From 2b277dd558fc9a0e35b88374eaecaca635545c2c Mon Sep 17 00:00:00 2001
From: binares <remileopard@gmail.com>
Date: Thu, 1 Aug 2019 19:47:38 +0300
Subject: [PATCH] Fix (de)serialization of negative timestamps (#1241)

---
 telethon/extensions/binaryreader.py | 11 ++++++-----
 telethon/tl/tlobject.py             | 28 +++++++++++++++++++++-------
 2 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/telethon/extensions/binaryreader.py b/telethon/extensions/binaryreader.py
index 5382caaf..80b76f94 100644
--- a/telethon/extensions/binaryreader.py
+++ b/telethon/extensions/binaryreader.py
@@ -2,14 +2,18 @@
 This module contains the BinaryReader utility class.
 """
 import os
-from datetime import datetime, timezone
+from datetime import datetime, timezone, timedelta
 from io import BufferedReader, BytesIO
 from struct import unpack
+import time
 
 from ..errors import TypeNotFoundError
 from ..tl.alltlobjects import tlobjects
 from ..tl.core import core_objects
 
+_EPOCH_NAIVE = datetime(*time.gmtime(0)[:6])
+_EPOCH = _EPOCH_NAIVE.replace(tzinfo=timezone.utc)
+
 
 class BinaryReader:
     """
@@ -120,10 +124,7 @@ class BinaryReader:
            into a Python datetime object.
         """
         value = self.read_int()
-        if value == 0:
-            return None
-        else:
-            return datetime.fromtimestamp(value, tz=timezone.utc)
+        return _EPOCH + timedelta(seconds=value)
 
     def tgread_object(self):
         """Reads a Telegram object."""
diff --git a/telethon/tl/tlobject.py b/telethon/tl/tlobject.py
index 49a11d3b..451fad17 100644
--- a/telethon/tl/tlobject.py
+++ b/telethon/tl/tlobject.py
@@ -1,7 +1,21 @@
 import base64
 import json
 import struct
-from datetime import datetime, date, timedelta
+from datetime import datetime, date, timedelta, timezone
+import time
+
+_EPOCH_NAIVE = datetime(*time.gmtime(0)[:6])
+_EPOCH_NAIVE_LOCAL = datetime(*time.localtime(0)[:6])
+_EPOCH = _EPOCH_NAIVE.replace(tzinfo=timezone.utc)
+
+
+def _datetime_to_timestamp(dt):
+    # If no timezone is specified, it is assumed to be in utc zone
+    if dt.tzinfo is None:
+        dt = dt.replace(tzinfo=timezone.utc)
+    # We use .total_seconds() method instead of simply dt.timestamp(), 
+    # because on Windows the latter raises OSError on datetimes ~< datetime(1970,1,1)
+    return int((dt - _EPOCH).total_seconds())
 
 
 def _json_default(value):
@@ -121,21 +135,21 @@ class TLObject:
 
     @staticmethod
     def serialize_datetime(dt):
-        if not dt:
+        if not dt and not isinstance(dt, timedelta):
             return b'\0\0\0\0'
 
         if isinstance(dt, datetime):
-            dt = int(dt.timestamp())
+            dt = _datetime_to_timestamp(dt)
         elif isinstance(dt, date):
-            dt = int(datetime(dt.year, dt.month, dt.day).timestamp())
+            dt = _datetime_to_timestamp(datetime(dt.year, dt.month, dt.day))
         elif isinstance(dt, float):
             dt = int(dt)
         elif isinstance(dt, timedelta):
-            # Timezones are tricky. datetime.now() + ... timestamp() works
-            dt = int((datetime.now() + dt).timestamp())
+            # Timezones are tricky. datetime.utcnow() + ... timestamp() works
+            dt = _datetime_to_timestamp(datetime.utcnow() + dt)
 
         if isinstance(dt, int):
-            return struct.pack('<I', dt)
+            return struct.pack('<i', dt)
 
         raise TypeError('Cannot interpret "{}" as a date.'.format(dt))