bpo-29406: asyncio SSL contexts leak sockets after calling close with certain servers (#409)

* asyncio SSL contexts leak sockets after calling close with certain servers

* cleanup _shutdown_timeout_handle on _fatal_error
diff --git a/Lib/asyncio/sslproto.py b/Lib/asyncio/sslproto.py
index 68499e5..a36725e 100644
--- a/Lib/asyncio/sslproto.py
+++ b/Lib/asyncio/sslproto.py
@@ -6,6 +6,8 @@
     ssl = None
 
 from . import base_events
+from . import compat
+from . import futures
 from . import protocols
 from . import transports
 from .log import logger
@@ -407,7 +409,7 @@
 
     def __init__(self, loop, app_protocol, sslcontext, waiter,
                  server_side=False, server_hostname=None,
-                 call_connection_made=True):
+                 call_connection_made=True, shutdown_timeout=5.0):
         if ssl is None:
             raise RuntimeError('stdlib ssl module not available')
 
@@ -438,6 +440,8 @@
         self._session_established = False
         self._in_handshake = False
         self._in_shutdown = False
+        self._shutdown_timeout = shutdown_timeout
+        self._shutdown_timeout_handle = None
         # transport, ex: SelectorSocketTransport
         self._transport = None
         self._call_connection_made = call_connection_made
@@ -552,6 +556,15 @@
             self._in_shutdown = True
             self._write_appdata(b'')
 
+        if self._shutdown_timeout is not None:
+            self._shutdown_timeout_handle = self._loop.call_later(
+                self._shutdown_timeout, self._on_shutdown_timeout)
+
+    def _on_shutdown_timeout(self):
+        if self._transport is not None:
+            self._fatal_error(
+                futures.TimeoutError(), 'Can not complete shitdown operation')
+
     def _write_appdata(self, data):
         self._write_backlog.append((data, 0))
         self._write_buffer_size += len(data)
@@ -679,12 +692,22 @@
             })
         if self._transport:
             self._transport._force_close(exc)
+            self._transport = None
+
+        if self._shutdown_timeout_handle is not None:
+            self._shutdown_timeout_handle.cancel()
+            self._shutdown_timeout_handle = None
 
     def _finalize(self):
         self._sslpipe = None
 
         if self._transport is not None:
             self._transport.close()
+            self._transport = None
+
+        if self._shutdown_timeout_handle is not None:
+            self._shutdown_timeout_handle.cancel()
+            self._shutdown_timeout_handle = None
 
     def _abort(self):
         try: