Issue #16350: Fix zlib decompressor handling of unused_data with multiple calls to...

Patch by Serhiy Storchaka.

diff --cc Lib/test/test_zlib.py
index d637c2d685e97ef2781b73a0a14b1771efbf0a4b,c17b4d0b36e1e04b08b62542474b8429bf215896..b6a60f4d689cd31c0b0273ae3620bb72b6319e1a
--- 1/Lib/test/test_zlib.py
--- 2/Lib/test/test_zlib.py
+++ b/Lib/test/test_zlib.py
@@@ -467,26 -434,19 +467,40 @@@ class CompressObjectTestCase(BaseCompre
          y += dco.flush()
          self.assertEqual(y, b'foo')
  
 +    def test_decompress_eof(self):
 +        x = b'x\x9cK\xcb\xcf\x07\x00\x02\x82\x01E'  # 'foo'
 +        dco = zlib.decompressobj()
 +        self.assertFalse(dco.eof)
 +        dco.decompress(x[:-5])
 +        self.assertFalse(dco.eof)
 +        dco.decompress(x[-5:])
 +        self.assertTrue(dco.eof)
 +        dco.flush()
 +        self.assertTrue(dco.eof)
 +
 +    def test_decompress_eof_incomplete_stream(self):
 +        x = b'x\x9cK\xcb\xcf\x07\x00\x02\x82\x01E'  # 'foo'
 +        dco = zlib.decompressobj()
 +        self.assertFalse(dco.eof)
 +        dco.decompress(x[:-5])
 +        self.assertFalse(dco.eof)
 +        dco.flush()
 +        self.assertFalse(dco.eof)
 +
+     def test_decompress_unused_data(self):
+         # Repeated calls to decompress() after EOF should accumulate data in
+         # dco.unused_data, instead of just storing the arg to the last call.
+         x = zlib.compress(HAMLET_SCENE) + HAMLET_SCENE
+         for step in 1, 2, 100:
+             dco = zlib.decompressobj()
+             data = b''.join(dco.decompress(x[i : i + step])
+                             for i in range(0, len(x), step))
+             data += dco.flush()
+ 
++            self.assertTrue(dco.eof)
+             self.assertEqual(data, HAMLET_SCENE)
+             self.assertEqual(dco.unused_data, HAMLET_SCENE)
+ 
      if hasattr(zlib.compressobj(), "copy"):
          def test_compresscopy(self):
              # Test copying a compression object

diff --cc Misc/NEWS
Simple merge

diff --cc Modules/zlibmodule.c
index 6519194fb57f0a70ed64d2fdcbbc59428d7af504,7734ba6dfaa7fbbe92866b5f522bb9a8a55639e4..888ef5388d63b18e984ecf2692d9b2e6526078f7
--- 1/Modules/zlibmodule.c
--- 2/Modules/zlibmodule.c
+++ b/Modules/zlibmodule.c
@@@ -693,14 -610,30 +693,31 @@@ PyZlib_objdecompress(compobject *self, 
         preserved.
      */
      if (err == Z_STREAM_END) {
-         Py_XDECREF(self->unused_data);  /* Free original empty string */
-         self->unused_data = PyBytes_FromStringAndSize(
-             (char *)self->zst.next_in, self->zst.avail_in);
-         if (self->unused_data == NULL) {
-             Py_DECREF(RetVal);
-             goto error;
+         if (self->zst.avail_in > 0) {
+             /* Append the leftover data to the existing value of unused_data. */
+             Py_ssize_t old_size = PyBytes_GET_SIZE(self->unused_data);
+             Py_ssize_t new_size = old_size + self->zst.avail_in;
+             PyObject *new_data;
+             if (new_size <= old_size) {  /* Check for overflow. */
+                 PyErr_NoMemory();
+                 Py_DECREF(RetVal);
+                 RetVal = NULL;
+                 goto error;
+             }
+             new_data = PyBytes_FromStringAndSize(NULL, new_size);
+             if (new_data == NULL) {
+                 Py_DECREF(RetVal);
+                 RetVal = NULL;
+                 goto error;
+             }
+             Py_MEMCPY(PyBytes_AS_STRING(new_data),
+                       PyBytes_AS_STRING(self->unused_data), old_size);
+             Py_MEMCPY(PyBytes_AS_STRING(new_data) + old_size,
+                       self->zst.next_in, self->zst.avail_in);
+             Py_DECREF(self->unused_data);
+             self->unused_data = new_data;
          }
 +        self->eof = 1;
          /* We will only get Z_BUF_ERROR if the output buffer was full
             but there wasn't more output when we tried again, so it is
             not an error condition.