Fix read_bytes

src/fsspec_xrootd/xrootd.py

@@ -386,7 +386,9 @@ async def _ls(self, path: str, detail: bool = True, **kwargs: Any) -> list[Any]:
             else:
                 return [os.path.basename(item["name"].rstrip("/")) for item in listing]
 
-    async def _cat_file(self, path: str, start: int, end: int, **kwargs: Any) -> Any:
+    async def _cat_file(
+        self, path: str, start: int | None, end: int | None, **kwargs: Any
+    ) -> Any:
         _myFile = client.File()
         try:
             status, _n = await _async_wrap(
@@ -397,10 +399,15 @@ async def _cat_file(self, path: str, start: int, end: int, **kwargs: Any) -> Any
             )
             if not status.ok:
                 raise OSError(f"File failed to read: {status.message}")
+
+            n_bytes = end
+            if start is not None and end is not None:
+                n_bytes = end - start
+
             status, data = await _async_wrap(
                 _myFile.read,
-                start,
-                end - start,
+                start or 0,
+                n_bytes or 0,
                 self.timeout,
             )
             if not status.ok:

tests/test_basicio.py

@@ -158,6 +158,17 @@ def test_write_fsspec(localserver, clear_server):
         assert f.read() == TESTDATA1
 
 
+@pytest.mark.parametrize("start, end", [(None, None), (None, 10), (1, None), (1, 10)])
+def test_read_bytes_fsspec(localserver, clear_server, start, end):
+    remoteurl, localpath = localserver
+    with open(localpath + "/testfile.txt", "w") as fout:
+        fout.write(TESTDATA1)
+
+    fs, _ = fsspec.core.url_to_fs(remoteurl)
+    data = fs.read_bytes(localpath + "/testfile.txt", start=start, end=end)
+    assert data == TESTDATA1.encode("utf-8")[start:end]
+
+
 def test_append_fsspec(localserver, clear_server):
     remoteurl, localpath = localserver
     with open(localpath + "/testfile.txt", "w") as fout: