Re-merge "BigFile: Fixes, Tests and on-server Append support"

This reverts

    4f3bb0c9    (Revert "BigFile: Fixes, Tests and on-server Append support")

and thus continues the story of

    193f5cdd    (BigFile: Fixes, Tests and on-server Append support)

and essentially restores the result of that merge.

Initial idea was to give people time to better see how to handle code
submisstion, but in the end Romain approved it as is.

Reference: https://lab.nexedi.cn/nexedi/erp5/merge_requests/5 (= merge request !5)

bt5/erp5_big_file/SkinTemplateItem/portal_skins/erp5_big_file/BigFileModule_viewBigFileList.xml

@@ -2,7 +2,7 @@
 <ZopeData>
   <record id="1" aka="AAAAAAAAAAE=">
     <pickle>
-      <global name="ERP5Form" module="Products.ERP5Form.Form"/>
+      <global name="ERP5 Form" module="erp5.portal_type"/>
     </pickle>
     <pickle>
       <dictionary>

bt5/erp5_big_file/SkinTemplateItem/portal_skins/erp5_big_file/BigFile_view.xml

@@ -2,7 +2,7 @@
 <ZopeData>
   <record id="1" aka="AAAAAAAAAAE=">
     <pickle>
-      <global name="ERP5Form" module="Products.ERP5Form.Form"/>
+      <global name="ERP5 Form" module="erp5.portal_type"/>
     </pickle>
     <pickle>
       <dictionary>

bt5/erp5_big_file/TestTemplateItem/portal_components/test.erp5.testBigFile.py

+# ERP5.Document | Tests for BigFile
+#
+# Copyright (C) 2015 Nexedi SA and Contributors. All Rights Reserved.
+#               Kirill Smelkov <kirr@nexedi.com>
+#
+# WARNING: This program as such is intended to be used by professional
+# programmers who take the whole responsability of assessing all potential
+# consequences resulting from its eventual inadequacies and bugs
+# End users who are looking for a ready-to-use solution with commercial
+# garantees and support are strongly adviced to contract a Free Software
+# Service Company
+#
+# This program is Free Software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+from cStringIO import StringIO
+
+from ZPublisher.HTTPRequest import HTTPRequest
+from ZPublisher.HTTPResponse import HTTPResponse
+from Products.ERP5Type.tests.ERP5TypeTestCase import ERP5TypeTestCase
+from Products.ERP5Type.BTreeData import BTreeData
+
+
+# like Testing.makerequest, but
+#
+#   1. always redirects stdout to stringio,
+#   2. stdin content can be specified and is processed,
+#   3. returns actual request object (not wrapped portal).
+#
+# see also: Products.CMFCore.tests.test_CookieCrumbler.makerequest()
+# TODO makerequest() is generic enough and deserves moving to testing utils
+def makerequest(environ=None, stdin=''):
+  stdout = StringIO()
+  stdin  = StringIO(stdin)
+  if environ is None:
+    environ = {}
+
+  # Header-Name -> HEADER_NAME
+  _ = {}
+  for k,v in environ.items():
+    k = k.replace('-', '_').upper()
+    _[k] = v
+  environ = _
+
+  response = HTTPResponse(stdout=stdout)
+  environ.setdefault('SERVER_NAME',    'foo')
+  environ.setdefault('SERVER_PORT',    '80')
+  request  = HTTPRequest(stdin, environ, response)
+  # process stdin data
+  request.processInputs()
+  return request
+
+# generate makerequest-like function for http method
+def request_function(method_name):
+  method_name = method_name.upper()
+  def method_func(environ=None, stdin=''):
+    if environ is None:
+      environ = {}
+    environ.setdefault('REQUEST_METHOD', method_name)
+    return makerequest(environ, stdin)
+  method_func.func_name = method_name
+  return method_func
+
+# requests
+get = request_function('GET')
+put = request_function('PUT')
+
+
+# FIXME Zope translates 308 to 500
+# https://github.com/zopefoundation/Zope/blob/2.13/src/ZPublisher/HTTPResponse.py#L223
+# https://github.com/zopefoundation/Zope/blob/2.13/src/ZPublisher/HTTPResponse.py#L64
+R308 = 500
+
+
+
+class TestBigFile(ERP5TypeTestCase):
+  """Tests for ERP5.Document.BigFile"""
+
+  def getBusinessTemplateList(self):
+    """bt5 required to run this tests"""
+    return ('erp5_big_file',
+               # test runner does not automatically install bt5 dependencies -
+               # - next erp5_big_file dependencies are specified manually
+               'erp5_dms',
+                 'erp5_web',
+                 'erp5_ingestion',
+                 'erp5_base',
+               )[::-1]	# NOTE install order is important
+
+
+  # check that object (document) method corresponding to request returns
+  # result, with expected response body, status and headers
+  def checkRequest(self, document, request, kw, result, body, status, header_dict):
+    # request -> method to call
+    method_name = request['REQUEST_METHOD']
+    if method_name == 'GET':
+      method_name = 'index_html'
+    method = getattr(document, method_name)
+
+    ret = method (request, request.RESPONSE, **kw)
+    # like in ZPublisher - returned RESPONSE means empty
+    if ret is request.RESPONSE:
+      ret = ''
+    self.assertEqual(ret,       result)
+    self.assertEqual(status,    request.RESPONSE.getStatus())
+    for h,v in header_dict.items():
+      rv = request.RESPONSE.getHeader(h)
+      self.assertEqual(v, rv, '%s: %r != %r' % (h, v, rv))
+
+    # force response flush to its stdout
+    request.RESPONSE.write('')
+    # body and headers are delimited by empty line (RFC 2616, 4.1)
+    response_body = request.RESPONSE.stdout.getvalue().split('\r\n\r\n', 1)[1]
+    self.assertEqual(body, response_body)
+
+
+  # basic tests for working with BigFile via its public interface
+  def testBigFile_01_Basic(self):
+    big_file_module = self.getPortal().big_file_module
+    f = big_file_module.newContent(portal_type='Big File')
+    check = lambda *args: self.checkRequest(f, *args)
+
+
+    # after creation file is empty and get(0-0) returns 416
+    self.assertEqual(f.getSize(), 0)
+    self.assertEqual(f.getData(), '')
+
+                                             #  result body status headers
+    check(get(), {'format': 'raw'},                 '', '', 200, {'Content-Length': '0'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '',R308, {                                  'Range': 'bytes 0--1'})  # XXX 0--1 ok?
+    check(get({        'Range': 'bytes=0-0'}),{},   '', '', 416, {'Content-Length': '0',    'Content-Range': 'bytes */0'})
+
+
+    # append empty chunk - the same
+    f._appendData('')
+    self.assertEqual(f.getSize(), 0)
+    self.assertEqual(f.getData(), '')
+
+    check(get(), {'format': 'raw'},                 '', '', 200, {'Content-Length': '0'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '',R308, {                                  'Range': 'bytes 0--1'})  # XXX 0--1 ok?
+    check(get({        'Range': 'bytes=0-0'}),{},   '', '', 416, {                          'Content-Range': 'bytes */0'})
+
+
+    # append 1 byte - file should grow up and get(0-0) returns 206
+    f._appendData('x')
+    self.assertEqual(f.getSize(), 1)
+    self.assertEqual(f.getData(), 'x')
+
+    check(get(), {'format': 'raw'},                 '', 'x', 200, {'Content-Length': '1'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '', R308, {                                'Range': 'bytes 0-0'})
+    check(get({        'Range': 'bytes=0-0'}),{},   '', 'x', 206, {'Content-Length': '1',  'Content-Range': 'bytes 0-0/1'})
+
+
+    # append another 2 bytes and try to get whole file and partial contents
+    f._appendData('yz')
+    self.assertEqual(f.getSize(), 3)
+    self.assertEqual(f.getData(), 'xyz')
+
+    check(get(), {'format': 'raw'},                 '', 'xyz',  200, {'Content-Length': '3'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '',    R308, {                                'Range': 'bytes 0-2'})
+    check(get({        'Range': 'bytes=0-0'}),{},   '', 'x'  ,  206, {'Content-Length': '1',  'Content-Range': 'bytes 0-0/3'})
+    check(get({        'Range': 'bytes=1-1'}),{},   '',  'y' ,  206, {'Content-Length': '1',  'Content-Range': 'bytes 1-1/3'})
+    check(get({        'Range': 'bytes=2-2'}),{},   '',   'z',  206, {'Content-Length': '1',  'Content-Range': 'bytes 2-2/3'})
+    check(get({        'Range': 'bytes=0-1'}),{},   '', 'xy' ,  206, {'Content-Length': '2',  'Content-Range': 'bytes 0-1/3'})
+    check(get({        'Range': 'bytes=1-2'}),{},   '',  'yz',  206, {'Content-Length': '2',  'Content-Range': 'bytes 1-2/3'})
+    check(get({        'Range': 'bytes=0-2'}),{},   '', 'xyz',  206, {'Content-Length': '3',  'Content-Range': 'bytes 0-2/3'})
+
+    # append via PUT with range
+    check(put({'Content-Range': 'bytes 3-4/5', 'Content-Length': '2'}, '01'),{},  '', '', 204, {})
+    self.assertEqual(f.getSize(), 5)
+    self.assertEqual(f.getData(), 'xyz01')
+    check(get(), {'format': 'raw'},                 '', 'xyz01',200, {'Content-Length': '5'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '',    R308, {                                'Range': 'bytes 0-4'})
+    check(get({        'Range': 'bytes=0-4'}),{},   '', 'xyz01',206, {'Content-Length': '5',  'Content-Range': 'bytes 0-4/5'})
+    check(get({        'Range': 'bytes=1-3'}),{},   '',  'yz0' ,206, {'Content-Length': '3',  'Content-Range': 'bytes 1-3/5'})
+    check(get({        'Range': 'bytes=1-2'}),{},   '',  'yz'  ,206, {'Content-Length': '2',  'Content-Range': 'bytes 1-2/5'})
+    check(get({        'Range': 'bytes=2-2'}),{},   '',   'z'  ,206, {'Content-Length': '1',  'Content-Range': 'bytes 2-2/5'})
+
+    # replace whole content via PUT without range
+    # (and we won't exercise GET with range routinely further)
+    check(put({'Content-Length': '3'}, 'abc'),{},  '', '', 204, {})
+    self.assertEqual(f.getSize(), 3)
+    self.assertEqual(f.getData(), 'abc')
+    check(get(), {'format': 'raw'},                 '', 'abc',  200, {'Content-Length': '3'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '',    R308, {                                'Range': 'bytes 0-2'})
+
+    # append via PUT with range (again)
+    check(put({'Content-Range': 'bytes 3-7/8', 'Content-Length': '5'}, 'defgh'),{},  '', '', 204, {})
+    self.assertEqual(f.getSize(), 8)
+    self.assertEqual(f.getData(), 'abcdefgh')
+    check(get(), {'format': 'raw'},                 '', 'abcdefgh', 200, {'Content-Length': '8'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '',        R308, {                            'Range': 'bytes 0-7'})
+
+    # append via ._appendData()  (again)
+    f._appendData('ij')
+    self.assertEqual(f.getSize(), 10)
+    self.assertEqual(f.getData(), 'abcdefghij')
+    check(get(), {'format': 'raw'},                 '', 'abcdefghij', 200, {'Content-Length': '10'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '',          R308, {                          'Range': 'bytes 0-9'})
+
+    # make sure PUT with incorrect/non-append range is rejected
+    check(put({'Content-Range': 'bytes 10-10/10', 'Content-Length': '1'}, 'k'),{}, '', '', 400, {'X-Explanation': 'Total size unexpected'})
+    self.assertEqual(f.getData(), 'abcdefghij')
+    check(put({'Content-Range': 'bytes 10-10/11', 'Content-Length': '2'}, 'k'),{}, '', '', 400, {'X-Explanation': 'Content length unexpected'})
+    self.assertEqual(f.getData(), 'abcdefghij')
+    check(put({'Content-Range': 'bytes 8-8/10',   'Content-Length': '1'}, '?'),{}, '', '', 400, {'X-Explanation': 'Can only append data'})
+    check(put({'Content-Range': 'bytes 9-9/10',   'Content-Length': '1'}, '?'),{}, '', '', 400, {'X-Explanation': 'Can only append data'})
+    check(put({'Content-Range': 'bytes 9-10/11',  'Content-Length': '2'},'??'),{}, '', '', 400, {'X-Explanation': 'Can only append data'})
+    check(put({'Content-Range': 'bytes 11-11/12', 'Content-Length': '1'}, '?'),{}, '', '', 400, {'X-Explanation': 'Can only append data'})
+
+    # TODO test 'If-Range' with GET
+    # TODO test multiple ranges in 'Range' with GET
+
+
+  # test BigFile's .data property can be of several types and is handled
+  # properly and we can still get data and migrate to BTreeData transparently
+  # (called from under testBigFile_02_DataVarious driver)
+  def _testBigFile_02_DataVarious(self):
+    # BigFile's .data can be:
+    # str       - because data comes from Data property sheet and default value is ''
+    # None      - because it can be changed
+    # BTreeData - because it is scalable way to work with large content
+    #
+    # str can be possibly non-empty because we could want to transparently
+    # migrate plain File documents to BigFiles.
+    #
+    # make sure BigFile correctly works in all those situations.
+
+    big_file_module = self.getPortal().big_file_module
+    f = big_file_module.newContent(portal_type='Big File')
+    check = lambda *args: self.checkRequest(f, *args)
+
+    # after creation .data is ''  (as per default from Data property sheet)
+    _ = f._baseGetData()
+    self.assertIsInstance(_, str)
+    self.assertEqual(_, '')
+
+    # make sure we can get empty content through all ways
+    # (already covered in testBigFile_01_Basic, but still)
+    self.assertEqual(f.getSize(), 0)
+    self.assertEqual(f.getData(), '')
+    check(get(), {'format': 'raw'},                 '', '', 200, {'Content-Length': '0'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '',R308, {                                'Range': 'bytes 0--1'})  # XXX 0--1 ok?
+    check(get({        'Range': 'bytes=0-0'}),{},   '', '', 416, {'Content-Length': '0',  'Content-Range': 'bytes */0'})
+
+
+    # set .data to non-empty str and make sure we can get content through all ways
+    f._baseSetData('abc')
+    _ = f._baseGetData()
+    self.assertIsInstance(_, str)
+    self.assertEqual(_, 'abc')
+    self.assertEqual(f.getSize(), 3)
+    self.assertEqual(f.getData(), 'abc')
+    check(get(), {'format': 'raw'},                 'abc', '',    200, {'Content-Length': '3'})
+    check(put({'Content-Range': 'bytes */*'}),{},   ''   , '',   R308, {                                'Range': 'bytes 0-2'})
+    check(get({        'Range': 'bytes=0-2'}),{},   ''   , 'abc', 206, {'Content-Length': '3',  'Content-Range': 'bytes 0-2/3'})
+
+    # and .data should remain str after access (though later this could be
+    # changed to transparently migrate to BTreeData)
+    _ = f._baseGetData()
+    self.assertIsInstance(_, str)
+    self.assertEqual(_, 'abc')
+
+
+    # on append .data should migrate to BTreeData
+    f._appendData('d')
+    _ = f._baseGetData()
+    self.assertIsInstance(_, BTreeData)
+    self.assertEqual(f.getSize(), 4)
+    self.assertEqual(f.getData(), 'abcd')
+    check(get(), {'format': 'raw'},                 '', 'abcd', 200, {'Content-Length': '4'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '',    R308, {                                'Range': 'bytes 0-3'})
+    check(get({        'Range': 'bytes=0-3'}),{},   '', 'abcd', 206, {'Content-Length': '4',  'Content-Range': 'bytes 0-3/4'})
+
+
+
+    # change .data to None and make sure we can still get empty content
+    # NOTE additionally to ._baseSetData(None), ._setData(None) also sets
+    #      .size=0 which is needed for correct BigFile bases operation.
+    #
+    #      see ERP5.Document.File._setSize() for details.
+    f._setData(None)
+    # NOTE still '' because it is default value specified in Data property
+    #      sheet for .data field
+    _ = f._baseGetData()
+    self.assertIsInstance(_, str)
+    self.assertEqual(_, '')
+    # but we can change property sheet default on the fly
+    # XXX ( only for this particular getter _baseGetData -
+    #       - because property type information is not stored in one place,
+    #       but is copied on getter/setter initialization - see Getter/Setter
+    #       in ERP5Type.Accessor.Base )
+    # NOTE this change is automatically reverted back in calling helper
+    self.assertIsInstance(f._baseGetData._default, str)
+    self.assertEqual(f._baseGetData._default, '')
+    f._baseGetData.im_func._default = None  # NOTE not possible to do on just f._baseGetData
+    self.assertIs(f._baseGetData._default, None)
+    self.assertIs(f._baseGetData(), None)   # <- oops
+
+    self.assertEqual(f.getSize(), 0)
+    self.assertIs   (f.getData(), None)
+    check(get(), {'format': 'raw'},                 '', '', 200, {'Content-Length': '0'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '',R308, {                                'Range': 'bytes 0--1'})  # XXX 0--1 ok?
+    check(get({        'Range': 'bytes=0-0'}),{},   '', '', 416, {'Content-Length': '0',  'Content-Range': 'bytes */0'})
+
+
+    # on append .data should become BTreeData
+    f._appendData('x')
+    _ = f._baseGetData()
+    self.assertIsInstance(_, BTreeData)
+    self.assertEqual(f.getSize(), 1)
+    self.assertEqual(f.getData(), 'x')
+    check(get(), {'format': 'raw'},                 '', 'x',    200, {'Content-Length': '1'})
+    check(put({'Content-Range': 'bytes */*'}),{},   '', '',    R308, {                                'Range': 'bytes 0-0'})
+    check(get({        'Range': 'bytes=0-3'}),{},   '', 'x',    206, {'Content-Length': '1',  'Content-Range': 'bytes 0-0/1'})
+
+
+
+  # helper to call _testBigFile_02_DataVarious() and restore .data._default
+  def testBigFile_02_DataVarious(self):
+    big_file_module = self.getPortal().big_file_module
+    f = big_file_module.newContent(portal_type='Big File')
+
+    # Data property sheet specifies .data default to ''
+    _ = f._baseGetData()
+    self.assertIsInstance(_, str)
+    self.assertEqual(_, '')
+
+    # NOTE obtaining getter is not possible via BigFile._baseGetData
+    g = f._baseGetData.im_func
+    self.assertIsInstance(g._default, str)
+    self.assertEqual(g._default, '')
+
+    try:
+      self._testBigFile_02_DataVarious()
+
+    # restore ._baseGetData._default and make sure restoration really worked
+    finally:
+      g._default = ''
+      f._baseSetData(None)    # so that we are sure getter returns class defaults
+      _ = f._baseGetData()
+      self.assertIsInstance(_, str)
+      self.assertEqual(_, '')
+
+
+
+  # TODO write big data to file and ensure it still works
+  # TODO test streaming works in chunks

bt5/erp5_big_file/TestTemplateItem/portal_components/test.erp5.testBigFile.xml

+<?xml version="1.0"?>
+<ZopeData>
+  <record id="1" aka="AAAAAAAAAAE=">
+    <pickle>
+      <global name="Test Component" module="erp5.portal_type"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>_recorded_property_dict</string> </key>
+            <value>
+              <persistent> <string encoding="base64">AAAAAAAAAAI=</string> </persistent>
+            </value>
+        </item>
+        <item>
+            <key> <string>default_reference</string> </key>
+            <value> <string>testBigFile</string> </value>
+        </item>
+        <item>
+            <key> <string>description</string> </key>
+            <value>
+              <none/>
+            </value>
+        </item>
+        <item>
+            <key> <string>id</string> </key>
+            <value> <string>test.erp5.testBigFile</string> </value>
+        </item>
+        <item>
+            <key> <string>portal_type</string> </key>
+            <value> <string>Test Component</string> </value>
+        </item>
+        <item>
+            <key> <string>sid</string> </key>
+            <value>
+              <none/>
+            </value>
+        </item>
+        <item>
+            <key> <string>text_content_error_message</string> </key>
+            <value>
+              <tuple/>
+            </value>
+        </item>
+        <item>
+            <key> <string>text_content_warning_message</string> </key>
+            <value>
+              <tuple/>
+            </value>
+        </item>
+        <item>
+            <key> <string>version</string> </key>
+            <value> <string>erp5</string> </value>
+        </item>
+        <item>
+            <key> <string>workflow_history</string> </key>
+            <value>
+              <persistent> <string encoding="base64">AAAAAAAAAAM=</string> </persistent>
+            </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+  <record id="2" aka="AAAAAAAAAAI=">
+    <pickle>
+      <global name="PersistentMapping" module="Persistence.mapping"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>data</string> </key>
+            <value>
+              <dictionary/>
+            </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+  <record id="3" aka="AAAAAAAAAAM=">
+    <pickle>
+      <global name="PersistentMapping" module="Persistence.mapping"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>data</string> </key>
+            <value>
+              <dictionary>
+                <item>
+                    <key> <string>component_validation_workflow</string> </key>
+                    <value>
+                      <persistent> <string encoding="base64">AAAAAAAAAAQ=</string> </persistent>
+                    </value>
+                </item>
+              </dictionary>
+            </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+  <record id="4" aka="AAAAAAAAAAQ=">
+    <pickle>
+      <global name="WorkflowHistoryList" module="Products.ERP5Type.patches.WorkflowTool"/>
+    </pickle>
+    <pickle>
+      <tuple>
+        <none/>
+        <list>
+          <dictionary>
+            <item>
+                <key> <string>action</string> </key>
+                <value> <string>validate</string> </value>
+            </item>
+            <item>
+                <key> <string>validation_state</string> </key>
+                <value> <string>validated</string> </value>
+            </item>
+          </dictionary>
+        </list>
+      </tuple>
+    </pickle>
+  </record>
+</ZopeData>

bt5/erp5_big_file/bt/change_log

+1.1 added tests for BigFile

bt5/erp5_big_file/bt/template_test_id_list

+test.erp5.testBigFile
\ No newline at end of file

bt5/erp5_big_file/bt/test_dependency_list

+erp5_full_text_mroonga_catalog
\ No newline at end of file

bt5/erp5_big_file/bt/version

-1
\ No newline at end of file
+1.1
\ No newline at end of file

product/ERP5/Document/BigFile.py

@@ -24,14 +24,42 @@ from ZPublisher.HTTPRequest import FileUpload
 from ZPublisher import HTTPRangeSupport
 from webdav.common import rfc1123_date
 from mimetools import choose_boundary
-from Products.CMFCore.utils import getToolByName, _setCacheHeaders,\
-    _ViewEmulator
+from Products.CMFCore.utils import _setCacheHeaders, _ViewEmulator
+from DateTime import DateTime
 import re
 
 class BigFile(File):
   """
   Support storing huge file.
   No convertion is allowed for now.
+
+
+  NOTE BigFile maintains the following invariant:
+
+    data property is either
+
+      - BTreeData instance,  or
+      - str(*),  or
+      - None.
+
+    (*) str has to be supported because '' is a default value for `data` field
+        from Data property sheet.
+
+        Even more - for
+
+            a) compatibility reasons, and
+            b) desire to support automatic migration of File-based documents
+               from document_module to BigFiles
+
+        non-empty str for data also have to be supported.
+
+        XXX(kirr) I'm not sure supporting non-empty str is a good idea (it
+            would be simpler if .data could be either BTreeData or "empty"),
+            but neither I'm experienced enough in erp5 nor know what are
+            appropriate compatibility requirements.
+
+            We discussed with Romain and settled on "None or str or BTreeData"
+            invariant for now.
   """
 
   meta_type = 'ERP5 Big File'
@@ -98,6 +126,11 @@ class BigFile(File):
 
     if data is None:
       btree = BTreeData()
+    elif isinstance(data, str):
+      # we'll want to append content to this file -
+      # - automatically convert str (empty or not) to BTreeData
+      btree = BTreeData()
+      btree.write(data, 0)
     else:
       btree = data
     seek(0)
@@ -116,6 +149,14 @@ class BigFile(File):
       self.serialize()
     return btree, len(btree)
 
+  def _data_mtime(self):
+    """get .data mtime if present and fallback to self._p_mtime"""
+    # there is no data._p_mtime when data is None or str.
+    # so try and fallback to self._p_mtime
+    data = self._baseGetData()
+    mtime = getattr(data, '_p_mtime', self._p_mtime)
+    return mtime
+
   def _range_request_handler(self, REQUEST, RESPONSE):
     # HTTP Range header handling: return True if we've served a range
     # chunk out of our data.
@@ -147,13 +188,10 @@ class BigFile(File):
           try: mod_since=long(DateTime(date).timeTime())
           except: mod_since=None
           if mod_since is not None:
-            if data is not None:
-              last_mod = long(data._p_mtime)
-            else:
-              if self._p_mtime:
-                last_mod = long(self._p_mtime)
-              else:
-                last_mod = long(0)
+            last_mod = self._data_mtime()
+            if last_mod is None:
+                last_mod = 0
+            last_mod = long(last_mod)
             if last_mod > mod_since:
               # Modified, so send a normal response. We delete
               # the ranges, which causes us to skip to the 200
@@ -172,10 +210,7 @@ class BigFile(File):
           RESPONSE.setHeader('Content-Range',
               'bytes */%d' % self.getSize())
           RESPONSE.setHeader('Accept-Ranges', 'bytes')
-          if data is not None:
-            RESPONSE.setHeader('Last-Modified', rfc1123_date(data._p_mtime))
-          else:
-            RESPONSE.setHeader('Last-Modified', rfc1123_date(self._p_mtime))
+          RESPONSE.setHeader('Last-Modified', rfc1123_date(self._data_mtime()))
           RESPONSE.setHeader('Content-Type', self.content_type)
           RESPONSE.setHeader('Content-Length', self.getSize())
           RESPONSE.setStatus(416)
@@ -188,10 +223,7 @@ class BigFile(File):
           start, end = ranges[0]
           size = end - start
 
-          if data is not None:
-            RESPONSE.setHeader('Last-Modified', rfc1123_date(data._p_mtime))
-          else:
-            RESPONSE.setHeader('Last-Modified', rfc1123_date(self._p_mtime))
+          RESPONSE.setHeader('Last-Modified', rfc1123_date(self._data_mtime()))
           RESPONSE.setHeader('Content-Type', self.content_type)
           RESPONSE.setHeader('Content-Length', size)
           RESPONSE.setHeader('Accept-Ranges', 'bytes')
@@ -199,6 +231,7 @@ class BigFile(File):
               'bytes %d-%d/%d' % (start, end - 1, self.getSize()))
           RESPONSE.setStatus(206) # Partial content
 
+          # NOTE data cannot be None here (if it is - ranges are not satisfiable)
           if isinstance(data, str):
             RESPONSE.write(data[start:end])
             return True
@@ -227,10 +260,7 @@ class BigFile(File):
 
           RESPONSE.setHeader('Content-Length', size)
           RESPONSE.setHeader('Accept-Ranges', 'bytes')
-          if data is not None:
-            RESPONSE.setHeader('Last-Modified', rfc1123_date(data._p_mtime))
-          else:
-            RESPONSE.setHeader('Last-Modified', rfc1123_date(self._p_mtime))
+          RESPONSE.setHeader('Last-Modified', rfc1123_date(self._data_mtime()))
           RESPONSE.setHeader('Content-Type',
               'multipart/%sbyteranges; boundary=%s' % (
                   draftprefix, boundary))
@@ -244,6 +274,7 @@ class BigFile(File):
                 'Content-Range: bytes %d-%d/%d\r\n\r\n' % (
                     start, end - 1, self.getSize()))
 
+            # NOTE data cannot be None here (if it is - ranges are not satisfiable)
             if isinstance(data, str):
               RESPONSE.write(data[start:end])
 
@@ -280,7 +311,7 @@ class BigFile(File):
     data = self._baseGetData()
     mime = self.getContentType()
 
-    RESPONSE.setHeader('Content-Length', len(data))
+    RESPONSE.setHeader('Content-Length', data is not None and  len(data)  or  0)
     RESPONSE.setHeader('Content-Type', mime)
     if inline is _MARKER:
       # by default, use inline for text and image formats
@@ -313,7 +344,8 @@ class BigFile(File):
 
     content_range = REQUEST.get_header('Content-Range', None)
     if content_range is None:
-      btree = None
+      # truncate the file
+      self._baseSetData(None)
     else:
       current_size = int(self.getSize())
       query_range = re.compile('bytes \*/\*')
@@ -321,8 +353,6 @@ class BigFile(File):
                                 '(?P<last_byte>[0-9]+)/' \
                                 '(?P<total_content_length>[0-9]+)')
       if query_range.match(content_range):
-        data = self._baseGetData()
-
         RESPONSE.setHeader('X-Explanation', 'Resume incomplete')
         RESPONSE.setHeader('Range', 'bytes 0-%s' % (current_size-1))
         RESPONSE.setStatus(308)
@@ -349,26 +379,29 @@ class BigFile(File):
           RESPONSE.setStatus(400)
           return RESPONSE
 
-        else:
-
-          btree = self._baseGetData()
-          if btree is None:
-            btree = BTreeData()
-
       else:
         RESPONSE.setHeader('X-Explanation', 'Can not parse range')
         RESPONSE.setStatus(400) # Partial content
         return RESPONSE
 
-    data, size = self._read_data(file, data=btree)
-
-    content_type=self._get_content_type(file, data, self.__name__,
-                                        type or self.content_type)
-    self.update_data(data, content_type, size)
+    self._appendData(file, content_type=type)
 
     RESPONSE.setStatus(204)
     return RESPONSE
 
+
+  def _appendData(self, data_chunk, content_type=None):
+    """append data chunk to the end of the file
+
+       NOTE if content_type is specified, it will change content_type for the
+            whole file.
+    """
+    data, size = self._read_data(data_chunk, data=self._baseGetData())
+    content_type=self._get_content_type(data_chunk, data, self.__name__,
+                                        content_type or self.content_type)
+    self.update_data(data, content_type, size)
+
+
 # CMFFile also brings the IContentishInterface on CMF 2.2, remove it.
 removeIContentishInterface(BigFile)