diff --git a/CHANGES.md b/CHANGES.md
index e92a1e23..0463652b 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -24,7 +24,7 @@
 * Update SimpleJSON library 3.8.1 (6022794) to 3.10.0 (c52efea)
 * Update Six compatibility library 1.10.0 (r405) to 1.10.0 (r433)
 * Update socks from SocksiPy 1.0 to PySocks 1.6.5 (b4323df)
-* Update Tornado Web Server 4.5.dev1 (92f29b8) to 4.5.dev1 (38e493e)
+* Update Tornado Web Server 4.5.dev1 (92f29b8) to 4.5.1 (79b2683)
 * Update unidecode library 0.04.18 to 0.04.20 (1e18d98)
 * Update xmltodict library 0.9.2 (eac0031) to 0.10.2 (375d3a6)
 * Update Bootstrap 3.2.0 to 3.3.7
@@ -87,6 +87,7 @@
 * Change restart/shutdown to use updated jQuery
 * Remove AlphaReign torrent provider
 * Update cachecontrol library 0.11.5 to 0.11.7 (3b3b776)
+* Update Tornado Web Server 4.5.dev1 (92f29b8) to 4.5.dev1 (38e493e)
 
 
 ### 0.12.26 (2017-08-20 13:05:00 UTC)
diff --git a/lib/tornado/__init__.py b/lib/tornado/__init__.py
index e856a5fe..f054e402 100644
--- a/lib/tornado/__init__.py
+++ b/lib/tornado/__init__.py
@@ -16,7 +16,7 @@
 
 """The Tornado web server and tools."""
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 # version is a human-readable version number.
 
@@ -25,5 +25,5 @@ from __future__ import absolute_import, division, print_function, with_statement
 # is zero for an official release, positive for a development branch,
 # or negative for a release candidate or beta (after the base version
 # number has been incremented)
-version = "4.5.dev1"
-version_info = (4, 5, 0, -100)
+version = "4.5.1"
+version_info = (4, 5, 1, 0)
diff --git a/lib/tornado/_locale_data.py b/lib/tornado/_locale_data.py
index e073afe5..6fa2c297 100644
--- a/lib/tornado/_locale_data.py
+++ b/lib/tornado/_locale_data.py
@@ -17,7 +17,7 @@
 
 """Data used by the tornado.locale module."""
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 LOCALE_NAMES = {
     "af_ZA": {"name_en": u"Afrikaans", "name": u"Afrikaans"},
diff --git a/lib/tornado/auth.py b/lib/tornado/auth.py
index 44144061..f02d2898 100644
--- a/lib/tornado/auth.py
+++ b/lib/tornado/auth.py
@@ -65,7 +65,7 @@ Example usage for Google OAuth:
    errors are more consistently reported through the ``Future`` interfaces.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import base64
 import binascii
@@ -954,6 +954,20 @@ class FacebookGraphMixin(OAuth2Mixin):
         .. testoutput::
            :hide:
 
+        This method returns a dictionary which may contain the following fields:
+
+        * ``access_token``, a string which may be passed to `facebook_request`
+        * ``session_expires``, an integer encoded as a string representing
+          the time until the access token expires in seconds. This field should
+          be used like ``int(user['session_expires'])``; in a future version of
+          Tornado it will change from a string to an integer.
+        * ``id``, ``name``, ``first_name``, ``last_name``, ``locale``, ``picture``,
+          ``link``, plus any fields named in the ``extra_fields`` argument. These
+          fields are copied from the Facebook graph API `user object <https://developers.facebook.com/docs/graph-api/reference/user>`_
+
+        .. versionchanged:: 4.5
+           The ``session_expires`` field was updated to support changes made to the
+           Facebook API in March 2017.
         """
         http = self.get_auth_http_client()
         args = {
@@ -978,10 +992,10 @@ class FacebookGraphMixin(OAuth2Mixin):
             future.set_exception(AuthError('Facebook auth error: %s' % str(response)))
             return
 
-        args = urlparse.parse_qs(escape.native_str(response.body))
+        args = escape.json_decode(response.body)
         session = {
-            "access_token": args["access_token"][-1],
-            "expires": args.get("expires")
+            "access_token": args.get("access_token"),
+            "expires_in": args.get("expires_in")
         }
 
         self.facebook_request(
@@ -1004,7 +1018,12 @@ class FacebookGraphMixin(OAuth2Mixin):
         for field in fields:
             fieldmap[field] = user.get(field)
 
-        fieldmap.update({"access_token": session["access_token"], "session_expires": session.get("expires")})
+        # session_expires is converted to str for compatibility with
+        # older versions in which the server used url-encoding and
+        # this code simply returned the string verbatim.
+        # This should change in Tornado 5.0.
+        fieldmap.update({"access_token": session["access_token"],
+                         "session_expires": str(session.get("expires_in"))})
         future.set_result(fieldmap)
 
     @_auth_return_future
diff --git a/lib/tornado/autoreload.py b/lib/tornado/autoreload.py
index 5e0d00d1..60571efe 100644
--- a/lib/tornado/autoreload.py
+++ b/lib/tornado/autoreload.py
@@ -45,7 +45,7 @@ incorrectly.
 
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import os
 import sys
@@ -103,10 +103,6 @@ except ImportError:
 # os.execv is broken on Windows and can't properly parse command line
 # arguments and executable name if they contain whitespaces. subprocess
 # fixes that behavior.
-# This distinction is also important because when we use execv, we want to
-# close the IOLoop and all its file descriptors, to guard against any
-# file descriptors that were not set CLOEXEC. When execv is not available,
-# we must not close the IOLoop because we want the process to exit cleanly.
 _has_execv = sys.platform != 'win32'
 
 _watched_files = set()
@@ -127,8 +123,6 @@ def start(io_loop=None, check_time=500):
     _io_loops[io_loop] = True
     if len(_io_loops) > 1:
         gen_log.warning("tornado.autoreload started more than once in the same process")
-    if _has_execv:
-        add_reload_hook(functools.partial(io_loop.close, all_fds=True))
     modify_times = {}
     callback = functools.partial(_reload_on_update, modify_times)
     scheduler = ioloop.PeriodicCallback(callback, check_time, io_loop=io_loop)
@@ -249,6 +243,7 @@ def _reload():
             # unwind, so just exit uncleanly.
             os._exit(0)
 
+
 _USAGE = """\
 Usage:
   python -m tornado.autoreload -m module.to.run [args...]
diff --git a/lib/tornado/concurrent.py b/lib/tornado/concurrent.py
index ec68dc4f..667e6b17 100644
--- a/lib/tornado/concurrent.py
+++ b/lib/tornado/concurrent.py
@@ -21,7 +21,7 @@ a mostly-compatible `Future` class designed for use from coroutines,
 as well as some utility functions for interacting with the
 `concurrent.futures` package.
 """
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import functools
 import platform
@@ -234,7 +234,10 @@ class Future(object):
         if self._result is not None:
             return self._result
         if self._exc_info is not None:
-            raise_exc_info(self._exc_info)
+            try:
+                raise_exc_info(self._exc_info)
+            finally:
+                self = None
         self._check_done()
         return self._result
 
@@ -340,6 +343,7 @@ class Future(object):
             app_log.error('Future %r exception was never retrieved: %s',
                           self, ''.join(tb).rstrip())
 
+
 TracebackFuture = Future
 
 if futures is None:
@@ -364,6 +368,7 @@ class DummyExecutor(object):
     def shutdown(self, wait=True):
         pass
 
+
 dummy_executor = DummyExecutor()
 
 
diff --git a/lib/tornado/curl_httpclient.py b/lib/tornado/curl_httpclient.py
index bef78419..eef4a17a 100644
--- a/lib/tornado/curl_httpclient.py
+++ b/lib/tornado/curl_httpclient.py
@@ -16,7 +16,7 @@
 
 """Non-blocking HTTP client implementation using pycurl."""
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import collections
 import functools
@@ -278,9 +278,9 @@ class CurlAsyncHTTPClient(AsyncHTTPClient):
         if curl_log.isEnabledFor(logging.DEBUG):
             curl.setopt(pycurl.VERBOSE, 1)
             curl.setopt(pycurl.DEBUGFUNCTION, self._curl_debug)
-        if hasattr(pycurl,'PROTOCOLS'): # PROTOCOLS first appeared in pycurl 7.19.5 (2014-07-12)
-            curl.setopt(pycurl.PROTOCOLS, pycurl.PROTO_HTTP|pycurl.PROTO_HTTPS)
-            curl.setopt(pycurl.REDIR_PROTOCOLS, pycurl.PROTO_HTTP|pycurl.PROTO_HTTPS)
+        if hasattr(pycurl, 'PROTOCOLS'):  # PROTOCOLS first appeared in pycurl 7.19.5 (2014-07-12)
+            curl.setopt(pycurl.PROTOCOLS, pycurl.PROTO_HTTP | pycurl.PROTO_HTTPS)
+            curl.setopt(pycurl.REDIR_PROTOCOLS, pycurl.PROTO_HTTP | pycurl.PROTO_HTTPS)
         return curl
 
     def _curl_setup_request(self, curl, request, buffer, headers):
diff --git a/lib/tornado/escape.py b/lib/tornado/escape.py
index 7a3b0e03..2ca3fe3f 100644
--- a/lib/tornado/escape.py
+++ b/lib/tornado/escape.py
@@ -20,7 +20,7 @@ Also includes a few other miscellaneous string manipulation functions that
 have crept in over time.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import json
 import re
@@ -199,6 +199,7 @@ def utf8(value):
         )
     return value.encode("utf-8")
 
+
 _TO_UNICODE_TYPES = (unicode_type, type(None))
 
 
@@ -216,6 +217,7 @@ def to_unicode(value):
         )
     return value.decode("utf-8")
 
+
 # to_unicode was previously named _unicode not because it was private,
 # but to avoid conflicts with the built-in unicode() function/type
 _unicode = to_unicode
@@ -264,6 +266,7 @@ def recursive_unicode(obj):
     else:
         return obj
 
+
 # I originally used the regex from
 # http://daringfireball.net/2010/07/improved_regex_for_matching_urls
 # but it gets all exponential on certain patterns (such as too many trailing
@@ -391,4 +394,5 @@ def _build_unicode_map():
         unicode_map[name] = unichr(value)
     return unicode_map
 
+
 _HTML_UNICODE_MAP = _build_unicode_map()
diff --git a/lib/tornado/gen.py b/lib/tornado/gen.py
index d7df3b52..99f91066 100644
--- a/lib/tornado/gen.py
+++ b/lib/tornado/gen.py
@@ -74,7 +74,7 @@ See the `convert_yielded` function to extend this mechanism.
    via ``singledispatch``.
 
 """
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import collections
 import functools
@@ -245,6 +245,7 @@ def coroutine(func, replace_callback=True):
     """
     return _make_coroutine_wrapper(func, replace_callback=True)
 
+
 # Ties lifetime of runners to their result futures. Github Issue #1769
 # Generators, like any object in Python, must be strong referenced
 # in order to not be cleaned up by the garbage collector. When using
@@ -264,6 +265,7 @@ def coroutine(func, replace_callback=True):
 # Runner alive.
 _futures_to_runners = weakref.WeakKeyDictionary()
 
+
 def _make_coroutine_wrapper(func, replace_callback):
     """The inner workings of ``@gen.coroutine`` and ``@gen.engine``.
 
@@ -315,6 +317,7 @@ def _make_coroutine_wrapper(func, replace_callback):
                     future.set_exc_info(sys.exc_info())
                 else:
                     _futures_to_runners[future] = Runner(result, future, yielded)
+                yielded = None
                 try:
                     return future
                 finally:
@@ -338,6 +341,8 @@ def _make_coroutine_wrapper(func, replace_callback):
 def is_coroutine_function(func):
     """Return whether *func* is a coroutine function, i.e. a function
     wrapped with `~.gen.coroutine`.
+
+    .. versionadded:: 4.5
     """
     return getattr(func, '__tornado_coroutine__', False)
 
@@ -715,6 +720,7 @@ def multi(children, quiet_exceptions=()):
     else:
         return multi_future(children, quiet_exceptions=quiet_exceptions)
 
+
 Multi = multi
 
 
@@ -960,6 +966,9 @@ coroutines that are likely to yield Futures that are ready instantly.
 Usage: ``yield gen.moment``
 
 .. versionadded:: 4.0
+
+.. deprecated:: 4.5
+   ``yield None`` is now equivalent to ``yield gen.moment``.
 """
 moment.set_result(None)
 
@@ -990,6 +999,7 @@ class Runner(object):
         # of the coroutine.
         self.stack_context_deactivate = None
         if self.handle_yield(first_yielded):
+            gen = result_future = first_yielded = None
             self.run()
 
     def register_callback(self, key):
@@ -1046,10 +1056,15 @@ class Runner(object):
                     except Exception:
                         self.had_exception = True
                         exc_info = sys.exc_info()
+                    future = None
 
                     if exc_info is not None:
-                        yielded = self.gen.throw(*exc_info)
-                        exc_info = None
+                        try:
+                            yielded = self.gen.throw(*exc_info)
+                        finally:
+                            # Break up a reference to itself
+                            # for faster GC on CPython.
+                            exc_info = None
                     else:
                         yielded = self.gen.send(value)
 
@@ -1082,6 +1097,7 @@ class Runner(object):
                     return
                 if not self.handle_yield(yielded):
                     return
+                yielded = None
         finally:
             self.running = False
 
@@ -1130,8 +1146,12 @@ class Runner(object):
                 self.future.set_exc_info(sys.exc_info())
 
         if not self.future.done() or self.future is moment:
+            def inner(f):
+                # Break a reference cycle to speed GC.
+                f = None # noqa
+                self.run()
             self.io_loop.add_future(
-                self.future, lambda f: self.run())
+                self.future, inner)
             return False
         return True
 
@@ -1153,6 +1173,7 @@ class Runner(object):
             self.stack_context_deactivate()
             self.stack_context_deactivate = None
 
+
 Arguments = collections.namedtuple('Arguments', ['args', 'kwargs'])
 
 
@@ -1172,6 +1193,7 @@ def _argument_adapter(callback):
             callback(None)
     return wrapper
 
+
 # Convert Awaitables into Futures. It is unfortunately possible
 # to have infinite recursion here if those Awaitables assume that
 # we're using a different coroutine runner and yield objects
@@ -1249,7 +1271,9 @@ def convert_yielded(yielded):
     .. versionadded:: 4.1
     """
     # Lists and dicts containing YieldPoints were handled earlier.
-    if isinstance(yielded, (list, dict)):
+    if yielded is None:
+        return moment
+    elif isinstance(yielded, (list, dict)):
         return multi(yielded)
     elif is_future(yielded):
         return yielded
@@ -1258,6 +1282,7 @@ def convert_yielded(yielded):
     else:
         raise BadYieldError("yielded unknown object %r" % (yielded,))
 
+
 if singledispatch is not None:
     convert_yielded = singledispatch(convert_yielded)
 
diff --git a/lib/tornado/http1connection.py b/lib/tornado/http1connection.py
index 055f1827..3c5ccaf6 100644
--- a/lib/tornado/http1connection.py
+++ b/lib/tornado/http1connection.py
@@ -19,7 +19,7 @@
 .. versionadded:: 4.0
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import re
 
@@ -257,6 +257,7 @@ class HTTP1Connection(httputil.HTTPConnection):
             if need_delegate_close:
                 with _ExceptionLoggingContext(app_log):
                     delegate.on_connection_close()
+            header_future = None
             self._clear_callbacks()
         raise gen.Return(True)
 
@@ -489,7 +490,7 @@ class HTTP1Connection(httputil.HTTPConnection):
         elif ("Content-Length" in headers or
               headers.get("Transfer-Encoding", "").lower() == "chunked" or
               getattr(start_line, 'method', None) in ("HEAD", "GET")):
-            # start_line may be a request or reponse start line; only
+            # start_line may be a request or response start line; only
             # the former has a method attribute.
             return connection_header == "keep-alive"
         return False
diff --git a/lib/tornado/httpclient.py b/lib/tornado/httpclient.py
index 2b5d1fba..8436ece4 100644
--- a/lib/tornado/httpclient.py
+++ b/lib/tornado/httpclient.py
@@ -38,7 +38,7 @@ To select ``curl_httpclient``, call `AsyncHTTPClient.configure` at startup::
     AsyncHTTPClient.configure("tornado.curl_httpclient.CurlAsyncHTTPClient")
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import functools
 import time
@@ -423,6 +423,9 @@ class HTTPRequest(object):
 
         .. versionadded:: 4.2
            The ``ssl_options`` argument.
+
+        .. versionadded:: 4.5
+           The ``proxy_auth_mode`` argument.
         """
         # Note that some of these attributes go through property setters
         # defined below.
@@ -670,5 +673,6 @@ def main():
             print(native_str(response.body))
     client.close()
 
+
 if __name__ == "__main__":
     main()
diff --git a/lib/tornado/httpserver.py b/lib/tornado/httpserver.py
index c7b9c2f8..d757be18 100644
--- a/lib/tornado/httpserver.py
+++ b/lib/tornado/httpserver.py
@@ -26,7 +26,7 @@ class except to start a server at the beginning of the process
    to `tornado.httputil.HTTPServerRequest`.  The old name remains as an alias.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import socket
 
@@ -62,6 +62,13 @@ class HTTPServer(TCPServer, Configurable,
     if Tornado is run behind an SSL-decoding proxy that does not set one of
     the supported ``xheaders``.
 
+    By default, when parsing the ``X-Forwarded-For`` header, Tornado will
+    select the last (i.e., the closest) address on the list of hosts as the
+    remote host IP address.  To select the next server in the chain, a list of
+    trusted downstream hosts may be passed as the ``trusted_downstream``
+    argument.  These hosts will be skipped when parsing the ``X-Forwarded-For``
+    header.
+
     To make this server serve SSL traffic, send the ``ssl_options`` keyword
     argument with an `ssl.SSLContext` object. For compatibility with older
     versions of Python ``ssl_options`` may also be a dictionary of keyword
@@ -124,6 +131,9 @@ class HTTPServer(TCPServer, Configurable,
 
     .. versionchanged:: 4.2
        `HTTPServer` is now a subclass of `tornado.util.Configurable`.
+
+    .. versionchanged:: 4.5
+       Added the ``trusted_downstream`` argument.
     """
     def __init__(self, *args, **kwargs):
         # Ignore args to __init__; real initialization belongs in
@@ -138,7 +148,8 @@ class HTTPServer(TCPServer, Configurable,
                    decompress_request=False,
                    chunk_size=None, max_header_size=None,
                    idle_connection_timeout=None, body_timeout=None,
-                   max_body_size=None, max_buffer_size=None):
+                   max_body_size=None, max_buffer_size=None,
+                   trusted_downstream=None):
         self.request_callback = request_callback
         self.no_keep_alive = no_keep_alive
         self.xheaders = xheaders
@@ -149,11 +160,13 @@ class HTTPServer(TCPServer, Configurable,
             max_header_size=max_header_size,
             header_timeout=idle_connection_timeout or 3600,
             max_body_size=max_body_size,
-            body_timeout=body_timeout)
+            body_timeout=body_timeout,
+            no_keep_alive=no_keep_alive)
         TCPServer.__init__(self, io_loop=io_loop, ssl_options=ssl_options,
                            max_buffer_size=max_buffer_size,
                            read_chunk_size=chunk_size)
         self._connections = set()
+        self.trusted_downstream = trusted_downstream
 
     @classmethod
     def configurable_base(cls):
@@ -172,7 +185,8 @@ class HTTPServer(TCPServer, Configurable,
 
     def handle_stream(self, stream, address):
         context = _HTTPRequestContext(stream, address,
-                                      self.protocol)
+                                      self.protocol,
+                                      self.trusted_downstream)
         conn = HTTP1ServerConnection(
             stream, self.conn_params, context)
         self._connections.add(conn)
@@ -219,7 +233,7 @@ class _CallableAdapter(httputil.HTTPMessageDelegate):
 
 
 class _HTTPRequestContext(object):
-    def __init__(self, stream, address, protocol):
+    def __init__(self, stream, address, protocol, trusted_downstream=None):
         self.address = address
         # Save the socket's address family now so we know how to
         # interpret self.address even after the stream is closed
@@ -243,6 +257,7 @@ class _HTTPRequestContext(object):
             self.protocol = "http"
         self._orig_remote_ip = self.remote_ip
         self._orig_protocol = self.protocol
+        self.trusted_downstream = set(trusted_downstream or [])
 
     def __str__(self):
         if self.address_family in (socket.AF_INET, socket.AF_INET6):
@@ -259,7 +274,10 @@ class _HTTPRequestContext(object):
         """Rewrite the ``remote_ip`` and ``protocol`` fields."""
         # Squid uses X-Forwarded-For, others use X-Real-Ip
         ip = headers.get("X-Forwarded-For", self.remote_ip)
-        ip = ip.split(',')[-1].strip()
+        # Skip trusted downstream hosts in X-Forwarded-For list
+        for ip in (cand.strip() for cand in reversed(ip.split(','))):
+            if ip not in self.trusted_downstream:
+                break
         ip = headers.get("X-Real-Ip", ip)
         if netutil.is_valid_ip(ip):
             self.remote_ip = ip
@@ -303,4 +321,5 @@ class _ProxyAdapter(httputil.HTTPMessageDelegate):
     def _cleanup(self):
         self.connection.context._unapply_xheaders()
 
+
 HTTPRequest = httputil.HTTPServerRequest
diff --git a/lib/tornado/httputil.py b/lib/tornado/httputil.py
index 8ea8a01e..818ea914 100644
--- a/lib/tornado/httputil.py
+++ b/lib/tornado/httputil.py
@@ -20,7 +20,7 @@ This module also defines the `HTTPServerRequest` class which is exposed
 via `tornado.web.RequestHandler.request`.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import calendar
 import collections
@@ -38,11 +38,12 @@ from tornado.util import ObjectDict, PY3
 if PY3:
     import http.cookies as Cookie
     from http.client import responses
-    from urllib.parse import urlencode
+    from urllib.parse import urlencode, urlparse, urlunparse, parse_qsl
 else:
     import Cookie
     from httplib import responses
     from urllib import urlencode
+    from urlparse import urlparse, urlunparse, parse_qsl
 
 
 # responses is unused in this file, but we re-export it to other files.
@@ -98,6 +99,7 @@ class _NormalizedHeaderCache(dict):
             del self[old_key]
         return normalized
 
+
 _normalized_headers = _NormalizedHeaderCache(1000)
 
 
@@ -601,11 +603,28 @@ def url_concat(url, args):
     >>> url_concat("http://example.com/foo?a=b", [("c", "d"), ("c", "d2")])
     'http://example.com/foo?a=b&c=d&c=d2'
     """
-    if not args:
+    if args is None:
         return url
-    if url[-1] not in ('?', '&'):
-        url += '&' if ('?' in url) else '?'
-    return url + urlencode(args)
+    parsed_url = urlparse(url)
+    if isinstance(args, dict):
+        parsed_query = parse_qsl(parsed_url.query, keep_blank_values=True)
+        parsed_query.extend(args.items())
+    elif isinstance(args, list) or isinstance(args, tuple):
+        parsed_query = parse_qsl(parsed_url.query, keep_blank_values=True)
+        parsed_query.extend(args)
+    else:
+        err = "'args' parameter should be dict, list or tuple. Not {0}".format(
+            type(args))
+        raise TypeError(err)
+    final_query = urlencode(parsed_query)
+    url = urlunparse((
+        parsed_url[0],
+        parsed_url[1],
+        parsed_url[2],
+        parsed_url[3],
+        final_query,
+        parsed_url[5]))
+    return url
 
 
 class HTTPFile(ObjectDict):
@@ -920,10 +939,12 @@ def split_host_and_port(netloc):
         port = None
     return (host, port)
 
+
 _OctalPatt = re.compile(r"\\[0-3][0-7][0-7]")
 _QuotePatt = re.compile(r"[\\].")
 _nulljoin = ''.join
 
+
 def _unquote_cookie(str):
     """Handle double quotes and escaping in cookie values.
 
@@ -965,11 +986,11 @@ def _unquote_cookie(str):
             k = q_match.start(0)
         if q_match and (not o_match or k < j):     # QuotePatt matched
             res.append(str[i:k])
-            res.append(str[k+1])
+            res.append(str[k + 1])
             i = k + 2
         else:                                      # OctalPatt matched
             res.append(str[i:j])
-            res.append(chr(int(str[j+1:j+4], 8)))
+            res.append(chr(int(str[j + 1:j + 4], 8)))
             i = j + 4
     return _nulljoin(res)
 
diff --git a/lib/tornado/ioloop.py b/lib/tornado/ioloop.py
index 1b1a07cd..ad35787f 100644
--- a/lib/tornado/ioloop.py
+++ b/lib/tornado/ioloop.py
@@ -26,7 +26,7 @@ In addition to I/O events, the `IOLoop` can also schedule time-based events.
 `IOLoop.add_timeout` is a non-blocking alternative to `time.sleep`.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import collections
 import datetime
@@ -715,7 +715,7 @@ class PollIOLoop(IOLoop):
         self._closing = True
         self.remove_handler(self._waker.fileno())
         if all_fds:
-            for fd, handler in self._handlers.values():
+            for fd, handler in list(self._handlers.values()):
                 self.close_fd(fd)
         self._waker.close()
         self._impl.close()
diff --git a/lib/tornado/iostream.py b/lib/tornado/iostream.py
index e3e70f04..4bf79a56 100644
--- a/lib/tornado/iostream.py
+++ b/lib/tornado/iostream.py
@@ -24,7 +24,7 @@ Contents:
 * `PipeIOStream`: Pipe-based IOStream implementation.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import collections
 import errno
@@ -82,6 +82,8 @@ _ERRNO_INPROGRESS = (errno.EINPROGRESS,)
 if hasattr(errno, "WSAEINPROGRESS"):
     _ERRNO_INPROGRESS += (errno.WSAEINPROGRESS,)  # type: ignore
 
+_WINDOWS = sys.platform.startswith('win')
+
 
 class StreamClosedError(IOError):
     """Exception raised by `IOStream` methods when the stream is closed.
@@ -158,11 +160,16 @@ class BaseIOStream(object):
                                    self.max_buffer_size // 2)
         self.max_write_buffer_size = max_write_buffer_size
         self.error = None
-        self._read_buffer = collections.deque()
-        self._write_buffer = collections.deque()
+        self._read_buffer = bytearray()
+        self._read_buffer_pos = 0
         self._read_buffer_size = 0
+        self._write_buffer = bytearray()
+        self._write_buffer_pos = 0
         self._write_buffer_size = 0
         self._write_buffer_frozen = False
+        self._total_write_index = 0
+        self._total_write_done_index = 0
+        self._pending_writes_while_frozen = []
         self._read_delimiter = None
         self._read_regex = None
         self._read_max_bytes = None
@@ -173,7 +180,7 @@ class BaseIOStream(object):
         self._read_future = None
         self._streaming_callback = None
         self._write_callback = None
-        self._write_future = None
+        self._write_futures = collections.deque()
         self._close_callback = None
         self._connect_callback = None
         self._connect_future = None
@@ -367,36 +374,37 @@ class BaseIOStream(object):
 
         If no ``callback`` is given, this method returns a `.Future` that
         resolves (with a result of ``None``) when the write has been
-        completed.  If `write` is called again before that `.Future` has
-        resolved, the previous future will be orphaned and will never resolve.
+        completed.
+
+        The ``data`` argument may be of type `bytes` or `memoryview`.
 
         .. versionchanged:: 4.0
             Now returns a `.Future` if no callback is given.
+
+        .. versionchanged:: 4.5
+            Added support for `memoryview` arguments.
         """
-        assert isinstance(data, bytes)
         self._check_closed()
-        # We use bool(_write_buffer) as a proxy for write_buffer_size>0,
-        # so never put empty strings in the buffer.
         if data:
             if (self.max_write_buffer_size is not None and
                     self._write_buffer_size + len(data) > self.max_write_buffer_size):
                 raise StreamBufferFullError("Reached maximum write buffer size")
-            # Break up large contiguous strings before inserting them in the
-            # write buffer, so we don't have to recopy the entire thing
-            # as we slice off pieces to send to the socket.
-            WRITE_BUFFER_CHUNK_SIZE = 128 * 1024
-            for i in range(0, len(data), WRITE_BUFFER_CHUNK_SIZE):
-                self._write_buffer.append(data[i:i + WRITE_BUFFER_CHUNK_SIZE])
-            self._write_buffer_size += len(data)
+            if self._write_buffer_frozen:
+                self._pending_writes_while_frozen.append(data)
+            else:
+                self._write_buffer += data
+                self._write_buffer_size += len(data)
+            self._total_write_index += len(data)
         if callback is not None:
             self._write_callback = stack_context.wrap(callback)
             future = None
         else:
-            future = self._write_future = TracebackFuture()
+            future = TracebackFuture()
             future.add_done_callback(lambda f: f.exception())
+            self._write_futures.append((self._total_write_index, future))
         if not self._connecting:
             self._handle_write()
-            if self._write_buffer:
+            if self._write_buffer_size:
                 self._add_io_state(self.io_loop.WRITE)
             self._maybe_add_error_listener()
         return future
@@ -445,9 +453,8 @@ class BaseIOStream(object):
             if self._read_future is not None:
                 futures.append(self._read_future)
                 self._read_future = None
-            if self._write_future is not None:
-                futures.append(self._write_future)
-                self._write_future = None
+            futures += [future for _, future in self._write_futures]
+            self._write_futures.clear()
             if self._connect_future is not None:
                 futures.append(self._connect_future)
                 self._connect_future = None
@@ -466,6 +473,7 @@ class BaseIOStream(object):
             # if the IOStream object is kept alive by a reference cycle.
             # TODO: Clear the read buffer too; it currently breaks some tests.
             self._write_buffer = None
+            self._write_buffer_size = 0
 
     def reading(self):
         """Returns true if we are currently reading from the stream."""
@@ -473,7 +481,7 @@ class BaseIOStream(object):
 
     def writing(self):
         """Returns true if we are currently writing to the stream."""
-        return bool(self._write_buffer)
+        return self._write_buffer_size > 0
 
     def closed(self):
         """Returns true if the stream has been closed."""
@@ -650,7 +658,7 @@ class BaseIOStream(object):
         except Exception as e:
             if 1 != e.errno:
                 gen_log.warning("error on read: %s" % e)
-            self.close(exc_info=True)
+            self.close(exc_info=e)
             return
         if pos is not None:
             self._read_from_buffer(pos)
@@ -744,7 +752,7 @@ class BaseIOStream(object):
             break
         if chunk is None:
             return 0
-        self._read_buffer.append(chunk)
+        self._read_buffer += chunk
         self._read_buffer_size += len(chunk)
         if self._read_buffer_size > self.max_buffer_size:
             gen_log.error("Reached maximum read buffer size")
@@ -792,30 +800,25 @@ class BaseIOStream(object):
             # since large merges are relatively expensive and get undone in
             # _consume().
             if self._read_buffer:
-                while True:
-                    loc = self._read_buffer[0].find(self._read_delimiter)
-                    if loc != -1:
-                        delimiter_len = len(self._read_delimiter)
-                        self._check_max_bytes(self._read_delimiter,
-                                              loc + delimiter_len)
-                        return loc + delimiter_len
-                    if len(self._read_buffer) == 1:
-                        break
-                    _double_prefix(self._read_buffer)
+                loc = self._read_buffer.find(self._read_delimiter,
+                                             self._read_buffer_pos)
+                if loc != -1:
+                    loc -= self._read_buffer_pos
+                    delimiter_len = len(self._read_delimiter)
+                    self._check_max_bytes(self._read_delimiter,
+                                          loc + delimiter_len)
+                    return loc + delimiter_len
                 self._check_max_bytes(self._read_delimiter,
-                                      len(self._read_buffer[0]))
+                                      self._read_buffer_size)
         elif self._read_regex is not None:
             if self._read_buffer:
-                while True:
-                    m = self._read_regex.search(self._read_buffer[0])
-                    if m is not None:
-                        self._check_max_bytes(self._read_regex, m.end())
-                        return m.end()
-                    if len(self._read_buffer) == 1:
-                        break
-                    _double_prefix(self._read_buffer)
-                self._check_max_bytes(self._read_regex,
-                                      len(self._read_buffer[0]))
+                m = self._read_regex.search(self._read_buffer,
+                                            self._read_buffer_pos)
+                if m is not None:
+                    loc = m.end() - self._read_buffer_pos
+                    self._check_max_bytes(self._read_regex, loc)
+                    return loc
+                self._check_max_bytes(self._read_regex, self._read_buffer_size)
         return None
 
     def _check_max_bytes(self, delimiter, size):
@@ -825,35 +828,56 @@ class BaseIOStream(object):
                 "delimiter %r not found within %d bytes" % (
                     delimiter, self._read_max_bytes))
 
+    def _freeze_write_buffer(self, size):
+        self._write_buffer_frozen = size
+
+    def _unfreeze_write_buffer(self):
+        self._write_buffer_frozen = False
+        self._write_buffer += b''.join(self._pending_writes_while_frozen)
+        self._write_buffer_size += sum(map(len, self._pending_writes_while_frozen))
+        self._pending_writes_while_frozen[:] = []
+
+    def _got_empty_write(self, size):
+        """
+        Called when a non-blocking write() failed writing anything.
+        Can be overridden in subclasses.
+        """
+
     def _handle_write(self):
-        while self._write_buffer:
+        while self._write_buffer_size:
+            assert self._write_buffer_size >= 0
             try:
-                if not self._write_buffer_frozen:
+                start = self._write_buffer_pos
+                if self._write_buffer_frozen:
+                    size = self._write_buffer_frozen
+                elif _WINDOWS:
                     # On windows, socket.send blows up if given a
                     # write buffer that's too large, instead of just
                     # returning the number of bytes it was able to
                     # process.  Therefore we must not call socket.send
                     # with more than 128KB at a time.
-                    _merge_prefix(self._write_buffer, 128 * 1024)
-                num_bytes = self.write_to_fd(self._write_buffer[0])
+                    size = 128 * 1024
+                else:
+                    size = self._write_buffer_size
+                num_bytes = self.write_to_fd(
+                    memoryview(self._write_buffer)[start:start + size])
                 if num_bytes == 0:
-                    # With OpenSSL, if we couldn't write the entire buffer,
-                    # the very same string object must be used on the
-                    # next call to send.  Therefore we suppress
-                    # merging the write buffer after an incomplete send.
-                    # A cleaner solution would be to set
-                    # SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER, but this is
-                    # not yet accessible from python
-                    # (http://bugs.python.org/issue8240)
-                    self._write_buffer_frozen = True
+                    self._got_empty_write(size)
                     break
-                self._write_buffer_frozen = False
-                _merge_prefix(self._write_buffer, num_bytes)
-                self._write_buffer.popleft()
+                self._write_buffer_pos += num_bytes
                 self._write_buffer_size -= num_bytes
+                # Amortized O(1) shrink
+                # (this heuristic is implemented natively in Python 3.4+
+                #  but is replicated here for Python 2)
+                if self._write_buffer_pos > self._write_buffer_size:
+                    del self._write_buffer[:self._write_buffer_pos]
+                    self._write_buffer_pos = 0
+                if self._write_buffer_frozen:
+                    self._unfreeze_write_buffer()
+                self._total_write_done_index += num_bytes
             except (socket.error, IOError, OSError) as e:
                 if e.args[0] in _ERRNO_WOULDBLOCK:
-                    self._write_buffer_frozen = True
+                    self._got_empty_write(size)
                     break
                 else:
                     if not self._is_connreset(e):
@@ -864,22 +888,38 @@ class BaseIOStream(object):
                                         self.fileno(), e)
                     self.close(exc_info=True)
                     return
-        if not self._write_buffer:
+
+        while self._write_futures:
+            index, future = self._write_futures[0]
+            if index > self._total_write_done_index:
+                break
+            self._write_futures.popleft()
+            future.set_result(None)
+
+        if not self._write_buffer_size:
             if self._write_callback:
                 callback = self._write_callback
                 self._write_callback = None
                 self._run_callback(callback)
-            if self._write_future:
-                future = self._write_future
-                self._write_future = None
-                future.set_result(None)
 
     def _consume(self, loc):
+        # Consume loc bytes from the read buffer and return them
         if loc == 0:
             return b""
-        _merge_prefix(self._read_buffer, loc)
+        assert loc <= self._read_buffer_size
+        # Slice the bytearray buffer into bytes, without intermediate copying
+        b = (memoryview(self._read_buffer)
+             [self._read_buffer_pos:self._read_buffer_pos + loc]
+             ).tobytes()
+        self._read_buffer_pos += loc
         self._read_buffer_size -= loc
-        return self._read_buffer.popleft()
+        # Amortized O(1) shrink
+        # (this heuristic is implemented natively in Python 3.4+
+        #  but is replicated here for Python 2)
+        if self._read_buffer_pos > self._read_buffer_size:
+            del self._read_buffer[:self._read_buffer_pos]
+            self._read_buffer_pos = 0
+        return b
 
     def _check_closed(self):
         if self.closed():
@@ -1125,7 +1165,7 @@ class IOStream(BaseIOStream):
            suitably-configured `ssl.SSLContext` to disable.
         """
         if (self._read_callback or self._read_future or
-                self._write_callback or self._write_future or
+                self._write_callback or self._write_futures or
                 self._connect_callback or self._connect_future or
                 self._pending_callbacks or self._closed or
                 self._read_buffer or self._write_buffer):
@@ -1252,6 +1292,17 @@ class SSLIOStream(IOStream):
     def writing(self):
         return self._handshake_writing or super(SSLIOStream, self).writing()
 
+    def _got_empty_write(self, size):
+        # With OpenSSL, if we couldn't write the entire buffer,
+        # the very same string object must be used on the
+        # next call to send.  Therefore we suppress
+        # merging the write buffer after an incomplete send.
+        # A cleaner solution would be to set
+        # SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER, but this is
+        # not yet accessible from python
+        # (http://bugs.python.org/issue8240)
+        self._freeze_write_buffer(size)
+
     def _do_ssl_handshake(self):
         # Based on code from test_ssl.py in the python stdlib
         try:
@@ -1499,53 +1550,6 @@ class PipeIOStream(BaseIOStream):
         return chunk
 
 
-def _double_prefix(deque):
-    """Grow by doubling, but don't split the second chunk just because the
-    first one is small.
-    """
-    new_len = max(len(deque[0]) * 2,
-                  (len(deque[0]) + len(deque[1])))
-    _merge_prefix(deque, new_len)
-
-
-def _merge_prefix(deque, size):
-    """Replace the first entries in a deque of strings with a single
-    string of up to size bytes.
-
-    >>> d = collections.deque(['abc', 'de', 'fghi', 'j'])
-    >>> _merge_prefix(d, 5); print(d)
-    deque(['abcde', 'fghi', 'j'])
-
-    Strings will be split as necessary to reach the desired size.
-    >>> _merge_prefix(d, 7); print(d)
-    deque(['abcdefg', 'hi', 'j'])
-
-    >>> _merge_prefix(d, 3); print(d)
-    deque(['abc', 'defg', 'hi', 'j'])
-
-    >>> _merge_prefix(d, 100); print(d)
-    deque(['abcdefghij'])
-    """
-    if len(deque) == 1 and len(deque[0]) <= size:
-        return
-    prefix = []
-    remaining = size
-    while deque and remaining > 0:
-        chunk = deque.popleft()
-        if len(chunk) > remaining:
-            deque.appendleft(chunk[remaining:])
-            chunk = chunk[:remaining]
-        prefix.append(chunk)
-        remaining -= len(chunk)
-    # This data structure normally just contains byte strings, but
-    # the unittest gets messy if it doesn't use the default str() type,
-    # so do the merge based on the type of data that's actually present.
-    if prefix:
-        deque.appendleft(type(prefix[0])().join(prefix))
-    if not deque:
-        deque.appendleft(b"")
-
-
 def doctests():
     import doctest
     return doctest.DocTestSuite()
diff --git a/lib/tornado/locale.py b/lib/tornado/locale.py
index c1cb6792..7dba10d6 100644
--- a/lib/tornado/locale.py
+++ b/lib/tornado/locale.py
@@ -39,7 +39,7 @@ supported by `gettext` and related tools).  If neither method is called,
 the `Locale.translate` method will simply return the original string.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import codecs
 import csv
@@ -187,7 +187,7 @@ def load_gettext_translations(directory, domain):
 
         {directory}/{lang}/LC_MESSAGES/{domain}.mo
 
-    Three steps are required to have you app translated:
+    Three steps are required to have your app translated:
 
     1. Generate POT translation file::
 
diff --git a/lib/tornado/locks.py b/lib/tornado/locks.py
index d84a9a87..4f9ecf6d 100644
--- a/lib/tornado/locks.py
+++ b/lib/tornado/locks.py
@@ -12,7 +12,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import collections
 
diff --git a/lib/tornado/log.py b/lib/tornado/log.py
index ac1bb95e..654afc02 100644
--- a/lib/tornado/log.py
+++ b/lib/tornado/log.py
@@ -28,7 +28,7 @@ These streams may be configured independently using the standard library's
 `logging` module.  For example, you may wish to send ``tornado.access`` logs
 to a separate file for analysis.
 """
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import logging
 import logging.handlers
@@ -37,6 +37,11 @@ import sys
 from tornado.escape import _unicode
 from tornado.util import unicode_type, basestring_type
 
+try:
+    import colorama
+except ImportError:
+    colorama = None
+
 try:
     import curses  # type: ignore
 except ImportError:
@@ -49,15 +54,21 @@ gen_log = logging.getLogger("tornado.general")
 
 
 def _stderr_supports_color():
-    color = False
-    if curses and hasattr(sys.stderr, 'isatty') and sys.stderr.isatty():
-        try:
-            curses.setupterm()
-            if curses.tigetnum("colors") > 0:
-                color = True
-        except Exception:
-            pass
-    return color
+    try:
+        if hasattr(sys.stderr, 'isatty') and sys.stderr.isatty():
+            if curses:
+                curses.setupterm()
+                if curses.tigetnum("colors") > 0:
+                    return True
+            elif colorama:
+                if sys.stderr is getattr(colorama.initialise, 'wrapped_stderr',
+                                         object()):
+                    return True
+    except Exception:
+        # Very broad exception handling because it's always better to
+        # fall back to non-colored logs than to break at startup.
+        pass
+    return False
 
 
 def _safe_unicode(s):
@@ -79,6 +90,17 @@ class LogFormatter(logging.Formatter):
     This formatter is enabled automatically by
     `tornado.options.parse_command_line` or `tornado.options.parse_config_file`
     (unless ``--logging=none`` is used).
+
+    Color support on Windows versions that do not support ANSI color codes is
+    enabled by use of the colorama__ library. Applications that wish to use
+    this must first initialize colorama with a call to ``colorama.init``.
+    See the colorama documentation for details.
+
+    __ https://pypi.python.org/pypi/colorama
+
+    .. versionchanged:: 4.5
+       Added support for ``colorama``. Changed the constructor
+       signature to be compatible with `logging.config.dictConfig`.
     """
     DEFAULT_FORMAT = '%(color)s[%(levelname)1.1s %(asctime)s %(module)s:%(lineno)d]%(end_color)s %(message)s'
     DEFAULT_DATE_FORMAT = '%y%m%d %H:%M:%S'
@@ -89,8 +111,8 @@ class LogFormatter(logging.Formatter):
         logging.ERROR: 1,  # Red
     }
 
-    def __init__(self, color=True, fmt=DEFAULT_FORMAT,
-                 datefmt=DEFAULT_DATE_FORMAT, colors=DEFAULT_COLORS):
+    def __init__(self, fmt=DEFAULT_FORMAT, datefmt=DEFAULT_DATE_FORMAT,
+                 style='%', color=True, colors=DEFAULT_COLORS):
         r"""
         :arg bool color: Enables color support.
         :arg string fmt: Log message format.
@@ -111,21 +133,28 @@ class LogFormatter(logging.Formatter):
 
         self._colors = {}
         if color and _stderr_supports_color():
-            # The curses module has some str/bytes confusion in
-            # python3.  Until version 3.2.3, most methods return
-            # bytes, but only accept strings.  In addition, we want to
-            # output these strings with the logging module, which
-            # works with unicode strings.  The explicit calls to
-            # unicode() below are harmless in python2 but will do the
-            # right conversion in python 3.
-            fg_color = (curses.tigetstr("setaf") or
-                        curses.tigetstr("setf") or "")
-            if (3, 0) < sys.version_info < (3, 2, 3):
-                fg_color = unicode_type(fg_color, "ascii")
+            if curses is not None:
+                # The curses module has some str/bytes confusion in
+                # python3.  Until version 3.2.3, most methods return
+                # bytes, but only accept strings.  In addition, we want to
+                # output these strings with the logging module, which
+                # works with unicode strings.  The explicit calls to
+                # unicode() below are harmless in python2 but will do the
+                # right conversion in python 3.
+                fg_color = (curses.tigetstr("setaf") or
+                            curses.tigetstr("setf") or "")
+                if (3, 0) < sys.version_info < (3, 2, 3):
+                    fg_color = unicode_type(fg_color, "ascii")
 
-            for levelno, code in colors.items():
-                self._colors[levelno] = unicode_type(curses.tparm(fg_color, code), "ascii")
-            self._normal = unicode_type(curses.tigetstr("sgr0"), "ascii")
+                for levelno, code in colors.items():
+                    self._colors[levelno] = unicode_type(curses.tparm(fg_color, code), "ascii")
+                self._normal = unicode_type(curses.tigetstr("sgr0"), "ascii")
+            else:
+                # If curses is not present (currently we'll only get here for
+                # colorama on windows), assume hard-coded ANSI color codes.
+                for levelno, code in colors.items():
+                    self._colors[levelno] = '\033[2;3%dm' % code
+                self._normal = '\033[0m'
         else:
             self._normal = ''
 
diff --git a/lib/tornado/netutil.py b/lib/tornado/netutil.py
index 20b4bdd6..c34c8c8b 100644
--- a/lib/tornado/netutil.py
+++ b/lib/tornado/netutil.py
@@ -16,7 +16,7 @@
 
 """Miscellaneous network utility code."""
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import errno
 import os
@@ -200,6 +200,7 @@ def bind_sockets(port, address=None, family=socket.AF_UNSPEC,
         sockets.append(sock)
     return sockets
 
+
 if hasattr(socket, 'AF_UNIX'):
     def bind_unix_socket(file, mode=0o600, backlog=_DEFAULT_BACKLOG):
         """Creates a listening unix socket.
diff --git a/lib/tornado/options.py b/lib/tornado/options.py
index 2fbb32ad..0a72cc65 100644
--- a/lib/tornado/options.py
+++ b/lib/tornado/options.py
@@ -82,7 +82,7 @@ instances to define isolated sets of options, such as for subcommands.
    underscores.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import datetime
 import numbers
diff --git a/lib/tornado/platform/asyncio.py b/lib/tornado/platform/asyncio.py
index 9556da61..830ee1f3 100644
--- a/lib/tornado/platform/asyncio.py
+++ b/lib/tornado/platform/asyncio.py
@@ -19,7 +19,7 @@ loops.
    Windows. Use the `~asyncio.SelectorEventLoop` instead.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 import functools
 
 import tornado.concurrent
@@ -30,7 +30,7 @@ from tornado import stack_context
 try:
     # Import the real asyncio module for py33+ first.  Older versions of the
     # trollius backport also use this name.
-    import asyncio # type: ignore
+    import asyncio  # type: ignore
 except ImportError as e:
     # Asyncio itself isn't available; see if trollius is (backport to py26+).
     try:
@@ -217,5 +217,6 @@ def to_asyncio_future(tornado_future):
     tornado.concurrent.chain_future(tornado_future, af)
     return af
 
+
 if hasattr(convert_yielded, 'register'):
     convert_yielded.register(asyncio.Future, to_tornado_future)  # type: ignore
diff --git a/lib/tornado/platform/auto.py b/lib/tornado/platform/auto.py
index 449b634b..1f4d7001 100644
--- a/lib/tornado/platform/auto.py
+++ b/lib/tornado/platform/auto.py
@@ -23,7 +23,7 @@ Most code that needs access to this functionality should do e.g.::
     from tornado.platform.auto import set_close_exec
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import os
 
diff --git a/lib/tornado/platform/caresresolver.py b/lib/tornado/platform/caresresolver.py
index 4205de30..fd6e9d27 100644
--- a/lib/tornado/platform/caresresolver.py
+++ b/lib/tornado/platform/caresresolver.py
@@ -1,4 +1,4 @@
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 import pycares  # type: ignore
 import socket
 
diff --git a/lib/tornado/platform/common.py b/lib/tornado/platform/common.py
index d78ee686..a73f8db7 100644
--- a/lib/tornado/platform/common.py
+++ b/lib/tornado/platform/common.py
@@ -1,5 +1,5 @@
 """Lowest-common-denominator implementations of platform functionality."""
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import errno
 import socket
@@ -8,6 +8,7 @@ import time
 from tornado.platform import interface
 from tornado.util import errno_from_exception
 
+
 def try_close(f):
     # Avoid issue #875 (race condition when using the file in another
     # thread).
diff --git a/lib/tornado/platform/epoll.py b/lib/tornado/platform/epoll.py
index b08cc628..80bfd8af 100644
--- a/lib/tornado/platform/epoll.py
+++ b/lib/tornado/platform/epoll.py
@@ -14,7 +14,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 """EPoll-based IOLoop implementation for Linux systems."""
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import select
 
diff --git a/lib/tornado/platform/interface.py b/lib/tornado/platform/interface.py
index cc062391..c0ef2905 100644
--- a/lib/tornado/platform/interface.py
+++ b/lib/tornado/platform/interface.py
@@ -21,7 +21,7 @@ for other tornado.platform modules.  Most code should import the appropriate
 implementation from `tornado.platform.auto`.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 
 def set_close_exec(fd):
@@ -62,5 +62,6 @@ class Waker(object):
         """Closes the waker's file descriptor(s)."""
         raise NotImplementedError()
 
+
 def monotonic_time():
     raise NotImplementedError()
diff --git a/lib/tornado/platform/kqueue.py b/lib/tornado/platform/kqueue.py
index f8f3e4a6..3a5d4174 100644
--- a/lib/tornado/platform/kqueue.py
+++ b/lib/tornado/platform/kqueue.py
@@ -14,7 +14,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 """KQueue-based IOLoop implementation for BSD/Mac systems."""
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import select
 
diff --git a/lib/tornado/platform/posix.py b/lib/tornado/platform/posix.py
index 572c0139..9bf1f188 100644
--- a/lib/tornado/platform/posix.py
+++ b/lib/tornado/platform/posix.py
@@ -16,7 +16,7 @@
 
 """Posix implementations of platform-specific functionality."""
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import fcntl
 import os
diff --git a/lib/tornado/platform/select.py b/lib/tornado/platform/select.py
index db52ef91..a18049f7 100644
--- a/lib/tornado/platform/select.py
+++ b/lib/tornado/platform/select.py
@@ -17,7 +17,7 @@
 
 Used as a fallback for systems that don't support epoll or kqueue.
 """
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import select
 
diff --git a/lib/tornado/platform/twisted.py b/lib/tornado/platform/twisted.py
index 92157c7c..0f9787e8 100644
--- a/lib/tornado/platform/twisted.py
+++ b/lib/tornado/platform/twisted.py
@@ -21,7 +21,7 @@ depending on which library's underlying event loop you want to use.
 This module has been tested with Twisted versions 11.0.0 and newer.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import datetime
 import functools
@@ -574,6 +574,7 @@ class TwistedResolver(Resolver):
         ]
         raise gen.Return(result)
 
+
 if hasattr(gen.convert_yielded, 'register'):
     @gen.convert_yielded.register(Deferred)  # type: ignore
     def _(d):
diff --git a/lib/tornado/platform/windows.py b/lib/tornado/platform/windows.py
index 9a319f27..e94a0cf1 100644
--- a/lib/tornado/platform/windows.py
+++ b/lib/tornado/platform/windows.py
@@ -2,7 +2,7 @@
 # for production use.
 
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 import ctypes  # type: ignore
 import ctypes.wintypes  # type: ignore
 
diff --git a/lib/tornado/process.py b/lib/tornado/process.py
index 7c876494..fae94f3c 100644
--- a/lib/tornado/process.py
+++ b/lib/tornado/process.py
@@ -18,7 +18,7 @@
 the server into multiple processes and managing subprocesses.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import errno
 import os
@@ -355,6 +355,10 @@ class Subprocess(object):
         else:
             assert os.WIFEXITED(status)
             self.returncode = os.WEXITSTATUS(status)
+        # We've taken over wait() duty from the subprocess.Popen
+        # object. If we don't inform it of the process's return code,
+        # it will log a warning at destruction in python 3.6+.
+        self.proc.returncode = self.returncode
         if self._exit_callback:
             callback = self._exit_callback
             self._exit_callback = None
diff --git a/lib/tornado/queues.py b/lib/tornado/queues.py
index b8e9b569..0041a800 100644
--- a/lib/tornado/queues.py
+++ b/lib/tornado/queues.py
@@ -12,7 +12,17 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-from __future__ import absolute_import, division, print_function, with_statement
+"""Asynchronous queues for coroutines.
+
+.. warning::
+
+   Unlike the standard library's `queue` module, the classes defined here
+   are *not* thread-safe. To use these queues from another thread,
+   use `.IOLoop.add_callback` to transfer control to the `.IOLoop` thread
+   before calling any queue methods.
+"""
+
+from __future__ import absolute_import, division, print_function
 
 import collections
 import heapq
diff --git a/lib/tornado/routing.py b/lib/tornado/routing.py
index 71c63b3d..6762dc05 100644
--- a/lib/tornado/routing.py
+++ b/lib/tornado/routing.py
@@ -12,16 +12,23 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-"""Basic routing implementation.
+"""Flexible routing implementation.
 
-Tornado routes HTTP requests to appropriate handlers using `Router` class implementations.
+Tornado routes HTTP requests to appropriate handlers using `Router`
+class implementations. The `tornado.web.Application` class is a
+`Router` implementation and may be used directly, or the classes in
+this module may be used for additional flexibility. The `RuleRouter`
+class can match on more criteria than `.Application`, or the `Router`
+interface can be subclassed for maximum customization.
 
-`Router` interface extends `~.httputil.HTTPServerConnectionDelegate` to provide additional
-routing capabilities. This also means that any `Router` implementation can be used directly
-as a ``request_callback`` for `~.httpserver.HTTPServer` constructor.
+`Router` interface extends `~.httputil.HTTPServerConnectionDelegate`
+to provide additional routing capabilities. This also means that any
+`Router` implementation can be used directly as a ``request_callback``
+for `~.httpserver.HTTPServer` constructor.
 
-`Router` subclass must implement a ``find_handler`` method to provide a suitable
-`~.httputil.HTTPMessageDelegate` instance to handle the request:
+`Router` subclass must implement a ``find_handler`` method to provide
+a suitable `~.httputil.HTTPMessageDelegate` instance to handle the
+request:
 
 .. code-block:: python
 
@@ -44,16 +51,18 @@ as a ``request_callback`` for `~.httpserver.HTTPServer` constructor.
     router = CustomRouter()
     server = HTTPServer(router)
 
-The main responsibility of `Router` implementation is to provide a mapping from a request
-to `~.httputil.HTTPMessageDelegate` instance that will handle this request. In the example above
-we can see that routing is possible even without instantiating an `~.web.Application`.
+The main responsibility of `Router` implementation is to provide a
+mapping from a request to `~.httputil.HTTPMessageDelegate` instance
+that will handle this request. In the example above we can see that
+routing is possible even without instantiating an `~.web.Application`.
 
-For routing to `~.web.RequestHandler` implementations we need an `~.web.Application` instance.
-`~.web.Application.get_handler_delegate` provides a convenient way to create
-`~.httputil.HTTPMessageDelegate` for a given request and `~.web.RequestHandler`.
+For routing to `~.web.RequestHandler` implementations we need an
+`~.web.Application` instance. `~.web.Application.get_handler_delegate`
+provides a convenient way to create `~.httputil.HTTPMessageDelegate`
+for a given request and `~.web.RequestHandler`.
 
-Here is a simple example of how we can we route to `~.web.RequestHandler` subclasses
-by HTTP method:
+Here is a simple example of how we can we route to
+`~.web.RequestHandler` subclasses by HTTP method:
 
 .. code-block:: python
 
@@ -81,16 +90,18 @@ by HTTP method:
     router = HTTPMethodRouter(Application())
     server = HTTPServer(router)
 
-`ReversibleRouter` interface adds the ability to distinguish between the routes and
-reverse them to the original urls using route's name and additional arguments.
-`~.web.Application` is itself an implementation of `ReversibleRouter` class.
+`ReversibleRouter` interface adds the ability to distinguish between
+the routes and reverse them to the original urls using route's name
+and additional arguments. `~.web.Application` is itself an
+implementation of `ReversibleRouter` class.
 
-`RuleRouter` and `ReversibleRuleRouter` are implementations of `Router` and `ReversibleRouter`
-interfaces and can be used for creating rule-based routing configurations.
+`RuleRouter` and `ReversibleRuleRouter` are implementations of
+`Router` and `ReversibleRouter` interfaces and can be used for
+creating rule-based routing configurations.
 
-Rules are instances of `Rule` class. They contain a `Matcher`, which provides the logic for
-determining whether the rule is a match for a particular request and a target, which can be
-one of the following.
+Rules are instances of `Rule` class. They contain a `Matcher`, which
+provides the logic for determining whether the rule is a match for a
+particular request and a target, which can be one of the following.
 
 1) An instance of `~.httputil.HTTPServerConnectionDelegate`:
 
@@ -159,9 +170,12 @@ In the example below `RuleRouter` is used to route between applications:
     server = HTTPServer(router)
 
 For more information on application-level routing see docs for `~.web.Application`.
+
+.. versionadded:: 4.5
+
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import re
 from functools import partial
diff --git a/lib/tornado/simple_httpclient.py b/lib/tornado/simple_httpclient.py
index adcf38b2..8fb70707 100644
--- a/lib/tornado/simple_httpclient.py
+++ b/lib/tornado/simple_httpclient.py
@@ -1,5 +1,5 @@
 #!/usr/bin/env python
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 from tornado.escape import utf8, _unicode
 from tornado import gen
@@ -499,7 +499,7 @@ class _HTTPConnection(httputil.HTTPMessageDelegate):
     def _should_follow_redirect(self):
         return (self.request.follow_redirects and
                 self.request.max_redirects > 0 and
-                self.code in (301, 302, 303, 307))
+                self.code in (301, 302, 303, 307, 308))
 
     def finish(self):
         data = b''.join(self.chunks)
diff --git a/lib/tornado/stack_context.py b/lib/tornado/stack_context.py
index 2c0d9ee7..61ae51f4 100644
--- a/lib/tornado/stack_context.py
+++ b/lib/tornado/stack_context.py
@@ -67,7 +67,7 @@ Here are a few rules of thumb for when it's necessary:
   block that references your `StackContext`.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import sys
 import threading
@@ -82,6 +82,8 @@ class StackContextInconsistentError(Exception):
 class _State(threading.local):
     def __init__(self):
         self.contexts = (tuple(), None)
+
+
 _state = _State()
 
 
diff --git a/lib/tornado/tcpclient.py b/lib/tornado/tcpclient.py
index 11146860..33074bd5 100644
--- a/lib/tornado/tcpclient.py
+++ b/lib/tornado/tcpclient.py
@@ -16,7 +16,7 @@
 
 """A non-blocking TCP connection factory.
 """
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import functools
 import socket
@@ -155,16 +155,30 @@ class TCPClient(object):
 
     @gen.coroutine
     def connect(self, host, port, af=socket.AF_UNSPEC, ssl_options=None,
-                max_buffer_size=None):
+                max_buffer_size=None, source_ip=None, source_port=None):
         """Connect to the given host and port.
 
         Asynchronously returns an `.IOStream` (or `.SSLIOStream` if
         ``ssl_options`` is not None).
+
+        Using the ``source_ip`` kwarg, one can specify the source
+        IP address to use when establishing the connection.
+        In case the user needs to resolve and
+        use a specific interface, it has to be handled outside
+        of Tornado as this depends very much on the platform.
+
+        Similarly, when the user requires a certain source port, it can
+        be specified using the ``source_port`` arg.
+
+        .. versionchanged:: 4.5
+           Added the ``source_ip`` and ``source_port`` arguments.
         """
         addrinfo = yield self.resolver.resolve(host, port, af)
         connector = _Connector(
             addrinfo, self.io_loop,
-            functools.partial(self._create_stream, max_buffer_size))
+            functools.partial(self._create_stream, max_buffer_size,
+                              source_ip=source_ip, source_port=source_port)
+        )
         af, addr, stream = yield connector.start()
         # TODO: For better performance we could cache the (af, addr)
         # information here and re-use it on subsequent connections to
@@ -174,13 +188,32 @@ class TCPClient(object):
                                             server_hostname=host)
         raise gen.Return(stream)
 
-    def _create_stream(self, max_buffer_size, af, addr):
+    def _create_stream(self, max_buffer_size, af, addr, source_ip=None,
+                       source_port=None):
         # Always connect in plaintext; we'll convert to ssl if necessary
         # after one connection has completed.
+        source_port_bind = source_port if isinstance(source_port, int) else 0
+        source_ip_bind = source_ip
+        if source_port_bind and not source_ip:
+            # User required a specific port, but did not specify
+            # a certain source IP, will bind to the default loopback.
+            source_ip_bind = '::1' if af == socket.AF_INET6 else '127.0.0.1'
+            # Trying to use the same address family as the requested af socket:
+            # - 127.0.0.1 for IPv4
+            # - ::1 for IPv6
+        socket_obj = socket.socket(af)
+        if source_port_bind or source_ip_bind:
+            # If the user requires binding also to a specific IP/port.
+            try:
+                socket_obj.bind((source_ip_bind, source_port_bind))
+            except socket.error:
+                socket_obj.close()
+                # Fail loudly if unable to use the IP/port.
+                raise
         try:
-            stream = IOStream(socket.socket(af),
-                            io_loop=self.io_loop,
-                            max_buffer_size=max_buffer_size)
+            stream = IOStream(socket_obj,
+                              io_loop=self.io_loop,
+                              max_buffer_size=max_buffer_size)
         except socket.error as e:
             fu = Future()
             fu.set_exception(e)
diff --git a/lib/tornado/tcpserver.py b/lib/tornado/tcpserver.py
index ac666698..f47ec89a 100644
--- a/lib/tornado/tcpserver.py
+++ b/lib/tornado/tcpserver.py
@@ -15,7 +15,7 @@
 # under the License.
 
 """A non-blocking, single-threaded TCP server."""
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import errno
 import os
diff --git a/lib/tornado/template.py b/lib/tornado/template.py
index 67c61e6b..3b2fa3fe 100644
--- a/lib/tornado/template.py
+++ b/lib/tornado/template.py
@@ -196,7 +196,7 @@ if you need to include a literal ``{{``, ``{%``, or ``{#`` in the output.
     `filter_whitespace` for available options. New in Tornado 4.3.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import datetime
 import linecache
diff --git a/lib/tornado/testing.py b/lib/tornado/testing.py
index 902bfdfc..74d04b60 100644
--- a/lib/tornado/testing.py
+++ b/lib/tornado/testing.py
@@ -10,7 +10,7 @@
   for the tornado.autoreload module to rerun the tests when code changes.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 try:
     from tornado import gen
@@ -656,7 +656,9 @@ def main(**kwargs):
 
     This test runner is essentially equivalent to `unittest.main` from
     the standard library, but adds support for tornado-style option
-    parsing and log formatting.
+    parsing and log formatting. It is *not* necessary to use this
+    `main` function to run tests using `AsyncTestCase`; these tests
+    are self-contained and can run with any test runner.
 
     The easiest way to run a test is via the command line::
 
@@ -735,5 +737,6 @@ def main(**kwargs):
             gen_log.error('FAIL')
         raise
 
+
 if __name__ == '__main__':
     main()
diff --git a/lib/tornado/util.py b/lib/tornado/util.py
index d0f83d1f..981b94c8 100644
--- a/lib/tornado/util.py
+++ b/lib/tornado/util.py
@@ -10,7 +10,7 @@ interface of its subclasses, including `.AsyncHTTPClient`, `.IOLoop`,
 and `.Resolver`.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import array
 import atexit
@@ -193,7 +193,11 @@ def exec_in(code, glob, loc=None):
 if PY3:
     exec("""
 def raise_exc_info(exc_info):
-    raise exc_info[1].with_traceback(exc_info[2])
+    try:
+        raise exc_info[1].with_traceback(exc_info[2])
+    finally:
+        exc_info = None
+
 """)
 else:
     exec("""
@@ -232,6 +236,7 @@ def _re_unescape_replacement(match):
         raise ValueError("cannot unescape '\\\\%s'" % group[0])
     return group
 
+
 _re_unescape_pattern = re.compile(r'\\(.)', re.DOTALL)
 
 
@@ -450,6 +455,7 @@ def _websocket_mask_python(mask, data):
     else:
         return unmasked_arr.tostring()
 
+
 if (os.environ.get('TORNADO_NO_EXTENSION') or
         os.environ.get('TORNADO_EXTENSION') == '0'):
     # These environment variables exist to make it easier to do performance
diff --git a/lib/tornado/web.py b/lib/tornado/web.py
index 9557a6f3..d79889fa 100644
--- a/lib/tornado/web.py
+++ b/lib/tornado/web.py
@@ -56,7 +56,7 @@ request.
 
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import base64
 import binascii
@@ -756,45 +756,21 @@ class RequestHandler(object):
             if body_part:
                 html_bodies.append(utf8(body_part))
 
-        def is_absolute(path):
-            return any(path.startswith(x) for x in ["/", "http:", "https:"])
         if js_files:
             # Maintain order of JavaScript files given by modules
-            paths = []
-            unique_paths = set()
-            for path in js_files:
-                if not is_absolute(path):
-                    path = self.static_url(path)
-                if path not in unique_paths:
-                    paths.append(path)
-                    unique_paths.add(path)
-            js = ''.join('<script src="' + escape.xhtml_escape(p) +
-                         '" type="text/javascript"></script>'
-                         for p in paths)
+            js = self.render_linked_js(js_files)
             sloc = html.rindex(b'</body>')
             html = html[:sloc] + utf8(js) + b'\n' + html[sloc:]
         if js_embed:
-            js = b'<script type="text/javascript">\n//<![CDATA[\n' + \
-                b'\n'.join(js_embed) + b'\n//]]>\n</script>'
+            js = self.render_embed_js(js_embed)
             sloc = html.rindex(b'</body>')
             html = html[:sloc] + js + b'\n' + html[sloc:]
         if css_files:
-            paths = []
-            unique_paths = set()
-            for path in css_files:
-                if not is_absolute(path):
-                    path = self.static_url(path)
-                if path not in unique_paths:
-                    paths.append(path)
-                    unique_paths.add(path)
-            css = ''.join('<link href="' + escape.xhtml_escape(p) + '" '
-                          'type="text/css" rel="stylesheet"/>'
-                          for p in paths)
+            css = self.render_linked_css(css_files)
             hloc = html.index(b'</head>')
             html = html[:hloc] + utf8(css) + b'\n' + html[hloc:]
         if css_embed:
-            css = b'<style type="text/css">\n' + b'\n'.join(css_embed) + \
-                b'\n</style>'
+            css = self.render_embed_css(css_embed)
             hloc = html.index(b'</head>')
             html = html[:hloc] + css + b'\n' + html[hloc:]
         if html_heads:
@@ -805,6 +781,64 @@ class RequestHandler(object):
             html = html[:hloc] + b''.join(html_bodies) + b'\n' + html[hloc:]
         self.finish(html)
 
+    def render_linked_js(self, js_files):
+        """Default method used to render the final js links for the
+        rendered webpage.
+
+        Override this method in a sub-classed controller to change the output.
+        """
+        paths = []
+        unique_paths = set()
+
+        for path in js_files:
+            if not is_absolute(path):
+                path = self.static_url(path)
+            if path not in unique_paths:
+                paths.append(path)
+                unique_paths.add(path)
+
+        return ''.join('<script src="' + escape.xhtml_escape(p) +
+                       '" type="text/javascript"></script>'
+                       for p in paths)
+
+    def render_embed_js(self, js_embed):
+        """Default method used to render the final embedded js for the
+        rendered webpage.
+
+        Override this method in a sub-classed controller to change the output.
+        """
+        return b'<script type="text/javascript">\n//<![CDATA[\n' + \
+               b'\n'.join(js_embed) + b'\n//]]>\n</script>'
+
+    def render_linked_css(self, css_files):
+        """Default method used to render the final css links for the
+        rendered webpage.
+
+        Override this method in a sub-classed controller to change the output.
+        """
+        paths = []
+        unique_paths = set()
+
+        for path in css_files:
+            if not is_absolute(path):
+                path = self.static_url(path)
+            if path not in unique_paths:
+                paths.append(path)
+                unique_paths.add(path)
+
+        return ''.join('<link href="' + escape.xhtml_escape(p) + '" '
+                       'type="text/css" rel="stylesheet"/>'
+                       for p in paths)
+
+    def render_embed_css(self, css_embed):
+        """Default method used to render the final embedded css for the
+        rendered webpage.
+
+        Override this method in a sub-classed controller to change the output.
+        """
+        return b'<style type="text/css">\n' + b'\n'.join(css_embed) + \
+               b'\n</style>'
+
     def render_string(self, template_name, **kwargs):
         """Generate the given template with the given arguments.
 
@@ -959,6 +993,9 @@ class RequestHandler(object):
         self._log()
         self._finished = True
         self.on_finish()
+        self._break_cycles()
+
+    def _break_cycles(self):
         # Break up a reference cycle between this handler and the
         # _ui_module closures to allow for faster GC on CPython.
         self.ui = None
@@ -1672,10 +1709,6 @@ def stream_request_body(cls):
     * The regular HTTP method (``post``, ``put``, etc) will be called after
       the entire body has been read.
 
-    There is a subtle interaction between ``data_received`` and asynchronous
-    ``prepare``: The first call to ``data_received`` may occur at any point
-    after the call to ``prepare`` has returned *or yielded*.
-
     See the `file receiver demo <https://github.com/tornadoweb/tornado/tree/master/demos/file_upload/>`_
     for example usage.
     """
@@ -1834,6 +1867,8 @@ class Application(ReversibleRouter):
     `StaticFileHandler` can be specified with the
     ``static_handler_class`` setting.
 
+    .. versionchanged:: 4.5
+       Integration with the new `tornado.routing` module.
     """
     def __init__(self, handlers=None, default_host=None, transforms=None,
                  **settings):
@@ -2218,6 +2253,9 @@ class RedirectHandler(RequestHandler):
 
     Use Python's :ref:`format string syntax <formatstrings>` to customize how
     values are substituted.
+
+    .. versionchanged:: 4.5
+       Added support for substitutions into the destination URL.
     """
     def initialize(self, url, permanent=True):
         self._url = url
@@ -3084,6 +3122,7 @@ def create_signed_value(secret, name, value, version=None, clock=None,
     else:
         raise ValueError("Unsupported version %d" % version)
 
+
 # A leading version number in decimal
 # with no leading zeros, followed by a pipe.
 _signed_value_version_re = re.compile(br"^([1-9][0-9]*)\|(.*)$")
@@ -3240,3 +3279,7 @@ def _create_signature_v2(secret, s):
     hash = hmac.new(utf8(secret), digestmod=hashlib.sha256)
     hash.update(utf8(s))
     return utf8(hash.hexdigest())
+
+
+def is_absolute(path):
+    return any(path.startswith(x) for x in ["/", "http:", "https:"])
diff --git a/lib/tornado/websocket.py b/lib/tornado/websocket.py
index 6e1220b3..69437ee4 100644
--- a/lib/tornado/websocket.py
+++ b/lib/tornado/websocket.py
@@ -16,7 +16,7 @@ the protocol (known as "draft 76") and are not compatible with this module.
    Removed support for the draft 76 protocol version.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 # Author: Jacob Kristhammar, 2010
 
 import base64
@@ -30,8 +30,8 @@ import zlib
 
 from tornado.concurrent import TracebackFuture
 from tornado.escape import utf8, native_str, to_unicode
-from tornado import httpclient, httputil
-from tornado.ioloop import IOLoop
+from tornado import gen, httpclient, httputil
+from tornado.ioloop import IOLoop, PeriodicCallback
 from tornado.iostream import StreamClosedError
 from tornado.log import gen_log, app_log
 from tornado import simple_httpclient
@@ -65,6 +65,10 @@ class WebSocketHandler(tornado.web.RequestHandler):
     override `open` and `on_close` to handle opened and closed
     connections.
 
+    Custom upgrade response headers can be sent by overriding
+    `~tornado.web.RequestHandler.set_default_headers` or
+    `~tornado.web.RequestHandler.prepare`.
+
     See http://dev.w3.org/html5/websockets/ for details on the
     JavaScript interface.  The protocol is specified at
     http://tools.ietf.org/html/rfc6455.
@@ -122,6 +126,17 @@ class WebSocketHandler(tornado.web.RequestHandler):
     to show the "accept this certificate" dialog but has nowhere to show it.
     You must first visit a regular HTML page using the same certificate
     to accept it before the websocket connection will succeed.
+
+    If the application setting ``websocket_ping_interval`` has a non-zero
+    value, a ping will be sent periodically, and the connection will be
+    closed if a response is not received before the ``websocket_ping_timeout``.
+
+    Messages larger than the ``websocket_max_message_size`` application setting
+    (default 10MiB) will not be accepted.
+
+    .. versionchanged:: 4.5
+       Added ``websocket_ping_interval``, ``websocket_ping_timeout``, and
+       ``websocket_max_message_size``.
     """
     def __init__(self, application, request, **kwargs):
         super(WebSocketHandler, self).__init__(application, request, **kwargs)
@@ -176,18 +191,42 @@ class WebSocketHandler(tornado.web.RequestHandler):
             gen_log.debug(log_msg)
             return
 
-        self.stream = self.request.connection.detach()
-        self.stream.set_close_callback(self.on_connection_close)
-
         self.ws_connection = self.get_websocket_protocol()
         if self.ws_connection:
             self.ws_connection.accept_connection()
         else:
-            if not self.stream.closed():
-                self.stream.write(tornado.escape.utf8(
-                    "HTTP/1.1 426 Upgrade Required\r\n"
-                    "Sec-WebSocket-Version: 7, 8, 13\r\n\r\n"))
-                self.stream.close()
+            self.set_status(426, "Upgrade Required")
+            self.set_header("Sec-WebSocket-Version", "7, 8, 13")
+            self.finish()
+
+    stream = None
+
+    @property
+    def ping_interval(self):
+        """The interval for websocket keep-alive pings.
+
+        Set websocket_ping_interval = 0 to disable pings.
+        """
+        return self.settings.get('websocket_ping_interval', None)
+
+    @property
+    def ping_timeout(self):
+        """If no ping is received in this many seconds,
+        close the websocket connection (VPNs, etc. can fail to cleanly close ws connections).
+        Default is max of 3 pings or 30 seconds.
+        """
+        return self.settings.get('websocket_ping_timeout', None)
+
+    @property
+    def max_message_size(self):
+        """Maximum allowed message size.
+
+        If the remote peer sends a message larger than this, the connection
+        will be closed.
+
+        Default is 10MiB.
+        """
+        return self.settings.get('websocket_max_message_size', None)
 
     def write_message(self, message, binary=False):
         """Sends the given message to the client of this Web Socket.
@@ -231,11 +270,22 @@ class WebSocketHandler(tornado.web.RequestHandler):
         If this method returns None (the default), compression will
         be disabled.  If it returns a dict (even an empty one), it
         will be enabled.  The contents of the dict may be used to
-        control the memory and CPU usage of the compression,
-        but no such options are currently implemented.
+        control the following compression options:
+
+        ``compression_level`` specifies the compression level.
+
+        ``mem_level`` specifies the amount of memory used for the internal compression state.
+
+         These parameters are documented in details here:
+         https://docs.python.org/3.6/library/zlib.html#zlib.compressobj
 
         .. versionadded:: 4.1
+
+        .. versionchanged:: 4.5
+
+           Added ``compression_level`` and ``mem_level``.
         """
+        # TODO: Add wbits option.
         return None
 
     def open(self, *args, **kwargs):
@@ -251,6 +301,10 @@ class WebSocketHandler(tornado.web.RequestHandler):
         """Handle incoming messages on the WebSocket
 
         This method must be overridden.
+
+        .. versionchanged:: 4.5
+
+           ``on_message`` can be a coroutine.
         """
         raise NotImplementedError
 
@@ -264,6 +318,10 @@ class WebSocketHandler(tornado.web.RequestHandler):
         """Invoked when the response to a ping frame is received."""
         pass
 
+    def on_ping(self, data):
+        """Invoked when the a ping frame is received."""
+        pass
+
     def on_close(self):
         """Invoked when the WebSocket is closed.
 
@@ -319,7 +377,7 @@ class WebSocketHandler(tornado.web.RequestHandler):
 
            This is an important security measure; don't disable it
            without understanding the security implications. In
-           particular, if your authenticatino is cookie-based, you
+           particular, if your authentication is cookie-based, you
            must either restrict the origins allowed by
            ``check_origin()`` or implement your own XSRF-like
            protection for websocket connections. See `these
@@ -376,6 +434,16 @@ class WebSocketHandler(tornado.web.RequestHandler):
         if not self._on_close_called:
             self._on_close_called = True
             self.on_close()
+            self._break_cycles()
+
+    def _break_cycles(self):
+        # WebSocketHandlers call finish() early, but we don't want to
+        # break up reference cycles (which makes it impossible to call
+        # self.render_string) until after we've really closed the
+        # connection (if it was established in the first place,
+        # indicated by status code 101).
+        if self.get_status() != 101 or self._on_close_called:
+            super(WebSocketHandler, self)._break_cycles()
 
     def send_error(self, *args, **kwargs):
         if self.stream is None:
@@ -393,18 +461,17 @@ class WebSocketHandler(tornado.web.RequestHandler):
             return WebSocketProtocol13(
                 self, compression_options=self.get_compression_options())
 
+    def _attach_stream(self):
+        self.stream = self.request.connection.detach()
+        self.stream.set_close_callback(self.on_connection_close)
+        # disable non-WS methods
+        for method in ["write", "redirect", "set_header", "set_cookie",
+                       "set_status", "flush", "finish"]:
+            setattr(self, method, _raise_not_supported_for_websockets)
 
-def _wrap_method(method):
-    def _disallow_for_websocket(self, *args, **kwargs):
-        if self.stream is None:
-            method(self, *args, **kwargs)
-        else:
-            raise RuntimeError("Method not supported for Web Sockets")
-    return _disallow_for_websocket
-for method in ["write", "redirect", "set_header", "set_cookie",
-               "set_status", "flush", "finish"]:
-    setattr(WebSocketHandler, method,
-            _wrap_method(getattr(WebSocketHandler, method)))
+
+def _raise_not_supported_for_websockets(*args, **kwargs):
+    raise RuntimeError("Method not supported for Web Sockets")
 
 
 class WebSocketProtocol(object):
@@ -420,14 +487,20 @@ class WebSocketProtocol(object):
     def _run_callback(self, callback, *args, **kwargs):
         """Runs the given callback with exception handling.
 
-        On error, aborts the websocket connection and returns False.
+        If the callback is a coroutine, returns its Future. On error, aborts the
+        websocket connection and returns None.
         """
         try:
-            callback(*args, **kwargs)
+            result = callback(*args, **kwargs)
         except Exception:
             app_log.error("Uncaught exception in %s",
-                          self.request.path, exc_info=True)
+                          getattr(self.request, 'path', None), exc_info=True)
             self._abort()
+        else:
+            if result is not None:
+                result = gen.convert_yielded(result)
+                self.stream.io_loop.add_future(result, lambda f: f.result())
+            return result
 
     def on_connection_close(self):
         self._abort()
@@ -441,7 +514,7 @@ class WebSocketProtocol(object):
 
 
 class _PerMessageDeflateCompressor(object):
-    def __init__(self, persistent, max_wbits):
+    def __init__(self, persistent, max_wbits, compression_options=None):
         if max_wbits is None:
             max_wbits = zlib.MAX_WBITS
         # There is no symbolic constant for the minimum wbits value.
@@ -449,14 +522,24 @@ class _PerMessageDeflateCompressor(object):
             raise ValueError("Invalid max_wbits value %r; allowed range 8-%d",
                              max_wbits, zlib.MAX_WBITS)
         self._max_wbits = max_wbits
+
+        if compression_options is None or 'compression_level' not in compression_options:
+            self._compression_level = tornado.web.GZipContentEncoding.GZIP_LEVEL
+        else:
+            self._compression_level = compression_options['compression_level']
+
+        if compression_options is None or 'mem_level' not in compression_options:
+            self._mem_level = 8
+        else:
+            self._mem_level = compression_options['mem_level']
+
         if persistent:
             self._compressor = self._create_compressor()
         else:
             self._compressor = None
 
     def _create_compressor(self):
-        return zlib.compressobj(tornado.web.GZipContentEncoding.GZIP_LEVEL,
-                                zlib.DEFLATED, -self._max_wbits)
+        return zlib.compressobj(self._compression_level, zlib.DEFLATED, -self._max_wbits, self._mem_level)
 
     def compress(self, data):
         compressor = self._compressor or self._create_compressor()
@@ -467,7 +550,7 @@ class _PerMessageDeflateCompressor(object):
 
 
 class _PerMessageDeflateDecompressor(object):
-    def __init__(self, persistent, max_wbits):
+    def __init__(self, persistent, max_wbits, compression_options=None):
         if max_wbits is None:
             max_wbits = zlib.MAX_WBITS
         if not (8 <= max_wbits <= zlib.MAX_WBITS):
@@ -526,6 +609,9 @@ class WebSocketProtocol13(WebSocketProtocol):
         # the effect of compression, frame overhead, and control frames.
         self._wire_bytes_in = 0
         self._wire_bytes_out = 0
+        self.ping_callback = None
+        self.last_ping = 0
+        self.last_pong = 0
 
     def accept_connection(self):
         try:
@@ -562,46 +648,42 @@ class WebSocketProtocol13(WebSocketProtocol):
             self.request.headers.get("Sec-Websocket-Key"))
 
     def _accept_connection(self):
-        subprotocol_header = ''
         subprotocols = self.request.headers.get("Sec-WebSocket-Protocol", '')
         subprotocols = [s.strip() for s in subprotocols.split(',')]
         if subprotocols:
             selected = self.handler.select_subprotocol(subprotocols)
             if selected:
                 assert selected in subprotocols
-                subprotocol_header = ("Sec-WebSocket-Protocol: %s\r\n"
-                                      % selected)
+                self.handler.set_header("Sec-WebSocket-Protocol", selected)
 
-        extension_header = ''
         extensions = self._parse_extensions_header(self.request.headers)
         for ext in extensions:
             if (ext[0] == 'permessage-deflate' and
                     self._compression_options is not None):
                 # TODO: negotiate parameters if compression_options
                 # specifies limits.
-                self._create_compressors('server', ext[1])
+                self._create_compressors('server', ext[1], self._compression_options)
                 if ('client_max_window_bits' in ext[1] and
                         ext[1]['client_max_window_bits'] is None):
                     # Don't echo an offered client_max_window_bits
                     # parameter with no value.
                     del ext[1]['client_max_window_bits']
-                extension_header = ('Sec-WebSocket-Extensions: %s\r\n' %
-                                    httputil._encode_header(
-                                        'permessage-deflate', ext[1]))
+                self.handler.set_header("Sec-WebSocket-Extensions",
+                                        httputil._encode_header(
+                                            'permessage-deflate', ext[1]))
                 break
 
-        if self.stream.closed():
-            self._abort()
-            return
-        self.stream.write(tornado.escape.utf8(
-            "HTTP/1.1 101 Switching Protocols\r\n"
-            "Upgrade: websocket\r\n"
-            "Connection: Upgrade\r\n"
-            "Sec-WebSocket-Accept: %s\r\n"
-            "%s%s"
-            "\r\n" % (self._challenge_response(),
-                      subprotocol_header, extension_header)))
+        self.handler.clear_header("Content-Type")
+        self.handler.set_status(101)
+        self.handler.set_header("Upgrade", "websocket")
+        self.handler.set_header("Connection", "Upgrade")
+        self.handler.set_header("Sec-WebSocket-Accept", self._challenge_response())
+        self.handler.finish()
 
+        self.handler._attach_stream()
+        self.stream = self.handler.stream
+
+        self.start_pinging()
         self._run_callback(self.handler.open, *self.handler.open_args,
                            **self.handler.open_kwargs)
         self._receive_frame()
@@ -631,7 +713,7 @@ class WebSocketProtocol13(WebSocketProtocol):
             else:
                 raise ValueError("unsupported extension %r", ext)
 
-    def _get_compressor_options(self, side, agreed_parameters):
+    def _get_compressor_options(self, side, agreed_parameters, compression_options=None):
         """Converts a websocket agreed_parameters set to keyword arguments
         for our compressor objects.
         """
@@ -642,9 +724,10 @@ class WebSocketProtocol13(WebSocketProtocol):
             options['max_wbits'] = zlib.MAX_WBITS
         else:
             options['max_wbits'] = int(wbits_header)
+        options['compression_options'] = compression_options
         return options
 
-    def _create_compressors(self, side, agreed_parameters):
+    def _create_compressors(self, side, agreed_parameters, compression_options=None):
         # TODO: handle invalid parameters gracefully
         allowed_keys = set(['server_no_context_takeover',
                             'client_no_context_takeover',
@@ -655,9 +738,9 @@ class WebSocketProtocol13(WebSocketProtocol):
                 raise ValueError("unsupported compression parameter %r" % key)
         other_side = 'client' if (side == 'server') else 'server'
         self._compressor = _PerMessageDeflateCompressor(
-            **self._get_compressor_options(side, agreed_parameters))
+            **self._get_compressor_options(side, agreed_parameters, compression_options))
         self._decompressor = _PerMessageDeflateDecompressor(
-            **self._get_compressor_options(other_side, agreed_parameters))
+            **self._get_compressor_options(other_side, agreed_parameters, compression_options))
 
     def _write_frame(self, fin, opcode, data, flags=0):
         if fin:
@@ -738,8 +821,7 @@ class WebSocketProtocol13(WebSocketProtocol):
                 if self._masked_frame:
                     self.stream.read_bytes(4, self._on_masking_key)
                 else:
-                    self.stream.read_bytes(self._frame_length,
-                                           self._on_frame_data)
+                    self._read_frame_data(False)
             elif payloadlen == 126:
                 self.stream.read_bytes(2, self._on_frame_length_16)
             elif payloadlen == 127:
@@ -747,6 +829,17 @@ class WebSocketProtocol13(WebSocketProtocol):
         except StreamClosedError:
             self._abort()
 
+    def _read_frame_data(self, masked):
+        new_len = self._frame_length
+        if self._fragmented_message_buffer is not None:
+            new_len += len(self._fragmented_message_buffer)
+        if new_len > (self.handler.max_message_size or 10 * 1024 * 1024):
+            self.close(1009, "message too big")
+            return
+        self.stream.read_bytes(
+            self._frame_length,
+            self._on_masked_frame_data if masked else self._on_frame_data)
+
     def _on_frame_length_16(self, data):
         self._wire_bytes_in += len(data)
         self._frame_length = struct.unpack("!H", data)[0]
@@ -754,7 +847,7 @@ class WebSocketProtocol13(WebSocketProtocol):
             if self._masked_frame:
                 self.stream.read_bytes(4, self._on_masking_key)
             else:
-                self.stream.read_bytes(self._frame_length, self._on_frame_data)
+                self._read_frame_data(False)
         except StreamClosedError:
             self._abort()
 
@@ -765,7 +858,7 @@ class WebSocketProtocol13(WebSocketProtocol):
             if self._masked_frame:
                 self.stream.read_bytes(4, self._on_masking_key)
             else:
-                self.stream.read_bytes(self._frame_length, self._on_frame_data)
+                self._read_frame_data(False)
         except StreamClosedError:
             self._abort()
 
@@ -773,8 +866,7 @@ class WebSocketProtocol13(WebSocketProtocol):
         self._wire_bytes_in += len(data)
         self._frame_mask = data
         try:
-            self.stream.read_bytes(self._frame_length,
-                                   self._on_masked_frame_data)
+            self._read_frame_data(True)
         except StreamClosedError:
             self._abort()
 
@@ -783,6 +875,8 @@ class WebSocketProtocol13(WebSocketProtocol):
         self._on_frame_data(_websocket_mask(self._frame_mask, data))
 
     def _on_frame_data(self, data):
+        handled_future = None
+
         self._wire_bytes_in += len(data)
         if self._frame_opcode_is_control:
             # control frames may be interleaved with a series of fragmented
@@ -815,12 +909,18 @@ class WebSocketProtocol13(WebSocketProtocol):
                 self._fragmented_message_buffer = data
 
         if self._final_frame:
-            self._handle_message(opcode, data)
+            handled_future = self._handle_message(opcode, data)
 
         if not self.client_terminated:
-            self._receive_frame()
+            if handled_future:
+                # on_message is a coroutine, process more frames once it's done.
+                handled_future.add_done_callback(
+                    lambda future: self._receive_frame())
+            else:
+                self._receive_frame()
 
     def _handle_message(self, opcode, data):
+        """Execute on_message, returning its Future if it is a coroutine."""
         if self.client_terminated:
             return
 
@@ -835,11 +935,11 @@ class WebSocketProtocol13(WebSocketProtocol):
             except UnicodeDecodeError:
                 self._abort()
                 return
-            self._run_callback(self.handler.on_message, decoded)
+            return self._run_callback(self.handler.on_message, decoded)
         elif opcode == 0x2:
             # Binary data
             self._message_bytes_in += len(data)
-            self._run_callback(self.handler.on_message, data)
+            return self._run_callback(self.handler.on_message, data)
         elif opcode == 0x8:
             # Close
             self.client_terminated = True
@@ -852,9 +952,11 @@ class WebSocketProtocol13(WebSocketProtocol):
         elif opcode == 0x9:
             # Ping
             self._write_frame(True, 0xA, data)
+            self._run_callback(self.handler.on_ping, data)
         elif opcode == 0xA:
             # Pong
-            self._run_callback(self.handler.on_pong, data)
+            self.last_pong = IOLoop.current().time()
+            return self._run_callback(self.handler.on_pong, data)
         else:
             self._abort()
 
@@ -883,6 +985,51 @@ class WebSocketProtocol13(WebSocketProtocol):
             self._waiting = self.stream.io_loop.add_timeout(
                 self.stream.io_loop.time() + 5, self._abort)
 
+    @property
+    def ping_interval(self):
+        interval = self.handler.ping_interval
+        if interval is not None:
+            return interval
+        return 0
+
+    @property
+    def ping_timeout(self):
+        timeout = self.handler.ping_timeout
+        if timeout is not None:
+            return timeout
+        return max(3 * self.ping_interval, 30)
+
+    def start_pinging(self):
+        """Start sending periodic pings to keep the connection alive"""
+        if self.ping_interval > 0:
+            self.last_ping = self.last_pong = IOLoop.current().time()
+            self.ping_callback = PeriodicCallback(
+                self.periodic_ping, self.ping_interval * 1000)
+            self.ping_callback.start()
+
+    def periodic_ping(self):
+        """Send a ping to keep the websocket alive
+
+        Called periodically if the websocket_ping_interval is set and non-zero.
+        """
+        if self.stream.closed() and self.ping_callback is not None:
+            self.ping_callback.stop()
+            return
+
+        # Check for timeout on pong. Make sure that we really have
+        # sent a recent ping in case the machine with both server and
+        # client has been suspended since the last ping.
+        now = IOLoop.current().time()
+        since_last_pong = now - self.last_pong
+        since_last_ping = now - self.last_ping
+        if (since_last_ping < 2 * self.ping_interval and
+                since_last_pong > self.ping_timeout):
+            self.close()
+            return
+
+        self.write_ping(b'')
+        self.last_ping = now
+
 
 class WebSocketClientConnection(simple_httpclient._HTTPConnection):
     """WebSocket client connection.
@@ -891,7 +1038,8 @@ class WebSocketClientConnection(simple_httpclient._HTTPConnection):
     `websocket_connect` function instead.
     """
     def __init__(self, io_loop, request, on_message_callback=None,
-                 compression_options=None):
+                 compression_options=None, ping_interval=None, ping_timeout=None,
+                 max_message_size=None):
         self.compression_options = compression_options
         self.connect_future = TracebackFuture()
         self.protocol = None
@@ -900,6 +1048,9 @@ class WebSocketClientConnection(simple_httpclient._HTTPConnection):
         self.key = base64.b64encode(os.urandom(16))
         self._on_message_callback = on_message_callback
         self.close_code = self.close_reason = None
+        self.ping_interval = ping_interval
+        self.ping_timeout = ping_timeout
+        self.max_message_size = max_message_size
 
         scheme, sep, rest = request.url.partition(':')
         scheme = {'ws': 'http', 'wss': 'https'}[scheme]
@@ -963,6 +1114,7 @@ class WebSocketClientConnection(simple_httpclient._HTTPConnection):
         self.headers = headers
         self.protocol = self.get_websocket_protocol()
         self.protocol._process_server_headers(self.key, self.headers)
+        self.protocol.start_pinging()
         self.protocol._receive_frame()
 
         if self._timeout is not None:
@@ -1016,13 +1168,18 @@ class WebSocketClientConnection(simple_httpclient._HTTPConnection):
     def on_pong(self, data):
         pass
 
+    def on_ping(self, data):
+        pass
+
     def get_websocket_protocol(self):
         return WebSocketProtocol13(self, mask_outgoing=True,
                                    compression_options=self.compression_options)
 
 
 def websocket_connect(url, io_loop=None, callback=None, connect_timeout=None,
-                      on_message_callback=None, compression_options=None):
+                      on_message_callback=None, compression_options=None,
+                      ping_interval=None, ping_timeout=None,
+                      max_message_size=None):
     """Client-side websocket support.
 
     Takes a url and returns a Future whose result is a
@@ -1051,6 +1208,10 @@ def websocket_connect(url, io_loop=None, callback=None, connect_timeout=None,
     .. versionchanged:: 4.1
        Added ``compression_options`` and ``on_message_callback``.
        The ``io_loop`` argument is deprecated.
+
+    .. versionchanged:: 4.5
+       Added the ``ping_interval``, ``ping_timeout``, and ``max_message_size``
+       arguments, which have the same meaning as in `WebSocketHandler`.
     """
     if io_loop is None:
         io_loop = IOLoop.current()
@@ -1066,7 +1227,10 @@ def websocket_connect(url, io_loop=None, callback=None, connect_timeout=None,
         request, httpclient.HTTPRequest._DEFAULTS)
     conn = WebSocketClientConnection(io_loop, request,
                                      on_message_callback=on_message_callback,
-                                     compression_options=compression_options)
+                                     compression_options=compression_options,
+                                     ping_interval=ping_interval,
+                                     ping_timeout=ping_timeout,
+                                     max_message_size=max_message_size)
     if callback is not None:
         io_loop.add_future(conn.connect_future, callback)
     return conn.connect_future
diff --git a/lib/tornado/wsgi.py b/lib/tornado/wsgi.py
index e9ead300..68a7615a 100644
--- a/lib/tornado/wsgi.py
+++ b/lib/tornado/wsgi.py
@@ -29,7 +29,7 @@ provides WSGI support in two ways:
   and Tornado handlers in a single server.
 """
 
-from __future__ import absolute_import, division, print_function, with_statement
+from __future__ import absolute_import, division, print_function
 
 import sys
 from io import BytesIO