Repository: mandiant/capa
File: capa/features/extractors/strings.py (Python)

Code before:
)
ASCII_RE_4 = re.compile(b"([%s]{%d,})" % (ASCII_BYTE, 4))
UNICODE_RE_4 = re.compile(b"((?:[%s]\x00){%d,})" % (ASCII_BYTE, 4))
REPEATS = {ord("A"), 0x00, 0xFE, 0xFF}
SLICE_SIZE = 4096
PRINTABLE_CHAR_SET = set(string.printable)


@dataclass
class String:
    s: str
    offset: int


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

    Returns:
        bool: True if all bytes in the buffer match the character, False otherwise.
        The empty buffer contains no bytes, therefore always returns False.
    """
    if not buf:
        return False

    if len(buf) < SLICE_SIZE:
        return all(b == character for b in buf)

    # single big allocation, re-used each loop
    dupe_chunk = bytes(character) * SLICE_SIZE

    for offset in range(0, len(buf), SLICE_SIZE):
        # bytes objects are immutable, so the slices share the underlying array,
        # and therefore this is cheap.
        current_chunk = buf[offset : offset + SLICE_SIZE]

        if len(current_chunk) == SLICE_SIZE:
            # chunk-aligned comparison

            if dupe_chunk != current_chunk:
                return False

        else:
            # last loop, final chunk size is not aligned
            if not all(b == character for b in current_chunk):
                return False

    return True

Review comment (suggestion):
It might be useful to add a check to `buf_filled_with` to assert `character` in the (0-255) range
```python
    if not (0 <= character <= 255):
        raise ValueError(f"Character value {character} outside valid byte range (0-255)")
```

Code after:
import contextlib
from dataclasses import dataclass
from collections.abc import Iterator

ASCII_BYTE = r" !\"#\$%&\'\(\)\*\+,-\./0123456789:;<=>\?@ABCDEFGHIJKLMNOPQRSTUVWXYZ\[\]\^_`abcdefghijklmnopqrstuvwxyz\{\|\}\\\~\t".encode(
    "ascii"
)
ASCII_RE_4 = re.compile(b"([%s]{%d,})" % (ASCII_BYTE, 4))
UNICODE_RE_4 = re.compile(b"((?:[%s]\x00){%d,})" % (ASCII_BYTE, 4))
REPEATS = {ord("A"), 0x00, 0xFE, 0xFF}
SLICE_SIZE = 4096
PRINTABLE_CHAR_SET = set(string.printable)


@dataclass
class String:
    s: str
    offset: int


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

    Returns:
        True if all bytes in the buffer match the character, False otherwise.
        The empty buffer contains no bytes, therefore always returns False.
    """
    if not buf:
        return False

    if not (0 <= character <= 255):
        raise ValueError(f"Character value {character} outside valid byte range (0-255)")

    if len(buf) < SLICE_SIZE:
        return all(b == character for b in buf)

    # single big allocation, re-used each loop
    dupe_chunk = bytes(character) * SLICE_SIZE

    for offset in range(0, len(buf), SLICE_SIZE):
        # bytes objects are immutable, so the slices share the underlying array,
        # and therefore this is cheap.
        current_chunk = buf[offset : offset + SLICE_SIZE]

        if len(current_chunk) == SLICE_SIZE:
            # chunk-aligned comparison