Double check strings algorithm

[mr-tz]

See mandiant/capa#2555

[0xRavenspar]

Hey @mr-tz, I would like to work on this issue if it's still open

[0xRavenspar]

I had a doubt,
In capa the input is a bytes buffer and ascii value of the character

def buf_filled_with(buf: bytes, character: int) -> bool:
    """Check if the given buffer is filled with the given character, repeatedly.
    Args:
        buf: The bytes buffer to check
        character: The byte value (0-255) to check for
williballenthin marked this conversation as resolved.
    Returns:
        True if all bytes in the buffer match the character, False otherwise.
        The empty buffer contains no bytes, therefore always returns False.
    """

but the tests in test_buf_filled_with.py we're testing for str and mmap.

tests = [
    ("A", True),
    ("AB", False),
    ("A" * 10000, True),
    (("A" * 10000) + "B", False),
    ("B" + ("A" * 5000), False),
    (("A" * 5000) + "B" + ("A" * 2000), False),
    (("A" * 5000) + ("B" * 5000), False),
]


def test_str():
    for test, expectation in tests:
        assert buf_filled_with(test, test[0]) == expectation


def test_mmap():
    for test, expectation in tests:
        f = tempfile.NamedTemporaryFile()
        f.write(test.encode("utf-8"))
        f.flush()
        test_mmap = mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ)
        assert buf_filled_with(test_mmap, test[0].encode("utf-8")) == expectation

Should the function check for str and mmap and change it to bytes or should it only accept a bytes buffer and int

[mr-tz]

It should likely be bytes only. Ideally we add missing type hints as part of this fix and verify all usages.