Fix file uploads on python 3.4 and up.

CHANGES.rst

@@ -4,7 +4,14 @@ Changes
 4.3.1 (unreleased)
 ------------------
 
-- TBD
+- Fix file uploads on python 3.4 and up. cgi.FieldStorage explicitly
+  closes files when it is garbage collected. For details, see:
+
+  * http://bugs.python.org/issue18394
+  * https://hg.python.org/cpython/rev/c0e9ba7b26d5
+
+  We now keep a reference to the FieldStorage till we are finished
+  processing the request.
 
 
 4.3.0 (2016-07-04)

src/zope/publisher/browser.py

@@ -302,6 +302,14 @@ def processInputs(self):
         args = {'encoding': 'utf-8'} if not PYTHON2 else {}
         fs = ZopeFieldStorage(fp=fp, environ=env,
                               keep_blank_values=1, **args)
+        # On python 3.4 and up, FieldStorage explictly closes files
+        # when it is garbage collected
+        # see:
+        #   http://bugs.python.org/issue18394
+        #   https://hg.python.org/cpython/rev/c0e9ba7b26d5
+        # so we keep a reference to the FieldStorage till we are
+        # finished processing the request.
+        self.hold(fs)
 
         fslist = getattr(fs, 'list', None)
         if fslist is not None:

src/zope/publisher/tests/test_browserrequest.py

@@ -217,6 +217,8 @@ def testFileUploadPost(self):
         request.processInputs()
         self.assertEqual(request.form['upload'].filename, 'notepad.exe')
 
+        # Test that we can actually read the file data
+        self.assertEqual(request.form['upload'].read(), b'Some data')
 
     def testDefault2(self):
         extra = {'PATH_INFO': '/folder/item2/view'}