add ssh active transport check (#808)

smart_open/ssh.py

@@ -111,7 +111,10 @@ def parse_uri(uri_as_string):
 
 
 def open_uri(uri, mode, transport_params):
-    smart_open.utils.check_kwargs(open, transport_params)
+    # `connect_kwargs` is a legitimate param *only* for sftp, so this filters it out of validation
+    #   (otherwise every call with this present complains it's not valid)
+    params_to_validate = {k: v for k, v in transport_params.items() if k != 'connect_kwargs'}
+    smart_open.utils.check_kwargs(open, params_to_validate)
     parsed_uri = parse_uri(uri)
     uri_path = parsed_uri.pop('uri_path')
     parsed_uri.pop('scheme')
@@ -266,6 +269,11 @@ def open(path, mode='r', host=None, user=None, password=None, port=None, transpo
     for attempt in range(attempts):
         try:
             ssh = _SSH[key]
+            # Validate that the cached connection is still an active connection
+            #   and if not, refresh the connection
+            if not ssh.get_transport().active:
+                ssh.close()
+                ssh = _SSH[key] = _connect_ssh(host, user, port, password, transport_params)
         except KeyError:
             ssh = _SSH[key] = _connect_ssh(host, user, port, password, transport_params)