If the response is compressed with gzip or deflate:
      1. decompress the response body
      2. delete the content-encoding header
      3. update content-length header to decompressed length

def decode_response(response):
    """
    If the response is compressed with gzip or deflate:
      1. decompress the response body
      2. delete the content-encoding header
      3. update content-length header to decompressed length
    """
    def is_compressed(headers):
        encoding = headers.get('content-encoding', [])
        return encoding and encoding[0] in ('gzip', 'deflate')

    def decompress_body(body, encoding):
        """Returns decompressed body according to encoding using zlib.
        to (de-)compress gzip format, use wbits = zlib.MAX_WBITS | 16
        """
        if encoding == 'gzip':
            return zlib.decompress(body, zlib.MAX_WBITS | 16)
        else:  # encoding == 'deflate'
            return zlib.decompress(body)

    # Deepcopy here in case `headers` contain objects that could
    # be mutated by a shallow copy and corrupt the real response.
    response = copy.deepcopy(response)
    headers = CaseInsensitiveDict(response['headers'])
    if is_compressed(headers):
        encoding = headers['content-encoding'][0]
        headers['content-encoding'].remove(encoding)
        if not headers['content-encoding']:
            del headers['content-encoding']

        new_body = decompress_body(response['body']['string'], encoding)
        response['body']['string'] = new_body
        headers['content-length'] = [str(len(new_body))]
        response['headers'] = dict(headers)
    return response