🔉 fix: Normalize audio MIME types in STT format validation

[danny-avila]

Summary

Browsers commonly report audio files with non-standard MIME types (e.g. audio/x-m4a for .m4a files, audio/x-wav, audio/x-flac). The STT azureOpenAIProvider rejects these because the format validation only checks the raw MIME subtype against the accepted formats list.

This is the same class of bug as #12608 (text/x-markdown rejected in file uploads). The fix reuses the existing MIME_TO_EXTENSION_MAP — which already has the correct MIME-to-extension mapping — to normalize the format before validation. Unknown MIME types are correctly rejected instead of silently falling through to a webm default. Raw subtype fallback is gated on audio/video prefix to prevent non-audio types from bypassing validation.

Fixes #12632
Continues #12633

Credit to @jona7o for the original PR.

Changes

• Use MIME_TO_EXTENSION_MAP directly for normalization instead of getFileExtensionFromMime() (which has a webm default fallback that would accept unknown audio subtypes)
• Gate raw subtype matching on audio/video prefix to reject types like text/webm
• Export MIME_TO_EXTENSION_MAP for test use
• Add negative tests for unknown audio subtypes and non-audio prefix bypass

Test plan

• 16 unit tests pass covering MIME normalization and format validation
• Known non-standard MIME types (audio/x-m4a, audio/x-wav, audio/x-flac) accepted
• Standard formats (audio/mpeg, audio/wav, etc.) accepted
• Unknown audio subtypes (audio/aac, audio/somethingelse) rejected
• Non-audio types with audio subtypes (text/webm) rejected
• application/ogg (valid Ogg container in the MIME map) accepted

[Copilot]

Pull request overview

Normalizes audio MIME types during Azure OpenAI STT format validation so common browser-reported vendor MIME types (e.g. audio/x-m4a) are accepted when they map to an allowed audio format, while unknown/unsafe MIME types remain rejected.

Changes:

• Update Azure OpenAI STT provider validation to normalize via MIME_TO_EXTENSION_MAP and restrict raw-subtype fallback to audio/ and video/ MIME prefixes.
• Export MIME_TO_EXTENSION_MAP (and getFileExtensionFromMime) for unit testing.
• Add Jest tests covering MIME normalization and negative cases (unknown audio subtypes, non-audio prefix bypass).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
api/server/services/Files/Audio/STTService.js	Normalize MIME types before validating accepted audio formats; export MIME map/util for tests.
api/server/services/Files/Audio/STTService.spec.js	New unit tests for MIME normalization and format acceptance/rejection scenarios.

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[Copilot]

The new tests validate a local isFormatAccepted() helper that re-implements the provider’s MIME/format check, but they never call STTService.azureOpenAIProvider() (the code changed in this PR). This can let the test suite pass even if the real provider logic diverges (e.g., acceptedFormats list or normalization rules change). Consider exercising azureOpenAIProvider() directly with mocked sttSchema/genAzureEndpoint and asserting it throws/doesn’t throw for the same mimetypes instead of duplicating the logic in the test.

[Copilot]

MIME_TO_EXTENSION_MAP is now exported, which makes it part of the module’s public surface and allows external code/tests to mutate it at runtime. To prevent hard-to-debug side effects, consider freezing the map (e.g., Object.freeze) or exporting a defensive copy so consumers can’t modify the internal lookup table.

[Copilot]

The thrown error now always interpolates rawFormat. For some invalid inputs rawFormat can be empty or misleading (e.g., malformed MIME strings without a subtype), which makes debugging harder. Consider including the full audioFile.mimetype and/or the computed normalizedFormat in the error message so logs clearly show what was rejected.

Suggested change

	throw new Error(`The audio file format ${rawFormat} is not accepted`);
	throw new Error(
	`The audio file format is not accepted (mimetype: "${audioFile.mimetype}", raw format: "${rawFormat}", normalized format: "${normalizedFormat}")`,
	);

[github-actions]

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[danny-avila]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Bravo.

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