Fix a year 2038 issue

the utcnow assumtion in the test failed for dates after 2038-01-19
because the date wraps back to 1902

This bug was found while working on reproducible builds for openSUSE.

bson/objectid.py

@@ -158,7 +158,7 @@ def from_datetime(cls, generation_time):
  generation_time = generation_time - generation_time.utcoffset()
  timestamp = calendar.timegm(generation_time.timetuple())
  oid = struct.pack(
- ">i", int(timestamp)) + b"\x00\x00\x00\x00\x00\x00\x00\x00"
+ ">L", int(timestamp) & 0xFFFFFFFF) + b"\x00\x00\x00\x00\x00\x00\x00\x00"
  return cls(oid)
 
  @classmethod
@@ -184,7 +184,7 @@ def __generate(self):
  """
 
  # 4 bytes current time
- oid = struct.pack(">i", int(time.time()))
+ oid = struct.pack(">L", int(time.time()) & 0xFFFFFFFF)
 
  # 3 bytes machine
  oid += ObjectId._machine_bytes

bson/tests/test_objectid.py

@@ -522,7 +522,7 @@ def test_from_datetime(self):
  if 'PyPy 1.8.0' in sys.version:
  # See https://bugs.pypy.org/issue1092
  raise SkipTest("datetime.timedelta is broken in pypy 1.8.0")
- d = datetime.datetime.utcnow()
+ d = datetime.datetime.utcfromtimestamp(2000000000)
  d = d - datetime.timedelta(microseconds=d.microsecond)
  oid = ObjectId.from_datetime(d)
  self.assertEqual(d, oid.generation_time.replace(tzinfo=None))