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Keep Unpacker.tell() at the start of an incomplete object #772

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Keep Unpacker.tell() at the start of an incomplete object #772

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7 changes: 7 additions & 0 deletions msgpack/_unpacker.pyx
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Original file line number Diff line number Diff line change
Expand Up @@ -325,6 +325,8 @@ cdef class Unpacker:
cdef object unicode_errors
cdef Py_ssize_t max_buffer_size
cdef uint64_t stream_offset
# stream_offset at the start of an incomplete object
cdef uint64_t object_offset
cdef bint _unpacking

def __dealloc__(self):
Expand Down Expand Up @@ -486,6 +488,8 @@ cdef class Unpacker:
raise RuntimeError("Unpacker cannot be called recursively while unpacking is in progress")
if self.ctx.execute != NULL and self.ctx.execute != execute:
raise ValueError("Cannot switch unpacking methods while an object is incomplete")
if self.ctx.execute == NULL:
self.object_offset = self.stream_offset

self._unpacking = True
try:
Expand Down Expand Up @@ -585,6 +589,9 @@ cdef class Unpacker:
number of bytes that were read from the input, also the starting
position of the next object.
"""
if self.ctx.execute != NULL:
# Part of the next object has been decoded, but it still starts here.
return self.object_offset
return self.stream_offset

def __iter__(self):
Expand Down
19 changes: 19 additions & 0 deletions test/test_sequnpack.py
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Original file line number Diff line number Diff line change
Expand Up @@ -169,3 +169,22 @@ def test_unpack_tell():
m2 = next(unpacker)
assert m == m2
assert o == unpacker.tell()


def test_unpack_tell_incomplete_object():
# tell() is where the next object starts, even when only part of it has arrived.
first = packb([1, 2, 3])
second = packb(["x" * 40, "y" * 40])
packed = first + second
for cut in (len(first) + 1, len(first) + 3, len(first) + 45):
unpacker = Unpacker()
unpacker.feed(packed[:cut])
assert list(unpacker) == [[1, 2, 3]]
assert unpacker.tell() == len(first)
unpacker.feed(packed[cut:])
assert list(unpacker) == [["x" * 40, "y" * 40]]
assert unpacker.tell() == len(packed)

unpacker = Unpacker(io.BytesIO(packed[:cut]), read_size=16)
assert list(unpacker) == [[1, 2, 3]]
assert unpacker.tell() == len(first)
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