Reset size and digests when retrying downloads

re #2078

CHANGES/2078.bugfix

@@ -1 +1,2 @@
 Fixed downloader retry logic with partially written files.
+Fixed validation logic in HttpDownloader for retries with partially downloaded files.

pulpcore/download/base.py

@@ -103,7 +103,7 @@ def __init__(
             self.semaphore = semaphore
         else:
             self.semaphore = asyncio.Semaphore()  # This will always be acquired
-        self._digests = {n: pulp_hashlib.new(n) for n in Artifact.DIGEST_FIELDS}
+        self._digests = {}
         self._size = 0
         if self.expected_digests:
             if not set(self.expected_digests).intersection(set(Artifact.DIGEST_FIELDS)):
@@ -124,6 +124,8 @@ def _ensure_writer_has_open_file(self):
         if not self._writer:
             self._writer = tempfile.NamedTemporaryFile(dir=os.getcwd(), delete=False)
             self.path = self._writer.name
+            self._digests = {n: pulp_hashlib.new(n) for n in Artifact.DIGEST_FIELDS}
+            self._size = 0
 
     async def handle_data(self, data):
         """
@@ -157,8 +159,6 @@ async def finalize(self):
                 :meth:`~pulpcore.plugin.download.BaseDownloader.handle_data`.
         """
         self._ensure_writer_has_open_file()
-        self._writer.flush()
-        os.fsync(self._writer.fileno())
         self._writer.close()
         self._writer = None
         self.validate_digests()