Fix memory leak in Raw.copy() (#709)

* Fix memory leak in Raw.copy().

Raw_New borrows a reference to its PyBytesObject argument, so Raw_Copy must
still dispose of it.

The following is a minimal repro for this issue:

import msgspec

DECODER = msgspec.msgpack.Decoder(type=msgspec.Raw)
PAYLOAD = b"\xda\xff\xff" + (65535 * b"\0") # array of 65535 zeros

for _ in range(1000000):
  raw = DECODER.decode(PAYLOAD)
  raw.copy()

* Add test for raw copy memleak

---------

Co-authored-by: Jim Crist-Harif <jcristharif@gmail.com>

msgspec/_core.c

@@ -1513,7 +1513,9 @@ Raw_copy(Raw *self, PyObject *unused)
     }
     PyObject *buf = PyBytes_FromStringAndSize(self->buf, self->len);
     if (buf == NULL) return NULL;
-    return Raw_New(buf);
+    PyObject *out = Raw_New(buf);
+    Py_DECREF(buf);
+    return out;
 }
 
 static PyMethodDef Raw_methods[] = {

tests/test_raw.py

@@ -1,5 +1,7 @@
 import operator
+import subprocess
 import sys
+import textwrap
 import weakref
 
 import pytest
@@ -69,6 +71,29 @@ def test_raw_copy():
     assert ref() is None
 
 
+def test_raw_copy_doesnt_leak():
+    """See https://github.com/jcrist/msgspec/pull/709"""
+    script = textwrap.dedent(
+        """
+        import msgspec
+        import tracemalloc
+
+        tracemalloc.start()
+
+        raw = msgspec.Raw(bytearray(1000))
+        for _ in range(10000):
+            raw.copy()
+
+        _, peak = tracemalloc.get_traced_memory()
+        print(peak)
+        """
+    )
+
+    output = subprocess.check_output([sys.executable, "-c", script])
+    peak = int(output.decode().strip())
+    assert peak < 10_000  # should really be ~2000
+
+
 def test_raw_pickle_bytes():
     orig_buffer = b"test"
     r = msgspec.Raw(orig_buffer)