[Linux] fix Process.open_files() for cases fdinfo has only flags (#2596)

psutil/_pslinux.py

@@ -1657,6 +1657,22 @@ def wrapper(self, *args, **kwargs):
     return wrapper
 
 
+def _parse_fdinfo(f):
+    # f:  a file opened in binary
+    pos, flags = None, None
+    for _ in [0, 1]:
+        line_vals = f.readline().split()
+        if line_vals is None or len(line_vals) < 2:
+            continue
+        key = decode(line_vals[0])
+        if key == "pos:":
+            pos = int(line_vals[1])
+        elif key == "flags:":
+            flags = int(line_vals[1], 8)
+
+    return pos, flags
+
+
 class Process:
     """Linux process implementation."""
 
@@ -2273,8 +2289,7 @@ def open_files(self):
                     file = f"{self._procfs_path}/{self.pid}/fdinfo/{fd}"
                     try:
                         with open_binary(file) as f:
-                            pos = int(f.readline().split()[1])
-                            flags = int(f.readline().split()[1], 8)
+                            pos, flags = _parse_fdinfo(f)
                     except (FileNotFoundError, ProcessLookupError):
                         # fd gone in the meantime; process may
                         # still be alive

psutil/tests/test_linux.py

@@ -1955,6 +1955,38 @@ def test_open_files_enametoolong(self):
                     assert p.open_files() == []
                     assert m.called
 
+    # Test parsing variants of fdinfo content ( during Process.open_files() )
+
+    def test_open_files_fdinfo_parsing_avg(self):
+        # Case typical fdinfo file content
+        fdinfo_content = """\
+pos:	0
+flags:	02100000
+mnt_id:	129
+ino:	29836347532685335"""
+        self._do_test_fdinfo_parsing(fdinfo_content, (0, 0o2100000))
+
+    def test_open_files_fdinfo_parsing_only_flags(self):
+        # Case only flags.
+        # Seen in Docker python + Google Cloud Run
+        # https://github.com/giampaolo/psutil/issues/2596
+        fdinfo_content = """\
+flags:	02100000"""
+        self._do_test_fdinfo_parsing(fdinfo_content, (None, 0o2100000))
+
+    def test_open_files_fdinfo_parsing_empty(self):
+        # extereme case the file is empty (not seen in practice)
+        fdinfo_content = ""
+        self._do_test_fdinfo_parsing(fdinfo_content, (None, None))
+
+    def _do_test_fdinfo_parsing(self, content, expected):
+        # `f`` needs to be a file in binary mode,
+        # simulating what is done in Process.open_flles()
+        f = io.BytesIO(content.encode())
+        actual_pos, actual_flags = psutil._pslinux._parse_fdinfo(f)
+        assert actual_pos == expected[0]
+        assert actual_flags == expected[1]
+
     # --- mocked tests
 
     def test_terminal_mocked(self):