fetching_unknown_mime_type_of_a_file test assumes servers won't return a MIME type for unknown files

[marktaborosi]

Hi,

First of all, thank you very much for maintaining Flysystem!
I've been using Flysystem for a long time in various projects, and it's been incredibly helpful. 🙏

Currently, I'm working on developing a Flysystem adapter for Nextcloud, using its WebDAV interface.

While running the adapter test suite (league/flysystem-adapter-test-utilities), I noticed that the fetching_unknown_mime_type_of_a_file test assumes that fetching the MIME type for an .md5 file should throw an UnableToRetrieveMetadata exception.

However, in practice, some servers (like Nextcloud WebDAV) return a valid MIME type like application/octet-stream for such files.
Because of this, the test fails even though the adapter behaves correctly according to Flysystem's expectations.

Test:

public function fetching_unknown_mime_type_of_a_file(): void
{
    $this->givenWeHaveAnExistingFile(
        'unknown-mime-type.md5',
        file_get_contents(__DIR__ . '/test_files/unknown-mime-type.md5')
    );

    $this->expectException(UnableToRetrieveMetadata::class);

    $this->runScenario(function () {
        $this->adapter()->mimeType('unknown-mime-type.md5');
    });
}

• As I can see, returning application/octet-stream is valid behavior when the actual MIME type is unknown.
• According to the IETF MIME standards (RFC 2046), application/octet-stream is the default MIME type when the actual content type is unknown or cannot be determined.
• Given that, should application/octet-stream still trigger an UnableToRetrieveMetadata exception in Flysystem?
• Or should it be considered a valid MIME type and accepted as a fallback, without throwing an exception?

Question:

• Is there any approach you would suggest for handling this case (should this be then handled as Uknown mime type)?

Thanks again for your time!