######################################################################
#
# File: b2sdk/transfer/inbound/downloader/abstract.py
#
# Copyright 2020 Backblaze Inc. All Rights Reserved.
#
# License https://www.backblaze.com/using_b2_code.html
#
######################################################################
import hashlib
from abc import abstractmethod
from concurrent.futures import ThreadPoolExecutor
from io import IOBase
from typing import Optional
from requests.models import Response
from b2sdk.file_version import DownloadVersion
from b2sdk.session import B2Session
from b2sdk.utils import B2TraceMetaAbstract
from b2sdk.utils.range_ import Range
from b2sdk.encryption.setting import EncryptionSetting
[docs]class EmptyHasher:
[docs] def __init__(self, *args, **kwargs):
pass
[docs] def update(self, data):
pass
[docs] def digest(self):
return b''
[docs] def hexdigest(self):
return ''
[docs] def copy(self):
return self
[docs]class AbstractDownloader(metaclass=B2TraceMetaAbstract):
REQUIRES_SEEKING = True
DEFAULT_THREAD_POOL_CLASS = staticmethod(ThreadPoolExecutor)
DEFAULT_ALIGN_FACTOR = 4096
[docs] def __init__(
self,
thread_pool: Optional[ThreadPoolExecutor] = None,
force_chunk_size: Optional[int] = None,
min_chunk_size: Optional[int] = None,
max_chunk_size: Optional[int] = None,
align_factor: Optional[int] = None,
check_hash: bool = True,
**kwargs
):
align_factor = align_factor or self.DEFAULT_ALIGN_FACTOR
assert force_chunk_size is not None or (
min_chunk_size is not None and max_chunk_size is not None and
0 < min_chunk_size <= max_chunk_size and max_chunk_size >= align_factor
)
self._min_chunk_size = min_chunk_size
self._max_chunk_size = max_chunk_size
self._forced_chunk_size = force_chunk_size
self._align_factor = align_factor
self._check_hash = check_hash
self._thread_pool = thread_pool if thread_pool is not None \
else self.DEFAULT_THREAD_POOL_CLASS()
super().__init__(**kwargs)
def _get_hasher(self):
if self._check_hash:
return hashlib.sha1()
return EmptyHasher()
def _get_chunk_size(self, content_length: Optional[int]):
if self._forced_chunk_size is not None:
return self._forced_chunk_size
ideal = max(content_length // 1000, self._align_factor)
non_aligned = min(max(ideal, self._min_chunk_size), self._max_chunk_size)
aligned = non_aligned // self._align_factor * self._align_factor
return aligned
@classmethod
def _get_remote_range(cls, response: Response, download_version: DownloadVersion):
"""
Get a range from response or original request (as appropriate).
:param response: requests.Response of initial request
:param download_version: b2sdk.v2.DownloadVersion
:return: a range object
"""
if 'Range' in response.request.headers:
return Range.from_header(response.request.headers['Range'])
return download_version.range_
[docs] def is_suitable(self, download_version: DownloadVersion, allow_seeking: bool):
"""
Analyze download_version (possibly against options passed earlier to constructor
to find out whether the given download request should be handled by this downloader).
"""
if self.REQUIRES_SEEKING and not allow_seeking:
return False
return True
[docs] @abstractmethod
def download(
self,
file: IOBase,
response: Response,
download_version: DownloadVersion,
session: B2Session,
encryption: Optional[EncryptionSetting] = None,
):
"""
@returns (bytes_read, actual_sha1)
"""
pass