Patched code sample

import zlib
import io

def safe_decompress_in_chunks(compressed_stream: io.BytesIO, *, limit: int):
    """
    Represents the principle of the aiohttp fix for stream decompression.

    Instead of decompressing the entire payload into memory at once, this function
    reads the compressed stream in small chunks and deompresses them
    incrementally. It continuously checks if the total size of the
    decompressed data has exceeded a predefined security limit.

    If the limit is exceeded, it raises an exception, preventing a potential
    Denial of Service (DoS) attack from a "zip bomb" that would otherwise
    consume excessive memory.

    Args:
        compressed_stream: A file-like object containing compressed data.
        limit: The maximum allowed size for the decompressed data in bytes.

    Raises:
        ValueError: If the decompressed data size exceeds the limit.

    Returns:
        The decompressed data as bytes, if it is within the size limit.
    """
    decompressor = zlib.decompressobj()
    decompressed_data = bytearray()
    
    # The fix is to process data in chunks rather than all at once.
    while True:
        # Read a small chunk from the input stream.
        chunk = compressed_stream.read(16 * 1024)  # 16KB chunks
        if not chunk:
            break
            
        # Decompress the chunk. The max_length argument provides an additional
        # layer of protection within the zlib library itself.
        decompressed_chunk = decompressor.decompress(chunk, limit - len(decompressed_data))
        
        # Check if the total size now exceeds the security limit.
        if len(decompressed_data) + len(decompressed_chunk) > limit:
            raise ValueError(f"Decompressed body size exceeds limit of {limit} bytes.")
            
        decompressed_data.extend(decompressed_chunk)

    # Handle any remaining data in the decompressor's buffer.
    final_chunk = decompressor.flush()
    if len(decompressed_data) + len(final_chunk) > limit:
        raise ValueError(f"Decompressed body size exceeds limit of {limit} bytes.")
        
    decompressed_data.extend(final_chunk)

    return bytes(decompressed_data)