feat: allow mime_type to be guessed for ByteStream

[kanenorman]

Related Issues

• fixes feat: allow mime_type to be guessed for ByteStream #9563

Proposed Changes:

• Add guess_mime_type parameter to ByteStream
• Refactor FileTypeRouter
• Add guess_mime_type parameter to haystack.components.converters.utils.get_bytestream_from_source

How did you test it?

• Added unit test for ByteStream
• Added unit test for get_bytestream_from_source
• Did not change test for FileTypeRouter

Notes for the reviewer

This is a breaking change so would like feedback 😄

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: and added ! in case the PR includes breaking changes.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[julian-risch]

Hello @kanenorman Thank you for opening this pull request!
I left a few comments and also saw that three unit tests are failing here:

FAILED test/components/converters/test_multi_file_converter.py::TestMultiFileConverter::test_run_error_handling - haystack.core.errors.PipelineRuntimeError: The following component failed to run:
Component name: 'router'
Component type: 'FileTypeRouter'
Error: [Errno 2] No such file or directory: '/home/runner/work/haystack/haystack/test/test_files/non_existent.txt'
FAILED test/components/routers/test_file_router.py::TestFileTypeRouter::test_unlisted_extensions - FileNotFoundError: [Errno 2] No such file or directory: '/home/runner/work/haystack/haystack/test/test_files/audio/ignored.mp3'
FAILED test/components/routers/test_file_router.py::TestFileTypeRouter::test_no_extension - FileNotFoundError: [Errno 2] No such file or directory: '/home/runner/work/haystack/haystack/test/test_files/txt/doc_2'

Please let me know if you need help looking into those. Other than need the pull request only needs a release note and we describe how you can generate one here. Please let me know in case you need help with that.
I was wondering why you wrote in the pull request description that it is a breaking change? With guess_mime_type being False as default and with FileTypeRouter using guess_mime_type True, the behavior remains the same, no?

Other than that the pull request looks quite good to me already! 🙂

[julian-risch]

Given that we have False as a default value, there is no reason to make this Optional. Let's change the type to bool

Suggested change

	source: Union[str, Path, ByteStream], guess_mime_type: Optional[bool] = False
	source: Union[str, Path, ByteStream], guess_mime_type: bool = False

[julian-risch]

and in from_file_path you also use bool instead of Optional[bool]

[julian-risch]

In addition to the test cases here, I suggest we add a test case for FileTypeRouter in test/components/routers/test_file_router.py checking that the parameter additional_mimetypes still works as expected. We're doing mimetypes.add_type(mime, ext) there and need to check that when get_bytestream_from_source it's taking into account these additional mimetypes, for example: {"application/vnd.openxmlformats-officedocument.wordprocessingml.document": ".docx"}.

[kanenorman]

Thanks for the feedback @julian-risch. I’ll get the changes implemented shortly.

I was wondering why you wrote in the pull request description that it is a breaking change? With guess_mime_type being False by default and FileTypeRouter using guess_mime_type=True, the behavior remains the same, no?

You’re absolutely right. I misspoke. Thanks for pointing that out! 😄

Regarding the failing unit test, I’ve identified the issue and will push a fix.

Before proceeding, I reviewed the latest haystack-ai source code (v2.15.1) and noticed that FileTypeRouter raises a FileNotFoundError only when a non-existent file is passed with the meta parameter. Without meta, the component does not raise an error and still classifies the file based on its extension.

Here’s a minimal example:

python-version: 3.11.3
mac-os: Sequoia 15
haystack-ai: 2.15.1

from haystack.components.routers import FileTypeRouter

router = FileTypeRouter(mime_types=[r'text/plain'])

# No meta - does not raise error
router.run(sources=["non_existent.txt"])
# → {'text/plain': [PosixPath('non_existent.txt')]}

# With meta - raises FileNotFoundError
router.run(sources=["non_existent.txt"], meta={"spam": "eggs"})
# → FileNotFoundError: [Errno 2] No such file or directory: 'non_existent.txt'

This feels inconsistent. Should metadata change how we treat missing files? Should the component:

• Maintain existing behavior?
• Skip missing files?
• Raise an error in all cases?
• Still classify the path even if the file doesn't exist?

Happy to align with whatever behavior is intended, just wanted to clarify before committing a fix.

[julian-risch]

Hi @kanenorman thanks for your patience! We discussed in the team and concluded that for now we would like to keep the inconsistency and not fix it in this PR. That makes this PR a bit more complex but doesn't break any current behavior.
We'll then open a separate issue on the inconsistency and plan to have a deprecation warning in the 2.16.0 release, and consistent behavior in 2.17.0.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 90.464%

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Totals
Change from base Build 16421645889:	0.01%
Covered Lines:	12077
Relevant Lines:	13350

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💛 - Coveralls

[julian-risch]

Looks good to me! 👍 Congratulations on your first pull request merged into Haystack!
The pull request now doesn't introduce any breaking changes, which is great. How you handled windows/unix mimetype differences in the test makes sense to me.