[PATCH v3 04/15] pylibfdt: Handle empty properties in as_str() and as_stringlist()

[Douglas Anderson]

Currently, calling `Property.as_str()` or `Property.as_stringlist()` on
an empty `Property` (`b''`) raises `IndexError: bytearray index out of
range` when indexing `self[-1]`.

Update `Property.as_str()` to raise `ValueError('Property lacks nul
termination')` on an empty property, and update
`Property.as_stringlist()` to return `[]` on an empty property. Add unit
tests in `tests/pylibfdt_tests.py`.

Assisted-by: Gemini:gemini-pro-prerelease
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---

Changes in v3:
- Split Property.as_str() and Property.as_stringlist() empty-property
  handling into a standalone patch and add direct Property unit tests
  (Simon Glass, David Gibson)

 pylibfdt/libfdt.i       | 4 +++-
 tests/pylibfdt_tests.py | 7 +++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/pylibfdt/libfdt.i b/pylibfdt/libfdt.i
index 5c8859b37df3..eb14312986ea 100644
--- a/pylibfdt/libfdt.i
+++ b/pylibfdt/libfdt.i
@@ -932,7 +932,7 @@ class Property(bytearray):
 
     def as_str(self):
         """Unicode is supported by decoding from UTF-8"""
-        if self[-1] != 0:
+        if not self or self[-1] != 0:
             raise ValueError('Property lacks nul termination')
         if 0 in self[:-1]:
             raise ValueError('Property contains embedded nul characters')
@@ -940,6 +940,8 @@ class Property(bytearray):
 
     def as_stringlist(self):
         """Unicode is supported by decoding from UTF-8"""
+        if not self:
+            return []
         if self[-1] != 0:
             raise ValueError('Property lacks nul termination')
         parts = self[:-1].split(b'\x00')
diff --git a/tests/pylibfdt_tests.py b/tests/pylibfdt_tests.py
index 93408745c575..20741d8f2df0 100644
--- a/tests/pylibfdt_tests.py
+++ b/tests/pylibfdt_tests.py
@@ -423,6 +423,10 @@ class PyLibfdtBasicTests(unittest.TestCase):
                          self.fdt.getprop(node, "compatible").as_stringlist())
         self.assertEqual(["this is a placeholder string", "string2"],
                          self.fdt.getprop(node, "placeholder").as_stringlist())
+        self.assertEqual([], libfdt.Property('empty', b'').as_stringlist())
+        with self.assertRaises(ValueError) as e:
+            libfdt.Property('bad', b'no-nul').as_stringlist()
+        self.assertIn('lacks nul termination', str(e.exception))
 
     def testReserveMap(self):
         """Test that we can access the memory reserve map"""
@@ -523,6 +527,9 @@ class PyLibfdtBasicTests(unittest.TestCase):
         with self.assertRaises(ValueError) as e:
             self.fdt.getprop(node, 'prop-int').as_str()
         self.assertIn('lacks nul termination', str(e.exception))
+        with self.assertRaises(ValueError) as e:
+            libfdt.Property('empty', b'').as_str()
+        self.assertIn('lacks nul termination', str(e.exception))
 
         node2 = self.fdt.path_offset('/subnode@1/subsubnode')
         with self.assertRaises(ValueError) as e:
-- 
2.56.0.317.g454f8302e1-goog