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gh-60107: avoid io.RawIOBase.read from reading into a temporary bytearray #138616

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gh-60107: avoid io.RawIOBase.read from reading into a temporary bytearray #138616

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allocate a bytes object directly instead and manually construct a wri…
taskevich Sep 7, 2025
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📜🤖 Added by blurb_it.
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gh-60107: gh-138616: Minor code changes
taskevich Sep 7, 2025
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Merge branch 'direct-read-bytes' of https://github.com/taskevich/cpyt…
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gh-60107: Change blurb_it
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Update Misc/NEWS.d/next/C_API/2025-09-07-10-52-09.gh-issue-60107.dhcb…
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Deleted incorrect news from C_API
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gh-60107: Tests for readinto
taskevich Sep 7, 2025
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43 changes: 43 additions & 0 deletions Lib/test/test_io/test_general.py
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Original file line number Diff line number Diff line change
Expand Up @@ -921,6 +921,49 @@ def test_RawIOBase_read(self):
self.assertEqual(rawio.read(2), None)
self.assertEqual(rawio.read(2), b"")

def test_exact_RawIOBase(self):
rawio = self.MockRawIOWithoutRead((b"ab", b"cd"))
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Maybe I wasn't precise enough. RawIOBase.read() is implemented in terms of readinto. So, what we want to do is provide a readinto method that does something bad as it's given the internal buffer we constructed in C. I don't know if it's possible to cause a segfault on main with that approach though.

Stated otherwise, we want some class:

class EvilReadInto(MockRawIOWithoutRead):
    def readinto(self, buf):
        # do something bad with 'buf'

And then

r = EvilReadInto(something_here)
r.read()  # on main, this call should crash, but not with this patch

buf = bytearray(2)
n = rawio.readinto(buf)
self.assertEqual(n, 2)
self.assertEqual(buf, b"ab")

n = rawio.readinto(buf)
self.assertEqual(n, 2)
self.assertEqual(buf, b"cd")

n = rawio.readinto(buf)
self.assertEqual(n, 0)
self.assertEqual(buf, b"cd")

def test_partial_readinto_write_RawIOBase(self):
rawio = self.MockRawIOWithoutRead((b"abcdef",))
buf = bytearray(3)
n = rawio.readinto(buf)
self.assertEqual(n, 3)
self.assertEqual(buf, b"abc")

n2 = rawio.readinto(buf)
self.assertEqual(n2, 3)
self.assertEqual(buf, b"def")

def test_readinto_none_RawIOBase(self):
rawio = self.MockRawIOWithoutRead((None, b"x"))
buf = bytearray(2)
n = rawio.readinto(buf)
self.assertIsNone(n)

n2 = rawio.readinto(buf)
self.assertEqual(n2, 1)
self.assertEqual(buf[0], ord('x'))

def test_read_default_via_readinto_RawIOBase(self):
rawio = self.MockRawIOWithoutRead((b"abcdef",))
result = rawio.read(4)
self.assertEqual(result, b"abcd")
result2 = rawio.read(4)
self.assertEqual(result2, b"ef")

def test_types_have_dict(self):
test = (
self.IOBase(),
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