From f2d92365653421c0ebc3151afcccf8d1406dbe1a Mon Sep 17 00:00:00 2001
From: Sandor Kertesz <Sandor.Kertesz@ecmwf.int>
Date: Fri, 23 Feb 2024 14:44:20 +0000
Subject: [PATCH] from_source should fail when try to load empty file

---
 earthkit/data/readers/__init__.py |  6 ++++++
 tests/data/empty_file.grib        |  0
 tests/readers/test_empty_file.py  | 31 +++++++++++++++++++++++++++++++
 3 files changed, 37 insertions(+)
 create mode 100644 tests/data/empty_file.grib
 create mode 100644 tests/readers/test_empty_file.py

diff --git a/earthkit/data/readers/__init__.py b/earthkit/data/readers/__init__.py
index 5871b999..51a19b21 100644
--- a/earthkit/data/readers/__init__.py
+++ b/earthkit/data/readers/__init__.py
@@ -169,6 +169,12 @@ def reader(source, path, **kwargs):
         return DirectoryReader(source, path).mutate()
     LOG.debug("Reader for %s", path)
 
+    if not os.path.exists(path):
+        raise FileExistsError(f"No such file exists: '{path}'")
+
+    if os.path.getsize(path) == 0:
+        raise Exception(f"File is empty: '{path}'")
+
     n_bytes = SETTINGS.get("reader-type-check-bytes")
     with open(path, "rb") as f:
         magic = f.read(n_bytes)
diff --git a/tests/data/empty_file.grib b/tests/data/empty_file.grib
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/readers/test_empty_file.py b/tests/readers/test_empty_file.py
new file mode 100644
index 00000000..4895cd1f
--- /dev/null
+++ b/tests/readers/test_empty_file.py
@@ -0,0 +1,31 @@
+#!/usr/bin/env python3
+
+# (C) Copyright 2020 ECMWF.
+#
+# This software is licensed under the terms of the Apache Licence Version 2.0
+# which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+# In applying this licence, ECMWF does not waive the privileges and immunities
+# granted to it by virtue of its status as an intergovernmental organisation
+# nor does it submit to any jurisdiction.
+#
+
+import pytest
+
+import earthkit.data
+from earthkit.data.testing import earthkit_test_data_file
+
+
+def test_empty_file_reader():
+    with pytest.raises(Exception):
+        earthkit.data.from_source("file", earthkit_test_data_file("empty_file.grib"))
+
+
+def test_nonexisting_file_reader():
+    with pytest.raises(FileExistsError):
+        earthkit.data.from_source("file", "__nonexistingfile__")
+
+
+if __name__ == "__main__":
+    from earthkit.data.testing import main
+
+    main(__file__)