gh-117716: Fix wave RIFF padding for data chunks

Lib/test/test_wave.py

@@ -430,6 +430,30 @@ def test_setframerate_rounds(self, arg, expected):
             f.setframerate(arg)
             self.assertEqual(f.getframerate(), expected)
 
+    def test_write_odd_data_chunk_pads_and_updates_riff_size(self):
+        # gh-117716: odd-sized data chunks must be padded with one zero byte.
+        with io.BytesIO() as output:
+            with wave.open(output, mode='wb') as w:
+                w.setnchannels(1)
+                w.setsampwidth(1)
+                w.setframerate(48000)
+                w.writeframes(b'\x80')
+
+            value = output.getvalue()
+
+        self.assertEqual(value[-1], 0)
+        self.assertEqual(
+            int.from_bytes(value[4:8], byteorder='little'),
+            38,
+        )
+
+        with wave.open(io.BytesIO(value), mode='rb') as r:
+            self.assertEqual(r.getnchannels(), 1)
+            self.assertEqual(r.getsampwidth(), 1)
+            self.assertEqual(r.getframerate(), 48000)
+            self.assertEqual(r.getnframes(), 1)
+            self.assertEqual(r.readframes(-1), b'\x80')
+
 
 class WaveOpen(unittest.TestCase):
     def test_open_pathlike(self):

Lib/wave.py

@@ -611,6 +611,8 @@ def close(self):
         try:
             if self._file:
                 self._ensure_header_written(0)
+                if self._datawritten & 1:
+                    self._file.write(b'\x00')
                 if self._datalength != self._datawritten:
                     self._patchheader()
                 self._file.flush()
@@ -651,7 +653,7 @@ def _write_header(self, initlength):
         has_fact = self._needs_fact_chunk()
         header_overhead = 36 + (12 if has_fact else 0)
         self._file.write(struct.pack('<L4s4sLHHLLHH',
-            header_overhead + self._datalength, b'WAVE', b'fmt ', 16,
+            header_overhead + self._datalength + (self._datalength & 1), b'WAVE', b'fmt ', 16,
             self._format, self._nchannels, self._framerate,
             self._nchannels * self._framerate * self._sampwidth,
             self._nchannels * self._sampwidth,
@@ -677,7 +679,7 @@ def _patchheader(self):
         curpos = self._file.tell()
         header_overhead = 36 + (12 if self._needs_fact_chunk() else 0)
         self._file.seek(self._form_length_pos, 0)
-        self._file.write(struct.pack('<L', header_overhead + self._datawritten))
+        self._file.write(struct.pack('<L', header_overhead + self._datawritten + (self._datawritten & 1)))
         if self._fact_sample_count_pos is not None:
             self._file.seek(self._fact_sample_count_pos, 0)
             nframes = self._datawritten // (self._nchannels * self._sampwidth)

Misc/NEWS.d/next/Library/2026-02-25-22-20-00.gh-issue-117716.w6kYp9.rst

@@ -0,0 +1 @@
+Fix :mod:`wave` writing of odd-sized ``data`` chunks by appending the required RIFF pad byte and correcting the RIFF chunk size field accordingly.