Function _compress

pymongo/message.py:294–310

Takes message data, compresses it, and adds an OP_COMPRESSED header.

(
    operation: int, data: bytes, ctx: Union[SnappyContext, ZlibContext, ZstdContext]
)

def _compress(
    operation: int, data: bytes, ctx: Union[SnappyContext, ZlibContext, ZstdContext]
) -> tuple[int, bytes]:
    """Takes message data, compresses it, and adds an OP_COMPRESSED header."""
    compressed = ctx.compress(data)
    request_id = _randint()

    header = _pack_compression_header(
        _COMPRESSION_HEADER_SIZE + len(compressed),  # Total message length
        request_id,  # Request id
        0,  # responseTo
        2012,  # operation id
        operation,  # original operation id
        len(data),  # uncompressed message length
        ctx.compressor_id,
    )  # compressor id
    return request_id, header + compressed


_pack_header = struct.Struct("<iiii").pack