fix: handle empty files in last_n_bytes_of

py/envoy.base.utils/envoy/base/utils/utils.py

@@ -139,7 +139,8 @@ def last_n_bytes_of(target: str | pathlib.Path, n: int = 1) -> bytes:
     """Return the last `n` bytes from a file, defaults to 1 byte."""
     with open(target, "rb") as f:
         f.seek(0, os.SEEK_END)
-        f.seek(f.tell() - n)
+        # Clamp to the start of the file so empty or short files do not raise on negative seek.
+        f.seek(max(f.tell() - n, 0))
         return f.read(n)
 
 

py/envoy.base.utils/tests/test_utils.py

@@ -1,4 +1,5 @@
 import pathlib
+import tempfile
 from unittest.mock import MagicMock
 
 import pytest
@@ -271,7 +272,7 @@ def test_last_n_bytes_of(patches, n):
     assert (
         m_open.return_value.__enter__.return_value.seek.call_args_list
         == [[(0, m_os.SEEK_END), {}],
-            [(23 - (n or 1), ), {}]])
+            [(max(23 - (n or 1), 0), ), {}]])
     assert (
         m_open.return_value.__enter__.return_value.tell.call_args
         == [(), {}])
@@ -280,6 +281,11 @@ def test_last_n_bytes_of(patches, n):
         == [(n or 1, ), {}])
 
 
+def test_last_n_bytes_of_empty_file():
+    with tempfile.NamedTemporaryFile() as f:
+        assert utils.last_n_bytes_of(f.name) == b""
+
+
 def test_minor_version_for(patches):
     patched = patches(
         "_version",