fix potential problems when BFSS uses a Windows SMB share (closes #2131435)

files on windows network share must be read / written by chunks of reasonable size
or you get some unusual os level errors.

--HG--
branch : stable

__init__.py

@@ -76,6 +76,49 @@ class Binary(StringIO):
                "Binary objects must use raw strings, not %s" % data.__class__
         StringIO.write(self, data)
 
+    def to_file(self, filename):
+        """write a binary to disk
+
+        the writing is performed in a safe way for files stored on
+        Windows SMB shares
+        """
+        pos = self.tell()
+        with open(filename, 'wb') as fobj:
+            self.seek(0)
+            if sys.platform == 'win32':
+                while True:
+                    # the 16kB chunksize comes from the shutil module
+                    # in stdlib
+                    chunk = self.read(16*1024)
+                    if not chunk:
+                        break
+                    fobj.write(chunk)
+            else:
+                fobj.write(self.read())
+        self.seek(pos)
+
+    @staticmethod
+    def from_file(filename):
+        """read a file and returns its contents in a Binary
+
+        the reading is performed in a safe way for files stored on
+        Windows SMB shares
+        """
+        binary = Binary()
+        with open(filename, 'rb') as fobj:
+            if sys.platform == 'win32':
+                while True:
+                    # the 16kB chunksize comes from the shutil module
+                    # in stdlib
+                    chunk = fobj.read(16*1024)
+                    if not chunk:
+                        break
+                    binary.write(chunk)
+            else:
+                binary.write(fobj.read())
+        return binary
+
+
 # use this dictionary to rename entity types while keeping bw compat
 ETYPE_NAME_MAP = {}
 

server/sources/storages.py

@@ -17,6 +17,7 @@
 # with CubicWeb.  If not, see <http://www.gnu.org/licenses/>.
 """custom storages for the system source"""
 
+import os
 from os import unlink, path as osp
 from contextlib import contextmanager
 
@@ -121,7 +122,7 @@ class BytesFileSystemStorage(Storage):
         """
         fpath = source.binary_to_str(value)
         try:
-            return Binary(file(fpath, 'rb').read())
+            return Binary.from_file(fpath)
         except EnvironmentError, ex:
             source.critical("can't open %s: %s", value, ex)
             return None
@@ -129,18 +130,18 @@ class BytesFileSystemStorage(Storage):
     def entity_added(self, entity, attr):
         """an entity using this storage for attr has been added"""
         if entity._cw.transaction_data.get('fs_importing'):
-            binary = Binary(file(entity.cw_edited[attr].getvalue(), 'rb').read())
+            binary = Binary.from_file(entity.cw_edited[attr].getvalue())
         else:
             binary = entity.cw_edited.pop(attr)
             fpath = self.new_fs_path(entity, attr)
             # bytes storage used to store file's path
             entity.cw_edited.edited_attribute(attr, Binary(fpath))
-            file(fpath, 'wb').write(binary.getvalue())
+            binary.to_file(fpath)
             AddFileOp.get_instance(entity._cw).add_data(fpath)
         return binary
 
     def entity_updated(self, entity, attr):
-        """an entity using this storage for attr has been updatded"""
+        """an entity using this storage for attr has been updated"""
         # get the name of the previous file containing the value
         oldpath = self.current_fs_path(entity, attr)
         if entity._cw.transaction_data.get('fs_importing'):
@@ -149,7 +150,7 @@ class BytesFileSystemStorage(Storage):
             # the file as the actual content of the attribute
             fpath = entity.cw_edited[attr].getvalue()
             assert fpath is not None
-            binary = Binary(file(fpath, 'rb').read())
+            binary = Binary.from_file(fpath)
         else:
             # We must store the content of the attributes
             # into a file to stay consistent with the behaviour of entity_add.
@@ -168,7 +169,7 @@ class BytesFileSystemStorage(Storage):
                 fpath = self.new_fs_path(entity, attr)
                 assert not osp.exists(fpath)
                 # write attribute value on disk
-                file(fpath, 'wb').write(binary.getvalue())
+                binary.to_file(fpath)
                 # Mark the new file as added during the transaction.
                 # The file will be removed on rollback
                 AddFileOp.get_instance(entity._cw).add_data(fpath)
@@ -208,9 +209,9 @@ class BytesFileSystemStorage(Storage):
         return fspath
 
     def current_fs_path(self, entity, attr):
-        """return the current fs_path of the tribute.
-
-        Return None is the attr is not stored yet."""
+        """return the current fs_path of the attribute, or None is the attr is
+        not stored yet.
+        """
         sysource = entity._cw.cnxset.source('system')
         cu = sysource.doexec(entity._cw,
                              'SELECT cw_%s FROM cw_%s WHERE cw_eid=%s' % (