storage/remote.py: Port to new CAS downloader helper

import io

import logging

import grpc

from buildgrid.client.cas import upload

from buildgrid._protos.google.bytestream import bytestream_pb2_grpc

from buildgrid.client.cas import download, upload

from buildgrid._protos.build.bazel.remote.execution.v2 import remote_execution_pb2, remote_execution_pb2_grpc

from buildgrid._protos.google.rpc import code_pb2

from buildgrid._protos.google.rpc import status_pb2

from buildgrid.utils import gen_fetch_blob

from buildgrid.settings import HASH

from .storage_abc import StorageABC

        self.instance_name = instance_name

        self.channel = channel

        self._stub_bs = bytestream_pb2_grpc.ByteStreamStub(channel)

        self._stub_cas = remote_execution_pb2_grpc.ContentAddressableStorageStub(channel)

    def has_blob(self, digest):

        return False

    def get_blob(self, digest):

        try:

            fetched_data = io.BytesIO()

            length = 0

            for data in gen_fetch_blob(self._stub_bs, digest, self.instance_name):

                length += fetched_data.write(data)

            assert digest.size_bytes == length

            fetched_data.seek(0)

            return fetched_data

        except grpc.RpcError as e:

            if e.code() == grpc.StatusCode.NOT_FOUND:

                pass

        with download(self.channel, instance=self.instance_name) as downloader:

            blob = downloader.get_blob(digest)

            if blob is not None:

                return io.BytesIO(blob)

            else:

                self.logger.error(e.details())

                raise

                return None

    def begin_write(self, digest):