[Feature]: I/O free, pure, tag detection

[scrabsha]

Problem Description

Hi! I use a custom testing environment at work in which each file has its own fake (mocked) filesystem (backed by filesystem) and it's not exactly easy to make filesystem and file-identify work together, as file-identify uses the host filesystem API.

Proposed Solution

I have two approaches in mind:

• Either add a filesystem feature (or whichever name makes more sense) and add (for instance) file_identify::tags_from_fs_path, that takes an additional impl FileSystem (or even an impl FakeFileSystem) argument and uses this instead of the host FS APIs.

#[cfg(filesystem)]
pub fn tags_from_fake_path<F, P>(filesystem: &F, path: P) -> Result<TagSet>
where
    F: FileSystem,
    P: AsRef<Path>,
{
    todo!()
}

That'd be neat, but it adds coupling with a third-party library that is not exactly well maintained 😅

• Provide (for instance) a file_identify::tags_from_parts function that takes more as arguments what it would normally get from the host FS APIs. Something along the lines of:

pub fn tags_from_path_pure<P, C>(path: P, content: C, metadata: &Metadata) -> Result<TagSet>
where
    P: AsRef<Path>,
    C: AsRef<[u8]>,
{
    todo!()
}

Where Metadata is a custom datatype, as the Metadata from the standard library cannot be constructed by the user.

That would certainly reduce coupling with third-party libraries, which I like, at the price of a more complex API.

---

I am fine with implementing and maintaining any of these two solutions or some variation of these. I'm also okay with any other solution that allows me to use file-identify without using host FS APIs. Let me know!

Alternatives Considered

No response

Impact Level

Medium - Useful for common use cases

Feature Type

• New file type support
• CLI improvement
• Library API enhancement
• Performance optimization
• Documentation improvement
• Developer experience

Use Case

Using file-identity with mocked filesystems in test suites.

Additional Context

No response