feat: add mime_type to ByteStream in LibreOfficeFileConverter

[StealthTensor]

Related Issues

• fixes Add mime_type to the returned ByteStreams from LibreOfficeFileConverter #3055

Proposed Changes:

Added a _resolve_mime_type helper method to ensure the mime_type field is properly populated when returning ByteStream objects.

• The logic first attempts to resolve the MIME type using Python's standard mimetypes.guess_type().
• If that returns None, it safely falls back to a deterministic MIME_TYPE_FALLBACKS dictionary based on the output file's extension.
• Hooked this resolution into both the run and run_async execution paths.

How did you test it?

Ran the local unit test suite using hatch run test:unit inside the integrations/libreoffice directory. All tests passed successfully without any regressions.

Notes for the reviewer

Thanks for tagging this as a good first issue! I didn't add any new unit tests since the existing suite covers the ByteStream creation, but let me know if you want a specific test added for the MIME resolution or if you need any tweaks to the fallback dictionary.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.

[Copilot]

Pull request overview

Adds MIME type detection to LibreOfficeFileConverter so returned ByteStream outputs include mime_type, improving downstream handling (fixes #3055).

Changes:

• Introduces a _resolve_mime_type() helper using mimetypes.guess_type() with an extension-based fallback map.
• Populates mime_type on ByteStream outputs in both run and run_async.

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[CLAassistant]

All committers have signed the CLA.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

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[StealthTensor]

Friendly ping — PR is ready for review. Happy to address any feedback. Thanks!

[julian-risch]

Looks good to me! Thank you for your contribution @StealthTensor and congratulations on your first haystack-core-integrations pull request! I extended the existing integration tests to check that the mime type is returned.
I also looked into adding more/extending existing unit tests to test the new mime types in the unit tests but it seemed overly complicated and increased complexity of the tests a lot. I didn't run integration tests locally, only unit tests because of installation steps.