bpo-33654: Support BufferedProtocol in set_protocol() and start_tls() (GH-7130)


In this commit:

* Support BufferedProtocol in set_protocol() and start_tls()
* Fix proactor to cancel readers reliably
* Update tests to be compatible with OpenSSL 1.1.1
* Clarify BufferedProtocol docs
* Bump TLS tests timeouts to 60 seconds; eliminate possible race from start_serving
* Rewrite test_start_tls_server_1
(cherry picked from commit dbf102271fcc316f353c7e0a283811b661d128f2)

Co-authored-by: Yury Selivanov <yury@magic.io>
diff --git a/Lib/asyncio/unix_events.py b/Lib/asyncio/unix_events.py
index 6cac137..639300f 100644
--- a/Lib/asyncio/unix_events.py
+++ b/Lib/asyncio/unix_events.py
@@ -20,6 +20,7 @@
 from . import events
 from . import futures
 from . import selector_events
+from . import tasks
 from . import transports
 from .log import logger
 
@@ -308,6 +309,9 @@
                                     ssl, backlog, ssl_handshake_timeout)
         if start_serving:
             server._start_serving()
+            # Skip one loop iteration so that all 'loop.add_reader'
+            # go through.
+            await tasks.sleep(0, loop=self)
 
         return server