import zlib
import binwalk.core.compat
import binwalk.core.plugin
from binwalk.core.common import BlockFile


class ZlibValidPlugin(binwalk.core.plugin.Plugin):

    '''
    Validates zlib compressed data.
    '''
    MODULES = ['Signature']

    MAX_DATA_SIZE = 33 * 1024

    def scan(self, result):
        # If this result is a zlib signature match, try to decompress the data
        if result.file and result.description.lower().startswith('zlib'):

            # If byte swapping is enabled, we need to start reading at a swap-size
            # aligned offset, then index in to the read data appropriately.
            if self.module.config.swap_size:
                adjust = result.offset % self.module.config.swap_size
            else:
                adjust = 0

            offset = result.offset - adjust

            # Seek to and read the suspected zlib data
            fd = self.module.config.open_file(result.file.name)
            fd.seek(offset)
            data = fd.read(self.MAX_DATA_SIZE)[adjust:]
            fd.close()

            # Check if this is valid zlib data. It is valid if:
            #
            #   1. It decompresses without error
            #   2. Decompression fails only because of truncated input
            try:
                zlib.decompress(binwalk.core.compat.str2bytes(data))
            except zlib.error as e:
                # Error -5, incomplete or truncated data input
                if not str(e).startswith("Error -5"):
                    result.valid = False
