Fix File helper extension handling (#4531)

Preserve explicit suffixes when building data-backed File resource URIs, while keeping the inferred-extension fallback for names without a suffix.

Closes #4530

Co-authored-by: chatgpt-codex-connector[bot] <199175422+chatgpt-codex-connector[bot]@users.noreply.github.com>

fastmcp_slim/fastmcp/utilities/types.py

@@ -421,7 +421,12 @@ class File:
         elif self.data is not None:
             raw_data = self.data
             if self._name:
-                uri_str = f"file:///{self._name}.{self._mime_type.split('/')[1]}"
+                extension = (
+                    ""
+                    if Path(self._name).suffix
+                    else f".{self._mime_type.split('/')[1]}"
+                )
+                uri_str = f"file:///{self._name}{extension}"
             else:
                 uri_str = f"file:///resource.{self._mime_type.split('/')[1]}"
         else:

tests/utilities/test_types.py

@@ -461,6 +461,22 @@ class TestFile:
         if isinstance(resource.resource, BlobResourceContents):
             assert resource.resource.blob == base64.b64encode(test_data).decode()
 
+    def test_to_resource_content_with_data_and_name_without_extension(self):
+        """Test data-backed File URI with a custom name that needs an extension."""
+        file = File(data=b"test file data", format="pdf", name="report")
+        resource = file.to_resource_content()
+
+        assert resource.resource.mime_type == "application/pdf"
+        assert str(resource.resource.uri) == "file:///report.pdf"
+
+    def test_to_resource_content_with_data_preserves_name_extension(self):
+        """Test data-backed File URI preserves a custom name with an extension."""
+        file = File(data=b"test file data", format="pdf", name="report.pdf")
+        resource = file.to_resource_content()
+
+        assert resource.resource.mime_type == "application/pdf"
+        assert str(resource.resource.uri) == "file:///report.pdf"
+
     def test_to_resource_content_with_text_data(self):
         """Test conversion to ResourceContent with text data (TextResourceContents)."""
         test_data = b"hello world"