Revert change to use time.strftime (from 3.0).

time.strftime is influenced by the user's locale (if one is set with
locale.setlocale), so it's not what we want.  Go back to the (slower)
email.utils functions.

Fixes #800.

tornado/httputil.py

@@ -18,8 +18,10 @@
 
 from __future__ import absolute_import, division, print_function, with_statement
 
+import calendar
 import collections
 import datetime
+import email.utils
 import numbers
 import re
 import time
@@ -382,15 +384,15 @@ def format_timestamp(ts):
     >>> format_timestamp(1359312200)
     'Sun, 27 Jan 2013 18:43:20 GMT'
     """
-    if isinstance(ts, (tuple, time.struct_time)):
+    if isinstance(ts, numbers.Real):
         pass
+    elif isinstance(ts, (tuple, time.struct_time)):
+        ts = calendar.timegm(ts)
     elif isinstance(ts, datetime.datetime):
-        ts = ts.utctimetuple()
-    elif isinstance(ts, numbers.Real):
-        ts = time.gmtime(ts)
+        ts = calendar.timegm(ts.utctimetuple())
     else:
         raise TypeError("unknown timestamp type: %r" % ts)
-    return time.strftime("%a, %d %b %Y %H:%M:%S GMT", ts)
+    return email.utils.formatdate(ts, usegmt=True)
 
 # _parseparam and _parse_header are copied and modified from python2.7's cgi.py
 # The original 2.7 version of this code did not correctly support some

tornado/test/runtests.py

@@ -2,6 +2,7 @@
 
 from __future__ import absolute_import, division, print_function, with_statement
 import gc
+import locale  # system locale module, not tornado.locale
 import logging
 import operator
 import textwrap
@@ -95,6 +96,8 @@ if __name__ == '__main__':
            "e.g. DEBUG_STATS or DEBUG_COLLECTABLE,DEBUG_OBJECTS",
            callback=lambda values: gc.set_debug(
             reduce(operator.or_, (getattr(gc, v) for v in values))))
+    define('locale', type=str, default=None,
+           callback=lambda x: locale.setlocale(locale.LC_ALL, x))
 
     def configure_ioloop():
         kwargs = {}

tornado/test/web_test.py

@@ -13,6 +13,7 @@ from tornado.web import RequestHandler, authenticated, Application, asynchronous
 
 import binascii
 import datetime
+import email.utils
 import logging
 import os
 import re
@@ -1160,8 +1161,8 @@ class DateHeaderTest(SimpleHandlerTestCase):
 
     def test_date_header(self):
         response = self.fetch('/')
-        header_date = datetime.datetime.strptime(response.headers['Date'],
-                                                 "%a, %d %b %Y %H:%M:%S GMT")
+        header_date = datetime.datetime(
+            *email.utils.parsedate(response.headers['Date'])[:6])
         self.assertTrue(header_date - datetime.datetime.utcnow() <
                         datetime.timedelta(seconds=2))
 

tornado/web.py

@@ -239,7 +239,7 @@ class RequestHandler(object):
         self._headers = httputil.HTTPHeaders({
             "Server": "TornadoServer/%s" % tornado.version,
             "Content-Type": "text/html; charset=UTF-8",
-            "Date": httputil.format_timestamp(time.gmtime()),
+            "Date": httputil.format_timestamp(time.time()),
         })
         self.set_default_headers()
         if (not self.request.supports_http_1_1() and

tox.ini

@@ -11,7 +11,7 @@
 [tox]
 # "-full" variants include optional dependencies, to ensure
 # that things work both in a bare install and with all the extras.
-envlist = py27-full, py27-curl, py32-full, pypy, py26, py26-full, py27, py32, py32-utf8, py33, py27-opt, py32-opt, pypy-full, py27-select, py27-monotonic, py33-monotonic, py27-twisted, py27-threadedresolver, py27-twistedresolver, py27-twistedlayered, py27-caresresolver, py32-caresresolver, py27-docs
+envlist = py27-full, py27-curl, py32-full, pypy, py26, py26-full, py27, py32, py32-utf8, py33, py27-opt, py32-opt, pypy-full, py27-select, py27-monotonic, py33-monotonic, py27-twisted, py27-threadedresolver, py27-twistedresolver, py27-twistedlayered, py27-caresresolver, py32-caresresolver, py27-locale, py27-docs
 [testenv]
 commands = python -m tornado.test.runtests {posargs:}
 
@@ -138,6 +138,10 @@ deps =
      twisted
 commands = python -m tornado.test.runtests --resolver=tornado.platform.caresresolver.CaresResolver {posargs:}
 
+[testenv:py27-locale]
+basepython = python2.7
+commands = python -m tornado.test.runtests --locale=zh_TW {posargs:}
+
 [testenv:pypy-full]
 # This configuration works with pypy 1.9.  pycurl installs ok but
 # curl_httpclient doesn't work.  Twisted works most of the time, but