Refactor to use BytesIO.

src/allmydata/immutable/layout.py

@@ -1,21 +1,14 @@
 """
 Ported to Python 3.
 """
-from __future__ import absolute_import
-from __future__ import division
-from __future__ import print_function
-from __future__ import unicode_literals
-
-from future.utils import PY2
-if PY2:
-    from future.builtins import filter, map, zip, ascii, chr, hex, input, next, oct, open, pow, round, super, bytes, dict, list, object, range, str, max, min  # noqa: F401
 
 import struct
+from io import BytesIO
 from zope.interface import implementer
 from twisted.internet import defer
 from allmydata.interfaces import IStorageBucketWriter, IStorageBucketReader, \
      FileTooLargeError, HASH_SIZE
-from allmydata.util import mathutil, observer, pipeline, log
+from allmydata.util import mathutil, observer, log
 from allmydata.util.assertutil import precondition
 from allmydata.storage.server import si_b2a
 
@@ -120,7 +113,7 @@ class WriteBucketProxy(object):
         self._block_size = block_size
         self._num_segments = num_segments
         self._written_bytes = 0
-        self._to_write = b""
+        self._to_write = BytesIO()
 
         effective_segments = mathutil.next_power_of_k(num_segments,2)
         self._segment_hash_size = (2*effective_segments - 1) * HASH_SIZE
@@ -258,9 +251,10 @@ class WriteBucketProxy(object):
         no holes.  As such, the offset is technically unnecessary, but is used
         to check the inputs.  Possibly we should get rid of it.
         """
-        assert offset == self._written_bytes + len(self._to_write)
-        self._to_write += data
-        if len(self._to_write) >= self._batch_size:
+        queued_size = len(self._to_write.getbuffer())
+        assert offset == self._written_bytes + queued_size
+        self._to_write.write(data)
+        if queued_size + len(data) >= self._batch_size:
             return self._actually_write()
         else:
             return defer.succeed(False)
@@ -268,14 +262,14 @@ class WriteBucketProxy(object):
     def _actually_write(self):
         """Actually write data to the server."""
         offset = self._written_bytes
-        data = self._to_write
-        self._written_bytes += len(self._to_write)
-        self._to_write = b""
+        data = self._to_write.getvalue()
+        self._written_bytes += len(data)
+        self._to_write = BytesIO()
         return self._rref.callRemote("write", offset, data)
 
     def close(self):
-        assert self._written_bytes + len(self._to_write) == self.get_allocated_size(), (
-            f"{self._written_bytes} + {len(self._to_write)} != {self.get_allocated_size()}"
+        assert self._written_bytes + len(self._to_write.getbuffer()) == self.get_allocated_size(), (
+            f"{self._written_bytes} + {len(self._to_write.getbuffer())} != {self.get_allocated_size()}"
         )
         d = self._actually_write()
         d.addCallback(lambda _: self._rref.callRemote("close"))