fix: avoid FileSchema string payload fallthrough

src/_bentoml_sdk/validators.py

@@ -128,12 +128,12 @@ def decode(self, obj: bytes | t.BinaryIO | UploadFile | PurePath | str) -> t.Any
 
         media_type: str | None = None
 
+        if isinstance(obj, PurePath):
+            return Path(obj)
         if isinstance(obj, str):
             body = obj.encode("utf-8")
             filename = None
-        if isinstance(obj, PurePath):
-            return Path(obj)
-        if isinstance(obj, UploadFile):
+        elif isinstance(obj, UploadFile):
             body = obj.file.read()
             filename = obj.filename
             media_type = obj.content_type

tests/unit/_bentoml_sdk/test_validators.py

@@ -25,3 +25,16 @@ def test_file_schema_decode_with_path_separator_in_filename(tmp_path: Path):
     assert result.exists()
     assert result.read_bytes() == file_content
     assert result.suffix == ".pdf"
+
+
+def test_file_schema_decode_with_string_payload(tmp_path: Path):
+    file_content = "test content"
+
+    with patch(
+        "bentoml._internal.context.request_temp_dir", return_value=str(tmp_path)
+    ):
+        result = FileSchema().decode(file_content)
+
+    assert isinstance(result, Path)
+    assert result.exists()
+    assert result.read_text() == file_content