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Add missing autoreset in Packer.pack_ext_type#663

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Merged
methane merged 3 commits into from
Jun 1, 2026
+25 −1
Merged

Add missing autoreset in Packer.pack_ext_type #663

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b691a8e
Add missing autoreset in Packer.pack_ext_type
bysiber Feb 20, 2026
1406cd4
add autoreset support to Packer.pack_ext_type()
methane Jun 1, 2026
907a1c5
add test
methane Jun 1, 2026
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4 changes: 4 additions & 0 deletions msgpack/_packer.pyx
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Original file line numberDiff line numberDiff line change
Expand Up@@ -291,6 +291,10 @@ cdef class Packer:
raise ValueError("ext data too large")
msgpack_pack_ext(&self.pk, typecode, len(data))
msgpack_pack_raw_body(&self.pk, data, len(data))
if self.autoreset:
buf = PyBytes_FromStringAndSize(self.pk.buf, self.pk.length)
self.pk.length = 0
return buf

@cython.critical_section
def pack_array_header(self, long long size):
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4 changes: 4 additions & 0 deletions msgpack/fallback.py
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Expand Up@@ -861,6 +861,10 @@ def pack_ext_type(self, typecode, data):
self._buffer.write(b"\xc9" + struct.pack(">I", L))
self._buffer.write(struct.pack("B", typecode))
self._buffer.write(data)
if self._autoreset:
ret = self._buffer.getvalue()
self._buffer = BytesIO()
return ret
Comment on lines +864 to +867

CopilotAIApr 21, 2026

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Please add a regression test that asserts Packer().pack_ext_type(...) returns the packed bytes when autoreset is enabled, and that the internal buffer is cleared (e.g., a subsequent packer.pack(99) should not include the previously packed ext bytes). This would have caught the original bug and will prevent it from reappearing.

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@methanemethaneApr 21, 2026

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@copilot apply changes based on this feedback

Comment on lines +864 to +867

CopilotAIApr 21, 2026

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This adds autoreset handling for the pure-Python fallback Packer only. The default C-extension implementation (msgpack/_packer.pyx:pack_ext_type) still doesn’t return bytes or reset its internal buffer when autoreset is enabled, so msgpack.Packer().pack_ext_type(...) will remain broken in typical installs unless the Cython path is updated too.

Copilot uses AI. Check for mistakes.

def _pack_array_header(self, n):
if n <= 0x0F:
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7 changes: 7 additions & 0 deletions pyproject.toml
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Expand Up@@ -19,6 +19,7 @@ classifiers = [
"Programming Language :: Python :: Implementation :: CPython",
"Programming Language :: Python :: Implementation :: PyPy",
]
dependencies = []

[project.urls]
Homepage = "https://msgpack.org/"
Expand All@@ -43,3 +44,9 @@ lint.select = [
"I", # isort
#"UP", pyupgrade
]

[dependency-groups]
dev = [
"cython>=3.2.5",
"pytest>=9.0.3",
]
11 changes: 10 additions & 1 deletion test/test_extension.py
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Expand Up@@ -6,7 +6,7 @@

def test_pack_ext_type():
def p(s):
packer = msgpack.Packer()
packer = msgpack.Packer(autoreset=False)
packer.pack_ext_type(0x42, s)
return packer.bytes()

Expand All@@ -20,6 +20,15 @@ def p(s):
assert p(b"A" * 0x00012345) == b"\xc9\x00\x01\x23\x45\x42" + b"A" * 0x00012345 # ext 32


def test_pack_ext_type_autoreset():
packer = msgpack.Packer()

assert packer.pack_ext_type(0x42, b"A") == b"\xd4\x42A"
assert packer.bytes() == b""
assert packer.pack_ext_type(0x42, b"ABC") == b"\xc7\x03\x42ABC"
assert packer.bytes() == b""


def test_unpack_ext_type():
def check(b, expected):
assert msgpack.unpackb(b) == expected
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