00458: test_ssl: Don't stop ThreadedEchoServer on OSError in ConnectionHandler

If `read()` in the ConnectionHandler thread raises `OSError` (except `ConnectionError`),
the ConnectionHandler shuts down the entire ThreadedEchoServer,
preventing further connections.
It also does that for `EPROTOTYPE` in `wrap_conn`.

Make sure that the context manager *is* used, and remove the `server.stop()`
calls from ConnectionHandler.

Backported from 3.12+:
python#126503

Co-authored-by: Petr Viktorin <encukou@gmail.com>

Author: 2 people

Lib/test/test_ssl.py

@@ -2516,7 +2516,6 @@ def wrap_conn(self):
                 # See also http://erickt.github.io/blog/2014/11/19/adventures-in-debugging-a-potential-osx-kernel-bug/
                 if e.errno != errno.EPROTOTYPE and sys.platform != "darwin":
                     self.running = False
-                    self.server.stop()
                     self.close()
                 return False
             else:
@@ -2651,10 +2650,6 @@ def run(self):
                     self.close()
                     self.running = False
 
-                    # normally, we'd just stop here, but for the test
-                    # harness, we want to stop the server
-                    self.server.stop()
-
     def __init__(self, certificate=None, ssl_version=None,
                  certreqs=None, cacerts=None,
                  chatty=True, connectionchatty=False, starttls_server=False,
@@ -2688,21 +2683,33 @@ def __init__(self, certificate=None, ssl_version=None,
         self.conn_errors = []
         threading.Thread.__init__(self)
         self.daemon = True
+        self._in_context = False
 
     def __enter__(self):
+        if self._in_context:
+            raise ValueError('Re-entering ThreadedEchoServer context')
+        self._in_context = True
         self.start(threading.Event())
         self.flag.wait()
         return self
 
     def __exit__(self, *args):
+        assert self._in_context
+        self._in_context = False
         self.stop()
         self.join()
 
     def start(self, flag=None):
+        if not self._in_context:
+            raise ValueError(
+                'ThreadedEchoServer must be used as a context manager')
         self.flag = flag
         threading.Thread.start(self)
 
     def run(self):
+        if not self._in_context:
+            raise ValueError(
+                'ThreadedEchoServer must be used as a context manager')
         self.sock.settimeout(1.0)
         self.sock.listen(5)
         self.active = True