core.common: move mime-related stuff to my.core.mime

no backward compat, unlikely it was used by anyone else

my/core/mime.py

@@ -0,0 +1,34 @@
+"""
+Utils for mime/filetype handling
+"""
+
+from .common import assert_subpackage; assert_subpackage(__name__)
+
+import functools
+
+from .common import PathIsh
+
+
+@functools.lru_cache(1)
+def _magic():
+    import magic  # type: ignore
+
+    # TODO also has uncompess=True? could be useful
+    return magic.Magic(mime=True)
+
+
+# TODO could reuse in pdf module?
+import mimetypes  # todo do I need init()?
+
+
+# todo wtf? fastermime thinks it's mime is application/json even if the extension is xz??
+# whereas magic detects correctly: application/x-zstd and application/x-xz
+def fastermime(path: PathIsh) -> str:
+    paths = str(path)
+    # mimetypes is faster, so try it first
+    (mime, _) = mimetypes.guess_type(paths)
+    if mime is not None:
+        return mime
+    # magic is slower but handles more types
+    # TODO Result type?; it's kinda racey, but perhaps better to let the caller decide?
+    return _magic().from_file(paths)