fix to the get_etag function; no unrelated modifications to other files or components are present.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

plugins/out_s3/s3_multipart.c (1)

655-656: Case-insensitive ETag lookup looks correct; clean up commented code and confirm strcasestr portability

Switching to strcasestr here correctly makes the ETag header lookup case-insensitive and should address the multipart failure with lowercase etag: responses.

Two minor follow-ups:

• The previous strstr call is now just commented out; it’s dead code and can be removed entirely to keep the function clean.
• strcasestr is a non-standard extension; please confirm it’s properly declared and available on all supported platforms (e.g., via a common header or CMake feature check) so this doesn’t introduce build issues on non-GNU libc targets.

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between ee881af and 37d7aed.

📒 Files selected for processing (1)

• plugins/out_s3/s3_multipart.c (1 hunks)