SFTP log noise

[jonasbardino]

We see regular exception tracebacks from various harmless client-side and network connection drops in sftp-subsys.log on Rocky 9:

2025-07-03 12:33:18,843 ERROR Exception in subsystem handler for "sftp": 
2025-07-03 12:33:18,844 ERROR Traceback (most recent call last):
2025-07-03 12:33:18,844 ERROR   File "/usr/lib/python3.9/site-packages/paramiko/server.py", line 683, in _run
2025-07-03 12:33:18,844 ERROR     self.start_subsystem(self.__name, self.__transport, self.__channel)
2025-07-03 12:33:18,844 ERROR   File "/usr/lib/python3.9/site-packages/paramiko/sftp_server.py", line 142, in start_subsystem
2025-07-03 12:33:18,844 ERROR     self._send_server_version()
2025-07-03 12:33:18,844 ERROR   File "/usr/lib/python3.9/site-packages/paramiko/sftp.py", line 145, in _send_server_version
2025-07-03 12:33:18,844 ERROR     t, data = self._read_packet()
2025-07-03 12:33:18,845 ERROR   File "/usr/lib/python3.9/site-packages/paramiko/sftp.py", line 201, in _read_packet
2025-07-03 12:33:18,845 ERROR     x = self._read_all(4)
2025-07-03 12:33:18,845 ERROR   File "/usr/lib/python3.9/site-packages/paramiko/sftp.py", line 188, in _read_all
2025-07-03 12:33:18,845 ERROR     raise EOFError()
2025-07-03 12:33:18,845 ERROR EOFError

and

2025-07-17 11:11:17,121 ERROR Exception in subsystem handler for "sftp": Garbage packet received
2025-07-17 11:11:17,123 ERROR Traceback (most recent call last):
2025-07-17 11:11:17,123 ERROR   File "/usr/lib/python3.9/site-packages/paramiko/server.py", line 685, in _run
2025-07-17 11:11:17,123 ERROR     self.start_subsystem(self.__name, self.__transport, self.__channel)
2025-07-17 11:11:17,123 ERROR   File "/usr/lib/python3.9/site-packages/paramiko/sftp_server.py", line 139, in start_subsystem
2025-07-17 11:11:17,123 ERROR     self._send_server_version()
2025-07-17 11:11:17,123 ERROR   File "/usr/lib/python3.9/site-packages/paramiko/sftp.py", line 156, in _send_server_version
2025-07-17 11:11:17,123 ERROR     t, data = self._read_packet()
2025-07-17 11:11:17,123 ERROR   File "/usr/lib/python3.9/site-packages/paramiko/sftp.py", line 216, in _read_packet
2025-07-17 11:11:17,123 ERROR     raise SFTPError("Garbage packet received")

and some from our own checks on client failure:

2025-06-30 18:51:02,347 ERROR Exception in subsystem handler for "sftp": reject client based on failed session checks
2025-06-30 18:51:02,348 ERROR Traceback (most recent call last):
2025-06-30 18:51:02,348 ERROR   File "/usr/lib/python3.9/site-packages/paramiko/server.py", line 683, in _run
2025-06-30 18:51:02,348 ERROR     self.start_subsystem(self.__name, self.__transport, self.__channel)
2025-06-30 18:51:02,348 ERROR   File "/usr/lib/python3.9/site-packages/paramiko/sftp_server.py", line 143, in start_subsystem
2025-06-30 18:51:02,348 ERROR     self.server.session_started()
2025-06-30 18:51:02,348 ERROR   File "/home/mig/mig/server/grid_sftp.py", line 583, in session_started
2025-06-30 18:51:02,348 ERROR     raise Exception("reject client based on failed session checks")
2025-06-30 18:51:02,348 ERROR Exception: reject client based on failed session checks

They can safely be ignored, as I think we also used to do with patching in older paramiko versions.

It's probably a matter of wrapping one or more sftp methods or parts in try/except and only logging them as warning.

[jonasbardino]

PR #320 does not cover the 'reject client based on failed session checks' noise. They originate from an exception we explicitly raise in start_session to terminate on various session check errors like too many open sessions.
We should probably wrap and catch that case somewhere instead.