Paramiko returns None intermittently #4
Description
For some reason, after paramiko sends a command to the remote server, sometimes it responds with a None instead of a string containing the server's response. I could not find a way to reproduce this behavior deterministically. However, if you set up a small script that uses paramiko and then run it several times in a row, it eventually happens.
Paramiko is only used in the sshKernel module. We could:
- Fix it, if we can guarantee this doesn't happen anymore
- Wrap a try/error around it
- Change how we connect via SSH
Here is a minimal example of a Python script to test this error. This should print the output of uname -a of the remote server. Just try and run it several times in a row.
import paramiko
username = 'USERNAME'
address = 'ADDRESS'
def query(command):
# Check if connection is made previously
if (sshClient):
stdin, stdout, stderr = sshClient.exec_command(command)
while not stdout.channel.exit_status_ready():
# Print stdout data
if stdout.channel.recv_ready():
stdin.close()
std_out = stdout.readlines()
return ''.join(std_out)
# the method below, although recommended in the docs,
# is returning intermitent Nones with HIGHER frequency
# alldata = stdout.channel.recv(1024)
# while stdout.channel.recv_ready():
# alldata += stdout.channel.recv(1024)
#
# # Print as string with utf8 encoding
# string = str(alldata).encode("utf-8")
# return string
else:
return "No connection."
sshClient = paramiko.client.SSHClient()
sshClient.set_missing_host_key_policy( paramiko.client.AutoAddPolicy() )
sshClient.connect( address, username=username, look_for_keys=True )
print( query( 'uname -a' ) )