Explicitly check for 'no' and 'false' in USE_SOCKET env var

This allows us to default to using unix sockets by default in the future once
this feature is better tested, and allow people to turn it off if needed.

Author: yuvipanda

jupyter_rsession_proxy/__init__.py

@@ -134,8 +134,15 @@ def _get_timeout(default=15):
             'icon_path': get_icon_path()
         }
     }
-    if os.getenv('JUPYTER_RSESSION_PROXY_USE_SOCKET'):
-        server_process['unix_socket'] = True
+
+    use_socket = os.getenv('JUPYTER_RSESSION_PROXY_USE_SOCKET')
+    if use_socket is not None:
+        # If this env var is anything other than case insensitive 'no' or 'false',
+        # use unix sockets instead of tcp sockets. This allows us to default to
+        # using unix sockets by default in the future once this feature is better
+        # tested, and allow people to turn it off if needed.
+        if use_socket.casefold() not in ('no', 'false'):
+            server_process['unix_socket'] = True
 
     return server_process